Develop Reference

MediaRecorder stop() failed

I know there are a few of these on SO already but none of them really were able to help my issue, but when I am running the code and start recording audio and then press my stop button it always fails because it is in the wrong state. I am not sure how I would go about fixing my states for this.
Here is my MainActivity.java code:
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.pm.PackageManager;
import android.media.AudioManager;
import android.media.MediaPlayer;
import android.media.MediaRecorder;
import android.os.Build;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.widget.Button;
import android.widget.RadioGroup;
import android.widget.Toast;
import androidx.annotation.RequiresApi;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;
import java.io.IOException;
import static android.Manifest.permission.RECORD_AUDIO;
import static android.Manifest.permission.WRITE_EXTERNAL_STORAGE;
public class MainActivity extends AppCompatActivity {
Button buttonStartRecording, buttonStopRecording, buttonPlayLastRecordAudio,
buttonStopPlayingRecording;
String AudioSavePathInDevice = null;
MediaRecorder mediaRecorder;
public static final int RequestPermissionCode = 1;
MediaPlayer mediaPlayer;
AudioManager audioManager;
boolean isAudioPlayInSameDevice = true;
// AudioRouter audioRouter;
RadioGroup mRadioGroup;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
buttonStartRecording = (Button) findViewById(R.id.start_recording);
buttonStopRecording = (Button) findViewById(R.id.stop_rec);
buttonPlayLastRecordAudio = (Button) findViewById(R.id.play_last_rec);
buttonStopPlayingRecording = (Button) findViewById(R.id.stop_playing_btn);
// mRadioGroup = (RadioGroup) findViewById(R.id.radioGroup);
buttonStopRecording.setEnabled(false);
buttonPlayLastRecordAudio.setEnabled(false);
buttonStopPlayingRecording.setEnabled(false);
buttonStartRecording.setOnClickListener(new View.OnClickListener() {
#RequiresApi(api = Build.VERSION_CODES.O)
#Override
public void onClick(View view) {
// Check audio permission
if (checkPermission()) {
AudioSavePathInDevice =
Environment.getExternalStorageDirectory().getAbsolutePath() + "/" + "AudioRecording.3gp";
// Start Media recorder
MediaRecorderReady();
try {
mediaRecorder.prepare();
mediaRecorder.start();
} catch (IllegalStateException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
buttonStartRecording.setEnabled(false);
buttonStopRecording.setEnabled(true);
Toast.makeText(MainActivity.this, "Recording started",
Toast.LENGTH_LONG).show();
} else {
requestPermission();
}
}
});
buttonStopRecording.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
buttonStopRecording.setEnabled(false);
buttonPlayLastRecordAudio.setEnabled(true);
buttonStartRecording.setEnabled(true);
buttonStopPlayingRecording.setEnabled(false);
// Stop Media recorder
mediaRecorder.stop();
Toast.makeText(MainActivity.this, "Recording Completed",
Toast.LENGTH_LONG).show();
}
});
buttonPlayLastRecordAudio.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) throws IllegalArgumentException,
SecurityException, IllegalStateException {
int selectedId = 1;
if (selectedId == 1) {
isAudioPlayInSameDevice = true;
} else {
isAudioPlayInSameDevice = false;
}
// if you want to play audio on your Mobile speaker then set isAudioPlayInSameDevice true
// and if you want to play audio to connected device then set isAudioPlayInSameDevice false.
if (isAudioPlayInSameDevice) {
audioManager.setMode(audioManager.STREAM_MUSIC);
audioManager.setSpeakerphoneOn(true);
} else {
audioManager.setSpeakerphoneOn(false);
audioManager.setMode(audioManager.MODE_NORMAL);
}
audioManager.setBluetoothScoOn(false);
audioManager.stopBluetoothSco();
buttonStopRecording.setEnabled(false);
buttonStartRecording.setEnabled(false);
buttonStopPlayingRecording.setEnabled(true);
mediaPlayer = new MediaPlayer();
try {
// Start media player
System.out.println("Recorded Audio Path-" + AudioSavePathInDevice);
mediaPlayer.setDataSource(AudioSavePathInDevice);
if (isAudioPlayInSameDevice) {
mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
}
mediaPlayer.prepare();
mediaPlayer.start();
} catch (IOException e) {
e.printStackTrace();
}
Toast.makeText(MainActivity.this, "Recording Playing",
Toast.LENGTH_LONG).show();
}
});
buttonStopPlayingRecording.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
buttonStopRecording.setEnabled(false);
buttonStartRecording.setEnabled(true);
buttonStopPlayingRecording.setEnabled(false);
buttonPlayLastRecordAudio.setEnabled(true);
if (mediaPlayer != null) {
// Stop Media Player
mediaPlayer.stop();
mediaPlayer.release();
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
MediaRecorderReady();
}
}
}
});
}
private BroadcastReceiver mBluetoothScoReceiver = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent intent) {
int state = intent.getIntExtra(AudioManager.EXTRA_SCO_AUDIO_STATE, -1);
System.out.println("ANDROID Audio SCO state: " + state);
if (AudioManager.SCO_AUDIO_STATE_CONNECTED == state) {
/*
* Now the connection has been established to the bluetooth device.
* Record audio or whatever (on another thread).With AudioRecord you can record with an object created like this:
* new AudioRecord(MediaRecorder.AudioSource.MIC, 8000, AudioFormat.CHANNEL_CONFIGURATION_MONO,
* AudioFormat.ENCODING_PCM_16BIT, audioBufferSize);
*
* After finishing, don't forget to unregister this receiver and
* to stop the bluetooth connection with am.stopBluetoothSco();
*/
}
}
};
#RequiresApi(api = Build.VERSION_CODES.O)
public void MediaRecorderReady() {
mediaRecorder = new MediaRecorder();
mediaRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
mediaRecorder.setOutputFormat(MediaRecorder.OutputFormat.MPEG_2_TS);
mediaRecorder.setAudioEncoder(MediaRecorder.OutputFormat.AMR_NB);
mediaRecorder.setOutputFile(AudioSavePathInDevice);
}
#Override
protected void onResume() {
super.onResume();
IntentFilter intentFilter = new IntentFilter(AudioManager.ACTION_SCO_AUDIO_STATE_UPDATED);
registerReceiver(mBluetoothScoReceiver, intentFilter);
audioManager = (AudioManager) getApplicationContext().getSystemService(getApplicationContext().AUDIO_SERVICE);
// Start Bluetooth SCO.
audioManager.setMode(audioManager.MODE_NORMAL);
audioManager.setBluetoothScoOn(true);
audioManager.startBluetoothSco();
// Stop Speaker.
audioManager.setSpeakerphoneOn(false);
}
#Override
protected void onDestroy() {
super.onDestroy();
unregisterReceiver(mBluetoothScoReceiver);
// Stop Bluetooth SCO.
audioManager.stopBluetoothSco();
audioManager.setMode(audioManager.MODE_NORMAL);
audioManager.setBluetoothScoOn(false);
// Start Speaker.
audioManager.setSpeakerphoneOn(true);
}
private void requestPermission() {
ActivityCompat.requestPermissions(MainActivity.this, new
String[]{WRITE_EXTERNAL_STORAGE, RECORD_AUDIO}, RequestPermissionCode);
}
#Override
public void onRequestPermissionsResult(int requestCode,
String permissions[], int[] grantResults) {
switch (requestCode) {
case RequestPermissionCode:
if (grantResults.length > 0) {
boolean StoragePermission = grantResults[0] ==
PackageManager.PERMISSION_GRANTED;
boolean RecordPermission = grantResults[1] ==
PackageManager.PERMISSION_GRANTED;
// if (StoragePermission && RecordPermission) {
// Toast.makeText(BluetoothAudioRecorder.this, "Permission Granted",
// Toast.LENGTH_LONG).show();
// } else {
// Toast.makeText(BluetoothAudioRecorder.this,"Permission Denied",Toast.LENGTH_LONG).show();
// }
}
break;
}
}
public boolean checkPermission() {
int result = ContextCompat.checkSelfPermission(getApplicationContext(),
WRITE_EXTERNAL_STORAGE);
int result1 = ContextCompat.checkSelfPermission(getApplicationContext(),
RECORD_AUDIO);
return result == PackageManager.PERMISSION_GRANTED &&
result1 == PackageManager.PERMISSION_GRANTED;
}
}
And then my logcat of when the error occurs:
2019-11-24 11:26:54.440 29627-29683/com.example.esense_application E/libc: Access denied finding property "vendor.gralloc.disable_ahardware_buffer"
2019-11-24 11:26:54.435 29627-29627/com.example.esense_application W/RenderThread: type=1400 audit(0.0:17779): avc: denied { read } for name="u:object_r:vendor_default_prop:s0" dev="tmpfs" ino=24699 scontext=u:r:untrusted_app:s0:c7,c257,c512,c768 tcontext=u:object_r:vendor_default_prop:s0 tclass=file permissive=0
2019-11-24 11:26:54.487 29627-29627/com.example.esense_application I/System.out: ANDROID Audio SCO state: 1
2019-11-24 11:26:54.487 29627-29627/com.example.esense_application I/System.out: ANDROID Audio SCO state: 2
2019-11-24 11:26:54.868 29627-29627/com.example.esense_application I/System.out: ANDROID Audio SCO state: 1
2019-11-24 11:26:57.769 29627-29627/com.example.esense_application I/System.out: ANDROID Audio SCO state: 1
2019-11-24 11:27:00.647 29627-29627/com.example.esense_application W/System.err: java.io.FileNotFoundException: /storage/emulated/0/AudioRecording.3gp: open failed: EACCES (Permission denied)
2019-11-24 11:27:00.647 29627-29627/com.example.esense_application W/System.err: at libcore.io.IoBridge.open(IoBridge.java:496)
2019-11-24 11:27:00.647 29627-29627/com.example.esense_application W/System.err: at java.io.RandomAccessFile.<init>(RandomAccessFile.java:289)
2019-11-24 11:27:00.647 29627-29627/com.example.esense_application W/System.err: at java.io.RandomAccessFile.<init>(RandomAccessFile.java:152)
2019-11-24 11:27:00.647 29627-29627/com.example.esense_application W/System.err: at android.media.MediaRecorder.prepare(MediaRecorder.java:1046)
2019-11-24 11:27:00.647 29627-29627/com.example.esense_application W/System.err: at com.example.esense_application.MainActivity$1.onClick(MainActivity.java:67)
2019-11-24 11:27:00.647 29627-29627/com.example.esense_application W/System.err: at android.view.View.performClick(View.java:7140)
2019-11-24 11:27:00.647 29627-29627/com.example.esense_application W/System.err: at android.view.View.performClickInternal(View.java:7117)
2019-11-24 11:27:00.647 29627-29627/com.example.esense_application W/System.err: at android.view.View.access$3500(View.java:801)
2019-11-24 11:27:00.647 29627-29627/com.example.esense_application W/System.err: at android.view.View$PerformClick.run(View.java:27351)
2019-11-24 11:27:00.647 29627-29627/com.example.esense_application W/System.err: at android.os.Handler.handleCallback(Handler.java:883)
2019-11-24 11:27:00.648 29627-29627/com.example.esense_application W/System.err: at android.os.Handler.dispatchMessage(Handler.java:100)
2019-11-24 11:27:00.648 29627-29627/com.example.esense_application W/System.err: at android.os.Looper.loop(Looper.java:214)
2019-11-24 11:27:00.648 29627-29627/com.example.esense_application W/System.err: at android.app.ActivityThread.main(ActivityThread.java:7356)
2019-11-24 11:27:00.648 29627-29627/com.example.esense_application W/System.err: at java.lang.reflect.Method.invoke(Native Method)
2019-11-24 11:27:00.648 29627-29627/com.example.esense_application W/System.err: at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
2019-11-24 11:27:00.648 29627-29627/com.example.esense_application W/System.err: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
2019-11-24 11:27:00.648 29627-29627/com.example.esense_application W/System.err: Caused by: android.system.ErrnoException: open failed: EACCES (Permission denied)
2019-11-24 11:27:00.648 29627-29627/com.example.esense_application W/System.err: at libcore.io.Linux.open(Native Method)
2019-11-24 11:27:00.648 29627-29627/com.example.esense_application W/System.err: at libcore.io.ForwardingOs.open(ForwardingOs.java:167)
2019-11-24 11:27:00.648 29627-29627/com.example.esense_application W/System.err: at libcore.io.BlockGuardOs.open(BlockGuardOs.java:252)
2019-11-24 11:27:00.648 29627-29627/com.example.esense_application W/System.err: at libcore.io.ForwardingOs.open(ForwardingOs.java:167)
2019-11-24 11:27:00.648 29627-29627/com.example.esense_application W/System.err: at android.app.ActivityThread$AndroidOs.open(ActivityThread.java:7255)
2019-11-24 11:27:00.648 29627-29627/com.example.esense_application W/System.err: at libcore.io.IoBridge.open(IoBridge.java:482)
2019-11-24 11:27:00.648 29627-29627/com.example.esense_application W/System.err: ... 15 more
2019-11-24 11:27:03.528 29627-29627/com.example.esense_application E/MediaRecorder: stop called in an invalid state: 4
2019-11-24 11:27:03.528 29627-29627/com.example.esense_application D/AndroidRuntime: Shutting down VM
2019-11-24 11:27:03.529 29627-29627/com.example.esense_application E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.esense_application, PID: 29627
java.lang.IllegalStateException
at android.media.MediaRecorder.stop(Native Method)
at com.example.esense_application.MainActivity$2.onClick(MainActivity.java:98)
at android.view.View.performClick(View.java:7140)
at android.view.View.performClickInternal(View.java:7117)
at android.view.View.access$3500(View.java:801)
at android.view.View$PerformClick.run(View.java:27351)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7356)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
2019-11-24 11:27:03.540 29627-29627/com.example.esense_application I/Process: Sending signal. PID: 29627 SIG: 9

Your MediaRecorder is throwing when you try to stop() it because it has never entered the "recording" state. In fact, it never even entered the "prepared" state, because your call to prepare() did not complete successfully.
SOLUTION
Do not allow a call to start() until the prepare() call has returned (without throwing).
Do not allow a call to stop() until the start() call has returned (without throwing).
Make sure you have chosen a valid location for your output file. Try using getExternalFilesDir( null ) instead of Environment.getExternalStorageDirectory(). The bad file path is the reason your prepare() call is currently failing with an EACCESS.
As you can see, swallowing exceptions without addressing their root cause (i.e., just doing a e.printStackTrace() and carrying on), can rapidly lead to problems -- even in rough code used for learning/experimentation. If you are going to add an exception handler, it is better to provide real error handling -- and always make sure you understand why an exception is being thrown.

java.io.FileNotFoundException: (Permission denied) Only in Oreo

I am downloading photos to smartphone. For versions lower than Oreo, there's no problem. But for Oreo, my code isn't not working. I tried this code in Emulator:
I implemented a function to save an image to external storage.
private void saveImageToExternalStorage(Bitmap finalBitmap,String name) {
String root = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES).toString();
File myDir = new File(root + "/xx");
myDir.mkdirs();
String fname = name + ".jpg";
File file = new File(myDir, fname);
if (file.exists())
file.delete();
try {
FileOutputStream out = new FileOutputStream(file);
finalBitmap.compress(Bitmap.CompressFormat.JPEG, 90, out);
out.flush();
out.close();
}
catch (Exception e) {
e.printStackTrace();
}
// Tell the media scanner about the new file so that it is
// immediately available to the user.
MediaScannerConnection.scanFile(this, new String[] { file.toString() }, null,
new MediaScannerConnection.OnScanCompletedListener() {
public void onScanCompleted(String path, Uri uri) {
Log.i("ExternalStorage", "Scanned " + path + ":");
Log.i("ExternalStorage", "-> uri=" + uri);
}
});
}
I am requesting permissions with dexter library.
Dexter.withActivity(MainActivity.this)
.withPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE)
.withListener(new PermissionListener() {
#Override
public void onPermissionGranted(PermissionGrantedResponse response) {
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(MainActivity.this);
if (!prefs.getBoolean("firstTime", false)) {
task.execute();
SharedPreferences.Editor editor = prefs.edit();
editor.putBoolean("firstTime", true);
editor.commit();
}
}
#Override
public void onPermissionDenied(PermissionDeniedResponse response) {
Toast.makeText(MainActivity.this, "You need to allow permission if you want to use camera", Toast.LENGTH_LONG).show();
}
#Override
public void onPermissionRationaleShouldBeShown(PermissionRequest permission, PermissionToken token) {
token.continuePermissionRequest();
Toast.makeText(MainActivity.this, "You need to allow permission if you want to use camera", Toast.LENGTH_LONG).show();
}
}).check();
I save images with asynctask
final AsyncTask<Void, Void, Void> task = new AsyncTask<Void, Void, Void>() {
private ProgressDialog dialog;
#Override
protected void onPreExecute()
{
this.dialog = new ProgressDialog(MainActivity.this);
this.dialog.setMessage(getString(R.string.newfeature));
this.dialog.setCancelable(false);
this.dialog.setOnCancelListener(new DialogInterface.OnCancelListener()
{
#Override
public void onCancel(DialogInterface dialog)
{
// cancel AsyncTask
cancel(false);
}
});
this.dialog.show();
}
#Override
protected Void doInBackground(Void... params)
{
// do your stuff
Bitmap myBitmap2 = BitmapFactory.decodeResource(getApplicationContext().getResources(), R.drawable.im2);
saveImageToExternalStorage(myBitmap2,"imag2");
myBitmap2.recycle();
return null;
}
#Override
protected void onPostExecute(Void result)
{
//called on ui thread
if (this.dialog != null) {
this.dialog.dismiss();
}
}
#Override
protected void onCancelled()
{
//called on ui thread
if (this.dialog != null) {
this.dialog.dismiss();
}
}
};
I can see Storage permission is granted when I look Settings --> Apps for my app. But images are not saved correctly. In fact images are saved but all of them is green square like this.
As a result, it gives permission denied error although permission is granted.
09-21 13:11:08.023 17636-17765/xx.xx W/System.err: java.io.FileNotFoundException: /storage/emulated/0/Pictures/xx/imag2.jpg (Permission denied)
09-21 13:11:08.024 17636-17765/xx.xx W/System.err: at java.io.FileOutputStream.open0(Native Method)
09-21 13:11:08.024 17636-17765/xx.xx W/System.err: at java.io.FileOutputStream.open(FileOutputStream.java:308)
09-21 13:11:08.033 17636-17765/xx.xx W/System.err: at java.io.FileOutputStream.<init>(FileOutputStream.java:238)
09-21 13:11:08.033 17636-17765/xx.xx W/System.err: at java.io.FileOutputStream.<init>(FileOutputStream.java:180)
09-21 13:11:08.033 17636-17765/xx.xx W/System.err: at xx.xx.MainActivity.saveImageToExternalStorage(MainActivity.java:804)
09-21 13:11:08.033 17636-17765/xx.xx W/System.err: at xx.xx.MainActivity.access$000(MainActivity.java:62)
09-21 13:11:08.033 17636-17765/xx.xx W/System.err: at xx.xx.MainActivity$1.doInBackground(MainActivity.java:119)
09-21 13:11:08.033 17636-17765/xx.xx W/System.err: at xx.xx.MainActivity$1.doInBackground(MainActivity.java:89)
09-21 13:11:08.033 17636-17765/xx.xx W/System.err: at android.os.AsyncTask$2.call(AsyncTask.java:333)
09-21 13:11:08.033 17636-17765/xx.xx W/System.err: at java.util.concurrent.FutureTask.run(FutureTask.java:266)
09-21 13:11:08.033 17636-17765/xx.xx W/System.err: at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245)
09-21 13:11:08.033 17636-17765/xx.xx W/System.err: at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
09-21 13:11:08.033 17636-17765/xx.xx W/System.err: at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
09-21 13:11:08.033 17636-17765/xx.xx W/System.err: at java.lang.Thread.run(Thread.java:764)

Access Sd-Card's files
Use DOCUMENT_TREE dialog to get sd-card's Uri.
Inform user about how to choose sd-card on the dialog. (with pictures or gif animations)
// call for document tree dialog
Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE);
startActivityForResult(intent, REQUEST_CODE_OPEN_DOCUMENT_TREE);
On onActivityResult you'll have the selected directory Uri. (sdCardUri)
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
switch (requestCode) {
case REQUEST_CODE_OPEN_DOCUMENT_TREE:
if (resultCode == Activity.RESULT_OK) {
sdCardUri = data.getData();
}
break;
}
}
Now must check if the user,
a. selected the sd-card
b. selected the sd-card that our file is on (some devices could have multiple sd-cards).
We check both a and b by finding the file through the hierarchy, from sd root to our file. If file found, both of a and b conditions are acquired.
//First we get `DocumentFile` from the `TreeUri` which in our case is `sdCardUri`.
DocumentFile documentFile = DocumentFile.fromTreeUri(this, sdCardUri);
//Then we split file path into array of strings.
//ex: parts:{"", "storage", "extSdCard", "MyFolder", "MyFolder", "myImage.jpg"}
// There is a reason for having two similar names "MyFolder" in
//my exmple file path to show you similarity in names in a path will not
//distract our hiarchy search that is provided below.
String[] parts = (file.getPath()).split("\\/");
// findFile method will search documentFile for the first file
// with the expected `DisplayName`
// We skip first three items because we are already on it.(sdCardUri = /storage/extSdCard)
for (int i = 3; i < parts.length; i++) {
if (documentFile != null) {
documentFile = documentFile.findFile(parts[i]);
}
}
if (documentFile == null) {
// File not found on tree search
// User selected a wrong directory as the sd-card
// Here must inform user about how to get the correct sd-card
// and invoke file chooser dialog again.
} else {
// File found on sd-card and it is a correct sd-card directory
// save this path as a root for sd-card on your database(SQLite, XML, txt,...)
// Now do whatever you like to do with documentFile.
// Here I do deletion to provide an example.
if (documentFile.delete()) {// if delete file succeed
// Remove information related to your media from ContentResolver,
// which documentFile.delete() didn't do the trick for me.
// Must do it otherwise you will end up with showing an empty
// ImageView if you are getting your URLs from MediaStore.
//
Uri mediaContentUri = ContentUris.withAppendedId(
MediaStore.Images.Media.EXTERNAL_CONTENT_URI,
longMediaId);
getContentResolver().delete(mediaContentUri , null, null);
}
}
Note:
You must provide access permission to the external storage inside your manifest and for os>=Marshmallow inside the app.
https://stackoverflow.com/a/32175771/2123400
Edit Sd-Card's Files
For editing an existing image on your sd-card you don't need any of above steps if you want to invoke another app to do it for you.
Here we invoke all the activities (from all the installed apps) with the capability of editing the images. (Programmers mark their apps in the manifest for its capabilities to provide accessibility from other apps (activities)).
on your editButton click event:
String mimeType = getMimeTypeFromMediaContentUri(mediaContentUri);
startActivityForResult(Intent.createChooser(new Intent(Intent.ACTION_EDIT).setDataAndType(mediaContentUri, mimeType).putExtra(Intent.EXTRA_STREAM, mediaContentUri).addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION), "Edit"), REQUEST_CODE_SHARE_EDIT_SET_AS_INTENT);
and this is how to get mimeType:
public String getMimeTypeFromMediaContentUri(Uri uri) {
String mimeType;
if (uri.getScheme().equals(ContentResolver.SCHEME_CONTENT)) {
ContentResolver cr = getContentResolver();
mimeType = cr.getType(uri);
} else {
String fileExtension = MimeTypeMap.getFileExtensionFromUrl(uri
.toString());
mimeType = MimeTypeMap.getSingleton().getMimeTypeFromExtension(
fileExtension.toLowerCase());
}
return mimeType;
}
Note:
On Android KitKat(4.4) don't ask the user to select the sd-card because on this version of Android DocumentProvideris not applicable, hence we have no chance to have access to the sd-card with this approach.
Look at the API level for the DocumentProvider
https://developer.android.com/reference/android/provider/DocumentsProvider.html
I couldn't find anything that works on Android KitKat(4.4). If you found anything useful with KitKat please share with us.
On versions below the KitKat access to sd-card is already provided by the OS.

Error inflating class android.view.InflateException, Didn't find class java.lang.ClassNotFoundException

When I'm trying to run the app I get the exception which is shown in the Title.
This is my xml File:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">
<com.example.ruben.fileapp.MainActivity.PlayButton
android:id="#+id/play_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<com.example.ruben.fileapp.MainActivity.RecordButton
android:id="#+id/record_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</LinearLayout>
</LinearLayout>
This is my MainActivity.java:
package com.example.ruben.fileapp;
import android.Manifest;
import android.content.Context;
import android.content.pm.PackageManager;
import android.media.MediaPlayer;
import android.media.MediaRecorder;
import android.support.annotation.NonNull;
import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.AppCompatButton;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.LinearLayout;
import java.io.IOException;
public class MainActivity extends AppCompatActivity {
private static final String LOG_TAG = "AudioRecordTest";
private static final int REQUEST_RECORD_AUDIO_PERMISSION = 200;
private static String mFileName = null;
private RecordButton mRecordButton = null;
private MediaRecorder mRecorder = null;
private PlayButton mPlayButton = null;
private MediaPlayer mPlayer = null;
// Requesting permission to RECORD_AUDIO
private boolean permissionToRecordAccepted = false;
private String [] permissions = {Manifest.permission.RECORD_AUDIO};
//region permissionMethod
#Override
public void onRequestPermissionsResult(int requestCode, #NonNull String[] permissions, #NonNull int[] grantResults) {
super.onRequestPermissionsResult(requestCode, permissions, grantResults);
switch (requestCode){
case REQUEST_RECORD_AUDIO_PERMISSION:
permissionToRecordAccepted = grantResults[0] == PackageManager.PERMISSION_GRANTED;
break;
}
if (!permissionToRecordAccepted ) finish();
}
//endregion
private void onRecord(boolean start) {
if (start) {
startRecording();
} else {
stopRecording();
}
}
private void onPlay(boolean start) {
if (start) {
startPlaying();
} else {
stopPlaying();
}
}
private void startPlaying() {
mPlayer = new MediaPlayer();
try {
mPlayer.setDataSource(mFileName);
mPlayer.prepare();
mPlayer.start();
} catch (IOException e) {
Log.e(LOG_TAG, "prepare() failed");
}
}
private void stopPlaying() {
mPlayer.release();
mPlayer = null;
}
private void startRecording() {
mRecorder = new MediaRecorder();
mRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
mRecorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP);
mRecorder.setOutputFile(mFileName);
mRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB);
try {
mRecorder.prepare();
} catch (IOException e) {
Log.e(LOG_TAG, "prepare() failed");
}
mRecorder.start();
}
private void stopRecording() {
mRecorder.stop();
mRecorder.release();
mRecorder = null;
}
//region RecordButton
public class RecordButton extends AppCompatButton {
boolean mStartRecording = true;
OnClickListener clicker = new OnClickListener() {
public void onClick( View v) {
onRecord(mStartRecording);
if (mStartRecording) {
setText("Stop recording");
} else {
setText("Start recording");
}
mStartRecording = !mStartRecording;
}
};
public RecordButton(Context ctx) {
super(ctx);
setText("Start recording");
setOnClickListener(clicker);
}
}
//endregion
//region PlayButton
public class PlayButton extends AppCompatButton {
boolean mStartPlaying = true;
OnClickListener clicker = new OnClickListener() {
public void onClick(View v) {
onPlay(mStartPlaying);
if (mStartPlaying) {
setText("Stop playing");
} else {
setText("Start playing");
}
mStartPlaying = !mStartPlaying;
}
};
public PlayButton(Context ctx) {
super(ctx);
setText("Start playing");
setOnClickListener(clicker);
}
}
//endregion
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Record to the external cache directory for visibility
mFileName = getExternalCacheDir().getAbsolutePath();
mFileName += "/audiorecordtest.3gp";
ActivityCompat.requestPermissions(this, permissions, REQUEST_RECORD_AUDIO_PERMISSION);
LinearLayout ll = new LinearLayout(this);
mRecordButton = (RecordButton) findViewById(R.id.record_button);
mPlayButton = (PlayButton) findViewById(R.id.play_button);
/*ll.addView(mRecordButton,
new LinearLayout.LayoutParams(
ViewGroup.LayoutParams.WRAP_CONTENT,
ViewGroup.LayoutParams.WRAP_CONTENT,
0));*/
//mPlayButton = new PlayButton(this);
/*ll.addView(mPlayButton,
new LinearLayout.LayoutParams(
ViewGroup.LayoutParams.WRAP_CONTENT,
ViewGroup.LayoutParams.WRAP_CONTENT,
0));
setContentView(ll);*/
}
#Override
public void onStop() {
super.onStop();
if (mRecorder != null) {
mRecorder.release();
mRecorder = null;
}
if (mPlayer != null) {
mPlayer.release();
mPlayer = null;
}
}
}
This is my full logcat:
09-04 12:36:45.898 6198-6198/? I/art: Late-enabling -Xcheck:jni
Reinit property: dalvik.vm.checkjni= false
09-04 12:36:46.143 6198-6198/com.example.ruben.fileapp W/System: ClassLoader referenced unknown path: /data/app/com.example.ruben.fileapp-1/lib/arm64
09-04 12:36:46.156 6198-6198/com.example.ruben.fileapp I/InstantRun: starting instant run server: is main process
09-04 12:36:46.185 6198-6198/com.example.ruben.fileapp I/HwCust: Constructor found for class android.app.HwCustActivityImpl
09-04 12:36:46.210 6198-6198/com.example.ruben.fileapp I/HwCust: Constructor found for class android.app.HwCustHwWallpaperManagerImpl
09-04 12:36:46.235 6198-6198/com.example.ruben.fileapp W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
09-04 12:36:46.318 6198-6198/com.example.ruben.fileapp E/HW-JPEG-DEC: [HME_JPEG_DEC_Delete](3321): HME_JPEG_DEC_Delete: decoder_ctx=null
09-04 12:36:46.344 6198-6198/com.example.ruben.fileapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.ruben.fileapp, PID: 6198
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.ruben.fileapp/com.example.ruben.fileapp.MainActivity}: android.view.InflateException: Binary XML file line #14: Binary XML file line #14: Error inflating class com.example.ruben.fileapp.MainActivity.PlayButton
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2793)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2864)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1567)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:156)
at android.app.ActivityThread.main(ActivityThread.java:6523)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:941)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:831)
Caused by: android.view.InflateException: Binary XML file line #14: Binary XML file line #14: Error inflating class com.example.ruben.fileapp.MainActivity.PlayButton
Caused by: android.view.InflateException: Binary XML file line #14: Error inflating class com.example.ruben.fileapp.MainActivity.PlayButton
Caused by: java.lang.ClassNotFoundException: Didn't find class "com.example.ruben.fileapp.MainActivity.PlayButton" on path: DexPathList[[zip file "/data/app/com.example.ruben.fileapp-1/base.apk", zip file "/data/app/com.example.ruben.fileapp-1/split_lib_dependencies_apk.apk", zip file "/data/app/com.example.ruben.fileapp-1/split_lib_slice_0_apk.apk", zip file "/data/app/com.example.ruben.fileapp-1/split_lib_slice_1_apk.apk", zip file "/data/app/com.example.ruben.fileapp-1/split_lib_slice_2_apk.apk", zip file "/data/app/com.example.ruben.fileapp-1/split_lib_slice_3_apk.apk", zip file "/data/app/com.example.ruben.fileapp-1/split_lib_slice_4_apk.apk", zip file "/data/app/com.example.ruben.fileapp-1/split_lib_slice_5_apk.apk", zip file "/data/app/com.example.ruben.fileapp-1/split_lib_slice_6_apk.apk", zip file "/data/app/com.example.ruben.fileapp-1/split_lib_slice_7_apk.apk", zip file "/data/app/com.example.ruben.fileapp-1/split_lib_slice_8_apk.apk", zip file "/data/app/com.example.ruben.fileapp-1/split_lib_slice_9_apk.apk"],nativeLibraryDirectories=[/data/app/com.example.ruben.fileapp-1/lib/arm64, /system/lib64, /vendor/lib64, /system/vendor/lib64, /product/lib64]]
at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
at java.lang.ClassLoader.loadClass(ClassLoader.java:380)
at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
at android.view.LayoutInflater.createView(LayoutInflater.java:616)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:798)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:738)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:869)
at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:832)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:872)
at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:832)
at android.view.LayoutInflater.inflate(LayoutInflater.java:518)
at android.view.LayoutInflater.inflate(LayoutInflater.java:426)
at android.view.LayoutInflater.inflate(LayoutInflater.java:377)
at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:287)
at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:139)
at com.example.ruben.fileapp.MainActivity.onCreate(MainActivity.java:158)
at android.app.Activity.performCreate(Activity.java:6910)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1123)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2746)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2864)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1567)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:156)
at android.app.ActivityThread.main(ActivityThread.java:6523)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:941)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:831)
09-04 12:36:46.353 6198-6198/com.example.ruben.fileapp I/Process: Sending signal. PID: 6198 SIG: 9
I would appreciate any kind of help.
Thank you
P.S.: This is my first question posted on stackoverflow, if something is bad in the way I'm asking, feel free to tell me.

You're calling MainActivity.RecordButton but the RecordButton isn't a subclass of MainActivity.
Your RecordButton and PlayButton are public classes, which means they are in their own files, probaly at the same level as the MainActivity.
try
<com.example.ruben.fileapp.PlayButton
android:id="#+id/play_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />

Make separate class for custom button instead of mainactivity
com.example.ruben.fileapp.MainActivity.PlayButton
move your PlayButton class into other location like
com.example.ruben.fileapp.PlayButton

Please make sure that android.enableJetifier=true exists in the gradle.properties it's not there by default anymore and you will face ambiguous exceptions when some library inside your code still uses the support libraries rather than AndroidX's.

and how do I fix it? E/UncaughtException: java.lang.NullPointerException: Attempt to invoke virtual method [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 5 years ago.
hello I have the following error
what file can be making the conflict?
I found the project on github
This is the error
this error
> it.unipi.iet.namefirebase E/UncaughtException:
> java.lang.NullPointerException: Attempt to invoke virtual method
> 'java.lang.String
> com.google.firebase.auth.FirebaseUser.getProviderId()' on a null
> object reference
> at it.unipi.iet.namefirebase.MainActivity$4$1.onComplete(MainActivity.java:112)
> at com.google.android.gms.tasks.zzc$1.run(Unknown Source)
> at android.os.Handler.handleCallback(Handler.java:739)
> at android.os.Handler.dispatchMessage(Handler.java:95)
> at android.os.Looper.loop(Looper.java:148)
> at android.app.ActivityThread.main(ActivityThread.java:5417)
> at java.lang.reflect.Method.invoke(Native Method)
> at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
> at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
> it.unipi.iet.namefirebase D/FA: Logging event (FE): _ae,
> Bundle[{_o=crash, timestamp=1509341623773, fatal=1}]
> it.unipi.iet.namefirebase V/FA: Using measurement service
> it.unipi.iet.namefirebase V/FA: Connecting to remote service
> com.google.android.gms W/FirebaseAuth: [PhoneNumberAuthPostProcessor]
> postProcess starts com.google.android.gms W/FirebaseAuth:
> [PhoneNumberAuthPostProcessor] postProcess ends
> it.unipi.iet.namefirebase E/AndroidRuntime: FATAL EXCEPTION: main
> Process: it.unipi.iet.namefirebase, PID: 6000
> java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String
> com.google.firebase.auth.FirebaseUser.getProviderId()' on a null
> object reference
> at it.unipi.iet.namefirebase.MainActivity$4$1.onComplete(MainActivity.java:112)
> at com.google.android.gms.tasks.zzc$1.run(Unknown Source)
> at android.os.Handler.handleCallback(Handler.java:739)
> at android.os.Handler.dispatchMessage(Handler.java:95)
> at android.os.Looper.loop(Looper.java:148)
> at android.app.ActivityThread.main(ActivityThread.java:5417)
> at java.lang.reflect.Method.invoke(Native Method)
> at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
> at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
> system_process W/ActivityManager: Force finishing activity
> it.unipi.iet.namefirebase/.MainActivity ? D/gralloc_ranchu:
> gralloc_alloc: Creating ashmem region of size 1806336
> it.unipi.iet.namefirebase I/FirebaseCrash: Sending crashes ?
> E/EGL_emulation: tid 1208: eglCreateSyncKHR(1881): error 0x3004
> (EGL_BAD_ATTRIBUTE)
Code mainactivity
package it.unipi.iet.namefirebase;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
import iit.unipi.iet.namefirebase.utilities.AuthUtilities;
import it.unipi.iet.namefirebase.utilities.DatabaseUtilities;
import com.facebook.AccessToken;
import com.facebook.CallbackManager;
import com.facebook.FacebookCallback;
import com.facebook.FacebookException;
import com.facebook.FacebookSdk;
import com.facebook.login.LoginResult;
import com.facebook.login.widget.LoginButton;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.AuthCredential;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FacebookAuthProvider;
import com.google.firebase.auth.FirebaseUser;
public class MainActivity extends Activity{
public static final String SIGN = "it.unipi.iet.namefirebase.SIGN";
private final String TAG = "MainActivity";
private AuthUtilities AuthUt;
private CallbackManager callbackManager;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
FacebookSdk.sdkInitialize(getApplicationContext());
callbackManager = CallbackManager.Factory.create();
setContentView(R.layout.activity_main);
// Check Authentication
AuthUt = new AuthUtilities();
if(AuthUt.getUser() != null ){
// if user is already logged changes activity
Log.d(TAG,"User already logged");
Intent i = new Intent(MainActivity.this,MapsActivity.class);
startActivity(i);}
else{
Log.d(TAG,"User not logged yet");
}
// Sign in Button
final Button SignIn = (Button) findViewById(R.id.button);
SignIn.setOnClickListener(new View.OnClickListener(){
public void onClick(View v){
Intent intent = new Intent(MainActivity.this,LoginActivity.class);
intent.putExtra(SIGN,"sign-in");
startActivity(intent);
}
});
// Sign up with email Button
final Button SignUp = (Button) findViewById(R.id.button2);
SignUp.setOnClickListener(new View.OnClickListener(){
public void onClick(View v){
Intent intent = new Intent(MainActivity.this,LoginActivity.class);
intent.putExtra(SIGN,"sign-up");
startActivity(intent);
}
});
// Connect with Facebook button
FacebookSdk.sdkInitialize(getApplicationContext());
callbackManager = CallbackManager.Factory.create();
LoginButton loginButton = (LoginButton) findViewById(R.id.button3);
loginButton.setReadPermissions("email", "public_profile");
loginButton.registerCallback(callbackManager, new FacebookCallback<LoginResult>() {
#Override
public void onSuccess(LoginResult loginResult) {
Log.d(TAG, "facebook:onSuccess:" + loginResult);
handleFacebookAccessToken(loginResult.getAccessToken());
}
#Override
public void onCancel() {
Log.d(TAG, "facebook:onCancel");
// ...
}
#Override
public void onError(FacebookException error) {
Log.d(TAG, "facebook:onError", error);
// ...
}
});
// Browse as a guest button
final Button GuestUser = (Button) findViewById(R.id.button4);
GuestUser.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// signin_anonymously
AuthUt.get_mAuth().signInAnonymously()
.addOnCompleteListener(MainActivity.this, new OnCompleteListener<AuthResult>() {
#Override
public void onComplete(#NonNull Task<AuthResult> task) {
Log.d(TAG, "signInAnonymously:onComplete:" + task.isSuccessful());
Log.d(TAG,"User Provider: "+ AuthUt.get_mAuth().getCurrentUser().getProviderId());
// start MapsActivity
Intent i = new Intent(MainActivity.this,MapsActivity.class);
startActivity(i);
// If sign in fails, display a message to the user. If sign in succeeds
// the auth state listener will be notified and logic to handle the
// signed in user can be handled in the listener.
if (!task.isSuccessful()) {
Log.w(TAG, "signInAnonymously", task.getException());
Toast.makeText(MainActivity.this, "Authentication failed.",
Toast.LENGTH_SHORT).show();
}
}
});
}
});
}
#Override
public void onStart() {
super.onStart();
AuthUt.addListner();
}
#Override
public void onStop() {
super.onStop();
AuthUt.removeListener();
}
/*
* Disable going back function
*/
#Override
public void onBackPressed() {
// disable going back to the previous Activity
moveTaskToBack(true);
}
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
callbackManager.onActivityResult(requestCode, resultCode, data);
}
private void handleFacebookAccessToken(AccessToken token) {
Log.d(TAG, "handleFacebookAccessToken:" + token);
AuthCredential credential = FacebookAuthProvider.getCredential(token.getToken());
AuthUt.get_mAuth().signInWithCredential(credential)
.addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
#Override
public void onComplete(#NonNull Task<AuthResult> task) {
Log.d(TAG, "signInWithCredential:onComplete:" + task.isSuccessful());
FirebaseUser user = AuthUt.get_mAuth().getCurrentUser();
Log.d(TAG,"url "+user.getPhotoUrl());
DatabaseUtilities db = new DatabaseUtilities();
db.writeNewUser(user.getUid(),user.getDisplayName(),null,user.getPhotoUrl().toString(),null, null);
Log.d(TAG,"Fb user created");
// start MapsActivity
Intent i = new Intent(MainActivity.this,MapsActivity.class);
startActivity(i);
// If sign in fails, display a message to the user. If sign in succeeds
// the auth state listener will be notified and logic to handle the
// signed in user can be handled in the listener.
if (!task.isSuccessful()) {
Log.w(TAG, "signInWithCredential", task.getException());
Toast.makeText(MainActivity.this, "Authentication failed.",
Toast.LENGTH_SHORT).show();
}
}
});
}
}

You will have to make a null check before using the object.
if(yourObject != null)
{
int id = yourObject.getProviderId();
} else{
// Handle what if null
}
Also, always make sure if you are uncertain that the object will be null at times, use try{} catch{} block.

Application stopped unexpectedly: Fatal Exception

could anyone help my with my app code. I tryied to make an application that could send data (number or letter) to arduino through bluetooth. This is how my JAVA code look:
package com.example.btprojektas;
import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Set;
import java.util.UUID;
public class MainActivity extends Activity{
private static final String TAG = "btprojektas";
Button btnON, btnOFF;
BluetoothAdapter bluetoothAdapter = null;
BluetoothDevice device = null;
OutputStream outputStream = null;
BluetoothSocket socket = null;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
btnON = (Button) findViewById(R.id.btnON);
btnOFF = (Button) findViewById(R.id.btnOFF);
if(!bluetoothAdapter.isEnabled()){
Intent enableBluetooth = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableBluetooth, 0);
}
loadPairedDevice();
connectBT();
btnON.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
sendData("0");
Toast.makeText(getBaseContext(), "Turn on LED", Toast.LENGTH_SHORT).show();
}
});
btnOFF.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
sendData("1");
Toast.makeText(getBaseContext(), "Turn off LED", Toast.LENGTH_SHORT).show();
}
});
}
private void connectBT() {
if (device != null) {
UUID uuid = UUID.fromString("00001101-0000-1000-8000-00805f9b34fb"); //Standard SerialPortService ID
try {
socket = device.createRfcommSocketToServiceRecord(uuid);
socket.connect();
outputStream = socket.getOutputStream();
} catch (IOException e) {
e.printStackTrace();
}
}
}
private void disconnect() {
try {
if (outputStream != null) outputStream.close();
if (socket != null) socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
private void loadPairedDevice() {
Set<BluetoothDevice> pairedDevices = bluetoothAdapter.getBondedDevices();
if (pairedDevices.size() > 0) {
Log.d(TAG, "Device found");
for (BluetoothDevice device : pairedDevices)
if (device.getName().equals("HC-06")) {
this.device = device;
break;
}
}
}
#Override
protected void onPause() {
super.onPause();
disconnect();
}
#Override
protected void onResume() {
super.onResume();
loadPairedDevice();
connectBT();
}
private void sendData(String message) {
byte[] buffer = message.getBytes();
Log.d(TAG,"Send data:"+ message);
try{
outputStream.write (buffer);
} catch (IOException e) {}
}
}
in XML I have two buttons. When the program starts I push one of those buttons and the "Applications ... stopped unexpectedly" appears with fatal exeption fault code:
01-08 15:55:15.439 15354-15354/com.example.btprojektas E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.NullPointerException
at com.example.btprojektas.MainActivity.sendData(MainActivity.java:122)
at com.example.btprojektas.MainActivity.access$000(MainActivity.java:22)
at com.example.btprojektas.MainActivity$1.onClick(MainActivity.java:55)
at android.view.View.performClick(View.java:2485)
at android.view.View$PerformClick.run(View.java:9080)
at android.os.Handler.handleCallback(Handler.java:587)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:130)
at android.app.ActivityThread.main(ActivityThread.java:3687)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:507)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
at dalvik.system.NativeStart.main(Native Method)
P.S. Sorry for this question I know that it is quite common but I am new at programming especially JAVA.

It's either the socket or the outputStream. In ConnectBT, you don't check if socket is not null. You directly call socket.connect() assuming socket is valid. The same applies to outputStream. You use it before making sure it's not null.
Also you call
startActivityForResult(enableBluetooth, 0);
but you don't check for the result which is whether bluetooth got enabled or not. This makes your device also suspicious.
Calling
loadPairedDevice();
connectBT();
makes sense only when bluetooth is enabled. Enabling bluetooth can take couple of seconds, but you call them right away.

A couple of tips:
you're calling loadPairedDevice() and connectBT() twice: in onCreate() and in onResume() - do it only once
before using outputStream, check if it's not null (as advised by others)
in sendData(), catch AND print your exception:
try {
if (outputStream != null) {
outputStream.write(buffer);
}
else {
Log.d("TAG", "sendData() - outputStream is null!");
}
}
catch (IOException e) {
e.printStackTrace();
}
in loadPairedDevice(), if you don't find the device "HC-06", your variable device will be null...
enabling bluetooth takes few seconds, so register and listen to ACTION_STATE_CHANGED broadcast Intent. It will contain extra field EXTRA_STATE; look for STATE_ON, and then call your loadPairedDevices() and connectBT() there:
create receiver (inside your MainActivity class):
private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
public void onReceive(Context context, Intent intent) {
final String action = intent.getAction();
//this is the action you are observing
if (BluetoothAdapter.ACTION_STATE_CHANGED.equals(action)) {
final int state = intent.getIntExtra(BluetoothAdapter.EXTRA_STATE, BluetoothAdapter.ERROR);
switch(state) {
//and the state we were looking for
//which means that bluetooth has switched on
//so now you can call your functions
//and set the flag to true, which then use in your
//onClick listeners
case BluetoothAdapter.STATE_ON:
loadPairedDevice();
connectBT();
isBluetoothOn = true;
break;
}
}
}
}
in onCreate(), create IntentFilter and register receiver with it
IntentFilter btFilter = new IntentFilter();
btFilter.addAction(BluetoothAdapter.ACTION_STATE_CHANGED);
registerReceiver(mReceiver, btFilter);
remember to unregister receiver in onPause():
unregisterReceiver(mReceiver);
disable your buttons and enable them in the above listener, when you know BT is switched on; alternatively, keep a flag and use it in your click listeners, eg.:
boolean isBluetoothOn = false;
then later in listener when you get STATE_ON
isBluetooth = true;
And in your button click listener:
//for btnON
public void onClick(View v) {
if (isBluetoothOn) {
sendData("0");
Toast.makeText(getBaseContext(), "Turn on LED", Toast.LENGTH_SHORT).show();
}
}
Do the same for btnOFF.