Having problems debugging an android networking application. I think I might have some problems with the import but I don't know which. If you can see the problem, please do let me know. Thank you.
MainActivity.java
package com.example.networkingfinals;
import androidx.appcompat.app.AppCompatActivity;
import android.app.LoaderManager;
import android.app.LoaderManager.LoaderCallbacks;
import android.content.Loader;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import java.util.List;
public class MainActivity extends AppCompatActivity implements LoaderCallbacks<List<BookInfo>> {
private String url;
private String input;
private BookAdapter bookAdapter;
private int LOADER_ID = 0;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button button = (Button) findViewById(R.id.submit);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
EditText editText = (EditText) findViewById(R.id.input);
input = String.valueOf(editText.getText());
url = "https://www.googleapis.com/books/v1/volumes?q="+input+"&maxResults=3";
}
});
LoaderManager loaderManager = getLoaderManager();
getLoaderManager().initLoader(LOADER_ID, null, this);//Set loader manager to call asyncloader in onCreateLoader
//TODO: Implement AsyncTaskLoader and LoadManager fetching network data on parallel thread
}
#Override
public Loader<List<BookInfo>> onCreateLoader(int id, Bundle args) {
Loader<List<BookInfo>> books = new BookAsync(this, url);
return books;
//Call oncreate Loader , fetching List of Book Info
}
#Override
public void onLoadFinished(Loader<List<BookInfo>> loader, List<BookInfo> data) {
Log.v("onLoadFinished", "Return " + data);
bookAdapter.addAll(data);
}
#Override
public void onLoaderReset(Loader loader) {
bookAdapter.clear();
}
Logcat
2021-01-10 18:44:55.950 13590-13590/com.example.networkingfinals V/onCreateLoader: Return BookAsync{814c192 id=0}
2021-01-10 18:44:56.045 13590-13590/com.example.networkingfinals V/onLoadFinished: Return null
2021-01-10 18:44:56.045 13590-13590/com.example.networkingfinals D/AndroidRuntime: Shutting down VM
2021-01-10 18:44:56.055 13590-13590/com.example.networkingfinals E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.networkingfinals, PID: 13590
java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.networkingfinals.BookAdapter.addAll(java.util.Collection)' on a null object reference
at com.example.networkingfinals.MainActivity.onLoadFinished(MainActivity.java:61)
at com.example.networkingfinals.MainActivity.onLoadFinished(MainActivity.java:17)
at android.app.LoaderManagerImpl$LoaderInfo.callOnLoadFinished(LoaderManager.java:497)
at android.app.LoaderManagerImpl$LoaderInfo.onLoadComplete(LoaderManager.java:465)
at android.content.Loader.deliverResult(Loader.java:157)
at android.content.AsyncTaskLoader.dispatchOnLoadComplete(AsyncTaskLoader.java:274)
at android.content.AsyncTaskLoader$LoadTask.onPostExecute(AsyncTaskLoader.java:97)
at android.os.AsyncTask.finish(AsyncTask.java:755)
at android.os.AsyncTask.access$900(AsyncTask.java:192)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:772)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7458)
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:935)
2021-01-10 18:44:56.138 13590-13590/com.example.networkingfinals I/Process: Sending signal. PID: 13590 SIG:
I think I don't understand how onCreateLoader() and onLoadFinished() works. I tried and find that onCreateLoader return non-null data but in onLoadFinished() the data passed into it was null.
This error is because your adapter is not initialized yet you need to initialize it in onCreate
this.bookAdapter = new BookAdapter();
the error message says
java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.networkingfinals.BookAdapter.addAll(java.util.Collection)' on a null object reference
that means is your adapter is null and you call addAll from the null object reference
Related
I am trying to set up Firebase to log events for Google Analytics on my Android App and I get the error above.
I followed the tutorial but I think maybe since I am using ReactActivity instead of AppCompatActivity, maybe this is why it does nor work.
I am very new to java and would really appreciate some help!
Here is MainActivity.java
package com.app;
import com.facebook.react.ReactActivity;
import com.google.firebase.analytics.FirebaseAnalytics;
import com.app.AnalyticsWebInterface;
import android.annotation.SuppressLint;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.os.Build;
import android.webkit.WebView;
import android.util.Log;
#SuppressLint({ "AddJavascriptInterface", "SetJavaScriptEnabled" })
public class MainActivity extends ReactActivity {
private static final String TAG = "MainActivity";
private FirebaseAnalytics mFirebaseAnalytics;
private WebView mWebView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// ATTENTION: This was auto-generated to handle app links.
Intent appLinkIntent = getIntent();
String appLinkAction = appLinkIntent.getAction();
Uri appLinkData = appLinkIntent.getData();
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
mWebView.addJavascriptInterface(
new AnalyticsWebInterface(this), AnalyticsWebInterface.TAG);
} else {
Log.w(TAG, "Not adding JavaScriptInterface, API Version: " + Build.VERSION.SDK_INT);
}
logSearchEvent();
logPurchaseEvent();
}
/**
* Returns the name of the main component registered from JavaScript. This is
* used to schedule
* rendering of the component.
*/
#Override
protected String getMainComponentName() {
return "App";
}
private void logPurchaseEvent() {
String transactionId = "transactionId";
String value = "1.99";
Bundle bundle = new Bundle();
bundle.putString(FirebaseAnalytics.Param.TRANSACTION_ID, transactionId);
bundle.putString(FirebaseAnalytics.Param.VALUE, value);
mFirebaseAnalytics.logEvent(FirebaseAnalytics.Event.PURCHASE, bundle);
}
private void logSearchEvent() {
String searchTerm = "searchTerm";
Bundle bundle = new Bundle();
bundle.putString(FirebaseAnalytics.Param.SEARCH_TERM, searchTerm);
mFirebaseAnalytics.logEvent(FirebaseAnalytics.Event.SEARCH, bundle);
}
}
and my Logcat
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.webkit.WebView.addJavascriptInterface(java.lang.Object, java.lang.String)' on a null object reference
As you can see it seems that new AnalyticsWebInterface(this)is null although I imported it.
Anybody knows what is causing this error ?
Thanks!
I am writing code where I need to google search item from textedit from previous screen. But when I press the button to search, android studio crashes, what do I do wrong?
package com.example.myapplication;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class Main2Activity extends AppCompatActivity {
TextView name;
Button button;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main2);
name = findViewById(R.id.textView3);
button = findViewById(R.id.Button2);
String Name = getIntent().getStringExtra("text");
name.setText(name.getText().toString()+ "" + Name);
name.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
//https://www.google.com/#q=
startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse("https://www.google.com/#q=" + name.getText())));
}
});
}
}
My crash stacktraces:
D/AndroidRuntime: Shutting down VM E/AndroidRuntime: FATAL EXCEPTION:
main Process: com.example.myapplication, PID: 17740
java.lang.IllegalStateException: Could not find method onClick(View)
in a parent or ancestor Context for android:onClick attribute defined
on view class androidx.appcompat.widget.AppCompatButton with id
'Button2' at
androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.resolveMethod(AppCompatViewInflater.java:436)
at
androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:393)
at android.view.View.performClick(View.java:7125) at
android.view.View.performClickInternal(View.java:7102) at
android.view.View.access$3500(View.java:801) at
android.view.View$PerformClick.run(View.java:27336) 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$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
I/Process: Sending signal. PID: 17740 SIG: 9 Disconnected from the
target VM, address: 'localhost:8621', transport: 'socket'
You do not define an onClickListerner for your button.
I think name.setOnClickListener must be button.setOnClickListener
BTW: Do not use the same variable name in two different cases:
TextView name; and
String Name =.
By convention variable names should start with lower case character
enter image description here
I put a listener on each button that takes me to different activities.
The login button works perfectly, but the register button stops the app when I click on it.
I've tried to put a Toast message in the _btnreg listener, and it worked...
I got this error:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.android.virtualshelter, PID: 24128
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.virtualshelter/com.example.android.virtualshelter.register}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2787)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1504)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6247)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:872)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:762)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.example.android.virtualshelter.register.onCreate(register.java:35)
at android.app.Activity.performCreate(Activity.java:6754)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2679)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2787)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1504)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6247)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:872)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:762)
package com.example.android.virtualshelter;
import android.content.ContentValues;
import android.content.Intent;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.*;
public class MainActivity extends AppCompatActivity
{
Button _btnreg, _btnlogin;
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
_btnlogin = findViewById(R.id.btnlogin);
_btnreg = findViewById(R.id.btnreg);
_btnreg.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v)
{
Intent intent = new Intent(MainActivity.this,register.class);
startActivity(intent);
}
});
_btnlogin.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v)
{
Intent intent = new Intent(MainActivity.this,login.class);
startActivity(intent);
}
});
}
}
My register.java code
package com.example.android.virtualshelter;
import android.content.ContentValues;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class register extends AppCompatActivity
{
SQLiteOpenHelper openHelper;
SQLiteDatabase db;
Button _btnReg;
EditText _txtfname, _txtlname, _txtpass, _txtemail, _txtphone;
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_register);
openHelper = new DatabaseHelper(register.this);
_txtfname = findViewById(R.id.txtfname);
_txtlname = findViewById(R.id.txtlname);
_txtpass = findViewById(R.id.txtpass);
_txtemail = findViewById(R.id.txtemail);
_txtphone = findViewById(R.id.txtphone);
_btnReg = findViewById(R.id.btnreg);
_btnReg.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v)
{
db = openHelper.getWritableDatabase();
String fname = _txtfname.getText().toString();
String lname = _txtlname.getText().toString();
String pass = _txtpass.getText().toString();
String email = _txtemail.getText().toString();
String phone = _txtphone.getText().toString();
insertdata(fname, lname, pass, email, phone);
Toast.makeText(getApplicationContext(), "register successfully", Toast.LENGTH_LONG).show();
}
});
}
public void insertdata(String fname, String lname, String pass, String email, String phone)
{
ContentValues contentValues = new ContentValues();
contentValues.put(DatabaseHelper.COL_2, fname);
contentValues.put(DatabaseHelper.COL_3, lname);
contentValues.put(DatabaseHelper.COL_4, pass);
contentValues.put(DatabaseHelper.COL_5, email);
contentValues.put(DatabaseHelper.COL_6, phone);
long id = db.insert(DatabaseHelper.TABLE_NAME, null, contentValues);
}
}
I expect to go to activity register.java, but the app is crashing
My hunch is, you are not able find the button, causing a NPE when setting the listner. Could be that you don't have the button defined in R.layout.activity_main, but in a different layout.
I am building a simple app which switches on the Bluetooth of a device and sets it to visible.
I have a separate java class file which has the Bluetooth functions I need, and these are called from another java class which is linked to my activity, through an object of the said class.
This is my code:
import android.bluetooth.BluetoothAdapter;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
/**
* Created by mark on 11/11/2016.
*/
public class Bluetooth_API extends AppCompatActivity{
BluetoothAdapter blueAdp;
public Bluetooth_API() {
blueAdp = BluetoothAdapter.getDefaultAdapter();
}
protected int bluetooth_ON() {
startActivityForResult(new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE), 0);
//blueAdp.enable(); //instead of above line - without alert dialog for permission
return 0;
}
protected int bluetooth_OFF() {
blueAdp.disable(); //
return 0;
}
protected int bluetooth_setVisible() {
if(!blueAdp.isDiscovering()) {
startActivityForResult(new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE), 0);
}
return 0;
}
}
And this is the part of the code from the other activity which is calling my functions:
scanButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Intent nextLayout = new Intent(getApplicationContext(), com.ai.mark.robot_dancing.Scanning_Devices.class);
startActivity(nextLayout);
blue.bluetooth_ON();
//blue.bluetooth_setVisible();
}
});
I am getting the error below once I run my code, I believe it has to do with the activity not being the right one since my Bluetooth functions are in another file (I also tried copying the methods to my activity class and they worked beautifully).
Error:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.ai.mark.robot_dancing, PID: 21314
java.lang.NullPointerException: Attempt to invoke virtual method 'android.app.ActivityThread$ApplicationThread
android.app.ActivityThread.getApplicationThread()' on a null object
reference
at android.app.Activity.startActivityForResult(Activity.java:3951)
at android.support.v4.app.BaseFragmentActivityJB.startActivityForResult(BaseFragmentActivityJB.java:48)
at android.support.v4.app.FragmentActivity.startActivityForResult(FragmentActivity.java:77)
at android.app.Activity.startActivityForResult(Activity.java:3912)
at android.support.v4.app.FragmentActivity.startActivityForResult(FragmentActivity.java:859)
at com.ai.mark.robot_dancing.Bluetooth_API.bluetooth_ON(Bluetooth_API.java:20)
at com.ai.mark.robot_dancing.Bluetooth_Panel$6.onClick(Bluetooth_Panel.java:146)
at android.view.View.performClick(View.java:5210)
at android.view.View$PerformClick.run(View.java:21328)
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:5551)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:730)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:620)
Any ideas on what is causing this?
Thanks.
Don't invoke such code in Activity constructor:
blueAdp = BluetoothAdapter.getDefaultAdapter();
Use onCreate(android.os.Bundle) for that:
#Override
protected void onCreate(Bundle savedInstanceState) {
blueAdp = BluetoothAdapter.getDefaultAdapter();
}
i am new to android development and i am writing an app for my college project .The app transmits a string of data stored in shared preferences .The data is stored by one time setup screen which is never shown again.The issue is after first time,when app is started again it shows that "app has unfortunately stopped working "and when i click ok the app starts.Can anybody tell me why this is happening?
Code:
package com.example.homeautomation.zigbeehomeauto;
import android.annotation.TargetApi;
import android.content.SharedPreferences;
import android.nfc.NdefMessage;
import android.nfc.NdefRecord;
import android.nfc.NfcAdapter;
import android.os.Build;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.View;
import android.widget.Toast;
public class MainScreen extends ActionBarActivity {
NdefMessage msg;
NfcAdapter nfcadapter;
public static final String PREFS_NAME = "MyPrefsFile";
public String pass2 ;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_screen);
SharedPreferences check = getSharedPreferences(PREFS_NAME, 0);
String Pass = check.getString("Str", "Nothing");
pass2 = Pass;
nfcadapter = NfcAdapter.getDefaultAdapter(this);
if (nfcadapter == null) {
Toast.makeText(this, "NFC is not available User", Toast.LENGTH_LONG)
.show();
finish();
}
}
public void ExApp(View v) {
finish();
System.exit(0);
}
#TargetApi(Build.VERSION_CODES.JELLY_BEAN)
public void Nsend(View v)
{
byte[] stringBytes = pass2.getBytes();
nfcadapter.setNdefPushMessage(msg = new NdefMessage(new NdefRecord[]{NdefRecord.createMime("text/plain", stringBytes)
}),this);
}
}
Logcat Ouput:
04-07 12:04:38.478 10836-10836/com.example.homeautomation.zigbeehomeauto E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.homeautomation.zigbeehomeauto, PID: 10836
android.util.SuperNotCalledException: Activity {com.example.homeautomation.zigbeehomeauto/com.example.homeautomation.zigbeehomeauto.SetupScreen} did not call through to super.onCreate()
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2510)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2603)
at android.app.ActivityThread.access$900(ActivityThread.java:174)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:146)
at android.app.ActivityThread.main(ActivityThread.java:5752)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1291)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1107)
at dalvik.system.NativeStart.main(Native Method)
Check in your SetupScreen.java do you have super.onCreate(savedInstanceState);
after onCreate() Method is starts .
post your SetupScreen.java code also ..
Your onCreate() method of class SetupScreen do not call the super.onCreate(). Add the statement and the error should go away.