How to prevent "IllegalStateException" when using Fragments - java

I'm currently programming a game app for the party game "Werewolves of Millers Hollow". When any character in the game should make a decision, a new fragment with all necessary information is created.This all works fine, until I start my game a second time, then, at the first commit, a IllegalStateException is thrown.
I already tried to use commitAllowingStateLoss(), but this only leads to an invisible UI. Removing all fragments from the fragment manager didn't help either.
My App starts with a main activity as a main 'menu'.
public class MainActivity extends AppCompatActivity {
//Some Code
private void startGame(View view) {
Intent intent = new Intent(this, GameActivity.class);
//Some extras
startActivity(intent);
}
}
This calls the following GameActivity:
public class GameActivity extends AppCompatActivity {
#Override
protected void onCreate(#Nullable Bundle savedInstanceState){
super.onCreate(savedInstanceState)
setContentView(R.layout.game_layout.xml); //only contains the fragment container
new GameTast().execute();
}
//IOMethod is an interface the game calls when something should be displayed or input is requested
class GameTask extends Asynctask<Void,Void,Void> implements IOMethod {
#Override
protected Void doInBackground(Void... voids){
//Starting my game and waiting for finish
Intent intent = new Intent(GameActivity.this, MainActivity.class);
startActivity(intent);
finish();
}
//Many methods for different views, e.g.
public List<Character> promptForCharacterSelection(/*Backend params*/){
getSupportFragmentManager().beginTransaction().replace(R.id.gameFrame, new IngameCharacterSelectionFragment()).commit();
//wait for user to finish input
}
}
}
The Game runs perfectly when executing it the first time, but on the second run, I get the following stacktrace:
2019-07-02 10:17:10.261 4392-4439/com.example.werewolves E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #2
Process: com.example.werewolves, PID: 4392
java.lang.RuntimeException: An error occurred while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:354)
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:383)
at java.util.concurrent.FutureTask.setException(FutureTask.java:252)
at java.util.concurrent.FutureTask.run(FutureTask.java:271)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
at java.lang.Thread.run(Thread.java:764)
Caused by: java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState
at android.support.v4.app.FragmentManagerImpl.checkStateLoss(FragmentManager.java:2080)
at android.support.v4.app.FragmentManagerImpl.enqueueAction(FragmentManager.java:2106)
at android.support.v4.app.BackStackRecord.commitInternal(BackStackRecord.java:683)
at android.support.v4.app.BackStackRecord.commit(BackStackRecord.java:637)
at com.example.werewolves.GameActivity$GameTask.promptForPlayerSelection(GameActivity.java:167)
at com.example.werewolvesgame.ClassicMethod.preStart(ClassicMethod.java:47)
at com.example.werewolvesgame.PlayingMethod.start(PlayingMethod.java:20)
at com.example.werewolvesgame.Game.start(Game.java:65)
at com.example.werewolvesgame.Manager.newGame(Manager.java:42)
at com.example.werewolves.GameActivity$GameTask.doInBackground(GameActivity.java:105)
at com.example.werewolves.GameActivity$GameTask.doInBackground(GameActivity.java:97)
at android.os.AsyncTask$2.call(AsyncTask.java:333)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245) 
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167) 
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641) 
at java.lang.Thread.run(Thread.java:764) 

Related

startActivity() in broadcast receiver bag(?)

I'm trying to start MainActivity with BluetoothDevice.ACTION_ACL_CONNECTED receive just like in some stack overflow answers
public class BTReceiver extends BroadcastReceiver {
#Override
public void onReceive(Context context, Intent intent) {
Log.d("BT", "Receive");
String action = intent.getAction();
...
switch (action) {
case BluetoothDevice.ACTION_ACL_CONNECTED:
Intent i = new Intent();
i.setClassName("com.opendashcam", "com.opendashcam.MainActivity");
i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
context.startActivity(i);
}
}
}
And like this
Intent intent1 = new Intent(context, MainActivity.class);
intent1.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
context.startActivity(intent1);
But all that I can see it's just these logs (first two say that receive was gotten and activity was started with connection to written MAC)
D/BT: Receive
D/BT: started app with 00:14:41:1E:26:27
I/Timeline: Timeline: Activity_launch_request time:129879532
My Main Activity's onCreate:
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Log.d("MA", "Started app");
init();
}

Since Android 10, according to Android Developers docs ,Android does not allow launching an activity from the background:
Android 10 (API level 29) and higher place restrictions on when apps can start activities when the app is running in the background. These restrictions help minimize interruptions for the user and keep the user more in control of what's shown on their screen.
As an alternative, you can show notification that will launch the activity if clicked:
In nearly all cases, apps that are in the background should display time-sensitive notifications to provide urgent information to the user instead of directly starting an activity.

Android App keeps on crashing upon new Intent

So I've got this error code: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
The line: Intent callMode = new Intent(MainActivity.this, IncallActivity.class);
What I'm trying to do is to set a new activity when I receive a call. The following function is what should "switch" to that activity.
public void callMode() {
Intent callMode = new Intent(MainActivity.this, IncallActivity.class);
startActivity(callMode);
}
And it is located inside of the MainActivity class, outside of the onCreate function.
When I try to put it inside of the onCreate function (without public void callMode() of course) it works, but that's not the goal.
I'm trying to activate this new activity from another class, which listens for calls.
public class CallReceiver extends BroadcastReceiver {
IncallActivity incallActivity = new IncallActivity();
public MainActivity mainActivity;
#Override
public void onReceive(Context context, Intent intent) {
if (intent.getStringExtra(TelephonyManager.EXTRA_STATE).equals(TelephonyManager.EXTRA_STATE_OFFHOOK)) {
mainActivity.callMode();
} else if (intent.getStringExtra(TelephonyManager.EXTRA_STATE).equals(TelephonyManager.EXTRA_STATE_IDLE)) {
incallActivity.endCallMode();
}
}
}
So why does this error show up?

I found a way to do it.
You need to add a public static Context context to your code, and then in onCreate, do context = getBaseContext();
From there you can launch the second activity from any class you'd like.

Trusted web activity Unable to start activity ComponentInfo Service Intent must be explicit: Intent

I have integrated Trusted Web Activity in my Android App when launching TwalauncherActivity as main Activity, App is not opening, it's stopping suddenly & closing automatically.
I have followed this link to add Trusted web Activity.
Logcat:-
FATAL EXCEPTION: main
Process: com.therightdoctors.cathlab, PID: 2906
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.therightdoctors.cathlab/com.therightdoctors.cathlab.TwaLauncherActivity}: java.lang.IllegalArgumentException: Service Intent must be explicit: Intent { act=android.support.customtabs.action.CustomTabsService }
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
Caused by: java.lang.IllegalArgumentException: Service Intent must be explicit: Intent { act=android.support.customtabs.action.CustomTabsService }
TwaLauncherActivity.java:-
package com.therightdoctors.dpmpatient;
import android.net.Uri;
import android.os.Bundle;
import android.support.customtabs.CustomTabsIntent;
import android.support.v7.app.AppCompatActivity;
public class TwaLauncherActivity extends AppCompatActivity
implements TwaSessionHelper.TwaSessionCallback {
private static final String TWA_ORIGIN = "https://dpmp.therightdoctors.com";
private static final String TARGET_URL = TWA_ORIGIN;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_twa_launcher);
Uri originUri = Uri.parse(TWA_ORIGIN);
TwaSessionHelper twaSessionHelper = TwaSessionHelper.getInstance();
twaSessionHelper.setTwaSessionCallback(this);
twaSessionHelper.bindService(this, originUri);
}
#Override
protected void onDestroy() {
super.onDestroy();
TwaSessionHelper twaSessionHelper = TwaSessionHelper.getInstance();
twaSessionHelper.setTwaSessionCallback(null);
}
public void openTwa() {
TwaSessionHelper twaSessionHelper = TwaSessionHelper.getInstance();
// Set an empty transition from TwaLauncherActivity to the TWA splash screen.
CustomTabsIntent customTabsIntent = twaSessionHelper.createIntentBuilder()
.setStartAnimations(this, 0, 0)
.build();
Uri openUri = Uri.parse(TARGET_URL);
twaSessionHelper.openTwa(this, customTabsIntent, openUri);
}
#Override
public void onTwaSessionReady() {
openTwa();
}
#Override
public void onTwaSessionDestroyed() {
}
#Override
public void onTwaOpened() {
finishAndRemoveTask();
}
}

The linked demo is outdated (the link is currently broken too, as the demo was moved here)
This is the current code for the update LauncherActivity, inside the Support Library.
The latest version of the Support Library supporting TWAs is being hosted in JitPack temporarily.
It will be merged into the official support library in the near future.

App crashes while can't perform AsyncTask

I have a problem with AsyncTask in my app. AsyncTask is located in SplashScreenAcivity.java. It downloads data using json for MainActivity.java while showing splash screen. When data is loaded, app shows MainActivity screen. However, when i turn off internet connection app crashes. Instead of it i would like to move to MainActivity.java and show toast that internet connection must be turned on. SplashScreen.java loads data for listView in MainActivity.
SplashActivityScreen.java
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_splash_screen);
new DownloadData().execute();
}
private class DownloadData extends AsyncTask<Void, Void, Void> {
#Override
protected Void doInBackground(Void... voids) {
SyncHttpClient clientOne = new SyncHttpClient();
clientOne.get("https://api.themoviedb.org/3/tv/top_rated?api_key=d253f520df9cd868af7db8daaa0db8fb&language=en-US", new JsonHttpResponseHandler() {
#Override
public void onSuccess(int statusCode, Header[] headers, JSONObject response) {
try {
tvseries0 = response.getJSONArray("results").getJSONObject(0).getString("name");
tvseries1 = response.getJSONArray("results").getJSONObject(1).getString("name");
tvseries2 = response.getJSONArray("results").getJSONObject(2).getString("name");
tvseries3 = response.getJSONArray("results").getJSONObject(3).getString("name");
tvseries4 = response.getJSONArray("results").getJSONObject(4).getString("name");
tvseries5 = response.getJSONArray("results").getJSONObject(5).getString("name");
tvseries6 = response.getJSONArray("results").getJSONObject(6).getString("name");
tvseries7 = response.getJSONArray("results").getJSONObject(7).getString("name");
tvseries8 = response.getJSONArray("results").getJSONObject(8).getString("name");
tvseries9 = response.getJSONArray("results").getJSONObject(9).getString("name");
tvseries10 = response.getJSONArray("results").getJSONObject(10).getString("name");
tvseries11 = response.getJSONArray("results").getJSONObject(11).getString("name");
tvseries12 = response.getJSONArray("results").getJSONObject(12).getString("name");
tvseries13 = response.getJSONArray("results").getJSONObject(13).getString("name");
tvseries14 = response.getJSONArray("results").getJSONObject(14).getString("name");
tvseries15 = response.getJSONArray("results").getJSONObject(15).getString("name");
tvseries16 = response.getJSONArray("results").getJSONObject(16).getString("name");
tvseries17 = response.getJSONArray("results").getJSONObject(17).getString("name");
tvseries18 = response.getJSONArray("results").getJSONObject(18).getString("name");
tvseries19 = response.getJSONArray("results").getJSONObject(19).getString("name");
} catch (JSONException e) {
e.printStackTrace();
}
}
#Override
public void onFailure(int statusCode, Header[] headers,Throwable e , JSONObject response) {
Toast.makeText(SplashScreenActivity.this, "Turn on the internet and swipe to refresh.", Toast.LENGTH_SHORT).show();
}
});
return null;
}
#Override
protected void onPostExecute(Void aVoid) {
super.onPostExecute(aVoid);
Intent i = new Intent(getApplicationContext(), MainActivity.class);
i.putExtra("tvseries0", tvseries0);
i.putExtra("tvseries1", tvseries1);
i.putExtra("tvseries2", tvseries2);
i.putExtra("tvseries3", tvseries3);
i.putExtra("tvseries4", tvseries4);
i.putExtra("tvseries5", tvseries5);
i.putExtra("tvseries6", tvseries6);
i.putExtra("tvseries7", tvseries7);
i.putExtra("tvseries8", tvseries8);
i.putExtra("tvseries9", tvseries9);
i.putExtra("tvseries10", tvseries10);
i.putExtra("tvseries11", tvseries11);
i.putExtra("tvseries12", tvseries12);
i.putExtra("tvseries13", tvseries13);
i.putExtra("tvseries14", tvseries14);
i.putExtra("tvseries15", tvseries15);
i.putExtra("tvseries16", tvseries16);
i.putExtra("tvseries17", tvseries17);
i.putExtra("tvseries18", tvseries18);
i.putExtra("tvseries19", tvseries19);
startActivity(i);
finish();
}
}
}
Crash 1
04-30 13:15:35.165 12349-12365/przemo.me.recommend.recommendme E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #1
Process: przemo.me.recommend.recommendme, PID: 12349
java.lang.RuntimeException: An error occurred while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:318)
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354)
at java.util.concurrent.FutureTask.setException(FutureTask.java:223)
at java.util.concurrent.FutureTask.run(FutureTask.java:242)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:243)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607)
at java.lang.Thread.run(Thread.java:761)
Caused by: java.lang.RuntimeException: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
at com.loopj.android.http.AsyncHttpResponseHandler.onUserException(AsyncHttpResponseHandler.java:304)
at com.loopj.android.http.AsyncHttpResponseHandler.handleMessage(AsyncHttpResponseHandler.java:395)
at com.loopj.android.http.AsyncHttpResponseHandler.sendMessage(AsyncHttpResponseHandler.java:401)
at com.loopj.android.http.AsyncHttpResponseHandler.sendFailureMessage(AsyncHttpResponseHandler.java:319)
at com.loopj.android.http.AsyncHttpRequest.run(AsyncHttpRequest.java:109)
at com.loopj.android.http.SyncHttpClient.sendRequest(SyncHttpClient.java:95)
at com.loopj.android.http.AsyncHttpClient.get(AsyncHttpClient.java:1078)
at com.loopj.android.http.AsyncHttpClient.get(AsyncHttpClient.java:1037)
at przemo.me.recommend.recommendme.SplashScreenActivity$DownloadData.doInBackground(SplashScreenActivity.java:64)
at przemo.me.recommend.recommendme.SplashScreenActivity$DownloadData.doInBackground(SplashScreenActivity.java:56)
at android.os.AsyncTask$2.call(AsyncTask.java:304)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:243) 
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133) 
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607) 
at java.lang.Thread.run(Thread.java:761) 
Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
at android.os.Handler.<init>(Handler.java:200)
at android.os.Handler.<init>(Handler.java:114)
at android.widget.Toast$TN.<init>(Toast.java:346)
at android.widget.Toast.<init>(Toast.java:101)
at android.widget.Toast.makeText(Toast.java:260)
at przemo.me.recommend.recommendme.SplashScreenActivity$DownloadData$1.onFailure(SplashScreenActivity.java:103)
at com.loopj.android.http.JsonHttpResponseHandler.onFailure(JsonHttpResponseHandler.java:233)
at com.loopj.android.http.AsyncHttpResponseHandler.handleMessage(AsyncHttpResponseHandler.java:359)
at com.loopj.android.http.AsyncHttpResponseHandler.sendMessage(AsyncHttpResponseHandler.java:401) 
at com.loopj.android.http.AsyncHttpResponseHandler.sendFailureMessage(AsyncHttpResponseHandler.java:319) 
at com.loopj.android.http.AsyncHttpRequest.run(AsyncHttpRequest.java:109) 
at com.loopj.android.http.SyncHttpClient.sendRequest(SyncHttpClient.java:95) 
at com.loopj.android.http.AsyncHttpClient.get(AsyncHttpClient.java:1078) 
at com.loopj.android.http.AsyncHttpClient.get(AsyncHttpClient.java:1037) 
at przemo.me.recommend.recommendme.SplashScreenActivity$DownloadData.doInBackground(SplashScreenActivity.java:64) 
at przemo.me.recommend.recommendme.SplashScreenActivity$DownloadData.doInBackground(SplashScreenActivity.java:56) 
at android.os.AsyncTask$2.call(AsyncTask.java:304) 
at java.util.concurrent.FutureTask.run(FutureTask.java:237) 
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:243) 
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133) 
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607) 
at java.lang.Thread.run(Thread.java:761) 
Crash 2
04-30 13:15:35.162 12349-12365/przemo.me.recommend.recommendme E/AsyncHttpRH: User-space exception detected!
java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
at android.os.Handler.<init>(Handler.java:200)
at android.os.Handler.<init>(Handler.java:114)
at android.widget.Toast$TN.<init>(Toast.java:346)
at android.widget.Toast.<init>(Toast.java:101)
at android.widget.Toast.makeText(Toast.java:260)
at przemo.me.recommend.recommendme.SplashScreenActivity$DownloadData$1.onFailure(SplashScreenActivity.java:103)
at com.loopj.android.http.JsonHttpResponseHandler.onFailure(JsonHttpResponseHandler.java:233)
at com.loopj.android.http.AsyncHttpResponseHandler.handleMessage(AsyncHttpResponseHandler.java:359)
at com.loopj.android.http.AsyncHttpResponseHandler.sendMessage(AsyncHttpResponseHandler.java:401)
at com.loopj.android.http.AsyncHttpResponseHandler.sendFailureMessage(AsyncHttpResponseHandler.java:319)
at com.loopj.android.http.AsyncHttpRequest.run(AsyncHttpRequest.java:109)
at com.loopj.android.http.SyncHttpClient.sendRequest(SyncHttpClient.java:95)
at com.loopj.android.http.AsyncHttpClient.get(AsyncHttpClient.java:1078)
at com.loopj.android.http.AsyncHttpClient.get(AsyncHttpClient.java:1037)
at przemo.me.recommend.recommendme.SplashScreenActivity$DownloadData.doInBackground(SplashScreenActivity.java:64)
at przemo.me.recommend.recommendme.SplashScreenActivity$DownloadData.doInBackground(SplashScreenActivity.java:56)
at android.os.AsyncTask$2.call(AsyncTask.java:304)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:243)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607)
at java.lang.Thread.run(Thread.java:761)

You can not do UI operations from non UI thread. Like in your code you are showing Toast in Async task thread.
You should replace
Toast.makeText(SplashScreenActivity.this, "Turn on the internet and swipe to refresh.", Toast.LENGTH_SHORT).show();
with this
runOnUiThread(new Runnable() {
#Override
public void run() {
Toast.makeText(SplashScreenActivity.this, "Turn on the internet and swipe to refresh.", Toast.LENGTH_SHORT).show();
}
});

use -
SplashScreenActivity.this.runOnUiThread(new Runnable() {
#Override
public void run() {
Toast.makeText(SplashScreenActivity.this, "Turn on the internet and swipe to refresh.", Toast.LENGTH_SHORT).show();
}
});

Here is a server connection AsyncTask task that I created years ago in Android Java. The background task works successfully. I used it to update in the background the data repository in the App I developed at that time.
public class DataExchangeStore extends Application {
public void startServerConnection(Context contextGlobal, Activity activityGlobal) {
this.contextGlobal = contextGlobal;
this.activityGlobal = activityGlobal;
connectTask = new ConnectTask();
connectTask.execute("");
}
private ConnectTask connectTask;
public class ConnectTask extends AsyncTask<String, String, TCPClient> {
#Override
protected TCPClient doInBackground(String... message) {
android.os.Process.setThreadPriority( android.os.Process.THREAD_PRIORITY_BACKGROUND);
// we create a TCPClient object
mTcpClient = new TCPClient(new TCPClient.OnMessageReceived() {
#Override
// here the messageReceived method is implemented
public void messageReceived(ChatMessage message) {
// this method calls the onProgressUpdate
publishProgress(message.getMessage());
}
}, contextGlobal, activityGlobal);
mTcpClient.run();
return null;
}
#Override
protected void onProgressUpdate(String... values) {
super.onProgressUpdate(values);
System.err.println(values[0]);
// do your stuff here
}
}
Import is to permanently lock the screen orientation of the activity, specifying the screenOrientation attribute in the Android-Manifest file with portrait or landscape values:
<activity android:screenOrientation="portrait" />

Although previous answers are not wrong, using runOnUiThread() to jump out of the background thread in the AsyncTask is not a good practice. You have the onPostExecute() method for that.
What you should be doing is passing a result object to onPostExecute(). This object would encapsulate the result state (ie: error or success) and the actual data received. Then in onPostExecute() you check the result state and display a Toast if the state is error.
And do yourself a favor and replace your 20 TvSerie objects by a List<TvSerie> and do a loop in you AsyncTask to populate the list.
Please refer to the AsyncTask documentation for details on how to properly use it.

Android Studio Bluetooth :- attempt to invoke a virtual method on a null object reference

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();
}

Categories

Resources