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Working on an app that is supposed to generate random characters via a broadcast. I need to broadcast the random characters generated by my custom service, so that the main activity registered to intercept the broadcast can get the random numbers and display them on an EditText. The layout is shown here: app layout

The start button will trigger the random character generator service. The EditText will display the random numbers generated in real time (without any button press). The stop button will stop the service. The EditText won’t display any numbers. I have created a service(RandomCharacterService) and registered it in my manifest. Upon running the app, my app crashes. I am sure it is because I did not register my broadcast in my manifest, but I do not understand how to do that. And perhaps there is something wrong with how I am handling the broadcast in my main activity. In my button click method for the start button, I tried to do a for-loop, but this resulted in the app crashing as well.

AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
 package="com.example.cs7455rehmarazzaklab8">

 <application
 android:allowBackup="true"
 android:icon="@mipmap/ic_launcher"
 android:label="@string/app_name"
 android:roundIcon="@mipmap/ic_launcher_round"
 android:supportsRtl="true"
 android:theme="@style/AppTheme">
 <activity android:name=".MainActivity">
 <intent-filter>
 <action android:name="android.intent.action.MAIN" />

 <category android:name="android.intent.category.LAUNCHER" />
 </intent-filter>
 </activity>
 <service android:name=".RandomCharacterService"></service>

 </application>

MainActivityjava:

 package com.example.cs7455rehmarazzaklab8;

 import android.content.ComponentName;
 import android.content.Context;
 import android.content.Intent;
 import android.content.ServiceConnection;
 import android.os.IBinder;
 import android.support.v7.app.AppCompatActivity;
 import android.os.Bundle;
 import android.view.View;
 import android.widget.Button;
 import android.widget.EditText;
 import android.content.BroadcastReceiver;
 import android.content.Intent;
 import android.content.IntentFilter;
 import android.graphics.Color;
 import android.graphics.drawable.ColorDrawable;
 import android.support.constraint.ConstraintLayout;
 import android.support.v4.content.LocalBroadcastManager;
 import android.support.v7.app.AppCompatActivity;
 import android.os.Bundle;
 import android.view.View;
 import android.view.Window;
 import android.widget.Button;
 import android.widget.Toast;
 import java.util.Random;

 public class MainActivity extends AppCompatActivity
 
 private Button btnStart, btnStop;
 private EditText myTV;

 private Intent serviceIntent;
 private RandomCharacterService myService;
 private ServiceConnection myServiceConnection;
 private boolean isServiceOn; //checks if the service is on

 private int myRandomCharacter;
 char MyRandomCharacter = (char)myRandomCharacter;
 private boolean isRandomGeneratorOn;

 private final int MIN = 65;
 char m = (char)MIN;
 private final int MAX = 26;
 char x = (char)MAX;
 private final String TAG = "Random Char Service: ";

 private final String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

 private Context mContext;
 private Random mRandom = new Random();

 // Initialize a new BroadcastReceiver instance
 private BroadcastReceiver mRandomCharReceiver = new BroadcastReceiver() 
 
 @Override
 public void onReceive(Context context, Intent intent) 
 // Get the received random number
 myRandomCharacter = intent.getIntExtra("RandomCharacter",-1);

 // Display a notification that the broadcast received
 Toast.makeText(context,"Received : " + myRandomCharacter,Toast.LENGTH_SHORT).show();
 
 ;

 @Override
 protected void onCreate(Bundle savedInstanceState)
 
 requestWindowFeature(Window.FEATURE_ACTION_BAR);
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);

 // Get the application context
 mContext = getApplicationContext();

 btnStart = (Button) findViewById(R.id.StartButton);
 btnStop = (Button) findViewById(R.id.StopButton);


 myTV = (EditText)findViewById(R.id.RandomCharText);

 // Register the local broadcast
 LocalBroadcastManager.getInstance(mContext).registerReceiver(mRandomCharReceiver, new IntentFilter("BROADCAST_RANDOM_CHARACTER"));

 // Change the action bar color
 getSupportActionBar().setBackgroundDrawable(new ColorDrawable(Color.parseColor("#FFFF00BF")));

 // Set a click listener for start button
 btnStart.setOnClickListener(new View.OnClickListener()
 
 @Override
 public void onClick(View view)
 
 isServiceOn = true;

 serviceIntent = new Intent(getApplicationContext(), RandomCharacterService.class);
 startService(serviceIntent);
 setRandomNumber();
 // Generate a random char
 myRandomCharacter = new Random().nextInt(x)+m;

 // Initialize a new intent instance
 Intent intent = new Intent("BROADCAST_RANDOM_CHARACTER");
 // Put the random character to intent to broadcast it
 intent.putExtra("RandomCharacter",myRandomCharacter);

 // Send the broadcast
 LocalBroadcastManager.getInstance(mContext).sendBroadcast(intent);

 // Update the TextView with random character
 myTV.setText(" " + myRandomCharacter );
 
 );

 btnStop.setOnClickListener(new View.OnClickListener()
 
 @Override
 public void onClick(View view)
 
 isServiceOn = false;

 stopService(serviceIntent);
 
 );
 
 private void setRandomNumber()
 
 myTV.setText("Random Character: " + (char)myService.getRandomCharacter());
 String alphabet = myTV.getText().toString();

 

RandomCharacterService.java:

 package com.example.cs7455rehmarazzaklab8;

 import android.app.Service;
 import android.content.Intent;
 import android.os.Binder;
 import android.os.IBinder;
 import android.support.annotation.IntDef;
 import android.support.annotation.Nullable;
 import android.util.Log;

 import java.util.Random;


 public class RandomCharacterService extends Service
 
 private int myRandomCharacter;
 char MyRandomCharacter = (char)myRandomCharacter;
 private boolean isRandomGeneratorOn;

 private final int MIN = 65;
 char m = (char)MIN;
 private final int MAX = 26;
 char x = (char)MAX;
 private final String TAG = "Random Char Service: ";

 private final String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

 class RandomCharacterServiceBinder extends Binder
 public RandomCharacterService getService()
 
 return RandomCharacterService.this;
 
 

 private IBinder myBinder = new RandomCharacterServiceBinder();

 @Override
 public int onStartCommand(Intent intent, int flags, int startId)
 
 Log.i(TAG, "In OnStartCommand Thread ID is "+Thread.currentThread().getId());
 isRandomGeneratorOn = true;

 new Thread(new Runnable()
 
 @Override
 public void run()
 
 startRandomGenerator();
 
 
 ).start();

 return START_STICKY;
 

 private void startRandomGenerator()
 
 while(isRandomGeneratorOn)
 
 char alphabet = 'A';
 for (int i = 65; i < 90; i++)
 
 try
 
 Thread.sleep(1000);
 if(isRandomGeneratorOn)
 
 alphabet++;
 myRandomCharacter = new Random().nextInt(x)+m;
 Log.i(TAG, "Thread ID is "+Thread.currentThread().getId() + ", Random character is "+(char)myRandomCharacter);
 
 
 catch(InterruptedException e)
 
 Log.i(TAG, "Thread Interrupted.");
 

 

 

 

 private void stopRandomGenerator()
 
 isRandomGeneratorOn = false;
 

 public int getRandomCharacter()
 
 return myRandomCharacter;
 

 public boolean isRandomGeneratorOn() 
 return isRandomGeneratorOn;
 

 @Override
 public void onDestroy()
 
 super.onDestroy();
 stopRandomGenerator();
 Log.i(TAG, "Service Destroyed.");
 

 @Nullable
 @Override
 public IBinder onBind(Intent intent)
 
 Log.i(TAG, "In onBind ...");
 return myBinder;
 

Call Stack:callstack from running the app

Call Stack from attempting to press the stop button:crash from attempting to press stop button

Since you are using the bound service (using Ibinder). You will have to start the service by calling bindService instead of startService. But before that you need to initialize your ServiceConnection variable and better use the isServiceOn boolean as in the below example.

private ServiceConnection myServiceConnection = new ServiceConnection() 
 @Override
 // IBinder interface is through which we receive the service object for communication.
 public void onServiceConnected(ComponentName name, IBinder binder) 
 RandomCharacterServiceBinder myBinder = (RandomCharacterServiceBinder) binder;
 isServiceOn = true;
 myService = myBinder.getService();
 Toast.makeText(context,"Service connected", Toast.LENGTH_SHORT).show();
 

 @Override
 public void onServiceDisconnected(ComponentName name) 
 isServiceOn = false;
 myService = null;
 
;

After onServiceConnected is called, you will get your service object. Most probably your service will be initialized before you perform a click. But just to ensure you can TOAST some message within it.

And you should start the service in Activity's onCreate method, so service will get some time in creation. So move the below code from you click listener to onCreate method.

serviceIntent = new Intent(getApplicationContext(), RandomCharacterService.class);
// startService(serviceIntent); <-- remove this line, call bindService
bindService(intent, myServiceConnection, Context.BIND_AUTO_CREATE);

and wait for the service connection Toast to appear.