Calling a method of an Activity from BroadCastReceiver class without creating the activity instance

Question

I want to do the exact same thing mentioned in the question in the following link Call an activity method from a BroadcastReceiver class. But solution given there is not working for me and I can't comment there as I don't have enough reputation. I did everything mentioned in the solution but my broadcast receiver is not working with that code.

I just want to call the method in the activity on receiving the broadcast request without creating an instance of the activity. Can it be done?

EDIT: Now I am adding the code.

Here is my MainActivity class

public class MainActivity extends Activity {

    public static final String TAG="App1";
    private ActionReceiver receiver = null;

    //private YourBroadcastReceiverClassName yourBR = null;

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

        // receiver= new ActionReceiver();
        //IntentFilter filter = new IntentFilter();
        //filter.addAction("com.example.app1.printSomething");

        // printSomething();

    }

    public void printSomething(){
        Toast.makeText(this,"Hello World",Toast.LENGTH_LONG);
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

  }

This is my ActionReceiver class which is BroadcastReceiver

public class ActionReceiver extends BroadcastReceiver{

    @Override
    public void onReceive(Context context, Intent intent) {
        if("com.example.app1.printSomething".equalsIgnoreCase(intent.getAction()))
            Toast.makeText(context,"Hello World", Toast.LENGTH_LONG).show();
    }
}

This is my AndroidManifest.xml file:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.app1"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="7"
        android:targetSdkVersion="16" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.app1.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

        </activity>
        <receiver android:name=".ActionReceiver">
            <intent-filter>
                <action android:name="com.example.app1.printSomething"/>
            </intent-filter>
        </receiver>
    </application>

</manifest>

Now, I want to call printSomething() Method written in MainActivity from onReceive() in ActionReceiver class. But I don't want to launch MainActivity for that. Can it be done?

Answer 1

you can call a method inside MainActivity without instantiating it. You just need to fetch a reference to the hosting Activity. Making it static is not obligatory:

((MainActivity) getActivity()).printSomething();

in MainActivity:

public void printSomething() {
      doStuff();
}

Answer 2

If u just need to execute a method without create an instance, make that method static.

if u cant make that method static, you need to get the instance of that activity.

EDIT:

if u want to execute a method in a instance, you have to create that instance. that means that u have to create and start an activity. if u want to execute a method without the activity, just create that method static.

modify the method in the activity:

public static void printSomething(){
    Toast.makeText(this,"Hello World",Toast.LENGTH_LONG);
}

and then call it from your broadcast:

@Override
    public void onReceive(Context context, Intent intent) {
        if("com.example.app1.printSomething".equalsIgnoreCase(intent.getAction()))
          MainActivity.printSomething();
    }

Answer 3

There are few possible solutions, you can use Local Broadcast Receiver to send the message to your activity, in this case you need to subscribe your activity.

Or you can use EventBus for that, that could be Otto event bus or GreenDroid... In this case you would do the same, subscribe your activity to event bus but in more elegant way :)

Answer 4

Create a Callback

You can use interface to communicate back to Activity(ie invoking methods of Activity).

1) Create a CallBack interface

public interface ReceiverCallback{

    public void doSomeTask();

} 

2) Add this Callback in your Broadcast receiver

public class ActionReceiver extends BroadcastReceiver{

    private ReceiverCallback callback; 

    public ActionReceiver(ReceiverCallback callback){
        this.callback = callback;         //<--- Initialse callback
    }

    @Override
    public void onReceive(Context context, Intent intent) {

        callback.doSomeTask();

    } 
}

3) Implement in your Activity and Override the doSomeTask() method

public class MainActivity extends Activity implements ReceiverCallback{

    // Activity related Code //


   public void printSomething(){
    Toast.makeText(this,"Hello World",Toast.LENGTH_LONG);
   }

   @Override
   public void doSomeTask(){
       printSomething()        //<-- call your method
   }

Advantage?

Using an interface makes a BroadcastReceiver decoupled(independent) of any Activity. You can use this BroadcastReceiver with any Activity without any code-change in the BroadcastReceiver. Which is awesome.

Relevant Link:

If you want to read an even deeper explanation you can READ THIS

Answer 5

You can do it like this in the BroadcastReceiver class:-

   MainActivity mainActivity;

@Override
public void onReceive(Context context, Intent intent) {
    if (intent.getAction().equals("android.intent.action.BOOT_COMPLETED")) {
        mainActivity= new MainActivity();
        mainActivity.printSomething();



    }