Correct context to use within callbacks

Question

The title pretty much says it all. If you have a callback from one class to another and need to call some method from within the callback that requires a context what is the correct context to use? A common example would be an AsyncTask with a callback to the Activity or Fragment that used it.

I generally try to avoid using getApplicationContext() but I cannot use this as the context from within a callback. Is this a case where using a broader context is appropriate?

To clarify further I'm thinking of a callback with an interface between an AsyncTask and an activity. Once I'm inside the overridden interface method I can't get the activities context from within there.

Answer 1

Use the Activity's context. Example:

MyAsyncTask mat = new MyAsyncTask(this);

MyAsyncTask contructor:

public MyAsyncTask(MyActivity context) {
    mContext = context;
}

To call MyActivity's method methodToCall() from within MyAsyncTask:

((MyActivity)mContext).methodToCall();

Edit 1:

I am guessing your problem is this:

public class MyActivity extends Activity {

    Button b;

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

        b = (Button) findViewById(...);

        b.setOnClickListener(new OnClickListener() {    
            @Override
            public void onClick(View v) {
                Button newButton = new Button(this);        // Won't work!!
            }
        });
    }
}

Workaround:

• Declare a method in MyActivity: getContext()

  public Context getContext() {
      return (Context)this;
  }
  
  b.setOnClickListener(new OnClickListener() {    
      @Override
      public void onClick(View v) {
          Button newButton = new Button(getContext());    // Will work
      }
  });
  

• Use MyActivity.this in place of this.

• Another way is to state that MyActivity implements the interface:

  public class MyActivity extends Activity implements View.OnClickListener {
  
      ....
      ....
  
      @Override
      public void onClick(View v) {
          Button newButton = Button (this)                // Will Work
      }
  }