How should a fragment communicate with another class in Android?

Question

I am currently building a camera app and have a problem: I have got a fragment that should contain a camerapreview. Now this camerapreview is a custom implementation as it extends SurfaceView.

Now my actual question is, how should my custom camerapreview talk to the fragment? For instance, I would like to be able to let my fragment know, that a touch event occured.

What approach should i use?

Answer 1

There are multiple ways to do this. If you don't need this to be reusable, then a solution with a higher amount of coupling is ok. In which case the fragment tells the view about itself and the view can just call a method:

class CustomCameraPreview extends SurfaceView
{
  FragmentA fragment;
  // Call from onCreateView() in the framgnet
  public void setFragment(FragmentA fragment)
  {
    this.fragment = fragment;
  }

  private void someMethod() {
    if ( fragment != null)
      fragment.callback();

  }

}

public class FragmentA extends Fragment {

  public void callback() {
    // called from the view
  }
}

If you need this to be more generic and reusable, then create a interface that contains the kind of callbacks the view would need to call and have the fragment implement that interface. This is basically the Observer pattern: http://en.wikipedia.org/wiki/Observer_pattern

interface CameraPreviewListener {

   public void callback1() ;
   public void callback2() ;

}

class CameraPreview extends SurfaceView 
{
  CameraPreviewListener listener;
  // Call from onCreateView() in the framgnet
  public void setFragment(CameraPreviewListener listener)
  {
    this.listener = listener;
  }

  private void someMethod1() {
    if ( listener != null)
      listener.callback1();    
  }

  private void someMethod2() {
    if ( listener != null)
      listener.callback2();    
  }

}

public class FragmentA extends Fragment implements CameraPreviewListener{

  public void callback1() {
    // called from the view
  }

  public void callback2() {
    // called from the view
  }
}