Java – Using context in a fragment

Thanks to Code Shogun, whose code I adapted to my situation.

Let your activity implementOnClickListener as usual:

public class SelectFilterActivity extends Activity implements OnClickListener {

  private static final int SWIPE_MIN_DISTANCE = 120;
  private static final int SWIPE_MAX_OFF_PATH = 250;
  private static final int SWIPE_THRESHOLD_VELOCITY = 200;
  private GestureDetector gestureDetector;
  View.OnTouchListener gestureListener;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    /* ... */

    // Gesture detection
    gestureDetector = new GestureDetector(this, new MyGestureDetector());
    gestureListener = new View.OnTouchListener() {
      public boolean onTouch(View v, MotionEvent event) {
        return gestureDetector.onTouchEvent(event);
      }
    };

  }

  class MyGestureDetector extends SimpleOnGestureListener {
    @Override
    public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
      try {
        if (Math.abs(e1.getY() - e2.getY()) > SWIPE_MAX_OFF_PATH)
          return false;
        // right to left swipe
        if(e1.getX() - e2.getX() > SWIPE_MIN_DISTANCE && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY) {
          Toast.makeText(SelectFilterActivity.this, "Left Swipe", Toast.LENGTH_SHORT).show();
        } else if (e2.getX() - e1.getX() > SWIPE_MIN_DISTANCE && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY) {
          Toast.makeText(SelectFilterActivity.this, "Right Swipe", Toast.LENGTH_SHORT).show();
        }
      } catch (Exception e) {
         // nothing
      }
      return false;
    }

    @Override
    public boolean onDown(MotionEvent e) {
      return true;
    }
  }
}

Attach your gesture listener to all the views you add to the main layout;

// Do this for each view added to the grid
imageView.setOnClickListener(SelectFilterActivity.this); 
imageView.setOnTouchListener(gestureListener);

Watch in awe as your overridden methods are hit, both the onClick(View v) of the activity and the onFling of the gesture listener.

public void onClick(View v) {
  Filter f = (Filter) v.getTag();
  FilterFullscreenActivity.show(this, input, f);
}

The post 'fling' dance is optional but encouraged.

There are actually many good reasons to consider using accessors rather than directly exposing fields of a class - beyond just the argument of encapsulation and making future changes easier.

Here are the some of the reasons I am aware of:

• Encapsulation of behavior associated with getting or setting the property - this allows additional functionality (like validation) to be added more easily later.
• Hiding the internal representation of the property while exposing a property using an alternative representation.
• Insulating your public interface from change - allowing the public interface to remain constant while the implementation changes without affecting existing consumers.
• Controlling the lifetime and memory management (disposal) semantics of the property - particularly important in non-managed memory environments (like C++ or Objective-C).
• Providing a debugging interception point for when a property changes at runtime - debugging when and where a property changed to a particular value can be quite difficult without this in some languages.
• Improved interoperability with libraries that are designed to operate against property getter/setters - Mocking, Serialization, and WPF come to mind.
• Allowing inheritors to change the semantics of how the property behaves and is exposed by overriding the getter/setter methods.
• Allowing the getter/setter to be passed around as lambda expressions rather than values.
• Getters and setters can allow different access levels - for example the get may be public, but the set could be protected.