Question

My application contains an area filled with buttons. I wish to implement the activity in such way, that fling gesture over the button area would switch it to one of two another areas (using ViewFlipper).

I’ve made two approaches on detecting gestures. The first one involved using GestureDetector. However, the touch motion events over the Button didn’t raised the onTouchEvent activity method, so – in result – I couldn’t have forwarded it to the GestureDetector class. A failure, in short.

The second approach – involved using the GestureOverlayView. This time, however, I’ve reached the second extreme: not only the gesture was detected, but also the button, over which gesture is performed, reported a click.

I wish the interface to work in the following way: if user touches button and releases the touch (or moves the finger only a little), the button reports click and no gesture is detected. On the other hand, if user touches the screen and makes a longer move, the gesture shall be detected and no click event reported by the button.

I’ve implemented a small proof-of-concept application. The activity XML code follows:

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout android:layout_width="match_parent" android:layout_height="match_parent"  xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical">
  <android.gesture.GestureOverlayView android:layout_width="match_parent" android:layout_height="match_parent" android:id="@+id/overlay">
    <LinearLayout android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical">
    <TextView android:id="@+id/display" android:layout_width="match_parent" android:layout_height="wrap_content" />
    <Button android:layout_width="match_parent" android:layout_height="match_parent" android:id="@+id/button"/>
    </LinearLayout>
  </android.gesture.GestureOverlayView>
</LinearLayout>

The activity java code follows:

package spk.sketchbook;

import android.app.Activity;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
import android.gesture.*;
import android.gesture.GestureOverlayView.OnGestureListener;

public class Main extends Activity implements OnGestureListener, OnClickListener
{       
  private void SetupEvents()
  {
    GestureOverlayView ov = (GestureOverlayView)findViewById(R.id.overlay);
    ov.addOnGestureListener(this);

    Button b = (Button)findViewById(R.id.button);
    b.setOnClickListener(this);
  }

  /** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState)
  {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.main);

    SetupEvents();
  }

  @Override
  public void onGesture(GestureOverlayView arg0, MotionEvent arg1)
  {
    TextView tv = (TextView)findViewById(R.id.display);
    tv.setText("Gesture");
  }

  @Override
  public void onGestureCancelled(GestureOverlayView arg0, MotionEvent arg1)
  {

  }

  @Override
  public void onGestureEnded(GestureOverlayView overlay, MotionEvent event)
  {

  }

  @Override
  public void onGestureStarted(GestureOverlayView overlay, MotionEvent event)
  {

  }

  @Override
  public void onClick(View v)
  {
    TextView tv = (TextView)findViewById(R.id.display);
    tv.setText("Click");
  }


}

The question is: how to implement such an interface, which can decide, if user action shall be treated as the gesture or button click?

Best regards — Spook.

Answer 1

Solved myself. The idea is to catch gesture events from GestureOverlayView and, apart from passing them to GestureDetector, measure the distance of user’s gesture. The distance shall be stored in a private activity’s field (thus available for all event handlers). Finally, fling and click handlers shall check the value of this field; if it is below certain value (say, 10 pixels shall be fine), it should be interpreted as a click. Otherwise – as a gesture.

Note, that the button will both look clicked and its click handler will be called. I’ve decided to create a low-level click handler (attached to all buttons over GestureOverlayView), which does the gesture/click check and if the result is a click, chooses one of higher-level click handlers.

The solution works for me; however if one wished to disable the clicked look of button and prevent the handler from being called, it would probably involve redefining the button and/or GestureOverlayView components.