Implementing the double tap on an ImageView

In this post I explain a simple example of an implementation of a double tap event on an ImageView that can be adapted with some changes for a TextView or an Activity.

1. 1. MainActivity.java, the main activity
      
      Java

      package eu.lucazanini.doubletap; import android.app.Activity; import android.os.Bundle; public class MainActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); } }

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      package eu.lucazanini.doubletap;   import android.app.Activity; import android.os.Bundle;   public class MainActivity extends Activity {       @Override     protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main);     } }

   2. res/layout/activity_main.xml, il layout per l’activity principale
      
      <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/LinearLayout1" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" android:gravity="center"> <eu.lucazanini.doubletap.DoubleTapView android:id="@+id/imageView1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:src="@drawable/ic_launcher" android:layout_gravity="center" /> </LinearLayout>

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      <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"     android:id="@+id/LinearLayout1"     android:layout_width="match_parent"     android:layout_height="match_parent"     android:orientation="vertical"     android:gravity="center">       <eu.lucazanini.doubletap.DoubleTapView         android:id="@+id/imageView1"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:src="@drawable/ic_launcher"         android:layout_gravity="center" />   </LinearLayout>

      
      at the line 8 there is a View linked to the class DoubleTapView that extends an ImageView

1. DoubleTapView.java
   
   ]package eu.lucazanini.doubletap; import android.content.Context; import android.support.v4.view.GestureDetectorCompat; import android.util.AttributeSet; import android.util.Log; import android.view.GestureDetector; import android.view.MotionEvent; import android.widget.ImageView; public class DoubleTapView extends ImageView { private class MyGestureListener extends GestureDetector.SimpleOnGestureListener { @Override public boolean onDoubleTap(MotionEvent event) { Log.d(TAG, "onDoubleTap"); return true; } @Override public boolean onDown(MotionEvent event) { return true; } } private final static String TAG = DoubleTapView.class.getName(); private GestureDetectorCompat mDetector; public DoubleTapView(Context context, AttributeSet attrs) { super(context, attrs); mDetector = new GestureDetectorCompat(context, new MyGestureListener()); } @Override public boolean onTouchEvent(MotionEvent e) { return mDetector.onTouchEvent(e); } }

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   ]package eu.lucazanini.doubletap;   import android.content.Context; import android.support.v4.view.GestureDetectorCompat; import android.util.AttributeSet; import android.util.Log; import android.view.GestureDetector; import android.view.MotionEvent; import android.widget.ImageView;   public class DoubleTapView extends ImageView {       private class MyGestureListener extends     GestureDetector.SimpleOnGestureListener {   @Override public boolean onDoubleTap(MotionEvent event) {     Log.d(TAG, "onDoubleTap");     return true; }   @Override public boolean onDown(MotionEvent event) {     return true; }     }       private final static String TAG = DoubleTapView.class.getName();     private GestureDetectorCompat mDetector;       public DoubleTapView(Context context, AttributeSet attrs) { super(context, attrs);   mDetector = new GestureDetectorCompat(context, new MyGestureListener());     }       @Override     public boolean onTouchEvent(MotionEvent e) { return mDetector.onTouchEvent(e);     }   }

   
   at the line 17 the method onDoubleTap handles the double tap but you need the following four important points:
   • line 34: creation of an object of the class GestureDetectorCompat (mDetector)
   • line 13: the inner class that extends GestureDetector.SimpleOnGestureListener and an object of this class is passed as argument to the constructor of mDetector of the previous point
   • line 38: the method onTouchEvent of ImageView is overridden and calls onTouchEvent of GestureDetectorCompat (mDetector)
   • line 23: in the inner class that extends GestureDetector.SimpleOnGestureListener the method onDown is overridden and returns true