ScaleGestureDetector

android.view.ScaleGestureDetector (Since API Level 8, Android 2.2) detects transformation gestures involving more than one pointer ("multitouch") using the supplied MotionEvents. The ScaleGestureDetector.OnScaleGestureListener callback will notify users when a particular gesture event has occurred. This class should only be used with MotionEvents reported via touch.




Normally, it can be used to detect pinch zoom.



To use this class:

• Create an instance of the ScaleGestureDetector for your View
• In the onTouchEvent(MotionEvent) method ensure you call onTouchEvent(MotionEvent). The methods defined in your callback will be executed when the events occur.

example:

package com.AndroidScaleGestureDetector;

import android.app.Activity;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.view.ScaleGestureDetector.SimpleOnScaleGestureListener;
import android.widget.TextView;

public class AndroidScaleGestureDetectorActivity extends Activity {

TextView textGestureAction;
private ScaleGestureDetector scaleGestureDetector;

  /** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.main);
      textGestureAction = (TextView)findViewById(R.id.GestureAction);
      scaleGestureDetector = new ScaleGestureDetector(this,
        new MySimpleOnScaleGestureListener());
  }

@Override
public boolean onTouchEvent(MotionEvent event) {
 // TODO Auto-generated method stub
 scaleGestureDetector.onTouchEvent(event);
 return true;
}

public class MySimpleOnScaleGestureListener extends
SimpleOnScaleGestureListener {

 @Override
 public boolean onScale(ScaleGestureDetector detector) {
  // TODO Auto-generated method stub
 
  float scaleFactor = detector.getScaleFactor();
  if(scaleFactor > 1){
   textGestureAction.setText("Scale Out: " + String.valueOf(scaleFactor));
  }else{
   textGestureAction.setText("Scale In: " + String.valueOf(scaleFactor));
  }
 
  return true;
 }
}
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:orientation="vertical"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  >
<TextView
  android:layout_width="fill_parent"
  android:layout_height="wrap_content"
  android:text="@string/hello"
  />
<TextView
  android:id="@+id/GestureAction"
  android:layout_width="fill_parent"
  android:layout_height="wrap_content"
  />
</LinearLayout>