Android example: ScaleGestureDetector

android.view.ScaleGestureDetector detects scaling transformation gestures using the supplied MotionEvents. The ScaleGestureDetector.OnScaleGestureListener callback will notify users when a particular gesture event has occurred.


MainActivity.java

package com.blogspot.android_er.androidscalegesturedetector;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    TextView textMsg;

    private ScaleGestureDetector scaleGestureDetector;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textMsg = (TextView)findViewById(R.id.msg);

        scaleGestureDetector = new ScaleGestureDetector(
                this, new MySimpleOnScaleGestureListener(textMsg));
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        scaleGestureDetector.onTouchEvent(event);
        return true;
        //return super.onTouchEvent(event);
    }

    private class MySimpleOnScaleGestureListener
            extends ScaleGestureDetector.SimpleOnScaleGestureListener{

        TextView viewMessage;

        public MySimpleOnScaleGestureListener(TextView v) {
            super();
            viewMessage = v;
        }

        @Override
        public boolean onScale(ScaleGestureDetector detector) {
            float scaleFactor = detector.getScaleFactor();
            viewMessage.setText(String.valueOf(scaleFactor));
            return true;
            //return super.onScale(detector);
        }
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="16dp"
    android:orientation="vertical"
    tools:context="com.blogspot.android_er.androidscalegesturedetector.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:autoLink="web"
        android:text="http://android-er.blogspot.com/"
        android:textStyle="bold" />
    <TextView
        android:id="@+id/msg"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textStyle="bold"
        android:textSize="24sp"/>
</LinearLayout>

Next:
- Implement pinch-to-zoom with ScaleGestureDetector