ScaleGestureDetector之手势缩放

概述

　　根据接收的MotionEvent, 侦测由多个触点（多点触控）引发的变形手势。callback方法 ScaleGestureDetector.OnScaleGestureListener 会在特定手势事件发生时通知用户。该类仅能和Touch事件引发的MotionEvent配合使用。使用该类需要
　　为你的View创建ScaleGestureDetector 实例
　　确保在onTouchEvent(MotionEvent)方法中调用 onTouchEvent (MotionEvent). [译者注：前者为该类的onTouchEvent方法，后者为View的onTouchEvent方法。] 在事件发生时，定义在callback中的方法会被调用。

<?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="fill_parent"
     android:layout_height="fill_parent"
     android:orientation="vertical" >

     <Button
         android:id="@+id/button"
         android:layout_width="fill_parent"
         android:layout_height="wrap_content"
         android:text="显示图片"
         />

     <SurfaceView
         android:id="@+id/surfaceview"
         android:layout_width="fill_parent"
         android:layout_height="fill_parent"
         />

 </LinearLayout>

java文件，主要是实现按钮的监听和定义一个类实现ScaleGestureDetector.OnScaleGestureListener接口：

package com.kingfly;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Rect;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
import android.widget.Button;

public class ShoushiActivity extends Activity {

    private Button mButton = null;
    private SurfaceView mSurfaceView = null;
    private SurfaceHolder mSurfaceHolder = null;
    private ScaleGestureDetector mScaleGestureDetector = null;
    private Bitmap mBitmap = null;

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

        mSurfaceView = (SurfaceView) this.findViewById(R.id.surfaceview);
        mSurfaceHolder = mSurfaceView.getHolder();
        mScaleGestureDetector = new ScaleGestureDetector(this,
                new ScaleGestureListener());
        mButton = (Button) this.findViewById(R.id.button);
        // 按钮监听
        mButton.setOnClickListener(new View.OnClickListener() {

            public void onClick(View v) {
                // TODO Auto-generated method stub
                mBitmap = BitmapFactory.decodeResource(getResources(),
                        R.drawable.mmm);
                // 锁定整个SurfaceView
                Canvas mCanvas = mSurfaceHolder.lockCanvas();
                // 画图
                mCanvas.drawBitmap(mBitmap, 0f, 0f, null);
                // 绘制完成，提交修改
                mSurfaceHolder.unlockCanvasAndPost(mCanvas);
                // 重新锁一次
                mSurfaceHolder.lockCanvas(new Rect(0, 0, 0, 0));
                mSurfaceHolder.unlockCanvasAndPost(mCanvas);
            }
        });

    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        // 返回给ScaleGestureDetector来处理
        return mScaleGestureDetector.onTouchEvent(event);
    }

    public class ScaleGestureListener implements
            ScaleGestureDetector.OnScaleGestureListener {

        public boolean onScale(ScaleGestureDetector detector) {
            // TODO Auto-generated method stub

            Matrix mMatrix = new Matrix();
            // 缩放比例
            float scale = detector.getScaleFactor() / 3;
            mMatrix.setScale(scale, scale);

            // 锁定整个SurfaceView
            Canvas mCanvas = mSurfaceHolder.lockCanvas();
            // 清屏
            mCanvas.drawColor(Color.BLACK);
            // 画缩放后的图
            mCanvas.drawBitmap(mBitmap, mMatrix, null);
            // 绘制完成，提交修改
            mSurfaceHolder.unlockCanvasAndPost(mCanvas);
            // 重新锁一次
            mSurfaceHolder.lockCanvas(new Rect(0, 0, 0, 0));
            mSurfaceHolder.unlockCanvasAndPost(mCanvas);

            return false;
        }

        public boolean onScaleBegin(ScaleGestureDetector detector) {
            // TODO Auto-generated method stub
            // 一定要返回true才会进入onScale()这个函数
            return true;
        }

        public void onScaleEnd(ScaleGestureDetector detector) {
            // TODO Auto-generated method stub

        }

    }

}