链接地址：

一、概述

      ScaleGestureDetector这个类是专门用来检测两个手指在屏幕上做缩放的手势用的，最简单的应用就是用来缩放图片或者缩放网页。

 

二、要求

     利用ScaleGestureDetector这个类实现图片缩放。

 

三、实现

     新建工程MyScale，修改main.xml文件，在里面添加一个Button和一个SurfaceView，如下：

1 
       2 
     
        6  7     
       13     14     
       19 20 
     

修改MyScaleActivity.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：

 

1 package com.nan.scale;   2   3 import android.app.Activity;   4 import android.graphics.Bitmap;   5 import android.graphics.BitmapFactory;   6 import android.graphics.Canvas;   7 import android.graphics.Color;   8 import android.graphics.Matrix;   9 import android.graphics.Rect;  10 import android.os.Bundle;  11 import android.view.MotionEvent;  12 import android.view.ScaleGestureDetector;  13 import android.view.SurfaceHolder;  14 import android.view.SurfaceView;  15 import android.view.View;  16 import android.widget.Button;  17  18  19  20 public class MyScaleActivity extends Activity  21 {
    22     private Button mButton = null;  23     private SurfaceView mSurfaceView = null;  24     private SurfaceHolder mSurfaceHolder = null;  25     private ScaleGestureDetector mScaleGestureDetector = null;  26     private Bitmap mBitmap = null;     27      28     /** Called when the activity is first created. */  29     @Override  30     public void onCreate(Bundle savedInstanceState)  31     {
    32         super.onCreate(savedInstanceState);  33         setContentView(R.layout.main);  34          35         mSurfaceView = (SurfaceView)this.findViewById(R.id.surfaceview);  36         mSurfaceHolder = mSurfaceView.getHolder();   37         mScaleGestureDetector = new ScaleGestureDetector(this,new ScaleGestureListener());  38         mButton = (Button)this.findViewById(R.id.button);  39         //按钮监听  40         mButton.setOnClickListener(new View.OnClickListener()  41         {
    42              43             @Override  44             public void onClick(View v)  45             {
    46                 // TODO Auto-generated method stub  47                 mBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.mmm);  48                 //锁定整个SurfaceView  49                 Canvas mCanvas = mSurfaceHolder.lockCanvas();  50                 //画图  51                 mCanvas.drawBitmap(mBitmap, 0f, 0f, null);  52                 //绘制完成，提交修改  53                 mSurfaceHolder.unlockCanvasAndPost(mCanvas);  54                 //重新锁一次  55                 mSurfaceHolder.lockCanvas(new Rect(0, 0, 0, 0));  56                 mSurfaceHolder.unlockCanvasAndPost(mCanvas);  57             }  58         });  59          60     }  61      62     @Override  63     public boolean onTouchEvent(MotionEvent event)  64     {             65         //返回给ScaleGestureDetector来处理  66         return mScaleGestureDetector.onTouchEvent(event);  67     }  68      69      70     public class ScaleGestureListener implements ScaleGestureDetector.OnScaleGestureListener  71     {
    72  73         @Override  74         public boolean onScale(ScaleGestureDetector detector)  75         {
    76             // TODO Auto-generated method stub  77              78             Matrix mMatrix = new Matrix();         79             //缩放比例  80             float scale = detector.getScaleFactor()/3;  81             mMatrix.setScale(scale, scale);  82              83             //锁定整个SurfaceView  84             Canvas mCanvas = mSurfaceHolder.lockCanvas();  85             //清屏  86             mCanvas.drawColor(Color.BLACK);  87             //画缩放后的图  88             mCanvas.drawBitmap(mBitmap, mMatrix, null);  89             //绘制完成，提交修改  90             mSurfaceHolder.unlockCanvasAndPost(mCanvas);  91             //重新锁一次  92             mSurfaceHolder.lockCanvas(new Rect(0, 0, 0, 0));  93             mSurfaceHolder.unlockCanvasAndPost(mCanvas);  94              95             return false;  96         }  97  98         @Override  99         public boolean onScaleBegin(ScaleGestureDetector detector) 100         {
   101             // TODO Auto-generated method stub    102             //一定要返回true才会进入onScale()这个函数 103             return true; 104         } 105 106         @Override 107         public void onScaleEnd(ScaleGestureDetector detector) 108         {
   109             // TODO Auto-generated method stub 110             111         } 112         113     } 114      115 }

运行该程序：

 

点击一下“显示图片”按钮：

 

然后用两个手指缩小图片：

 

放大图片：

 

好了。可以发现，每次一开始缩放图片的时候都有一个突变，如果用来做应用的话这个程序还需要改善。

 

PS：图片来源于互联网