多点触控

实现图片缩放效果

package com.example.myandroid_test;

import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.view.Menu;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.Window;
import android.widget.ImageView;

public class MainActivity extends Activity {
private int iX=0;
private int iY=0;
private SurfaceHolder holder=null;
private int sWidth=0;
private int sHeight=0;
private int iWidth=0;
private int iHeight=0;
private Bitmap bitmap=null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
super.requestWindowFeature(Window.FEATURE_NO_TITLE);
//获取屏幕的宽高
this.sWidth =  super.getWindowManager().getDefaultDisplay().getWidth();
this.sHeight=super.getWindowManager().getDefaultDisplay().getHeight();

//图片对象
this.bitmap=BitmapFactory.decodeResource(super.getResources(),R.drawable.android_book);
//获取图片的宽高
this.iWidth=this.bitmap.getWidth();
this.iHeight=this.bitmap.getHeight();

//得到图片起始位置的xy坐标
this.iX=(this.sWidth-this.iWidth)/2;
this.iY=(this.sHeight-this.iHeight)/2;

super.setContentView(new MySurFaceView(this));

}

private class MySurFaceView extends SurfaceView implements SurfaceHolder.Callback{

public MySurFaceView(Context context) {
super(context);
//获取控制器
MainActivity.this.holder = super.getHolder();
// 给SurfaceView当前的持有者一个回调对象。
MainActivity.this.holder.addCallback(this);
// 获得焦点，进行触摸事件
super.setFocusable(true);
}
//在surface的大小发生改变时激发
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width,
int height) {

}
//在创建时激发，一般在这里调用画图的线程。
@Override
public void surfaceCreated(SurfaceHolder holder) {
MainActivity.this.setImage(1,350,500);

}
//销毁时激发，一般在这里将画图的线程停止、释放。
@Override
public void surfaceDestroyed(SurfaceHolder holder) {

}

}

//设置图片的方法
private void setImage(float scale,int width,int height)
{
//获得Canvas对象并锁定画布
Canvas canvas = MainActivity.this.holder.lockCanvas();
//创建画笔
Paint paint = new Paint();
paint.setAntiAlias(true);
//绘制矩形
canvas.drawRect(0,0,MainActivity.this.sWidth,MainActivity.this.sHeight,paint);
//创建对图像处理的Matrix类，进行缩放交换，采用post方式（后乘）
//post是后乘，因为矩阵的乘法不满足交换律，因此先乘、后乘必须要严格区分。后乘相当于矩阵运算中的左乘
Matrix matrix = new Matrix();
//等量缩放
matrix.postScale(scale, scale);
//创建缩放后的新图片
Bitmap target = Bitmap.createBitmap(MainActivity.this.bitmap,0,0,width,height,matrix,true);

//获取新图片的宽高
this.iWidth = target.getWidth();
this.iHeight= target.getHeight();
//重新计算图片的xy坐标
this.iX=(this.sWidth-this.iWidth)/2;
this.iY=(this.sHeight-this.iHeight)/2;

//平移到指定位置
canvas.translate(this.iX,this.iY);
//重新绘制图形
canvas.drawBitmap(this.bitmap, matrix, paint);
//解锁画布，并提交图像
MainActivity.this.holder.unlockCanvasAndPost(canvas);

}

//触摸监听
@Override
public boolean onTouchEvent(MotionEvent event) {

int pointCount = event.getPointerCount() ;
if (pointCount == 2) {
float pointA = event.getY(0) ;
float pointB = event.getY(1) ;
if(pointA < pointB) {
float temp = pointA ;
pointA = pointB ;
pointB = temp ;
}
if(!(event.getAction() == MotionEvent.ACTION_UP)) {
float scale = this.getScale(pointA, pointB);
MainActivity.this.setImage(scale, 350, 500) ;
}
}
return super.onTouchEvent(event);
}
private float getScale(float pointA,float pointB) {
float scale = pointA / pointB ;
return scale ;
}

}