Android多点触摸放大缩小图片

1.Activity

package com.fit.touchimage;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Matrix;
import android.graphics.PointF;
import android.os.Bundle;
import android.util.FloatMath;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.view.ViewGroup.MarginLayoutParams;
import android.widget.ImageView;

public class MainActivity extends Activity implements OnTouchListener {
    /** Called when the activity is first created. */
 
 //放大缩小
 Matrix matrix=new Matrix();
 Matrix savedMatrix=new Matrix();
 
 PointF start=new PointF();
 PointF mid=new PointF();
 float oldDist;
 
 private ImageView myImageView;
 
 //模式
 static final int NONE=0;
 static final int DRAG=1;
 static final int ZOOM=2;
 int mode=NONE;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
       
        myImageView=(ImageView) findViewById(R.id.myImage);
        myImageView.setOnTouchListener(this);
       
    }

@Override
 public boolean onTouch(View v, MotionEvent event) {
  ImageView myImageView=(ImageView) v;
  switch(event.getAction()&MotionEvent.ACTION_MASK){
   //设置拖拉模式
  case MotionEvent.ACTION_DOWN:
   matrix.set(myImageView.getImageMatrix());
   savedMatrix.set(matrix);
   start.set(event.getX(),event.getY());
   mode=DRAG;
  break;
  case MotionEvent.ACTION_UP:
  case MotionEvent.ACTION_POINTER_UP:
   mode=NONE;
   break;
  
  //设置多点触摸模式
  case MotionEvent.ACTION_POINTER_DOWN:
   oldDist=spacing(event);
   if(oldDist>10f){
    savedMatrix.set(matrix);
    midPoint(mid, event);
    mode=ZOOM;
   }
   break;
   //若为DRAG模式，则点击移动图片
  case MotionEvent.ACTION_MOVE:
   if(mode==DRAG){
    matrix.set(savedMatrix);
    matrix.postTranslate(event.getX()-start.x,event.getY()-start.y);
   }
   //若为ZOOM模式，则点击触摸缩放
   else if(mode==ZOOM){
    float newDist=spacing(event);
    if(newDist>10f){
     matrix.set(savedMatrix);
     float scale=newDist/oldDist;
     //设置硕放比例和图片的中点位置
     matrix.postScale(scale,scale, mid.x,mid.y);
    }
   }
   break;
  } 
  myImageView.setImageMatrix(matrix);
  return true;
 }
 //计算移动距离
 private float spacing(MotionEvent event){
  float x=event.getX(0)-event.getX(1);
  float y=event.getY(0)-event.getY(1);
  return FloatMath.sqrt(x*x+y*y);
 }
 //计算中点位置
 private void midPoint(PointF point,MotionEvent event){
  float x=event.getX(0)+event.getX(1);
  float y=event.getY(0)+event.getY(1);
  point.set(x/2,y/2);
 }
}

2.布局

<?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" android:gravity="center">
 <ImageView android:layout_width="fill_parent"
  android:layout_height="fill_parent" android:scaleType="matrix"
  android:id="@+id/myImage" android:src="@drawable/xiaoxiong"/>
</LinearLayout>