android 多点触摸图片缩放的具体实现方法

<?xml version="1.0" encoding="utf-8"?>
<relativelayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/relativelayout1"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

    <button
        android:id="@+id/zoom_in"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignparentleft="true"
        android:layout_alignparenttop="true"
        android:text="zoom_in" />
    <button
        android:id="@+id/zoom_out"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignparentright="true"
        android:layout_alignparenttop="true"
        android:text="zoom_out" />

    <scrollview
        android:id="@+id/imagecontainer"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_below="@+id/zoom_in"
        android:fadingedge="none"
        android:scrollbars="none" >

        <horizontalscrollview
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:layout_centerhorizontal="true"
            android:fadingedge="none"
            android:scrollbars="none" >

            <imageview
                android:id="@+id/imageview"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_alignparenttop="true"
                android:layout_centerhorizontal="true"
                android:scaletype="matrix" />
        </horizontalscrollview>
    </scrollview>

</relativelayout>

package taokun.demo.mutiltouchdemo;

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.util.log;

import android.view.motionevent;
import android.view.view;
import android.view.view.onclicklistener;
import android.view.view.ontouchlistener;
import android.widget.button;
import android.widget.imageview;

public class mutiltouchdemoactivity extends activity implements ontouchlistener, onclicklistener {
   private static final string tag = "touch" ;

   // these matrices will be used to move and zoom image
   matrix matrix = new matrix();
   matrix savedmatrix = new matrix();
   pointf start = new pointf();
   pointf mid = new pointf();
   float  olddist;
   private imageview view;
   private button zoomin, zoomout;

   //button zoom
   private float scalewidth = 1;
        private float scaleheight = 1;
        private bitmap bmp, zoomedbmp;
        private int zoom_level = 0;
        private static final double zoom_in_scale = 1.25;//放大系数
        private static final double zoom_out_scale = 0.8;//缩小系数

   // we can be in one of these 3 states
   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);
      //放大按钮
      zoomin = (button) findviewbyid(r.id.zoom_in);
       //缩小按钮
      zoomout = (button) findviewbyid(r.id.zoom_out);
      zoomin.setonclicklistener(this);
      zoomout.setonclicklistener(this);
      view = (imageview) findviewbyid(r.id.imageview);
      view.setontouchlistener(this);
      //取得drawable中图片，放大，缩小，多点触摸的作用对象    
       bmp = bitmapfactory.decoderesource(mutiltouchdemoactivity.this.getresources(), r.drawable.splash);

              }

   public boolean ontouch(view v, motionevent event) {
      // handle touch events here...
      imageview view = (imageview) v;

      // handle touch events here...
      switch (event.getaction() & motionevent.action_mask) {
        //设置拖拉模式
        case motionevent.action_down:
            savedmatrix.set(matrix);
            start.set(event.getx(), event.gety());
            log.d(tag, "mode=drag" );
            mode = drag;
            break;

         case motionevent.action_up:
         case motionevent.action_pointer_up:
            mode = none;
            log.d(tag, "mode=none" );
            break;
         //设置多点触摸模式
         case motionevent.action_pointer_down:
            olddist = spacing(event);
            log.d(tag, "olddist=" + olddist);
            if (olddist > 10f) {
               savedmatrix.set(matrix);
               midpoint(mid, event);
               mode = zoom;
               log.d(tag, "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);
               // 设置位移
               matrix.posttranslate(event.getx() - start.x,
              event.getx() - start.x);
            }
            //若为zoom模式，则多点触摸缩放
               else if (mode == zoom) {
               float newdist = spacing(event);
               log.d(tag, "newdist=" + newdist);
               if (newdist > 10f) {
                  matrix.set(savedmatrix);
                  float scale = newdist / olddist;
                  //设置缩放比例和图片中点位置
                  matrix.postscale(scale, scale, mid.x, mid.y);
               }
            }
            break;
      }

      // perform the transformation
      view.setimagematrix(matrix);

      return true; // indicate event was handled
   }
//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);
   }

//放大，缩小按钮点击事件
@override
public void onclick(view v) {
        if(v == zoomin){
                enlarge();
        }else if (v == zoomout) {
                small();
        }

}

//按钮点击缩小函数
private void small() {

        int bmpwidth = bmp.getwidth();
        int bmpheight = bmp.getheight();

        scalewidth = (float) (scalewidth * zoom_out_scale);
        scaleheight = (float) (scaleheight * zoom_out_scale);

        matrix matrix = new matrix();
        matrix.postscale(scalewidth, scaleheight);
        zoomedbmp = bitmap.createbitmap(bmp, 0, 0, bmpwidth, bmpheight, matrix,
                        true);
        view.setimagebitmap(zoomedbmp);
}

//按钮点击放大函数
private void enlarge() {
        try {
                int bmpwidth = bmp.getwidth();
                int bmpheight = bmp.getheight();

                scalewidth = (float) (scalewidth * zoom_in_scale);
                scaleheight = (float) (scaleheight * zoom_in_scale);

                matrix matrix = new matrix();
                matrix.postscale(scalewidth, scaleheight);
                zoomedbmp = bitmap.createbitmap(bmp, 0, 0, bmpwidth, bmpheight, matrix,
                                true);
                view.setimagebitmap(zoomedbmp);
        } catch (exception e) {

        }

}
}