以前程序中用到了图片缩放，按照新浪微博效果写了一个（点击图片出现缩放按钮，过一会消失）。分享给大家，代码整理过，可以直接用！
package com.Johnson.p_w_picpath.zoom;

import android.app.Activity;
import android.app.Dialog;
import android.app.ProgressDialog;
import android.content.DialogInterface;
import android.content.DialogInterface.OnKeyListener;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Matrix;
import android.os.Bundle;
import android.os.Handler;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.RelativeLayout;
import android.widget.ZoomControls;

public class MainActivity extends Activity {
        /** Called when the activity is first created. */
    


  private final int LOADING_IMAGE = 1;
  public static String KEY_IMAGEURI = "ImageUri";
  private ZoomControls zoom;
  private ImageView mImageView;
  private LinearLayout layoutImage;
  private int displayWidth;
  private int displayHeight;
  /**图片资源*/
  private Bitmap bmp;
  /**宽的缩放比例*/
  private float scaleWidth = 1;
  /**高的缩放比例*/
  private float scaleHeight = 1;
  /**用来计数放大+1    缩小-1*/
  private int    zoomNumber=0;
  /**点击屏幕显示缩放按钮，三秒消失*/
  private int showTime=3000;

    
  RelativeLayout rl;
  Handler mHandler = new Handler();
  private Runnable task = new Runnable() {
    public void run() {
        
      zoom.setVisibility(View.INVISIBLE);
        
    }
  };
        @Override
        public void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.main);
    //showDialog(LOADING_IMAGE);
    //图片是从网络上获取的话，需要加入滚动条
        bmp=BitmapFactory.decodeResource(getResources(), R.drawable.p_w_picpath);
    //removeDialog(LOADING_IMAGE);
         initZoom();
}
        
        
  @Override
  protected Dialog onCreateDialog(int id) {
    switch (id) {
    case LOADING_IMAGE: {
      final ProgressDialog dialog = new ProgressDialog(this);
      dialog.setOnKeyListener(new OnKeyListener() {
        @Override
        public boolean onKey(DialogInterface dialog, int keyCode,
            KeyEvent event) {
          if (keyCode == KeyEvent.KEYCODE_BACK) {
            finish();
          }
          return false;
        }
      });
      dialog.setMessage("正在加载图片请稍后...");
      dialog.setIndeterminate(true);
      dialog.setCancelable(true);
      return dialog;
    }
    }
    return null;
  }
    
    
  public void initZoom() {

    /* 取得屏幕分辨率大小 */
    DisplayMetrics dm = new DisplayMetrics();
    getWindowManager().getDefaultDisplay().getMetrics(dm);
    displayWidth = dm.widthPixels;
    displayHeight = dm.heightPixels;
    mImageView = (ImageView) findViewById(R.id.myImageView);
    mImageView.setImageBitmap(bmp);
    layoutImage = (LinearLayout) findViewById(R.id.layoutImage);
    mImageView.setOnClickListener(new OnClickListener() {
        
      @Override
      public void onClick(View v) {
        // TODO Auto-generated method stub
                                /**
                                 * 在图片上和整个view上同时添加点击监听捕捉屏幕
                                 * 点击事件，来显示放大缩小按钮    
                                 * */        
        zoom.setVisibility(View.VISIBLE);
        mHandler.removeCallbacks(task);
        mHandler.postDelayed(task, showTime);
      }
    });
    
    layoutImage.setOnClickListener(new OnClickListener() {
        
      @Override
      public void onClick(View v) {
        // TODO Auto-generated method stub
        
        zoom.setVisibility(View.VISIBLE);
        mHandler.removeCallbacks(task);
        mHandler.postDelayed(task, showTime);
      }
    });
    
    zoom = (ZoomControls) findViewById(R.id.zoomcontrol);
    zoom.setIsZoomInEnabled(true);
    zoom.setIsZoomOutEnabled(true);
    // 图片放大
    zoom.setOnZoomInClickListener(new OnClickListener() {
      public void onClick(View v) {
        big();
      }
    });
    // 图片减小
    zoom.setOnZoomOutClickListener(new OnClickListener() {

      public void onClick(View v) {
        small();
      }

    });
    
    
    
    zoom.setVisibility(View.VISIBLE);
    mHandler.postDelayed(task, showTime);

  }

  @Override
  public boolean onTouchEvent(MotionEvent event) {
    // TODO Auto-generated method stub
         /**
                 * 在图片上和整个view上同时添加点击监听捕捉屏幕
                 * 点击事件，来显示放大缩小按钮    
                 * */    
    zoom.setVisibility(View.VISIBLE);
    mHandler.removeCallbacks(task);
    mHandler.postDelayed(task, showTime);
    return false;
  }

  @Override
  public boolean onKeyDown(int keyCode, KeyEvent event) {
    // TODO Auto-generated method stub
    super.onKeyDown(keyCode, event);

    return true;
  }

  /* 图片缩小的method */
  private void small() {
    
    
    
    --zoomNumber;
    int bmpWidth = bmp.getWidth();
    int bmpHeight = bmp.getHeight();

    Log.i("","bmpWidth = " + bmpWidth + ", bmpHeight = " + bmpHeight);

    /* 设置图片缩小的比例 */
    double scale = 0.8;
    /* 计算出这次要缩小的比例 */
    scaleWidth = (float) (scaleWidth * scale);
    scaleHeight = (float) (scaleHeight * scale);
    /* 产生reSize后的Bitmap对象 */
    Matrix matrix = new Matrix();
    matrix.postScale(scaleWidth, scaleHeight);
    Bitmap resizeBmp = Bitmap.createBitmap(bmp, 0, 0, bmpWidth, bmpHeight,
        matrix, true);
    mImageView.setImageBitmap(resizeBmp);

    /* 限制缩小尺寸 */
    if ((scaleWidth * scale * bmpWidth < bmpWidth / 4
        || scaleHeight * scale * bmpHeight > bmpWidth /4
        || scaleWidth * scale * bmpWidth > displayWidth / 5
        || scaleHeight * scale * bmpHeight > displayHeight / 5)&&(zoomNumber==-1) ){
        
    zoom.setIsZoomOutEnabled(false);
    
    } else {
        
    zoom.setIsZoomOutEnabled(true);
    
    }
    
    zoom.setIsZoomInEnabled(true);
    System.gc();
  }

  /* 图片放大的method */
  private void big() {
    ++zoomNumber;
    int bmpWidth = bmp.getWidth();
    int bmpHeight = bmp.getHeight();

    /* 设置图片放大的比例 */
    double scale = 1.25;
    /* 计算这次要放大的比例 */
    scaleWidth = (float) (scaleWidth * scale);
    scaleHeight = (float) (scaleHeight * scale);
    /* 产生reSize后的Bitmap对象 */
    Matrix matrix = new Matrix();
    matrix.postScale(scaleWidth, scaleHeight);
    Bitmap resizeBmp = Bitmap.createBitmap(bmp, 0, 0, bmpWidth, bmpHeight,
        matrix, true);
    mImageView.setImageBitmap(resizeBmp);
    /* 限制放大尺寸 */
    if (scaleWidth * scale * bmpWidth > bmpWidth * 4
        || scaleHeight * scale * bmpHeight > bmpWidth * 4
        || scaleWidth * scale * bmpWidth > displayWidth * 5
        || scaleHeight * scale * bmpHeight > displayHeight * 5) {
        
      zoom.setIsZoomInEnabled(false);
    
    } else {
        
      zoom.setIsZoomInEnabled(true);
    
    }
    
    zoom.setIsZoomOutEnabled(true);
    
  System.gc();
  }
    
}
 
 
布局文件
 
<?xml version="1.0" encoding="utf-8"?>    
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"    
        android:orientation="vertical"    
        android:layout_width="fill_parent"    
        android:layout_height="fill_parent"    
        android:id="@+id/layout1"    
            >    
        
     <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    
                android:layout_width="fill_parent"    
                android:layout_height="fill_parent"    
             android:id="@+id/rl"    
                >    
                
        <ScrollView xmlns:android="http://schemas.android.com/apk/res/android"            
                android:layout_width="fill_parent"    
                android:layout_height="fill_parent"        
                android:layout_weight="19"    
                android:scrollbars="none"    
                android:fadingEdge="vertical"
                android:layout_gravity="center"    
                android:gravity="center"
    
             >    
                
        <HorizontalScrollView        
                android:layout_height="fill_parent"    
                android:layout_width="fill_parent"
                android:scrollbars="none"
                 android:layout_gravity="center"    
                android:gravity="center"    
                android:id="@+id/hs"
                
                    >    
                <LinearLayout
                        android:orientation="horizontal"    
                        android:layout_width="fill_parent"    
                        android:layout_height="fill_parent"    
                        android:id="@+id/layoutImage"    
                        android:layout_gravity="center"    
                        android:gravity="center"    
                        >    
                        <ImageView    
                            android:layout_gravity="center"    
                            android:gravity="center"    
                                android:id="@+id/myImageView"    
                                android:layout_width="fill_parent"    
                                android:layout_height="fill_parent"    
                                android:layout_weight="19"    
                                android:paddingTop="5dip"    
                                android:paddingBottom="5dip"    
                
                                />    
                </LinearLayout>    
        </HorizontalScrollView >    
        </ScrollView>    
        
            
                
             <ZoomControls android:id="@+id/zoomcontrol"
      android:layout_width="wrap_content" android:layout_height="wrap_content"
      android:layout_centerHorizontal="true"
            android:layout_alignParentBottom="true"
      >
    </ZoomControls>
        </RelativeLayout>    

</FrameLayout>