android 多点触摸图片缩放的具体实现方法

    <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>

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) {

        }

}
}