Android实现对imageview的拖动以及缩放

package org.wch.gesture;

import android.graphics.Matrix;
import android.graphics.PointF;
import android.util.FloatMath;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.ImageView;
import android.widget.ImageView.ScaleType;

public class MulitPointTouchListener implements OnTouchListener {

Matrix matrix = new Matrix();
Matrix savedMatrix = new Matrix();

public ImageView image;
static final int NONE = 0;
static final int DRAG = 1;
static final int ZOOM = 2;
int mode = NONE;

PointF start = new PointF();
PointF mid = new PointF();
float oldDist = 1f;

public MulitPointTouchListener(ImageView image) {
super();
this.image = image;
}

@Override
public boolean onTouch(View v, MotionEvent event) {
this.image.setScaleType(ScaleType.MATRIX);

ImageView view = (ImageView) v;
//		dumpEvent(event);

switch (event.getAction() & MotionEvent.ACTION_MASK) {

case MotionEvent.ACTION_DOWN:

Log.w("FLAG", "ACTION_DOWN");
matrix.set(view.getImageMatrix());
savedMatrix.set(matrix);
start.set(event.getX(), event.getY());
mode = DRAG;
break;
case MotionEvent.ACTION_POINTER_DOWN:
Log.w("FLAG", "ACTION_POINTER_DOWN");
oldDist = spacing(event);
if (oldDist > 10f) {
savedMatrix.set(matrix);
midPoint(mid, event);
mode = ZOOM;
}
break;
case MotionEvent.ACTION_UP:
Log.w("FLAG", "ACTION_UP");
case MotionEvent.ACTION_POINTER_UP:
Log.w("FLAG", "ACTION_POINTER_UP");
mode = NONE;
break;
case MotionEvent.ACTION_MOVE:
Log.w("FLAG", "ACTION_MOVE");
if (mode == DRAG) {
matrix.set(savedMatrix);
matrix.postTranslate(event.getX() - start.x, event.getY()
- start.y);
} else if (mode == ZOOM) {
float newDist = spacing(event);
if (newDist > 10f) {
matrix.set(savedMatrix);
float scale = newDist / oldDist;
matrix.postScale(scale, scale, mid.x, mid.y);
}
}
break;
}

view.setImageMatrix(matrix);
return true;
}

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);
}

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);
}
}