android 圖片瀏覽時 兩手指控制縮放 、移動

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

    <ImageView
        android:id="@+id/image_view"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:scaleType="matrix"
        android:src="@drawable/test" >
    </ImageView>

</LinearLayout>

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public class Main extends Activity {

private static final int NONE = 0;
private static final int DRAG = 1;
private static final int ZOOM = 2;

private int mode = NONE;
private float oldDist;
private Matrix matrix = new Matrix();
private Matrix savedMatrix = new Matrix();
private PointF start = new PointF();
private PointF mid = new PointF();

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ImageView view = (ImageView) findViewById(R.id.image_view);
view.setOnTouchListener(new OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
ImageView view = (ImageView) v;
switch (event.getAction() & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_DOWN:
savedMatrix.set(matrix); //把原始  Matrix對象儲存起來
start.set(event.getX(), event.getY());  //設定x,y座標
mode = DRAG;
break;
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_POINTER_UP:
mode = NONE;
break;
case MotionEvent.ACTION_POINTER_DOWN:
oldDist = spacing(event);
if (oldDist > 10f) {
savedMatrix.set(matrix);
midPoint(mid, event);  //求出手指兩點的中點
mode = ZOOM;
}
break;
case MotionEvent.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;
}

//求兩點距離
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);
}

//求兩點間中點
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);
}});
}