手势识别兼容Android 1.x和2.x的代码

public class TouchExampleView extends View {
    private Drawable mIcon; //我们以一个图片为参照物，根据手势控制
    private float mPosX;
    private float mPosY;

    private VersionedGestureDetector mDetector; 
    private float mScaleFactor = 1.f; //原始缩放比例为1.0

    public TouchExampleView(Context context) {
        this(context, null, 0);
    }

    public TouchExampleView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public TouchExampleView(Context context, AttributeSet attrs, int defStyle) { //实现我们自定义View的构造
        super(context, attrs, defStyle);
        mIcon = context.getResources().getDrawable(R.drawable.icon);
        mIcon.setBounds(0, 0, mIcon.getIntrinsicWidth(), mIcon.getIntrinsicHeight());

        mDetector = VersionedGestureDetector.newInstance(context, new GestureCallback()); //实例化刚才的版本自适应手势控制类
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) { //重写onTouchEvent方法，使用VersionedGestureDetector类得出的数据。
        mDetector.onTouchEvent(ev);
        return true;
    }

    @Override
    public void onDraw(Canvas canvas) { //处理自定义View绘制方法
        super.onDraw(canvas);

        canvas.save();
        canvas.translate(mPosX, mPosY); //进行平移操作，根据mPosX和mPosY坐标
        canvas.scale(mScaleFactor, mScaleFactor); //进行缩放操作，参数就是刚才定义的float类型的缩放比例
        mIcon.draw(canvas); //直接绘制图片变化到画布中
        canvas.restore();
    }

    private class GestureCallback implements VersionedGestureDetector.OnGestureListener { 
        public void onDrag(float dx, float dy) { //这里Android123提示大家在2.2中这个回调方法将可以支持拖拽的坐标处理
            mPosX += dx;
            mPosY += dy;
            invalidate();
        }

        public void onScale(float scaleFactor) {
            mScaleFactor *= scaleFactor; //缩放控制

            mScaleFactor = Math.max(0.1f, Math.min(mScaleFactor, 5.0f)); //限制最小缩放比例为1.0最大为5.0倍数

            invalidate();
        }
    }
}

TouchExampleView view = new TouchExampleView(this);
view.setLayoutParams(new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,ViewGroup.LayoutParams.MATCH_PARENT));

setContentView(view);  //替换掉原始的res.layout.main