Android 手势识别—缩放

      上一篇讲解了手势识别中的点击和双击事件的识别，用到的是GestureDetector类和GestureDetectorCompat类，用于监听用户触摸屏幕中的简单动作。

缩放

基本用法如下，可以通过缩放手势缩放一个View

public class ScaleGestureActivity extends BaseActivity {

    private View mView;
    private ScaleGestureDetector mScaleGestureDetector;
    private static final String TAG = "ScaleGestureActivity";
    private float mScaleFactor = 1.0f;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_scale_gesture);
        mView = findViewById(R.id.scale_view);
        mScaleGestureDetector = new ScaleGestureDetector(this,mScaleGestureListener);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        mScaleGestureDetector.onTouchEvent(event);
        return super.onTouchEvent(event);
    }

    private ScaleGestureDetector.OnScaleGestureListener mScaleGestureListener = new ScaleGestureDetector.OnScaleGestureListener() {
        @Override
        public boolean onScale(ScaleGestureDetector scaleGestureDetector) {
            mScaleFactor  *= scaleGestureDetector.getScaleFactor();
            mView.setScaleX(mScaleFactor);
            mView.setScaleY(mScaleFactor);
            Log.i(TAG, "onScale: "+ scaleGestureDetector.getScaleFactor()+"----"+mScaleFactor);
            return true;
        }

        @Override
        public boolean onScaleBegin(ScaleGestureDetector scaleGestureDetector) {
            return true;
        }

        @Override
        public void onScaleEnd(ScaleGestureDetector scaleGestureDetector) {

        }
    };
}

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