Android 手勢識別—縮放

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      上一篇講解了手勢識別中的點擊和雙擊事件的識別，用到的是GestureDetector類和GestureDetectorCompat類，用於監聽使用者觸控螢幕幕中的簡單動作。

縮放

基本用法如下，可以通過縮放手勢縮放一個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) {        }    };}

View Code

ScaleGestureDetector 官方對該類的解釋如下：

Detects scaling transformation gestures using the supplied MotionEvents. The ScaleGestureDetector.OnScaleGestureListener callback will notify users when a particular gesture event has occurred. This class should only be used with MotionEvents reported via touch. To use this class:

• Create an instance of the ScaleGestureDetector for your View
• In the onTouchEvent(MotionEvent) method ensure you call onTouchEvent(MotionEvent). The methods defined in your callback will be executed when the events occur.

該類的構造方法如下：

public ScaleGestureDetector(Context context, ScaleGestureDetector.OnScaleGestureListener listener)

由構造方法可知需要為一個縮放類設定一個縮放的監聽介面，具體實現見代碼中監聽類介面的實現，下面具體介紹幾個函數的含義：

1. public boolean onScale(ScaleGestureDetector detector);

         縮放時會被調用，傳回值代表本次縮放事件是否已被處理。如果已被處理，那麼detector就會重設縮放事件；如果未被處理，detector會繼續進行計算，修改getScaleFactor()的傳回值，直到被處理為止。因此，它常用在判斷只有縮放值達到一定數值時才進行縮放。下面的代碼錶示只有當縮放倍數達到2倍時才對其進行縮放，否則該事件不處理。

public boolean onScale(ScaleGestureDetector detector) {System.out.println(detector.getScaleFactor());if(detector.getScaleFactor()< 2){return false;}mMatrix.preScale(detector.getScaleFactor(), detector.getScaleFactor());setImageMatrix(mMatrix);return true;}

    2.public boolean onScaleBegin(ScaleGestureDetector detector)

       縮放開始時會被調用。傳回值表示該detector是否處理後繼的縮放事件。返回false時，不會執行後續的onScale()。

    3. public void onScaleEnd(ScaleGestureDetector scaleGestureDetector)

      縮放結束時的回調

http://blog.csdn.net/qiwenmingshiwo/article/details/70850406

https://github.com/Almeros/android-gesture-detectors

https://github.com/Almeros/android-gesture-detectors-example/blob/master/app/src/main/java/com/almeros/android/multitouch/example/TouchActivity.java

Android 手勢識別—縮放