Android 手势识别—缩放 _Android

提兵百万西湖上，立马吴山第一峰！这篇文章主要讲述Android 手势识别—缩放相关的知识，希望能为你提供帮助。
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

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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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ScaleGestureDetector 官方对该类的解释如下：

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.

该类的构造方法如下：

public ScaleGestureDetector(Context context, ScaleGestureDetector.OnScaleGestureListener listener)

由构造方法可知需要为一个缩放类设置一个缩放的监听接口，具体实现见代码中监听类接口的实现，下面具体介绍几个函数的含义：

public boolean onScale(ScaleGestureDetector detector);

缩放时会被调用，返回值代表本次缩放事件是否已被处理。如果已被处理，那么detector就会重置缩放事件；如果未被处理，detector会继续进行计算，修改getScaleFactor()的返回值，直到被处理为止。因此，它常用在判断只有缩放值达到一定数值时才进行缩放。下面的代码表示只有当缩放倍数达到2倍时才对其进行缩放，否则该事件不处理。

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)
缩放开始时会被调用。返回值表示该detector是否处理后继的缩放事件。返回false时，不会执行后续的onScale()。
3. public void onScaleEnd(ScaleGestureDetector scaleGestureDetector)
缩放结束时的回调
http://blog.csdn.net/qiwenmingshiwo/article/details/70850406
https://github.com/Almeros/android-gesture-detectors
【Android 手势识别—缩放】https://github.com/Almeros/android-gesture-detectors-example/blob/master/app/src/main/java/com/almeros/android/multitouch/example/TouchActivity.java