Android 触摸及手势操作GestureDetector
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现在的智能手机不敢说百分百的都是触摸屏,也应该是百分之九九以上为触摸屏了,触摸屏为我们操作无键盘、无鼠标的手机系统带来了很多的便利。当用户触摸屏幕时会产生很多的触摸事件,down、up、move等等。View类有个View.OnTouchListener内部接口,通过重写他的onTouch(View v, MotionEvent event)方法,我们可以处理一些touch事件,如下:
- public class MainActivity extends Activity {
- ...
- // This example shows an Activity, but you would use the same approach if
- // you were subclassing a View.
- @Override
- public boolean onTouchEvent(MotionEvent event){
- int action = MotionEventCompat.getActionMasked(event);
- switch(action) {
- case (MotionEvent.ACTION_DOWN) :
- Log.d(DEBUG_TAG,"Action was DOWN");
- return true;
- case (MotionEvent.ACTION_MOVE) :
- Log.d(DEBUG_TAG,"Action was MOVE");
- return true;
- case (MotionEvent.ACTION_UP) :
- Log.d(DEBUG_TAG,"Action was UP");
- return true;
- case (MotionEvent.ACTION_CANCEL) :
- Log.d(DEBUG_TAG,"Action was CANCEL");
- return true;
- case (MotionEvent.ACTION_OUTSIDE) :
- Log.d(DEBUG_TAG,"Movement occurred outside bounds " +
- "of current screen element");
- return true;
- default :
- return super.onTouchEvent(event);
- }
- }
OnTouch提供的事件还是相对较简单,如果需要处理一些复杂的手势,用这个接口就会很麻烦,因为我们要根据用户触摸的轨迹去判断是什么手势。Android sdk给我们提供了GestureDetector(Gesture:手势Detector:识别)类,通过这个类我们可以识别很多的手势。
public class GestureDetector extends Object
java.lang.Object
android.view.GestureDetector
GestureDetector属于android.view包,android还提供了android.gesture包支持更多的手势操作,以后我们会介绍到。官方的介绍中使用了GestureDetectorCompat处理手势识别,为什么使用GestureDetectorCompat替换了GestureDetector呢,官方的是这样解释的:
GestureDetectorCompat实例化有下面两种方法:
GestureDetector类对外提供了两个接口:OnGestureListener,OnDoubleTapListener,还有一个内部类SimpleOnGestureListener;SimpleOnGestureListener类是GestureDetector提供给我们的一个更方便的响应不同手势的类,它实现了上述两个接口,该类是static class,也就是说它实际上是一个外部类,我们可以在外部继承这个类,重写里面的手势处理方法。因此实现手势识别有两种方法,一种实现OnGestureListener接口,另一种是使用SimpleOnGestureListener类。
OnGestureListener有下面的几个动作:
按下(onDown): 刚刚手指接触到触摸屏的那一刹那,就是触的那一下。
抛掷(onFling): 手指在触摸屏上迅速移动,并松开的动作。
长按(onLongPress): 手指按在持续一段时间,并且没有松开。
滚动(onScroll): 手指在触摸屏上滑动。
按住(onShowPress): 手指按在触摸屏上,它的时间范围在按下起效,在长按之前。
抬起(onSingleTapUp):手指离开触摸屏的那一刹那。
使用OnGestureListener接口,这样需要重载OnGestureListener接口所有的方法,适合监听所有的手势,正如官方文档提到的“Detecing All Supported Gestures”。
- public class MainActivity extends Activity implements
- GestureDetector.OnGestureListener,
- GestureDetector.OnDoubleTapListener{
- private static final String DEBUG_TAG = "Gestures";
- private GestureDetectorCompat mDetector;
- // Called when the activity is first created.
- @Override
- public void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.activity_main);
- // Instantiate the gesture detector with the
- // application context and an implementation of
- // GestureDetector.OnGestureListener
- mDetector = new GestureDetectorCompat(this,this);
- // Set the gesture detector as the double tap
- // listener.
- mDetector.setOnDoubleTapListener(this);
- }
- @Override
- public boolean onTouchEvent(MotionEvent event){
- this.mDetector.onTouchEvent(event);
- // Be sure to call the superclass implementation
- return super.onTouchEvent(event);
- }
- @Override
- public boolean onDown(MotionEvent event) {
- Log.d(DEBUG_TAG,"onDown: " + event.toString());
- return true;
- }
- @Override
- public boolean onFling(MotionEvent event1, MotionEvent event2,
- float velocityX, float velocityY) {
- Log.d(DEBUG_TAG, "onFling: " + event1.toString()+event2.toString());
- return true;
- }
- @Override
- public void onLongPress(MotionEvent event) {
- Log.d(DEBUG_TAG, "onLongPress: " + event.toString());
- }
- @Override
- public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX,
- float distanceY) {
- Log.d(DEBUG_TAG, "onScroll: " + e1.toString()+e2.toString());
- return true;
- }
- @Override
- public void onShowPress(MotionEvent event) {
- Log.d(DEBUG_TAG, "onShowPress: " + event.toString());
- }
- @Override
- public boolean onSingleTapUp(MotionEvent event) {
- Log.d(DEBUG_TAG, "onSingleTapUp: " + event.toString());
- return true;
- }
- @Override
- public boolean onDoubleTap(MotionEvent event) {
- Log.d(DEBUG_TAG, "onDoubleTap: " + event.toString());
- return true;
- }
- @Override
- public boolean onDoubleTapEvent(MotionEvent event) {
- Log.d(DEBUG_TAG, "onDoubleTapEvent: " + event.toString());
- return true;
- }
- @Override
- public boolean onSingleTapConfirmed(MotionEvent event) {
- Log.d(DEBUG_TAG, "onSingleTapConfirmed: " + event.toString());
- return true;
- }
- }
这样会造成有些手势动作我们用不到,但是还要重载。SimpleOnGestureListener类的出现为我们解决了这个问题,如果你想“Detecting a Subset of Supported Gestures”,SimpleOnGestureListener是最好的选择。
- public class MainActivity extends Activity {
- private GestureDetectorCompat mDetector;
- @Override
- public void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.activity_main);
- mDetector = new GestureDetectorCompat(this, new MyGestureListener());
- }
- @Override
- public boolean onTouchEvent(MotionEvent event){
- this.mDetector.onTouchEvent(event);
- return super.onTouchEvent(event);
- }
- class MyGestureListener extends GestureDetector.SimpleOnGestureListener {
- private static final String DEBUG_TAG = "Gestures";
- @Override
- public boolean onDown(MotionEvent event) {
- Log.d(DEBUG_TAG,"onDown: " + event.toString());
- return true;
- }
- @Override
- public boolean onFling(MotionEvent event1, MotionEvent event2,
- float velocityX, float velocityY) {
- Log.d(DEBUG_TAG, "onFling: " + event1.toString()+event2.toString());
- return true;
- }
- }
- }
最后了我们也解释两个问题:
1、onTouchEvent中为什么使用了MotionEventCompat,而不直接使用MotionEvent。因为MotionEventCompat使更多的Action适配到API 4。
2、Android的view怎么使用手势,方法如下:
- View myView = findViewById(R.id.my_view);
- myView.setOnTouchListener(new OnTouchListener() {
- public boolean onTouch(View v, MotionEvent event) {
- // ... Respond to touch events
- this.mDetector.onTouchEvent(event);
- return super.onTouchEvent(event);
- }
- });
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