理解Android的手势识别
基础
GestureDetector的工作原理是,当我们接收到用户触摸消息时,将这个消息交给GestureDetector去加工,我们通过设置侦听器获得GestureDetector处理后的手势。
GestureDetector提供了两个侦听器接口,OnGestureListener处理单击类消息,OnDoubleTapListener处理双击类消息。
OnGestureListener的接口有这几个:
// 单击,触摸屏按下时立刻触发
abstract boolean onDown(MotionEvent e);
// 抬起,手指离开触摸屏时触发(长按、滚动、滑动时,不会触发这个手势)
abstract boolean onSingleTapUp(MotionEvent e);
// 短按,触摸屏按下后片刻后抬起,会触发这个手势,如果迅速抬起则不会
abstract void onShowPress(MotionEvent e);
// 长按,触摸屏按下后既不抬起也不移动,过一段时间后触发
abstract void onLongPress(MotionEvent e);
// 滚动,触摸屏按下后移动
abstract boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY);
// 滑动,触摸屏按下后快速移动并抬起,会先触发滚动手势,跟着触发一个滑动手势
abstract boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY);
OnDoubleTapListener的接口有这几个:
// 双击,手指在触摸屏上迅速点击第二下时触发
abstract boolean onDoubleTap(MotionEvent e);
// 双击的按下跟抬起各触发一次
abstract boolean onDoubleTapEvent(MotionEvent e);
// 单击确认,即很快的按下并抬起,但并不连续点击第二下
abstract boolean onSingleTapConfirmed(MotionEvent e);
有时候我们并不需要处理上面所有手势,方便起见,Android提供了另外一个类SimpleOnGestureListener实现了如上接口,我们只需要继承SimpleOnGestureListener然后重载感兴趣的手势即可。
应用
STEP 1: 创建手势侦听对象
package noodies.blog.csdn.net; import android.content.Context; import android.view.MotionEvent; import android.view.GestureDetector.SimpleOnGestureListener; import android.widget.Toast; public class MyGestureListener extends SimpleOnGestureListener { private Context mContext; MyGestureListener(Context context) { mContext = context; } @Override public boolean onDown(MotionEvent e) { Toast.makeText(mContext, "DOWN " + e.getAction(), Toast.LENGTH_SHORT).show(); return false; } @Override public void onShowPress(MotionEvent e) { Toast.makeText(mContext, "SHOW " + e.getAction(), Toast.LENGTH_SHORT).show(); } @Override public boolean onSingleTapUp(MotionEvent e) { Toast.makeText(mContext, "SINGLE UP " + e.getAction(), Toast.LENGTH_SHORT).show(); return false; } @Override public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) { Toast.makeText(mContext, "SCROLL " + e2.getAction(), Toast.LENGTH_SHORT).show(); return false; } @Override public void onLongPress(MotionEvent e) { Toast.makeText(mContext, "LONG " + e.getAction(), Toast.LENGTH_SHORT).show(); } @Override public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) { Toast.makeText(mContext, "FLING " + e2.getAction(), Toast.LENGTH_SHORT).show(); return false; } @Override public boolean onDoubleTap(MotionEvent e) { Toast.makeText(mContext, "DOUBLE " + e.getAction(), Toast.LENGTH_SHORT).show(); return false; } @Override public boolean onDoubleTapEvent(MotionEvent e) { Toast.makeText(mContext, "DOUBLE EVENT " + e.getAction(), Toast.LENGTH_SHORT).show(); return false; } @Override public boolean onSingleTapConfirmed(MotionEvent e) { Toast.makeText(mContext, "SINGLE CONF " + e.getAction(), Toast.LENGTH_SHORT).show(); return false; } }
STEP 2: 设置手势识别
我们可以在Activity里设置手势识别:
package noodies.blog.csdn.net; import android.app.Activity; import android.os.Bundle; import android.view.GestureDetector; import android.view.MotionEvent; public class GestureTestActivity extends Activity { private GestureDetector mGestureDetector; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); mGestureDetector = new GestureDetector(this, new MyGestureListener(this)); } @Override public boolean onTouchEvent(MotionEvent event) { return mGestureDetector.onTouchEvent(event); } } 也可以在自定义的View里面设置手势识别: package noodies.blog.csdn.net; import android.content.Context; import android.util.AttributeSet; import android.view.GestureDetector; import android.view.MotionEvent; import android.view.View; public class MyView extends View { private GestureDetector mGestureDetector; public MyView(Context context, AttributeSet attrs) { super(context, attrs); mGestureDetector = new GestureDetector(context, new MyGestureListener(context)); setLongClickable(true); this.setOnTouchListener(new OnTouchListener() { public boolean onTouch(View v, MotionEvent event) { return mGestureDetector.onTouchEvent(event); } }); } }
陷阱
对于自定义View,使用手势识别有两处陷阱可能会浪费你的不少时间。
1:View必须设置longClickable为true,否则手势识别无法正确工作,只会返回Down, Show, Long三种手势
2:必须在View的onTouchListener中调用手势识别,而不能像Activity一样重载onTouchEvent,否则同样手势识别无法正确工作
测试结果
下面是各种操作返回的手势序列,数值0表示触摸屏按下,1表示抬起
单击:down 0, single up 1, single conf 0
短按:down 0, show 0, single up 1
长按:down 0, show 0, long 0
双击:down 0, single up 1, double 0, double event 0, down 0, double event 1
滚动:down 0, (show 0), scrool 2...
滑动:down 0, (show 0), scrool 2..., fling 1