Android手势GestureDetector分析（二）——源码

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1接口定义相关

//frameworks/base/core/java/android/view/GestureDetector.java

public class GestureDetector {
	
	//OnGestureListener
	public interface OnGestureListener {

        //Notified when a tap occurs with the down that triggered it.
        boolean onDown(@NonNull MotionEvent e);

		//The user has performed a down and not performed a move or up yet.       
        void onShowPress(@NonNull MotionEvent e);

        //Notified when a tap occurs with the up that triggered it.
        boolean onSingleTapUp(@NonNull MotionEvent e);

        //Notified when a scroll occurs with the initial on down and the current move.
        boolean onScroll(@NonNull MotionEvent e1, @NonNull MotionEvent e2, float distanceX, float distanceY);

        //Notified when a long press occurs with the initial on down that trigged it.
        void onLongPress(@NonNull MotionEvent e);

        //Notified of a fling event when it occurs with the initial on down and the matching up.
        boolean onFling(@NonNull MotionEvent e1, @NonNull MotionEvent e2, float velocityX, float velocityY);
    }


	//OnDoubleTapListener
	public interface OnDoubleTapListener {
       
       	//Notified when a single-tap occurs.
        boolean onSingleTapConfirmed(@NonNull MotionEvent e);
 
        //Notified when a double-tap occurs. Triggered on the down event of second tap.
        boolean onDoubleTap(@NonNull MotionEvent e);

        //Notified when an event within a double-tap gesture occurs, including the down, move, and up events.
        boolean onDoubleTapEvent(@NonNull MotionEvent e);
    }


	//OnContextClickListener
	public interface OnContextClickListener {

        //Notified when a context click occurs.
        boolean onContextClick(@NonNull MotionEvent e);
    }
}

	// A convenience class to extend when you only want to listen for a subset of all the gestures. 
    public static class SimpleOnGestureListener implements OnGestureListener, OnDoubleTapListener,  OnContextClickListener {

        public boolean onSingleTapUp(@NonNull MotionEvent e) {
            return false;
        }

        public void onLongPress(@NonNull MotionEvent e) {
        }

        public boolean onScroll(@NonNull MotionEvent e1, @NonNull MotionEvent e2, float distanceX, float distanceY) {
            return false;
        }

        public boolean onFling(@NonNull MotionEvent e1, @NonNull MotionEvent e2, float velocityX, float velocityY) {
            return false;
        }

        public void onShowPress(@NonNull MotionEvent e) {
        }

        public boolean onDown(@NonNull MotionEvent e) {
            return false;
        }

        public boolean onDoubleTap(@NonNull MotionEvent e) {
            return false;
        }

        public boolean onDoubleTapEvent(@NonNull MotionEvent e) {
            return false;
        }

        public boolean onSingleTapConfirmed(@NonNull MotionEvent e) {
            return false;
        }

        public boolean onContextClick(@NonNull MotionEvent e) {
            return false;
        }
    }

2构造器和监听器相关

private final OnGestureListener mListener;
private OnDoubleTapListener mDoubleTapListener;
private OnContextClickListener mContextClickListener;


public GestureDetector(@Nullable @UiContext Context context,
            @NonNull OnGestureListener listener, @Nullable Handler handler) {
        if (handler != null) {
            mHandler = new GestureHandler(handler);
        } else {
            mHandler = new GestureHandler();
        }
        mListener = listener;
        if (listener instanceof OnDoubleTapListener) {
            setOnDoubleTapListener((OnDoubleTapListener) listener);
        }
        if (listener instanceof OnContextClickListener) {
            setContextClickListener((OnContextClickListener) listener);
        }
        init(context);
    }


public void setOnDoubleTapListener(@Nullable OnDoubleTapListener onDoubleTapListener) {
        mDoubleTapListener = onDoubleTapListener;
    }

public void setContextClickListener(@Nullable OnContextClickListener onContextClickListener) {
        mContextClickListener = onContextClickListener;
    }

3触发函数

public boolean onTouchEvent(@NonNull MotionEvent ev) {

        final int action = ev.getAction();

        switch (action & MotionEvent.ACTION_MASK) {
        
            case MotionEvent.ACTION_POINTER_DOWN:
             	//...
                break;
            case MotionEvent.ACTION_POINTER_UP:
                //...
                break;
            case MotionEvent.ACTION_DOWN:
               	//...
                break;
            case MotionEvent.ACTION_MOVE:
                //...
                break;
            case MotionEvent.ACTION_UP:
                //...
                break;
            case MotionEvent.ACTION_CANCEL:
               //...
                break;
        }
        return handled;
    }