MyGestureDetector extends SimpleOnGestureListener

问题:

I am implementing a MyGestureDetector that extends a SimpleOnGestureListener. I borrowed the class from: http://www.codeshogun.com/blog/tag/view-flipper/ to allow a swipe action in a ViewFlipper. I can not get if to function on the emulator. Any suggestions?

Below is all of the code:

The main.java

import android.app.Activity;
import android.os.Bundle;
import android.view.GestureDetector;
import android.view.KeyEvent;
import android.view.MotionEvent;import android.view.View;
import android.view.GestureDetector.SimpleOnGestureListener;
import android.view.animation.Animation;
import android.view.animation.AnimationUtils;
import android.webkit.WebView;
import android.widget.ViewFlipper;


public class main extends Activity {

private static final int SWIPE_MIN_DISTANCE = 120;
private static final int SWIPE_MAX_OFF_PATH = 250;
private static final int SWIPE_THRESHOLD_VELOCITY = 200;
private GestureDetector gestureDetector;
View.OnTouchListener gestureListener;
private Animation slideLeftIn;
private Animation slideLeftOut;
private Animation slideRightIn;
private Animation slideRightOut;
private ViewFlipper viewFlipper;

    @Override
    public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    // ---------------------------------Sets Swipe Animation to Next View -->       
    viewFlipper = (ViewFlipper)findViewById(R.id.AC4313);
    slideLeftIn = AnimationUtils.loadAnimation(this, R.anim.slide_left_in);
    slideLeftOut = AnimationUtils.loadAnimation(this, R.anim.slide_left_out);
    slideRightIn = AnimationUtils.loadAnimation(this, R.anim.slide_right_in);
    slideRightOut = AnimationUtils.loadAnimation(this, R.anim.slide_right_out);

    gestureDetector = new GestureDetector(new MyGestureDetector());
    gestureListener = new View.OnTouchListener() {
        public boolean onTouch(View v, MotionEvent event) {
            if (gestureDetector.onTouchEvent(event)) {
                return true;
            }
            return false;
        }
    };     
}

class MyGestureDetector extends SimpleOnGestureListener {
    @Override
    public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,float velocityY) {
        try {
            if (Math.abs(e1.getY() - e2.getY()) > SWIPE_MAX_OFF_PATH)
                return false;
            // right to left swipe
            if(e1.getX() - e2.getX() > SWIPE_MIN_DISTANCE && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY) {
                viewFlipper.setInAnimation(slideLeftIn);
                viewFlipper.setOutAnimation(slideLeftOut);
                viewFlipper.showNext();
            }  else if (e2.getX() - e1.getX() > SWIPE_MIN_DISTANCE && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY) {
                viewFlipper.setInAnimation(slideRightIn);
                viewFlipper.setOutAnimation(slideRightOut);
                viewFlipper.showPrevious();
            }
        } catch (Exception e) {
            // nothing
        }
        return false;
    }
}    

@Override // ------------------------------ Catch the Gesture Event by Overriding onTouch() method: -->
public boolean onTouchEvent(MotionEvent event) {
    if (gestureDetector.onTouchEvent(event))
        return true;
    else
        return false;
} 

The anim *.xml's:

<?xml version="1.0" encoding="utf-8"?>

<set xmlns:android="http://schemas.android.com/apk/res/android">
    <translate android:fromXDelta="100%p" android:toXDelta="0" android:duration="800"/>
</set> 

回答1:

I think the problem is that you don't override the OnDown event. Add this code snippet to your MyGestureDetector class, and it should be work.

@Override
public boolean onDown(MotionEvent e) {
    return true;        
}

The onDown event return false by default, and every gesture start with onDown so your onFling event will not fire.

Istvan

回答2:

Seems like you can now solve this problem with a lot less code using a gesture detector, like this:

import android.content.Context;
import android.util.AttributeSet;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.View;
import android.widget.GridView;

public class ScrollingGridView extends GridView {
    private GestureDetector gestureDetector;

    public ScrollingGridView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public ScrollingGridView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        setupGestureListener();
    }

    private void setupGestureListener() {
        GestureDetector.SimpleOnGestureListener gestureListener = new GestureDetector.SimpleOnGestureListener() {
            @Override
            public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
                scrollBy((int)distanceX, (int)distanceY);
                return true;
            }
        };
        gestureDetector = new GestureDetector(getContext(), gestureListener);
        setOnTouchListener(new OnTouchListener() {
            @Override
            public boolean onTouch(View view, MotionEvent motionEvent) {
                gestureDetector.onTouchEvent(motionEvent);
                return true;
            }
        });
    }
}