通过UI反馈动态控制ViewPager的滚动方向

Question

/* (non-Javadoc)
 * @see android.support.v4.view.ViewPager#onInterceptTouchEvent(android.view.MotionEvent)
 */
@Override
public boolean onInterceptTouchEvent(MotionEvent event) {
    if (this.canGoLeft || this.canGoRight) {
        return super.onInterceptTouchEvent(event);
    }

    return false;
}

/* (non-Javadoc)
 * @see android.support.v4.view.ViewPager#onTouchEvent(android.view.MotionEvent)
 */
@Override
public boolean onTouchEvent(MotionEvent ev) {
    boolean lockScroll = false;
    switch (ev.getAction()) {
    case MotionEvent.ACTION_DOWN:
        lastX = ev.getX();
        lockScroll = false;
        return super.onTouchEvent(ev);
    case MotionEvent.ACTION_MOVE:
        if (canGoLeft && lastX < ev.getX()) {
            lockScroll = false;
        } else if (canGoRight && lastX > ev.getX()) {
            lockScroll = false;
        } else {
            lockScroll = true;
        }


        lastX = ev.getX();

        break;
    }

    lastX = ev.getX();

    if (lockScroll) {
        //make callback to prevent movement
        if (mOnPreventCallback != null) {
            mOnPreventCallback.onPreventMovement();
        }
        return false;
    } else {
        return super.onTouchEvent(ev);
    }
}

我想在这里做三件事：

1. 在选定项目或其他内容之前，禁止滚动到下一个屏幕
2. 阻止滚动到上一个屏幕（部分实现）
3. 向用户提供反馈，以显示滚动被禁用，就像Android用渐变显示顶部和底部屏幕的方式一样。

Answer 1

当我面对一个类似的问题时，我用一个gestureDetector制作了自己的监听器，使它对滑动完全没有反应，你可以很容易地将它调整为只有在某种条件下才对向右滑动没有反应。这应该回答你的数字1和2。

这是听众：

public class OnSwipeTouchListener implements OnTouchListener {

@SuppressWarnings("deprecation")
private final GestureDetector gestureDetector = new GestureDetector(new GestureListener());

public boolean onTouch(final View v, final MotionEvent event) {
    return gestureDetector.onTouchEvent(event);
}

private final class GestureListener extends SimpleOnGestureListener {

    private static final int SWIPE_THRESHOLD = 100;
    private static final int SWIPE_VELOCITY_THRESHOLD = 100;

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


    @Override
    public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
        boolean result = false;
        try {
            float diffY = e2.getY() - e1.getY();
            float diffX = e2.getX() - e1.getX();
            if (Math.abs(diffX) > Math.abs(diffY)) {
                if (Math.abs(diffX) > SWIPE_THRESHOLD && Math.abs(velocityX) > SWIPE_VELOCITY_THRESHOLD) {
                    if (diffX > 0) {
                        onSwipeRight();
                    } else {
                        onSwipeLeft();
                    }
                }
            } else {
               // onTouch(e);
            }
        } catch (Exception exception) {
            exception.printStackTrace();
        }
        return result;
    }
}
public void onTouch(MotionEvent e) {
}
public void onSwipeRight() {
//call this only if your condition was set
}

public void onSwipeLeft() {
//nothing, this means,swipes to left will be ignored
}

public void onSwipeTop() {
}

public void onSwipeBottom() {
}
}

这是一个使用示例：

viewPager.setOnTouchListener(new OnSwipeTouchListener() {
public void onSwipeRight() {
  if(your conditionIsMet){
// move your pager view to the right
     }
   }

});