当我们到达 Horizo​​ntalScrollView 中的最后一项时指示器消失

Question

我有一个 Horizo​​ntalScrollView 的子类，我在其中添加多个图像。 我必须在屏幕的左右端显示某种指示器，以显示左右两侧是否有剩余物品。当我们到达相关终点时，相应的指示器也会消失。

谁能告诉我可用的选项？

     protected void onScrollChanged(int l, int t, int oldl, int oldt) {

             View view = (View) takeparent().getChildAt(takeparent().getChildCount()-1);  //this is the last view
             int diff = (view.getRight()-(getRight()+getScrollX()));// Calculate the scrolldiff
             if( diff == 0 ){  // if diff is zero, then the rightmost end has been reached
                 right.setVisibility(View.GONE); //setting the right button invisible
             }


             View viewleft = (View) takeparent().getChildAt(0);  taking the first View 
             int diffleft2 = (viewleft.getLeft()-(getLeft()+getScrollX()));// Calculate the scrolldiff

             if( diffleft2 == 0 ){  // if diff is zero, then the bottom has been reached
                 left.setVisibility(View.GONE);
                 }



             super.onScrollChanged(l, t, oldl, oldt);
     }

Answer 1

这是您现在修改的问题的答案：

@Override
public boolean canScrollHorizontally(int direction)
{
    final int offset = computeHorizontalScrollOffset();
    final int range = computeHorizontalScrollRange() - computeHorizontalScrollExtent();
    if(range == 0){
        return false;
    }
    return (direction < 0) ? (offset > 0) : (offset < range - 1);
}

protected void onScrollChanged(int l, int t, int oldl, int oldt)
{
    left .setVisibility(canScrollHorizontally(-1) ? View.VISIBLE : View.GONE);
    right.setVisibility(canScrollHorizontally( 1) ? View.VISIBLE : View.GONE);
}

我会推荐 Drawables 而不是使用 Views。

所以，我扩展了HorizontalScrollView 并覆盖了draw() 方法，以将自己的Drawable 绘制到指标的canvas。剩下的只是使用setBounds 管理它们的位置，现在是按下状态。

代码：https://gist.github.com/slightfoot/4c017f776663bf6dd5d8#file-indicatedhorizontalscrollview-java