ScrollView scrollTo不起作用

Question

与ScrollView相同的问题.scrollTo无法正常工作？在旋转时保存ScrollView位置

我在onCreate中动态添加项目到scrollView.添加完所有项目后,我会尝试以下操作:

    // no effect
    ScrollView mainScroll = (ScrollView) findViewById(R.id.average_scroll_mainScroll);

    // no effect
    ScrollView mainScroll = (ScrollView) findViewById(R.id.average_scroll_mainScroll);
    mainScroll.post(new Runnable() {
        public void run(){
            ScrollView mainScroll = (ScrollView) findViewById(R.id.average_scroll_mainScroll);
            mainScroll.scrollTo(0, 0);
        } 
    });

    // works like a charm
    ScrollView mainScroll = (ScrollView) findViewById(R.id.average_scroll_mainScroll);
    mainScroll.postDelayed(new Runnable() {
        public void run(){
            ScrollView mainScroll = (ScrollView) findViewById(R.id.average_scroll_mainScroll);
            mainScroll.scrollTo(0, 0);
        } 
    }, 30);

我得出结论,有一些事件像'DOM-ready'？有没有回调？

Answer 1

你并不需要延长滚动型,并创建自己按照所提供的答案大卫Daudelin了这个问题.

获取ViewTreeObserver的ScrollView和补充OnGlobalLayoutListener的ViewTreeObserver.然后ScrollView.scrollTo(x,y)从onGlobalLayout()方法中调用方法OnGlobalLayoutListener.码:

 ScrollView mainScroll = (ScrollView) findViewById(R.id.average_scroll_mainScroll);

 ViewTreeObserver vto = scrollView.getViewTreeObserver();
 vto.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
      public void onGlobalLayout() {
           mainScroll.scrollTo(0, 0);
      }
 });

Answer 2

这对我有用，替换scrollView.scrollTo()为

     scrollView.post(new Runnable() {
        @Override
        public void run() {
            scrollView.scrollTo(0, ScrollViewYPosition);//0 is x position
        }
    });

瓦西里·卡布诺夫 (Vasily Kabunov) 的回答帮助了我

ScrollView .scrollTo 不起作用？在旋转时保存 ScrollView 位置

Answer 3

当您对 ScrollView 进行一些更改时，它需要一段时间才能将布局更改复制到显示列表并通知 ScrollView 它确实可以滚动到某个位置。

我已经设法通过扩展ScrollView我自己的 ScrollView 并添加一个方法来使其工作，该方法OnGlobalLayoutListener根据需要添加（如 MH 建议的）并稍后滚动到那里。与将其应用于您需要的每个案例相比，它的自动化程度更高（但随后您需要使用 new ScrollView）。无论如何，这是相关代码：

public class ZScrollView extends ScrollView {

    // Properties
    private int desiredScrollX = -1;
    private int desiredScrollY = -1;
    private OnGlobalLayoutListener gol;

    // ================================================================================================================
    // CONSTRUCTOR ----------------------------------------------------------------------------------------------------

    public ZScrollView(Context __context) {
        super(__context);
    }

    public ZScrollView(Context __context, AttributeSet __attrs) {
        super(__context, __attrs);
    }

    public ZScrollView(Context __context, AttributeSet __attrs, int __defStyle) {
        super(__context, __attrs, __defStyle);
    }

    // ================================================================================================================
    // PUBLIC INTERFACE -----------------------------------------------------------------------------------------------

    public void scrollToWithGuarantees(int __x, int __y) {
        // REALLY Scrolls to a position
        // When adding items to a scrollView, you can't immediately scroll to it - it takes a while
        // for the new addition to cycle back and update the scrollView's max scroll... so we have
        // to wait and re-set as necessary

        scrollTo(__x, __y);

        desiredScrollX = -1;
        desiredScrollY = -1;

        if (getScrollX() != __x || getScrollY() != __y) {
            // Didn't scroll properly: will create an event to try scrolling again later

            if (getScrollX() != __x) desiredScrollX = __x;
            if (getScrollY() != __y) desiredScrollY = __y;

            if (gol == null) {
                gol = new OnGlobalLayoutListener() {
                    @Override
                    public void onGlobalLayout() {
                        int nx = desiredScrollX == -1 ? getScrollX() : desiredScrollX;
                        int ny = desiredScrollY == -1 ? getScrollY() : desiredScrollY;
                        desiredScrollX = -1;
                        desiredScrollY = -1;
                        scrollTo(nx, ny);
                    }
                };

                getViewTreeObserver().addOnGlobalLayoutListener(gol);
            }
        }
    }
}

对我来说非常有用，因为我想在添加后立即滚动到 ScrollView 内的给定视图。