Question

我使用Scrollview进行无限时间选择器轮播＆＃34;并发现，这不是最好的方法（last question）

现在，我找到了Recycler View，但我无法在recyclerView的X方向上获得当前的滚动偏移？（假设每个项目的宽度为100px，第二个项目只有50％可见，因此滚动偏移量为150px）

所有项目都有相同的宽度，但在第一项之后，在最后一项
recyclerView.getScrollX()返回0（文档说：初始滚动值）
LayoutManager有findFirstVisibleItemPosition，但我无法用

更新

我刚刚找到了一种跟踪X-Position的方法，同时使用onScrolled回调更新了值，但我更愿意获取实际值，而不是一直跟踪它！

private int overallXScroll = 0;
//...
mRecyclerView.setOnScrollListener(new RecyclerView.OnScrollListener() {
        @Override
        public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);

            overallXScroll = overallXScroll + dx;

            Log.i("check","overallXScroll->" + overallXScroll);

        }
    });

Answer 1

RecyclerView已经有获取水平和垂直滚动偏移的方法

mRecyclerView.computeHorizontalScrollOffset()
mRecyclerView.computeVerticalScrollOffset()

这适用于包含相同高度（垂直滚动偏移）和相同宽度（水平滚动偏移）的单元格的RecyclerViews

Answer 2

enter image description here

解决方案1： setOnScrollListener

将您的X-Position保存为类变量，并更新onScrollListener中的每个更改。确保您不重置overallXScroll（f.e。onScreenRotationChange）

 private int overallXScroll = 0;
 //...
 mRecyclerView.setOnScrollListener(new RecyclerView.OnScrollListener() {
    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        super.onScrolled(recyclerView, dx, dy);

        overallXScroll = overallXScroll + dx;
        Log.i("check","overall X  = " + overallXScroll);

    }
 });

解决方案2：计算当前位置。

在我的情况下，我有一个水平列表，其中填充了时间值（0：00,0：30,1：00,1：30 ...... 23：00,23：30）。我正在计算时间项目的时间，该时间项目位于屏幕中间（计算点）。这就是我需要RecycleView

的确切X-Scroll位置的原因

每次项目的宽度相同为60dp（fyi：60dp = 30min，2dp = 1min）

第一项（标题项）有一个额外的填充，将0分钟设置为中心

private int mScreenWidth = 0;
private int mHeaderItemWidth = 0;
private int mCellWidth = 0;

@Override
protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);

  //init recycle views
  //...
  LinearLayoutManager mLLM = (LinearLayoutManager) getLayoutManager();
  DisplayMetrics displaymetrics = new DisplayMetrics();
  this.getWindowManager().getDefaultDisplay().getMetrics(displaymetrics);
  this.mScreenWidth = displaymetrics.widthPixels;

  //calculate value on current device
  mCellWidth = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 60, getResources()
        .getDisplayMetrics());

  //get offset of list to the right (gap to the left of the screen from the left side of first item)
  final int mOffset = (this.mScreenWidth / 2) - (mCellWidth / 2);

  //HeaderItem width (blue rectangle in graphic)
  mHeaderItemWidth = mOffset + mCellWidth;

  mRecyclerView.setOnScrollListener(new RecyclerView.OnScrollListener() {

    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        super.onScrolled(recyclerView, dx, dy);

        //get first visible item
        View firstVisibleItem = mLLM.findViewByPosition(mLLM.findFirstVisibleItemPosition());

        int leftScrollXCalculated = 0;
        if (firstItemPosition == 0){
               //if first item, get width of headerview (getLeft() < 0, that's why I Use Math.abs())
            leftScrollXCalculated = Math.abs(firstVisibleItem.getLeft());
        }
        else{

               //X-Position = Gap to the right + Number of cells * width - cell offset of current first visible item
               //(mHeaderItemWidth includes already width of one cell, that's why I have to subtract it again)
            leftScrollXCalculated = (mHeaderItemWidth - mCellWidth) + firstItemPosition  * mCellWidth + firstVisibleItem.getLeft();
        }

        Log.i("asdf","calculated X to left = " + leftScrollXCalculated);

    }
});

}

Answer 3

感谢@ umar-qureshi的正确领导！您似乎可以使用array1，Offset和Extent确定滚动百分比，以便

Range

例如（要放入percentage = 100 * offset / (range - extent)）：

OnScrollListener

Answer 4

public class CustomRecyclerView extends RecyclerView {

    public CustomRecyclerView(Context context) {
        super(context);
    }

    public CustomRecyclerView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

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

    public int getHorizontalOffset() {
        return super.computeHorizontalScrollOffset();
    }
}

比你需要获得偏移的地方：

recyclerView.getHorizontalOffset()

Answer 5

如果你需要知道当前页面及其偏移量与RecyclerView的宽度相比，你可能想尝试这样的事情：

recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
    @Override
    public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
        super.onScrollStateChanged(recyclerView, newState);
    }

    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        super.onScrolled(recyclerView, dx, dy);

        final int scrollOffset = recyclerView.computeHorizontalScrollOffset();
        final int width = recyclerView.getWidth();
        final int currentPage = scrollOffset / width;
        final float pageOffset = (float) (scrollOffset % width) / width;

        // the following lines just the example of how you can use it
        if (currentPage == 0) {
            leftIndicator.setAlpha(pageOffset);
        }

        if (adapter.getItemCount() <= 1) {
            rightIndicator.setAlpha(pageOffset);
        } else if (currentPage == adapter.getItemCount() - 2) {
            rightIndicator.setAlpha(1f - pageOffset);
        }
    }
});

如果currentPage的索引为0，那么leftIndicator（箭头）将是透明的，如果只有一个rightIndicator，那么page将是透明的（在示例中，适配器始终至少有一个要显示的项目，因此不会检查空值。

通过这种方式，您基本上可以使用与pageScrolled中使用回调ViewPager.OnPageChangeListener几乎相同的功能。

Answer 6

通过覆盖RecyclerView onScrolled(int dx,int dy)，您可以获得滚动偏移量。但是当您添加或删除该项时，该值可能是错误的。

public class TempRecyclerView extends RecyclerView {
   private int offsetX = 0;
   private int offsetY = 0;
   public TempRecyclerView(Context context) {
       super(context);
   }

   public TempRecyclerView(Context context, @Nullable AttributeSet attrs) {
      super(context, attrs);
   }

   public TempRecyclerView(Context context, @Nullable AttributeSet attrs,int defStyle){
      super(context, attrs, defStyle);
   }
/**
 * Called when the scroll position of this RecyclerView changes. Subclasses 
   should usethis method to respond to scrolling within the adapter's data 
   set instead of an explicit listener.
 * <p>This method will always be invoked before listeners. If a subclass 
   needs to perform any additional upkeep or bookkeeping after scrolling but 
   before listeners run, this is a good place to do so.</p>
 */
   @Override
   public void onScrolled(int dx, int dy) {
  //  super.onScrolled(dx, dy);
      offsetX+=dx;
      offsetY+=dy;
     }
 }

Android：如何获取RecyclerView的当前X偏移量？

6 个答案: