Android：如何获取 RecyclerView 的当前 X 偏移量？

Question

我将Scrollview 用于无限的“时间选择器轮播”，发现这不是最好的方法 (last question)

现在，我找到了Recycler View，但我无法获取recyclerView X 方向的当前滚动偏移量？ （假设每个item是100px宽，第二个item只有50%可见，所以scroll-offset是150px）

• 所有项目的宽度相同，但在第一个项目之前，最后一个项目之后有一些差距
• recyclerView.getScrollX() 返回 0（文档说：初始滚动值）
• LayoutManager 有findFirstVisibleItemPosition，但我无法用它计算 X 偏移量

更新

我刚刚找到了一种方法来继续跟踪 X 位置，同时使用 onScrolled 回调更新值，但我更喜欢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 已经有了获取水平和垂直滚动偏移量的方法

mRecyclerView.computeHorizontalScrollOffset()
mRecyclerView.computeVerticalScrollOffset()

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

Answer 2

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。确保不要重置 overallXScroll（例如 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。

就我而言，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）。我正在从屏幕中间的时间项（计算点）计算时间。这就是为什么我需要 RecycleView 的确切 X-Scroll 位置

• 每个时间项的宽度相同，均为 60dp（仅供参考：60dp = 30min，2dp = 1min）

• 第一项（标题项）有一个额外的填充，设置 0min 到中心

  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 提供正确的线索！看来您可以使用Offset、Extent 和Range 来确定滚动百分比，这样

percentage = 100 * offset / (range - extent)

例如（放入OnScrollListener）：

int offset = recyclerView.computeVerticalScrollOffset();
int extent = recyclerView.computeVerticalScrollExtent();
int range = recyclerView.computeVerticalScrollRange();

int percentage = (int)(100.0 * offset / (float)(range - extent));

Log.i("RecyclerView, "scroll percentage: "+ percentage + "%");

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();
    }
}

比你需要获取偏移量的地方：

recyclerView.getHorizontalOffset()

Answer 5

如果您需要知道当前页面及其与 RecyclerView 宽度相比的偏移量，您可能想尝试以下操作：

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，则 leftIndicator（箭头）将是透明的，如果只有一个 rightIndicator，则 rightIndicator 也是如此（在示例中，适配器始终至少有一项显示所以没有检查空值）。

这样，您基本上将拥有与使用来自ViewPager.OnPageChangeListener 的回调pageScrolled 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项目时，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;
     }
 }

Answer 7

recyclerViewScrollListener = new RecyclerView.OnScrollListener() {

    @Override
    public void onScrollStateChanged(@NonNull @NotNull RecyclerView recyclerView, int newState) {
        super.onScrollStateChanged(recyclerView, newState);
        
    }

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

       

        int scrollBetween += dy;

        int scrollBetweenDP = pxToDp(scrollBetween, getContext());

        if (scrollBetweenDP > 50 ) {
            // scroll down distance 50dp

        } else if (scrollBetweenDP < -50) {
           //scroll up distance 50dp
        }

       
    }
};