如何使用 SnapHelper 將快照 position 從 RecycleView 的中心移動到左側？

Question

我有一個包含 ImageView 的 RecycleView，我的問題是如何將快照移動到 RecycleView 的左側而不是中心？

當我移動 ImageViews 時，它們會在中心捕捉，我可以通過覆蓋CalculateDistanceToFinalSnap方法將它們移動到該“捕捉窗口”內的左側或右側。 我想我現在需要將那個“快照窗口”移動到 RecycleView 的左側，但我不知道如何，或者也許還有另一種方法，請幫忙。

這是我的問題的圖片，也許它會幫助您更清楚地理解：圖片

Answer 1

@Jessie Zhang -MSFT 的解決方案對我有用。 代碼的格式有點奇怪，我很難把它拿過來。 這是 Kotlin 中的相同解決方案（僅適用於水平捕捉）。

class StartSnapHelper: LinearSnapHelper() {
    override fun calculateDistanceToFinalSnap(layoutManager: RecyclerView.LayoutManager, targetView: View): IntArray? {
        return if (layoutManager.canScrollHorizontally()) {
            val outer = mutableListOf<Int>()
            outer.add(distanceToStart(targetView, getHorizontalHelper(layoutManager)))
            outer.add(0)

            outer.toIntArray()
        } else {
            super.calculateDistanceToFinalSnap(layoutManager, targetView)
        }
    }

    override fun findSnapView(layoutManager: RecyclerView.LayoutManager?): View? {
        return if (layoutManager is LinearLayoutManager) {
            if (layoutManager.canScrollHorizontally()) {
            getStartView(layoutManager, getHorizontalHelper(layoutManager))
            } else {
                super.findSnapView(layoutManager)
            }
        } else {
            super.findSnapView(layoutManager)
        }
    }

    private fun distanceToStart(targetView: View, helper: OrientationHelper): Int {
        return helper.getDecoratedStart(targetView) - helper.startAfterPadding
    }

    private fun getStartView(layoutManager: RecyclerView.LayoutManager, orientationHelper: OrientationHelper): View? {
        val firstChild = (layoutManager as LinearLayoutManager).findFirstVisibleItemPosition()
        val isLastItem = (layoutManager.findLastCompletelyVisibleItemPosition() == layoutManager.itemCount - 1)

        if (firstChild == RecyclerView.NO_POSITION || isLastItem) {
            return null
        }

        val child = layoutManager.findViewByPosition(firstChild)

        return if (orientationHelper.getDecoratedEnd(child) >= orientationHelper.getDecoratedMeasurement(child) / 2
        && orientationHelper.getDecoratedEnd(child) > 0) {
        child;
        } else {
            if (layoutManager.findFirstCompletelyVisibleItemPosition() == layoutManager.itemCount -1) {
                null
            } else {
                layoutManager.findViewByPosition(firstChild + 1)
            }
        }
    }

    private fun getHorizontalHelper(layoutManager: RecyclerView.LayoutManager): OrientationHelper {
        return OrientationHelper.createHorizontalHelper(layoutManager)
    }
}

Answer 2

我已經實現了這個功能，我們需要創建一個類和范圍類LinearSnapHelper並覆蓋方法CalculateDistanceToFinalSnap和FindSnapView 。 您可以在此處查看完整的演示。

主要代碼如下：

 public class StartSnapHelper: LinearSnapHelper
 {
    private OrientationHelper mVerticalHelper, mHorizontalHelper;

    public StartSnapHelper()
    {
    }

    public override void AttachToRecyclerView(RecyclerView recyclerView)
    {
        base.AttachToRecyclerView(recyclerView);
    }

    public override int[] CalculateDistanceToFinalSnap(RecyclerView.LayoutManager layoutManager, View targetView)
    {
        //return base.CalculateDistanceToFinalSnap(layoutManager, targetView);
        int[] outer = new int[2];

        if (layoutManager.CanScrollHorizontally())
        {
            outer[0] = distanceToStart(targetView, getHorizontalHelper(layoutManager));
        } else {
            outer[0] = 0;
        }

    if (layoutManager.CanScrollVertically()) {
            outer[1] = distanceToStart(targetView, getVerticalHelper(layoutManager));
    } else {
            outer[1] = 0;
    }
    return outer;
    }

    private int distanceToStart(View targetView, OrientationHelper helper)
    {
        return helper.GetDecoratedStart(targetView) - helper.StartAfterPadding;
    }

    public override View FindSnapView(RecyclerView.LayoutManager layoutManager)
    {
        if (layoutManager is LinearLayoutManager) {

            if (layoutManager.CanScrollHorizontally())
            {
                return getStartView(layoutManager, getHorizontalHelper(layoutManager));
            }
            else
            {
                return getStartView(layoutManager, getVerticalHelper(layoutManager));
            }
        }

        return base.FindSnapView(layoutManager);
    }

    private View getStartView(RecyclerView.LayoutManager layoutManager,
                          OrientationHelper helper)
    {

        if (layoutManager is LinearLayoutManager) {
            int firstChild = ((LinearLayoutManager)layoutManager).FindFirstVisibleItemPosition();

            bool isLastItem = ((LinearLayoutManager)layoutManager)
                    .FindLastCompletelyVisibleItemPosition()
                    == layoutManager.ItemCount - 1;

            if (firstChild == RecyclerView.NoPosition || isLastItem)
            {
                return null;
            }

            View child = layoutManager.FindViewByPosition(firstChild);

            if (helper.GetDecoratedEnd(child) >= helper.GetDecoratedMeasurement(child) / 2
                    && helper.GetDecoratedEnd(child) > 0)
            {
                return child;
            }
            else
            {
                if (((LinearLayoutManager)layoutManager).FindLastCompletelyVisibleItemPosition()
                        == layoutManager.ItemCount - 1)
                {
                    return null;
                }
                else
                {
                    return layoutManager.FindViewByPosition(firstChild + 1);
                }
            }
        }
        return base.FindSnapView(layoutManager);
    }


    private OrientationHelper getVerticalHelper(RecyclerView.LayoutManager layoutManager)
    {
        if (mVerticalHelper == null)
        {
            mVerticalHelper = OrientationHelper.CreateVerticalHelper(layoutManager);
        }
        return mVerticalHelper;
    }

    private OrientationHelper getHorizontalHelper(RecyclerView.LayoutManager layoutManager)
    {
        if (mHorizontalHelper == null)
        {
            mHorizontalHelper = OrientationHelper.CreateHorizontalHelper(layoutManager);
        }
        return mHorizontalHelper;
    }
}

並像這樣使用：

  SnapHelper snapHelperStart = new StartSnapHelper();
  snapHelperStart.AttachToRecyclerView(recyclerView);