android - 捕捉到特定类型的ItemView的RecyclerView

我正在尝试创建一个垂直列表的RecyclerView，该列表捕捉到第一项。为了解决这个问题，我在SnapHelper中添加了以下RecyclerView类。

public class StartSnapHelper extends LinearSnapHelper {

    private OrientationHelper mVerticalHelper, mHorizontalHelper;

    public StartSnapHelper() {

    }

    @Override
    public void attachToRecyclerView(@Nullable RecyclerView recyclerView)
            throws IllegalStateException {
        super.attachToRecyclerView(recyclerView);
    }

    @Override
    public int[] calculateDistanceToFinalSnap(@NonNull RecyclerView.LayoutManager layoutManager,
                                              @NonNull View targetView) {
        int[] out = new int[2];

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

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

    @Override
    public View findSnapView(RecyclerView.LayoutManager layoutManager) {

        if (layoutManager instanceof LinearLayoutManager) {

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

        return super.findSnapView(layoutManager);
    }

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

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

        if (layoutManager instanceof LinearLayoutManager) {
            int firstChild = ((LinearLayoutManager) layoutManager).findFirstVisibleItemPosition();

            boolean isLastItem = ((LinearLayoutManager) layoutManager).findLastCompletelyVisibleItemPosition()== layoutManager.getItemCount() - 1;

            if (firstChild == RecyclerView.NO_POSITION || 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.getItemCount() - 1) {
                    return null;
                } else {
                    return layoutManager.findViewByPosition(firstChild + 1);
                }
            }
        }

        return super.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;
    }
}

一切正常。但是问题在于列表还包含标头。我想捕捉到所有标题以外的项目。有什么办法可以通过在getItemViewType内部调用StartSnapHelper来解决它？还是有什么方法可以创建在滚动时捕捉到特定ItemViewType的SnapHelper？

最佳答案

在有权访问布局管理器的任何地方，都可以通过调用以下命令来确定视图类型：

LayoutManager.getItemViewType(View)

例如，在getStartView()中，您可以执行以下操作：

View child = layoutManager.findViewByPosition(firstChild);
int viewType = layoutManager.getItemViewType(child);

如果返回的视图类型是标题的视图类型，那么您将有机会更改所选的子项。