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注意 似乎这个功能现在在leanback 支持库的22.1.1 版本中可用，这使得这个问题稍微过时了。但是，问题仍然存在，为什么公共标准文档要先于公共可用的库版本？

我正在浏览 API 文档，我看到有这个接口： OnChildLaidOutListener然后还有这个方法Horizo​​ntalGridView#setOnChildLaidOutListener。我尝试使用它们，但 Android Studio 说不存在这样的东西。我查看了 Horizo​​ntalGridView 的源代码（在 Studio 中），里面没有这样的东西。我尝试搜索不同版本的兼容性库，但没有一个具有此功能。从这里我可以看到此提交中添加了此功能减少 DPAD 滚动多列网格的内存消耗。

这一切是怎么回事？他们在官方 Android API 文档中记录了所有未来某一天无法使用的 API，或者为什么会在此处记录？还是我的 Android Studio 安装/配置有问题，只是我在那里有旧版本的支持库或发生了什么？

我真的很想使用这些东西……这正是我所需要的。

编辑：详细说明我在做什么的示例代码（尽管我仍然不明白这与为什么根据 API 文档这些方法应该存在的问题有关，但至少我不能使用它们）。因此，我要解决的问题是以编程方式将 GridView 初始化为选定的项目，然后在其上调用 requestLayout，否则放大的视图将从底部截断。

public class MinimalisticLeanbackFragment extends Fragment {

    private HorizontalGridView gridView;
    private boolean positionInitied = false;

    public SimplifiedEpgFragment() {
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(android.support.v17.leanback.R.layout.lb_list_row, container, false);
    }

    public ItemBridgeAdapter initItemBridgeAdapter(ObjectAdapter objectAdapter) {
        ItemBridgeAdapter iba = new ItemBridgeAdapter(objectAdapter);

        ItemBridgeAdapter.Wrapper mWrapper = new ItemBridgeAdapter.Wrapper() {
            @Override
            public View createWrapper(View root) {
                ShadowOverlayContainer wrapper = new ShadowOverlayContainer(root.getContext());
                wrapper.setLayoutParams(
                        new ViewGroup.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT));
                wrapper.initialize(needsDefaultShadow(), true, false);
                return wrapper;
            }
            @Override
            public void wrap(View wrapper, View wrapped) {
                ((ShadowOverlayContainer) wrapper).wrap(wrapped);
            }
        };

        iba.setWrapper(mWrapper);

        FocusHighlightHelper.setupBrowseItemFocusHighlight(iba, FocusHighlight.ZOOM_FACTOR_LARGE, false);

        return iba;
    }

    private boolean needsDefaultShadow() {
        return true;
    }

    private ObjectAdapter initObjectAdapter() {
        ContentsPresenter contentsPresenter = new ContentsPresenter();
        ArrayObjectAdapter contentsAdapter = new ArrayObjectAdapter(contentsPresenter);
        contentsAdapter.addAll(0, ProgramList.collectionList());
        return contentsAdapter;
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        gridView = initGridView((HorizontalGridView) view.findViewById(R.id.row_content));

        ItemBridgeAdapter mBridgeAdapter = initItemBridgeAdapter(initObjectAdapter());

        gridView.setAdapter(mBridgeAdapter);
    }

    private HorizontalGridView initGridView(final HorizontalGridView gridView) {
        gridView.isLaidOut();
        ShadowOverlayContainer.prepareParentForShadow(gridView);
        gridView.setClipChildren(false);
        gridView.setFocusDrawingOrderEnabled(false); //Or?
        gridView.setOnChildSelectedListener(new OnChildSelectedListener() {
            @Override
            public void onChildSelected(ViewGroup parent, View view, int position, long id) {
                Log.d(Configs.TAG, "Child selected");
            }
        });

        gridView.setFadingLeftEdge(false);
        gridView.setFadingRightEdge(false);

        //TODO: wtf? It seems the only way to do this would be to rewrite the entire HorizontalGridView and all of its dependencies injecting these newer
        //features this updated version.
        /*
        gridView.setOnChildLaidOutListener(new android.support.v17.leanback.widget.OnChildLaidOutListener() {
            @Override
            public void onChildLaidOut(ViewGroup parent, View view, int position, long id) {
                initGridState();
            }
        });
        */

        //Maybe this could work then...
        final ViewTreeObserver viewTreeObserver = gridView.getViewTreeObserver();
        viewTreeObserver.addOnDrawListener(new ViewTreeObserver.OnDrawListener() {
            @Override
            public void onDraw() {
                if (initGridState()) {
                    Log.d(Configs.TAG, "state init succeeded!");
                    viewTreeObserver.removeOnDrawListener(this);
                } else {
                    Log.d(Configs.TAG, "onDraw of the gridview, children not ready yet..");
                }
            }
        });

        return gridView;
    }

    private boolean initGridState() {
        int position = gridView.getSelectedPosition();
        if (position == RecyclerView.NO_POSITION) {
            position = 0;
            gridView.setSelectedPosition(0);
        }
        if (!this.positionInitied) {
            View child = gridView.getChildAt(position);
            if (child != null) {
                Log.d(Configs.TAG, "Child available, requesting focus the the selected position...");
                child.requestFocus();
                gridView.requestLayout();
            } else {
                Log.e(Configs.TAG, "Could not focus to child... grid has: " + gridView.getChildCount()+" children, is " + (gridView.isActivated() ? "" : " not ") + "activated");
                return false;
            }
        } else {
            Log.d(Configs.TAG, "Child focus already inited... doing nothing..");
        }
        return true;
    }
}
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