Android 使用 gridlayoutmanager 在 recyclerview 的最后一个元素下方添加间距

Question

我正在尝试在 RecyclerView 和 GridLayoutManager 中的最后一个元素行下方添加间距。为此，我使用自定义 ItemDecoration 和底部填充，最后一个元素如下：

public class SpaceItemDecoration extends RecyclerView.ItemDecoration {
private int space;
private int bottomSpace = 0;

public SpaceItemDecoration(int space, int bottomSpace) {
    this.space = space;
    this.bottomSpace = bottomSpace;
}

public SpaceItemDecoration(int space) {
    this.space = space;
    this.bottomSpace = 0;
}

@Override
public void getItemOffsets(Rect outRect, View view,
                           RecyclerView parent, RecyclerView.State state) {

    int childCount = parent.getChildCount();
    final int itemPosition = parent.getChildAdapterPosition(view);
    final int itemCount = state.getItemCount();

    outRect.left = space;
    outRect.right = space;
    outRect.bottom = space;
    outRect.top = space;

    if (itemCount > 0 && itemPosition == itemCount - 1) {
        outRect.bottom = bottomSpace;
    }
}
}

但这种方法的问题是它弄乱了最后一行网格中的元素高度。我猜测 GridLayoutManager 会根据左侧间距更改元素的高度。实现此目标的正确方法是什么？

这将适用于 LinearLayoutManager。以防万一 GridLayoutManager 它有问题。

如果您在底部有一个 FAB 并且需要最后一行的项目滚动到 FAB 上方以便它们可见，这将非常有用。

Answer 1

你可以做的是在你的 recyclerview 中添加一个空的页脚。您的填充将是页脚的大小。

@Override
public Holder onCreateViewHolder( ViewGroup parent, int viewType) {
    if (viewType == FOOTER) {
        return new FooterHolder();
    }
    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item, parent, false);
    return new Holder(view);
}

@Override
public void onBindViewHolder(final Holder holder, final int position) {
    //if footer
    if (position == items.getSize() - 1) {
    //do nothing
        return;
    }
    //do regular object bindding

}

@Override
public int getItemViewType(int position) {
    return (position == items.getSize() - 1) ? FOOTER : ITEM_VIEW_TYPE_ITEM;
}

@Override
public int getItemCount() {
    //add one for the footer
    return items.size() + 1;
}

Answer 2

您可以使用下面的代码来检测网格视图中的第一行和最后一行，并相应地设置顶部和底部偏移量。

@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, State state) {
    LayoutParams params = (LayoutParams) view.getLayoutParams();
    int pos = params.getViewLayoutPosition();
    int spanCount = mGridLayoutManager.getSpanCount();

    boolean isFirstRow = pos < spanCount;
    boolean isLastRow = state.getItemCount() - 1 - pos < spanCount;

    if (isFirstRow) {
      outRect.top = top offset value here
    }

    if (isLastRow) {
      outRect.bottom = bottom offset value here
    }
}

// you also need to keep reference to GridLayoutManager to know the span count
private final GridLayoutManager mGridLayoutManager;

Answer 3

解决这个问题的方法是覆盖 GridLayoutManager 的 SpanSizeLookup。

您必须更改 Activity 中的 GridlayoutManager 或您正在膨胀 RecylerView 的 Fragment。

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    //your code 
    recyclerView.addItemDecoration(new PhotoGridMarginDecoration(context));

    // SPAN_COUNT is the number of columns in the Grid View
    GridLayoutManager gridLayoutManager = new GridLayoutManager(context, SPAN_COUNT);

    // With the help of this method you can set span for every type of view
    gridLayoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
        @Override
        public int getSpanSize(int position) {
            if (list.get(position).getType() == TYPE_HEADER) {
                // Will consume the whole width
                return gridLayoutManager.getSpanCount();
            } else if (list.get(position).getType() == TYPE_CONTENT) {
                // will consume only one part of the SPAN_COUNT
                return 1;
            } else if(list.get(position).getType() == TYPE_FOOTER) {
                // Will consume the whole width
                // Will take care of spaces to be left,
                // if the number of views in a row is not equal to 4
                return gridLayoutManager.getSpanCount();
            }
            return gridLayoutManager.getSpanCount();
        }
    });
    recyclerView.setLayoutManager(gridLayoutManager);
}

Answer 4

像这样的事情，建议使用 ItemDecoration 来解决，因为它们就是为此而设计的。

public class ListSpacingDecoration extends RecyclerView.ItemDecoration {

  private static final int VERTICAL = OrientationHelper.VERTICAL;

  private int orientation = -1;
  private int spanCount = -1;
  private int spacing;


  public ListSpacingDecoration(Context context, @DimenRes int spacingDimen) {

    spacing = context.getResources().getDimensionPixelSize(spacingDimen);
  }

  public ListSpacingDecoration(int spacingPx) {

    spacing = spacingPx;
  }

  @Override
  public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {

    super.getItemOffsets(outRect, view, parent, state);

    if (orientation == -1) {
        orientation = getOrientation(parent);
    }

    if (spanCount == -1) {
        spanCount = getTotalSpan(parent);
    }

    int childCount = parent.getLayoutManager().getItemCount();
    int childIndex = parent.getChildAdapterPosition(view);

    int itemSpanSize = getItemSpanSize(parent, childIndex);
    int spanIndex = getItemSpanIndex(parent, childIndex);

    /* INVALID SPAN */
    if (spanCount < 1) return;

    setSpacings(outRect, parent, childCount, childIndex, itemSpanSize, spanIndex);
  }

  protected void setSpacings(Rect outRect, RecyclerView parent, int childCount, int childIndex, int itemSpanSize, int spanIndex) {

    if (isBottomEdge(parent, childCount, childIndex, itemSpanSize, spanIndex)) {
        outRect.bottom = spacing;
    }
  }

  @SuppressWarnings("all")
  protected int getTotalSpan(RecyclerView parent) {

    RecyclerView.LayoutManager mgr = parent.getLayoutManager();
    if (mgr instanceof GridLayoutManager) {
        return ((GridLayoutManager) mgr).getSpanCount();
    } else if (mgr instanceof StaggeredGridLayoutManager) {
        return ((StaggeredGridLayoutManager) mgr).getSpanCount();
    } else if (mgr instanceof LinearLayoutManager) {
        return 1;
    }

    return -1;
  }

  @SuppressWarnings("all")
  protected int getItemSpanSize(RecyclerView parent, int childIndex) {

    RecyclerView.LayoutManager mgr = parent.getLayoutManager();
    if (mgr instanceof GridLayoutManager) {
        return ((GridLayoutManager) mgr).getSpanSizeLookup().getSpanSize(childIndex);
    } else if (mgr instanceof StaggeredGridLayoutManager) {
        return 1;
    } else if (mgr instanceof LinearLayoutManager) {
        return 1;
    }

    return -1;
  }

  @SuppressWarnings("all")
  protected int getItemSpanIndex(RecyclerView parent, int childIndex) {

    RecyclerView.LayoutManager mgr = parent.getLayoutManager();
    if (mgr instanceof GridLayoutManager) {
        return ((GridLayoutManager) mgr).getSpanSizeLookup().getSpanIndex(childIndex, spanCount);
    } else if (mgr instanceof StaggeredGridLayoutManager) {
        return childIndex % spanCount;
    } else if (mgr instanceof LinearLayoutManager) {
        return 0;
    }

    return -1;
  }

  @SuppressWarnings("all")
  protected int getOrientation(RecyclerView parent) {

    RecyclerView.LayoutManager mgr = parent.getLayoutManager();
    if (mgr instanceof LinearLayoutManager) {
        return ((LinearLayoutManager) mgr).getOrientation();
    } else if (mgr instanceof GridLayoutManager) {
        return ((GridLayoutManager) mgr).getOrientation();
    } else if (mgr instanceof StaggeredGridLayoutManager) {
        return ((StaggeredGridLayoutManager) mgr).getOrientation();
    }

    return VERTICAL;
  }

  protected boolean isBottomEdge(RecyclerView parent, int childCount, int childIndex, int itemSpanSize, int spanIndex) {

    if (orientation == VERTICAL) {

        return isLastItemEdgeValid((childIndex >= childCount - spanCount), parent, childCount, childIndex, spanIndex);

    } else {

        return (spanIndex + itemSpanSize) == spanCount;
    }
  }

  protected boolean isLastItemEdgeValid(boolean isOneOfLastItems, RecyclerView parent, int childCount, int childIndex, int spanIndex) {

    int totalSpanRemaining = 0;
    if (isOneOfLastItems) {
        for (int i = childIndex; i < childCount; i++) {
            totalSpanRemaining = totalSpanRemaining + getItemSpanSize(parent, i);
        }
    }

    return isOneOfLastItems && (totalSpanRemaining <= spanCount - spanIndex);
  }
}

我从我的原始答案中复制了一个编辑过的内容，它实际上是等间距的，但它是相同的概念。

Answer 5

只需添加一个填充并设置android:clipToPadding="false"

<RecyclerView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="8dp"
    android:clipToPadding="false" />

多亏了这个精彩answer！

Answer 6

你可以把DividerItemDecoration.java作为源码的例子，替换成

for (int i = 0; i < childCount; i++)

和

for (int i = 0; i < childCount - 1; i++)

在 drawVertical() 和 drawHorizontal() 中

Answer 7

仅在最后一项的情况下，应使用 Recycler View 中的 Decoration 作为底部边距

recyclerView.addItemDecoration(MemberItemDecoration())

public class MemberItemDecoration extends RecyclerView.ItemDecoration {

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        // only for the last one
        if (parent.getChildAdapterPosition(view) == parent.getAdapter().getItemCount() - 1) {
            outRect.bottom = 50/* set your margin here */;
        }
    }
}

Answer 8

我遇到了类似的问题并回复了。为了帮助其他登陆此页面的人，我将在此处重新发布。

阅读所有其他回复后，我发现布局更改 xml 的 recyclerview 按预期适用于我的回收站视图：

android:paddingBottom="127px"
android:clipToPadding="false"
android:scrollbarStyle="outsideOverlay"

完整的布局如下：

<android.support.v7.widget.RecyclerView
        android:id="@+id/library_list"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginStart="160px"
        android:layout_marginEnd="160px"
        tools:listitem="@layout/library_list_item" />

Answer 9

查看可能的解决方案，我想写一些笔记和适当的解决方案：

如果你为 RecyclerView 使用填充，它应该在大多数情况下工作，但是一旦你开始使用自定义项目装饰（快速滚动）或处理透明导航栏，你将得到查看各种问题。
您始终可以为 RecyclerView 适配器创建一个 ViewType，它将成为它的页脚，占据整个跨度。这非常有效，但比其他解决方案需要更多的工作。
此处提供的 ItemDecoration 解决方案在大多数情况下都有效，但不适用于 GridLayoutManager，因为它有时会为最后一行上方的行添加间距（此处要求添加更好的解决方案).

我在 android-x 上找到了一些似乎可以解决它的代码，不过，在某种程度上与汽车有关：

BottomOffsetDecoration

/**
 * A {@link RecyclerView.ItemDecoration} that will add a bottom offset to the last item in the
 * RecyclerView it is added to.
 *
 * @hide
 */
@RestrictTo(LIBRARY_GROUP_PREFIX)
public class BottomOffsetDecoration extends RecyclerView.ItemDecoration {
    private int mBottomOffset;

    public BottomOffsetDecoration(int bottomOffset) {
        mBottomOffset = bottomOffset;
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent,
            RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);

        RecyclerView.Adapter adapter = parent.getAdapter();

        if (adapter == null || adapter.getItemCount() == 0) {
            return;
        }

        if (parent.getLayoutManager() instanceof GridLayoutManager) {
            if (GridLayoutManagerUtils.isOnLastRow(view, parent)) {
                outRect.bottom = mBottomOffset;
            }
        } else if (parent.getChildAdapterPosition(view) == adapter.getItemCount() - 1) {
            // Only set the offset for the last item.
            outRect.bottom = mBottomOffset;
        } else {
            outRect.bottom = 0;
        }
    }

    /** Sets the value to use for the bottom offset. */
    public void setBottomOffset(int bottomOffset) {
        mBottomOffset = bottomOffset;
    }

    /** Returns the set bottom offset. If none has been set, then 0 will be returned. */
    public int getBottomOffset() {
        return mBottomOffset;
    }
}

GridLayoutManagerUtils

/**
 * Utility class that helps navigating in GridLayoutManager.
 *
 * <p>Assumes parameter {@code RecyclerView} uses {@link GridLayoutManager}.
 *
 * <p>Assumes the orientation of {@code GridLayoutManager} is vertical.
 *
 * @hide
 */
@RestrictTo(LIBRARY_GROUP_PREFIX)
public class GridLayoutManagerUtils {
    private GridLayoutManagerUtils() {}

    /**
     * Returns the number of items in the first row of a RecyclerView that has a
     * {@link GridLayoutManager} as its {@code LayoutManager}.
     *
     * @param recyclerView RecyclerView that uses GridLayoutManager as LayoutManager.
     * @return number of items in the first row in {@code RecyclerView}.
     */
    public static int getFirstRowItemCount(RecyclerView recyclerView) {
        GridLayoutManager manager = (GridLayoutManager) recyclerView.getLayoutManager();
        int itemCount = recyclerView.getAdapter().getItemCount();
        int spanCount = manager.getSpanCount();

        int spanSum = 0;
        int numOfItems = 0;
        while (numOfItems < itemCount && spanSum < spanCount) {
            spanSum += manager.getSpanSizeLookup().getSpanSize(numOfItems);
            numOfItems++;
        }
        return numOfItems;
    }

    /**
     * Returns the span index of an item.
     */
    public static int getSpanIndex(View item) {
        GridLayoutManager.LayoutParams layoutParams =
                ((GridLayoutManager.LayoutParams) item.getLayoutParams());
        return layoutParams.getSpanIndex();
    }

    /**
     * Returns whether or not the given view is on the last row of a {@code RecyclerView} with a
     * {@link GridLayoutManager}.
     *
     * @param view The view to inspect.
     * @param parent {@link RecyclerView} that contains the given view.
     * @return {@code true} if the given view is on the last row of the {@code RecyclerView}.
     */
    public static boolean isOnLastRow(View view, RecyclerView parent) {
        return getLastItemPositionOnSameRow(view, parent) == parent.getAdapter().getItemCount() - 1;
    }

    /**
     * Returns the position of the last item that is on the same row as input {@code view}.
     *
     * @param view The view to inspect.
     * @param parent {@link RecyclerView} that contains the given view.
     */
    public static int getLastItemPositionOnSameRow(View view, RecyclerView parent) {
        GridLayoutManager layoutManager = ((GridLayoutManager) parent.getLayoutManager());

        GridLayoutManager.SpanSizeLookup spanSizeLookup = layoutManager.getSpanSizeLookup();
        int spanCount = layoutManager.getSpanCount();
        int lastItemPosition = parent.getAdapter().getItemCount() - 1;

        int currentChildPosition = parent.getChildAdapterPosition(view);
        int spanSum = getSpanIndex(view) + spanSizeLookup.getSpanSize(currentChildPosition);
        // Iterate to the end of the row starting from the current child position.
        while (currentChildPosition <= lastItemPosition && spanSum <= spanCount) {
            spanSum += spanSizeLookup.getSpanSize(currentChildPosition + 1);
            if (spanSum > spanCount) {
                return currentChildPosition;
            }
            currentChildPosition++;
        }
        return lastItemPosition;
    }
}

所以，我制作了一个 Kotlin 解决方案来解决所有问题（此处提供示例和库）：

//https://androidx.de/androidx/car/widget/itemdecorators/BottomOffsetDecoration.html
class BottomOffsetDecoration(private val mBottomOffset: Int, private val layoutManagerType: LayoutManagerType) : ItemDecoration() {
    enum class LayoutManagerType {
        GRID_LAYOUT_MANAGER, LINEAR_LAYOUT_MANAGER
    }

    override fun getItemOffsets(outRect: Rect, view: View, parent: RecyclerView, state: RecyclerView.State) {
        super.getItemOffsets(outRect, view, parent, state)
        when (layoutManagerType) {
            LayoutManagerType.LINEAR_LAYOUT_MANAGER -> {
                val position = parent.getChildAdapterPosition(view)
                outRect.bottom =
                        if (state.itemCount <= 0 || position != state.itemCount - 1)
                            0
                        else
                            mBottomOffset
            }
            LayoutManagerType.GRID_LAYOUT_MANAGER -> {
                val adapter = parent.adapter
                outRect.bottom =
                        if (adapter == null || adapter.itemCount == 0 || GridLayoutManagerUtils.isOnLastRow(view, parent))
                            0
                        else
                            mBottomOffset
            }
        }
    }
}

//https://androidx.de/androidx/car/util/GridLayoutManagerUtils.html
/**
 * Utility class that helps navigating in GridLayoutManager.
 *
 *
 * Assumes parameter `RecyclerView` uses [GridLayoutManager].
 *
 *
 * Assumes the orientation of `GridLayoutManager` is vertical.
 */
object GridLayoutManagerUtils {
    /**
     * Returns whether or not the given view is on the last row of a `RecyclerView` with a
     * [GridLayoutManager].
     *
     * @param view   The view to inspect.
     * @param parent [RecyclerView] that contains the given view.
     * @return `true` if the given view is on the last row of the `RecyclerView`.
     */
    fun isOnLastRow(view: View, parent: RecyclerView): Boolean {
        return getLastItemPositionOnSameRow(view, parent) == parent.adapter!!.itemCount - 1
    }

    /**
     * Returns the position of the last item that is on the same row as input `view`.
     *
     * @param view   The view to inspect.
     * @param parent [RecyclerView] that contains the given view.
     */
    private fun getLastItemPositionOnSameRow(view: View, parent: RecyclerView): Int {
        val layoutManager = parent.layoutManager as GridLayoutManager
        val spanSizeLookup = layoutManager.spanSizeLookup
        val spanCount = layoutManager.spanCount
        val lastItemPosition = parent.adapter!!.itemCount - 1
        var currentChildPosition = parent.getChildAdapterPosition(view)
        val itemSpanIndex = (view.layoutParams as GridLayoutManager.LayoutParams).spanIndex
        var spanSum = itemSpanIndex + spanSizeLookup.getSpanSize(currentChildPosition)
        // Iterate to the end of the row starting from the current child position.
        while (currentChildPosition <= lastItemPosition && spanSum <= spanCount) {
            spanSum += spanSizeLookup.getSpanSize(currentChildPosition + 1)
            if (spanSum > spanCount)
                return currentChildPosition
            ++currentChildPosition
        }
        return lastItemPosition
    }
}

Answer 10

<androidx.recyclerview.widget.RecyclerView
    ...
    android:clipToPadding="false"
    android:paddingTop="16dp"
    android:paddingBottom="16dp"
    ...
    />

android:clipToPadding="false"

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