看看可能的解决方案，我想写一些笔记和一个适当的解决方案：
-
如果您为 RecyclerView 使用填充，它应该在大多数情况下都可以工作，但是一旦您开始使用自定义项目装饰（快速滚动）或处理透明导航栏，您将看到各种问题。
-
您始终可以为 RecyclerView 适配器创建一个 ViewType，它将作为它的页脚，占据整个跨度。这非常有效，但只需要比其他解决方案更多的工作。
-
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（在此处请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问题的代码，不过，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
}
}