选择的答案几乎是完美的，但根据空间的不同，项目的宽度可能不相等。(对我来说，这很关键)。所以我最终用这个代码增加了一点空间，所以项目都是相同的宽度。

   class GridSpacingItemDecoration(private val columnCount: Int, @Px preferredSpace: Int, private val includeEdge: Boolean): RecyclerView.ItemDecoration() {

    /**
     * In this algorithm space should divide by 3 without remnant or width of items can have a difference
     * and we want them to be exactly the same
     */
    private val space = if (preferredSpace % 3 == 0) preferredSpace else (preferredSpace + (3 - preferredSpace % 3))

    override fun getItemOffsets(outRect: Rect, view: View, parent: RecyclerView, state: RecyclerView.State?) {
        val position = parent.getChildAdapterPosition(view)

        if (includeEdge) {

            when {
                position % columnCount == 0 -> {
                    outRect.left = space
                    outRect.right = space / 3
                }
                position % columnCount == columnCount - 1 -> {
                    outRect.right = space
                    outRect.left = space / 3
                }
                else -> {
                    outRect.left = space * 2 / 3
                    outRect.right = space * 2 / 3
                }
            }

            if (position < columnCount) {
                outRect.top = space
            }

            outRect.bottom = space

        } else {

            when {
                position % columnCount == 0 -> outRect.right = space * 2 / 3
                position % columnCount == columnCount - 1 -> outRect.left = space * 2 / 3
                else -> {
                    outRect.left = space / 3
                    outRect.right = space / 3
                }
            }

            if (position >= columnCount) {
                outRect.top = space
            }
        }
    }

}

对于StaggeredGridLayoutManager用户，要小心，这里有很多答案，包括投票最多的一个计算项目列，使用以下代码:

int column = position % spanCount

假设第1 /3 /5 /..物品总是放在左边和第二/第四/第六/..物品总是放在右边。这个假设总是正确的吗?不。

假设你的第一件物品是100dp高，第二件只有50dp高，猜猜你的第三件物品位于哪里，左边还是右边?

如果你使用Header和GridLayoutManager，使用以下代码在Kotlin中编写的网格间距:

inner class SpacesItemDecoration(itemSpace: Int) : RecyclerView.ItemDecoration() {

    var space: Int = itemSpace

    override fun getItemOffsets(outRect: Rect?, view: View?, parent: RecyclerView?, state: RecyclerView.State?) {
        super.getItemOffsets(outRect, view, parent, state)
        val position = parent!!.getChildAdapterPosition(view)
        val viewType = parent.adapter.getItemViewType(position)
        
        // Check to not to set any margin to header item 
        if (viewType == GridViewAdapter.TYPE_HEADER) {
            outRect!!.top = 0
            outRect.left = 0
            outRect.right = 0
            outRect.bottom = 0
        } else {
            outRect!!.left = space
            outRect.right = space
            outRect.bottom = space

            if (parent.getChildLayoutPosition(view) == 0) {
                outRect.top = space
            } else {
                outRect.top = 0
            }
        }
    }
}

并将ItemDecoration传递给RecyclerView为:

gridView.addItemDecoration(SpacesItemDecoration(10))

如果你已经滚动到这个答案，我写了一个等间距库，支持垂直/水平，LTR/RTL，线性布局/GridLayout管理器和边缘包含。它基本上是一个文件，所以你可以复制粘贴该文件到你的代码中。

我试图支持StaggeredGridLayout，但这个布局返回的跨度索引不可靠。我很乐意听到任何有关这方面的建议。

如果你想要物品周围的间距和物品大小相等，下面是一步一步的简单解决方案。

ItemOffsetDecoration

public class ItemOffsetDecoration extends RecyclerView.ItemDecoration {

    private int mItemOffset;

    public ItemOffsetDecoration(int itemOffset) {
        mItemOffset = itemOffset;
    }

    public ItemOffsetDecoration(@NonNull Context context, @DimenRes int itemOffsetId) {
        this(context.getResources().getDimensionPixelSize(itemOffsetId));
    }

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

实现

在源代码中，将ItemOffsetDecoration添加到RecyclerView中。 项偏移值应该是实际值的一半大小，作为项之间的空间。

mRecyclerView.setLayoutManager(new GridLayoutManager(context, NUM_COLUMNS);
ItemOffsetDecoration itemDecoration = new ItemOffsetDecoration(context, R.dimen.item_offset);
mRecyclerView.addItemDecoration(itemDecoration);

同样，设置项目偏移值为itsRecyclerView的填充，并指定android:clipToPadding=false。

<android.support.v7.widget.RecyclerView
    android:id="@+id/recyclerview_grid"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:clipToPadding="false"
    android:padding="@dimen/item_offset"/>

对于任何像我一样，想要最好的答案，但在kotlin，这里是:

class GridItemDecoration(
    val spacing: Int,
    private val spanCount: Int,
    private val includeEdge: Boolean
) :
    RecyclerView.ItemDecoration() {

    /**
     * Applies padding to all sides of the [Rect], which is the container for the view
     */
    override fun getItemOffsets(
        outRect: Rect,
        view: View,
        parent: RecyclerView,
        state: RecyclerView.State
    ) {
        val position = parent.getChildAdapterPosition(view) // item position
        val column = position % spanCount // item column
        if (includeEdge) {
            outRect.left =
                spacing - column * spacing / spanCount // spacing - column * ((1f / spanCount) * spacing)
            outRect.right =
                (column + 1) * spacing / spanCount // (column + 1) * ((1f / spanCount) * spacing)
            if (position < spanCount) { // top edge
                outRect.top = spacing
            }
            outRect.bottom = spacing // item bottom
        } else {
            outRect.left =
                column * spacing / spanCount // column * ((1f / spanCount) * spacing)
            outRect.right =
                spacing - (column + 1) * spacing / spanCount // spacing - (column + 1) * ((1f /    spanCount) * spacing)
            if (position >= spanCount) {
                outRect.top = spacing // item top
            }
        }
    }
}

如果你想从dimensions .xml中获取数字，然后将其转换为原始像素，你可以使用getDimensionPixelOffset简单地做到这一点，就像这样:

recyclerView.addItemDecoration(
                GridItemDecoration(
                    resources.getDimensionPixelOffset(R.dimen.h1),
                    3,
                    true
                )
            )