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Android GridLayoutManager Decoration

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GridLayoutManager 很少用，所以它的Decoration用法这里做一下备忘。

  • 主要记住行、列的计算，第一行、最后一行、第一列、最后一列的计算。
  • Item的布局要用 match_parent 采用自动适应的效果。
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public class TestGridDecoration extends RecyclerView.ItemDecoration{

    private int offset;

    public TestGridDecoration(int offset) {
        this.offset = offset;
    }

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

        int childLayoutPosition = parent.getChildLayoutPosition(view);

        //每行的元素数量
        int spanCount = ((GridLayoutManager)parent.getLayoutManager()).getSpanCount();

        //总行数
        int maxRow = state.getItemCount() / spanCount;
        //所处的行号
        int row = childLayoutPosition / spanCount;
        //所处的列号
        int column = childLayoutPosition % spanCount;


        if(row == 0){
            //第一行
            outRect.top = 0;
            outRect.bottom = 0;
        }else if(row == maxRow){
            //最后一行
            outRect.top = offset;
            outRect.bottom = offset;
        }else{
            //中间行
            outRect.top = offset;
            outRect.bottom = 0;
        }


        if(column == 0){
            //第一列
            outRect.left = offset;
            outRect.right = offset / 2;
        }else if(column == spanCount - 1){
            //最后一列
            outRect.left = offset / 2;
            outRect.right = offset;
        }else{
            //中间列
            outRect.left = offset / 2;
            outRect.right = offset / 2;
        }

    }
}