无法将 LinearLayoutManager 转换为 GridLayoutManager

Question

if (mLayoutManager instanceof GridLayoutManager) {
                        ((GridLayoutManager) mLayoutManager).setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
                            @Override
                            public int getSpanSize(int position) {
                                return listResultAdapter.isHeaderOrFooter(position) ? ((GridLayoutManager) mLayoutManager).getSpanCount() : 1;
                            }
                        });
                    }

上面的代码崩溃了，说 java.lang.ClassCastException: android.support.v7.widget.LinearLayoutManager cannot be cast to android.support.v7.widget.GridLayoutManager

我发现下面一行导致崩溃

((GridLayoutManager) mLayoutManager).getSpanCount()

有什么办法可以避免崩溃

mLayoutManager 被声明为 LinearLayoutManager

Answer 1

你也应该在getSpanSize里面做类检查：

public int getSpanSize(int position) {
     return mLayoutManager instanceof GridLayoutManager && listResultAdapter.isHeaderOrFooter(position) 
             ? ((GridLayoutManager) mLayoutManager).getSpanCount() : 1;
}