無法投LinearLayoutManager到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; 
          } 
         }); 
        } 

上面的代碼是崩潰說java.lang.ClassCastException：android.support.v7.widget.LinearLayoutManager不能轉換到android.support.v7.widget.GridLayoutManager

我想通了以下行導致崩潰

((GridLayoutManager) mLayoutManager).getSpanCount() 

什麼方法可以解決，以避免碰撞

mLayoutManager被聲明爲LinearLayoutManager

Answer 1

你也應該做內部getSpanSize類檢查：

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