通過key去獲取到控件的BuildContext,而我們知道BuildContext的實現(xiàn)其實是Element,而Element持有RenderObject,所以我們知道的RenderObject,實際上獲取到的就是RenderBox,那么通過RenderBox我們就可以獲取大小跟位置.

 showSizes() {
    RenderBox renderBoxRed = fileListKey.currentContext.findRenderObject();
    print(renderBoxRed.size);
  }

  showPositions() {
    RenderBox renderBoxRed = fileListKey.currentContext.findRenderObject();
    print(renderBoxRed.localToGlobal(Offset.zero));
  }