小编Far*_*zam的帖子

So currently I'm building apps with Flutter which's still new to me, and I'm stuck at those exception in that title.

The problem is when I tried to call "widget.usernames.length" at ListView.builder, it would return those exception if it's null and no exception when there's a data.

我想要完成的是get Length函数应该返回null或0值，以便ListView在没有数据时不显示任何内容。

return new Expanded(
  child: ListView.builder(
      padding: new EdgeInsets.all(8.0),
      itemExtent: 20.0,
      itemCount: widget.usernames.length,
      itemBuilder: (BuildContext context, int index){
        return Text("Bank ${widget.usernames[index] ?? " "}");
      }
  ),
);

我已经试过了

itemCount: widget.usernames.length ?? 0 …