flutter 异步请求中调用 SnackBar

直接在异步代码中这样调用会报错

Scaffold.of(this.context).showSnackBar(SnackBar(
       content: Text(res.data["errorMsg"].toString()),
));

如下错误信息：

E/flutter (15261): [ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: Scaffold.of() called with a context that does not contain a Scaffold.

改成如下这种方式可以正常使用，见粗体部分：

class _XXXPageStateextends State {

var _scaffoldkey =new GlobalKey();

@override
 Widget build(BuildContext context) {
return Scaffold(
key:_scaffoldkey,
...

);
}

Future  DioRequest()async {
        ...
        showSnackBar("这样调用可以显示");

}

void showSnackBar(String message) {
    var snackBar = SnackBar(content:     Text(message));_scaffoldkey.currentState.showSnackBar(snackBar);
}

}