Flutter：bloc，如何显示alert对话框

我是新加入集团模式和流媒体的人.我想在按下按钮时显示一个alert 对话框，但我找不到方法.实际上我的代码是:

Widget button() {
  return RaisedButton(
      child: Text('Show alert'),
      color: Colors.blue[700],
      textColor: Colors.white,
      onPressed: () {
        bloc.submit();
      });
   }



return Scaffold(
        appBar: AppBar(
          title: Text("Title"),
        ),
        body: StreamBuilder(
            stream: bloc.getAlert,
            builder: (context, snapshot) {
              if (snapshot.hasData) {
                return Text("I have Dataaaaaa ${snapshot.data}");
              } else
                return ListView(
                  children: <Widget>[
                    Container(
                     button()
                    )
                ...

和集团:

final _submissionController = StreamController();
Stream get submissionStream=> _submissionController.stream;
Sink get submissionSink=> _submissionController.sink;

我试着做一些类似的事情:

Widget button() {
  return StreamBuilder(
stream: submissionStream
builder: (context, snapshot){
if (snapshot.hasData){
return showDialog(...)
}else
 return RaisedButton(
      child: Text('Show alert'),
      color: Colors.blue[700],
      textColor: Colors.white,
      onPressed: () {
        bloc.submit();
      });
   }

但是，当然，它没有起作用.