Question

我正在尝试从appBar上的firebase检索用户名。它成功检索到它。但是在成功显示用户名之前，它会在屏幕上显示错误几秒钟。错误os

I / flutter（24143）：构建时引发了以下NoSuchMethodError StreamBuilder（脏，状态：

I / flutter（24143）：_StreamBuilderBaseState ＃c10cf）：

I / flutter（24143）：在null上调用了getter'documents'。

I / flutter（24143）：接收方：空

I / flutter（24143）：尝试调用：文档

Class Data{    
    Widget build(BuildContext context) {
    
        SystemChrome.setPreferredOrientations([
          DeviceOrientation.portraitUp,
        ]);
        CurrentUser _currentUser = Provider.of<CurrentUser>(context, listen: false);
        return Scaffold(
          backgroundColor: Colors.grey[600],
          resizeToAvoidBottomPadding: false,
          appBar: AppBar(
            title: Text('Property Host'),
            centerTitle: true,
            actions: <Widget>[
              Expanded(
    
                child: Row(
                mainAxisAlignment: MainAxisAlignment.spaceAround,
                  children: <Widget>[
                    Container(
                        margin: new EdgeInsets.only(left: 50),
                        child: Text('Property Host',style: TextStyle(fontWeight: FontWeight.bold,fontSize: 19),)),
                    StreamBuilder(stream: Firestore.instance.collection('users').where("uid", isEqualTo: userid).snapshots(),
    
        // ignore: missing_return
        builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
          if (snapshot.data == null)
            CircularProgressIndicator();
            //final userDocument = snapshot.data;
            //final title=  snapshot.data.userocument['displayName']);
            //CircularProgressIndicator();
            return Expanded(
              child: ListView.builder(
                  itemCount: snapshot.data.documents.length,
                  // ignore: missing_return
                  itemBuilder: (BuildContext context, int index) {
                    print(user.uid);
                    return user != null
                        ? Container(
                      margin: EdgeInsets.only(top: 17, left: 40),
                      child: Text(
                          snapshot.data.documents.elementAt(index)['displayName']),
                    )
                        : IconButton(
                      icon: Icon(Icons.person),
                      // ignore: missing_return
                      onPressed: () {
                        Navigator.pushNamed(context, '/LoginScreen');
                      },
                    );
                  }
              ),
            );

}

Answer 1

使用snapshot.hasData来确保您在检索到数据后构建主窗口小部件（扩展），并使用CircularProgessIndicator在返回数据之前保持其位置

 builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
              if (snapshot.hasData){
                return Expanded(
                  child: ListView.builder(
                      itemCount: snapshot.data.documents.length,
                      // ignore: missing_return
                      itemBuilder: (BuildContext context, int index) {
                        print(user.uid);
                        return user != null
                            ? Container(
                          margin: EdgeInsets.only(top: 17, left: 40),
                          child: Text(
                              snapshot.data.documents.elementAt(index)['displayName']),
                        )
                            : IconButton(
                          icon: Icon(Icons.person),
                          // ignore: missing_return
                          onPressed: () {
                            Navigator.pushNamed(context, '/LoginScreen');
                          },
                        );
                      }
                  ),
                );
                }
                 else {
                   return CircularProgressIndicator();
                   }
    
    }

getter'documents'在显示为null的一段时间内被调用

1 个答案: