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同事 ！我是 Flutter 中的菜鸟。这是我的第一个应用程序，我仅在用户从下拉按钮中选择一个值时才尝试启用该按钮。我试图找到一个类似的问题，但没有找到。

class Reserve extends StatefulWidget {
  @override
  _ReserveState createState() => _ReserveState();
}

class _ReserveState extends State<Reserve> {
  var _category;

  final formKey = GlobalKey<FormState>();

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
        appBar: new AppBar(
          title: new Text(
              globals.salonname == "" ? "Reserve" : globals.salonname),
          backgroundColor: Colors.deepOrange,
        ),
        drawer: new Drawer(
            child: new ListView(children: <Widget>[
              new ListTile(
                  title: new Text("Close"),
                  trailing: new Icon(Icons.arrow_upward),
                  onTap: () {
                    Navigator.of(context).pop();
                  })
            ])),
        body: Card(
            child: Padding(
                padding: EdgeInsets.all(8.0),
                child: Form(
                    key: formKey,
                    child: Column(
                        mainAxisSize: MainAxisSize.max,
                        children: <Widget>[
                          new Calendar(
                            isExpandable: true,
                           onDateSelected: null,
                          ),
                          Row(children: <Widget>[
                            new Container(
                              alignment: Alignment(1.0, 0.0),
                              child: new Center(
                                  child: new StreamBuilder<QuerySnapshot> 
 (
                                      stream: Firestore.instance
                                          .collection('salons').document(
                                          globals.salonkey).collection(
                                          'employee')
                                          .snapshots(),
                                      builder: (context, snapshot) {
                                        try {
                                          if 
(snapshot.data.documents.length ==
                                              0) {
                                            return new Text("No employees 
found!");
                                      }
                                      else {
                                        return new DropdownButton(
                                            hint: new Text(
                                                "Choose an employee"),
                                            items: snapshot.data.documents
                                                .map(
                                                    (
                                                    DocumentSnapshot document) {
                                                  return DropdownMenuItem(
                                                      value: document
                                                          .data["name"],
                                                      child: new Text(
                                                          document
                                                              .data["name"]));
                                                }).toList(),
                                            value: _category,
                                            onChanged: (value) {
                                              setState(() {
                                                _category = value;
                                              });
                                            });
                                      }
                                    }
                                    catch (ex) {
                                      return new Text("Try again!");
                                    }
                                  })),
                        )
                      ]),
                      new Row(
                          mainAxisAlignment: MainAxisAlignment.end,
                          children: <Widget>[
                            _buildButton(),
                          ])
                    ])))));
  }

  Widget _buildButton() {
return new RaisedButton(
  padding: const EdgeInsets.all(8.0),
  color: _category == true ? Colors.orangeAccent : Colors.grey,
  child: Text("Choose employee"),
    onPressed: _category==null ? null : () => setState(() => Navigator.of(context).push(
        new MaterialPageRoute(
            builder: (BuildContext context) =>
            new ReserveTable()))));

  }
}

所以我只想在下拉按钮中选择员工时启用 Raised 按钮。

谢谢。

4

1 回答 1

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您将不得不稍微修改您的代码，如果您需要根据流更改按钮，请StreamBuilder在您的Column级别移动您并添加一个变量以检查流何时有数据。

在这里，您的代码已修复：

            class _ReserveState extends State<Reserve> {
      var _category;
      bool enableButton = false;

      final formKey = GlobalKey<FormState>();

      @override
      Widget build(BuildContext context) {
        return new Scaffold(
            appBar: new AppBar(
              title:
                  new Text(globals.salonname == "" ? "Reserve" : globals.salonname),
              backgroundColor: Colors.deepOrange,
            ),
            drawer: new Drawer(
                child: new ListView(children: <Widget>[
              new ListTile(
                  title: new Text("Close"),
                  trailing: new Icon(Icons.arrow_upward),
                  onTap: () {
                    Navigator.of(context).pop();
                  })
            ])),
            body: Card(
                child: Padding(
              padding: EdgeInsets.all(8.0),
              child: Form(
                  key: formKey,
                  child: new StreamBuilder<QuerySnapshot>(
                      stream: Firestore.instance
                          .collection('salons')
                          .document(globals.salonkey)
                          .collection('employee')
                          .snapshots(),
                      builder: (context, snapshot) {
                        return Column(
                            mainAxisSize: MainAxisSize.max,
                            children: <Widget>[
                              new Calendar(
                                isExpandable: true,
                                onDateSelected: null,
                              ),
                              Row(children: <Widget>[
                                new Container(
                                    alignment: Alignment(1.0, 0.0),
                                    child: new Center(
                                        child: (!snapshot.hasData ||
                                                snapshot.data.documents.length == 0)
                                            ? new Text("No employees found!")
                                            : new DropdownButton(
                                                hint:
                                                    new Text("Choose an employee"),
                                                items: snapshot.data.documents.map(
                                                    (DocumentSnapshot document) {
                                                  return DropdownMenuItem(
                                                      value: document.data["name"],
                                                      child: new Text(
                                                          document.data["name"]));
                                                }).toList(),
                                                value: _category,
                                                onChanged: (value) {
                                                  setState(() {
                                                    _category = value;
                                                  });
                                                })))
                              ]),
                              new Row(
                                  mainAxisAlignment: MainAxisAlignment.end,
                                  children: <Widget>[
                                    _buildButton(),
                                  ])
                            ]);

                      })),
            )));
      }

      Widget _buildButton() {
        return new RaisedButton(
            padding: const EdgeInsets.all(8.0),
            color: _category!=null ? Colors.orangeAccent : Colors.grey,
            child: Text("Choose employee"),
            onPressed: _category==null
                ? null
                : () => setState(() => Navigator.of(context).push(
                    new MaterialPageRoute(
                        builder: (BuildContext context) => ReserveTable()))));
      }
    }
于 2019-01-06T23:55:01.677 回答