从一页过渡到另一页 - Flutter

Question

所以，我得到了一个简单的单页应用程序。我在该页面上创建了一个复选框，以便在单击该复选框时转换到另一个页面。但是，复选框的 onChanged 参数出现错误。具体如下：

Checkbox(
value: false, onChanged: (bool newValue) {
Navigator.push(
context,
new MaterialPageRoute(builder: (ctxt) => new SecondScreen()),
);
})

但是最后一行代码报了如下错误，不知如何解决：

*

The return type 'SecondScreen' isn't a widget as required by the closure's context.

因此，SecondScreen 不是无状态的小部件。但是如何修改 MaterialPageRouter 才能成功过渡到这个新页面。

我的副屏如下：

   class SensorPage extends StatefulWidget {
   const SensorPage({Key key, this.device}) : super(key: key);
   final BluetoothDevice device;

   @override
   _SensorPageState createState() => _SensorPageState();
   }

   class SecondScreen extends State<SensorPage> {
   final String SERVICE_UUID = "0000ffe0-0000-1000-8000-00805f9b34fb";
   final String CHARACTERISTIC_UUID = "0000ffe1-0000-1000-8000-00805f9b34fb";
  bool isReady;
  Stream<List<int>> stream;
  List<double> traceDust;

  String _dataParser2(List<int> dataFromDevice) {
    return utf8.decode(dataFromDevice);
  }

  @override
  void initState() {
    super.initState();
    isReady = false;
  }

  @override
  Widget build (BuildContext ctxt) {
    Oscilloscope oscilloscope = Oscilloscope(
      showYAxis: true,
      padding: 0.0,
      backgroundColor: Colors.black,
      traceColor: Colors.white,
      yAxisMax: 500.0,
      yAxisMin: 0.0,
      dataSet: traceDust,
    );

    return new Scaffold(
      appBar: new AppBar(
        title: new Text("Home"),
      ),
      body: Container(
          child: !isReady
              ? Center(
            child: Text(
              "Waiting...",
              style: TextStyle(fontSize: 24, color: Colors.red),
            ),
          )
              : Container(
            child: StreamBuilder<List<int>>(
              stream: stream,
              builder: (BuildContext context,
                  AsyncSnapshot<List<int>> snapshot) {
                if (snapshot.hasError)
                  return Text('Error: ${snapshot.error}');

                if (snapshot.connectionState ==
                    ConnectionState.active){
                  var currentValue2 = _dataParser2(snapshot.data);
                  traceDust.add(double.tryParse(currentValue2) ?? 0);
                  return Center(
                      child: Column(
                        mainAxisAlignment: MainAxisAlignment.center,
                        children: <Widget>[
                          Expanded(flex: 1, child:Column(
                              mainAxisAlignment: MainAxisAlignment.center,
                              children: <Widget>[
                                Text('Home',
                                    style: TextStyle(fontSize: 14)),
                                Text('${currentValue2} IamHome',
                                    style: TextStyle(
                                        fontWeight: FontWeight.bold,
                                        fontSize: 24))
                              ]),
                          ),
                          Expanded(
                            flex: 1,
                            child: oscilloscope,)
                        ],
                      ));
                } else {
                  return Text('Check the stream');
                }
              },),
          ))
    );
  }
}

Answer 1

您正在使用小部件 Navigator，而您应该使用 Navigator.of(context)。

您的代码应如下所示：

Checkbox(
    value: false, onChanged: (bool newValue) {
    Navigator.of(context).push(MaterialPageRoute(
                          builder: (BuildContext context) =>
                              SecondScreen()));
})

Answer 2

您定义 SensorPage 状态的 class 名称的方式有误。对于您的情况，它应该是 _SensorPageState

请查看下面的代码：

import 'package:flutter/material.dart';
// add the rest of packages

void main() {
  runApp(MaterialApp(
      home: MyApp()));
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {

  @override
  void initState() {
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return SafeArea(
      child: Scaffold(
        body: Container(
          child: Checkbox(
            value: false,
            onChanged: (bool newValue) {
              Navigator.push(
                context,
                new MaterialPageRoute(builder: (context) => new SensorPage()),
              );
            }
          ),
        ),
      ),
    );
  }
}

class SensorPage extends StatefulWidget {
  const SensorPage({Key key, this.device}) : super(key: key);
  final BluetoothDevice device;

  @override
  _SensorPageState createState() => _SensorPageState();
}

class _SensorPageState extends State<SensorPage> {
  final String SERVICE_UUID = "0000ffe0-0000-1000-8000-00805f9b34fb";
  final String CHARACTERISTIC_UUID = "0000ffe1-0000-1000-8000-00805f9b34fb";
  bool isReady;
  Stream<List<int>> stream;
  List<double> traceDust;

  String _dataParser2(List<int> dataFromDevice) {
    return utf8.decode(dataFromDevice);
  }

  @override
  void initState() {
    super.initState();
    isReady = false;
  }

  @override
  Widget build (BuildContext ctxt) {
    Oscilloscope oscilloscope = Oscilloscope(
      showYAxis: true,
      padding: 0.0,
      backgroundColor: Colors.black,
      traceColor: Colors.white,
      yAxisMax: 500.0,
      yAxisMin: 0.0,
      dataSet: traceDust,
    );

    return new Scaffold(
        appBar: new AppBar(
          title: new Text("Home"),
        ),
        body: Container(
            child: !isReady
                ? Center(
              child: Text(
                "Waiting...",
                style: TextStyle(fontSize: 24, color: Colors.red),
              ),
            )
                : Container(
              child: StreamBuilder<List<int>>(
                stream: stream,
                builder: (BuildContext context,
                    AsyncSnapshot<List<int>> snapshot) {
                  if (snapshot.hasError)
                    return Text('Error: ${snapshot.error}');

                  if (snapshot.connectionState ==
                      ConnectionState.active){
                    var currentValue2 = _dataParser2(snapshot.data);
                    traceDust.add(double.tryParse(currentValue2) ?? 0);
                    return Center(
                        child: Column(
                          mainAxisAlignment: MainAxisAlignment.center,
                          children: <Widget>[
                            Expanded(flex: 1, child:Column(
                                mainAxisAlignment: MainAxisAlignment.center,
                                children: <Widget>[
                                  Text('Home',
                                      style: TextStyle(fontSize: 14)),
                                  Text('${currentValue2} IamHome',
                                      style: TextStyle(
                                          fontWeight: FontWeight.bold,
                                          fontSize: 24))
                                ]),
                            ),
                            Expanded(
                              flex: 1,
                              child: oscilloscope,)
                          ],
                        ));
                  } else {
                    return Text('Check the stream');
                  }
                },),
            ))
    );
  }
}

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