无法在初始化程序中访问实例成员 'context'。扑

Question

Heelo Community 我正在做一个液体滑动屏幕。该应用程序有 4 个容器，带有一个页面索引。在最后一个容器上，我添加了一个按钮，当按下时： (){ Navigator.pushNamedAndRemoveUntil(context, MainScreen.idScreen, (route) => false);} 由于某些原因，我的代码抱怨上下文。

我尝试过的东西----> 我尝试创建一个

 setState(() {
      if(isSelected == true){
        print("Selected is true2");
        Navigator.pushNamedAndRemoveUntil(context, MainScreen.idScreen, (route) => false);
        displayToastMessage("you are logged-in now.", context);
      }

然后在我的 MaterialButton onPressed 中我有：

Container(
                  padding: EdgeInsets.fromLTRB(20, 10, 20, 40),
                  child: RawMaterialButton(
                    onPressed: () => {

                      isSelected = true,

                      if(isSelected == true){
                        print("Selected is true1")
                      }
                    },

                    fillColor: Colors.blueAccent,
                    splashColor: Colors.blue,

                    child: Padding(
                      padding: EdgeInsets.all(10.0),
                      child: Row(
                        mainAxisSize: MainAxisSize.min,
                        children: const <Widget>[
                          SizedBox(
                            width: 20.0,
                          ),
                          Text(
                            "Accept EULA",
                            maxLines: 1,
                            style: TextStyle(color: Colors.white),
                          ),
                          Icon(
                            Icons.arrow_forward,
                            color: Colors.white,
                          ),
                        ],
                      ),
                    ),
                    shape: const StadiumBorder(),
                  ),
                ),

但是当我运行程序按钮不起作用时

我只想在按下 MaterialRawButton 时导航到主屏幕

这是我的代码：

class InformationScreens extends StatefulWidget {
  static const String idScreen = "informationScreen";
  
  @override
  _WithPages createState() => _WithPages();
}

class _WithPages extends State<InformationScreens> {

  int page = 0;
  LiquidController liquidController;
  UpdateType updateType;


  @override
  void initState() {
    liquidController = LiquidController();
    super.initState();

  }

  final pages = [
    Container(),
    Container(),
    Container(),
    Container(),
    Container(
              padding: EdgeInsets.fromLTRB(20, 10, 20, 20),
              height: 600,
              child: SingleChildScrollView(
                child: Text(
                  ''' this is some text'''
                ),
              ),
            ),
            Column(
              children: <Widget>[
                Container(
                  padding: EdgeInsets.fromLTRB(20, 10, 20, 40),
                  child: RawMaterialButton(
                    onPressed: () => {

  Navigator.pushNamedAndRemoveUntil(context, MainScreen.idScreen, (route) => false);
  displayToastMessage("you are logged-in now.", context);
                    },

                    fillColor: Colors.blueAccent,
                    splashColor: Colors.blue,

                    child: Padding(
                      padding: EdgeInsets.all(10.0),
                      child: Row(
                        mainAxisSize: MainAxisSize.min,
                        children: const <Widget>[
                          SizedBox(
                            width: 20.0,
                          ),
                          Text(
                            "Accept EULA",
                            maxLines: 1,
                            style: TextStyle(color: Colors.white),
                          ),
                          Icon(
                            Icons.arrow_forward,
                            color: Colors.white,
                          ),
                        ],
                      ),
                    ),
                    shape: const StadiumBorder(),
                  ),
                ),
              ],
            ),
          ],
        ),
      ),
    ),
  ];


  Widget _buildDot(int index) {
    double selectedness = Curves.easeOut.transform(
      max(
        0.0,
        1.0 - ((page ?? 0) - index).abs(),
      ),
    );
    
    double zoom = 1.0 + (2.0 - 1.0) * selectedness;
    return new Container(
      width: 25.0,
      child: new Center(
        child: new Material(

          color: Colors.blueAccent,
          type: MaterialType.circle,
          child: new Container(
            width: 8.0 * zoom,
            height: 8.0 * zoom,
          ),
        ),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Stack(
          children: <Widget>[
            LiquidSwipe(
              pages: pages,
              positionSlideIcon: 0.8,
              slideIconWidget: Icon(Icons.arrow_back_ios),
              onPageChangeCallback: pageChangeCallback,
              waveType: WaveType.liquidReveal,
              liquidController: liquidController,
              ignoreUserGestureWhileAnimating: true,
            ),
            Padding(
              padding: EdgeInsets.all(20),
              child: Column(
                children: <Widget>[
                  Expanded(child: SizedBox()),
                  Row(
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: List<Widget>.generate(pages.length, _buildDot),
                  ),
                ],
              ),
            ),
            Align(
              alignment: Alignment.bottomRight,
              child: Padding(
                padding: const EdgeInsets.all(25.0),
                child: FlatButton(
                  onPressed: () {
                    liquidController.animateToPage(
                        page: pages.length - 1, duration: 700);
                  },
                  child: Text("Skip to End"),
                  color: Colors.white.withOpacity(0.01),
                ),
              ),
            ),
            Align(
              alignment: Alignment.bottomLeft,
              child: Padding(
                padding: const EdgeInsets.all(25.0),
                child: FlatButton(
                  onPressed: () {
                    liquidController.jumpToPage(page: liquidController.currentPage + 1 > 
                    pages.length - 1
                                ? 0
                                : liquidController.currentPage + 1);
                  },

                  child: Text("Next"),
                  color: Colors.white.withOpacity(0.01),
                ),
              ),
            ),
          ],
        ),
      ),
    );


  }
  pageChangeCallback(int lpage) {
    setState(() {
      page = lpage;

    });
  }
}

Answer 1

除非您知道自己在做什么，否则不要将小部件存储在变量中。它只会制造更多你无法理解的问题。要么使它们像您拥有的 _buildDot 方法一样，要么直接将其插入 build.

使用 getter 方法的示例：

List<Widget> get pages => [
    Container(),
    Container(),
    Container(),
    Container(),
    Container(
              padding: EdgeInsets.fromLTRB(20, 10, 20, 20),
              height: 600,
              child: SingleChildScrollView(
                child: Text(
                  ''' this is some text'''
                ),
              ),
            ),
            Column(
              children: <Widget>[
                Container(
                  padding: EdgeInsets.fromLTRB(20, 10, 20, 40),
                  child: RawMaterialButton(
                    onPressed: () => {

  Navigator.pushNamedAndRemoveUntil(context, MainScreen.idScreen, (route) => false);
  displayToastMessage("you are logged-in now.", context);
                    },

                    fillColor: Colors.blueAccent,
                    splashColor: Colors.blue,

                    child: Padding(
                      padding: EdgeInsets.all(10.0),
                      child: Row(
                        mainAxisSize: MainAxisSize.min,
                        children: const <Widget>[
                          SizedBox(
                            width: 20.0,
                          ),
                          Text(
                            "Accept EULA",
                            maxLines: 1,
                            style: TextStyle(color: Colors.white),
                          ),
                          Icon(
                            Icons.arrow_forward,
                            color: Colors.white,
                          ),
                        ],
                      ),
                    ),
                    shape: const StadiumBorder(),
                  ),
                ),
              ],
            ),
          ],
        ),
      ),
    ),
  ];

无法在初始化程序中访问实例成员 'context'。扑

The instance member 'context' can't be accessed in an initializer. Flutter

widget

dart

android-studio

flutter