在 flutter dart 中对 null 调用了方法“findAncestorStateOfType”

Question

我正在创建一个应用程序，我是扑扑，飞镖的新手。我在“上下文”中有问题。我想替换页面/屏幕 onTab()。但我有以下错误：

> ?????? Exception caught by gesture ???????????????????????? The
> following NoSuchMethodError was thrown while handling a gesture: The
> method 'findAncestorStateOfType' was called on null. Receiver: null
> Tried calling: findAncestorStateOfType<NavigatorState>()

这是我的代码：

class Theorytest extends StatelessWidget {

    Widget  customcard(String testName ){
      return Padding(
        padding: EdgeInsets.all(10.0),
        child: InkWell(
          onTap: (){

                      Navigator.of(context).pushReplacement(MaterialPageRoute(

              builder: (context) => GetTestData(),
           ),
           );
          },
          child: Material(     
            borderRadius: BorderRadius.circular(50.0),
            elevation: 20.0,
            child : Container(
              child: Column(
                children : <Widget>[
                  Padding(
                    padding: EdgeInsets.fromLTRB(5.0, 20.0, 10.0, 20.0),
                    child: Text( testName,
                    style: TextStyle(
                      fontSize: 24.0,
                    ),
                    ),
                    ),
                ],
              ),
            ),
          ),
        ),
      );
    }
    @override
    Widget build(BuildContext context) {
      return Scaffold(
        backgroundColor: Colors.white,
        body: ListView(
          children : <Widget>[
            customcard('Theory Test 1'),
            customcard('Theory Test 2'),
            customcard('Theory Test 3'),
            customcard('Theory Test 4'),
            customcard('Theory Test 5'),
            customcard('Theory Test 6'),
            customcard('Theory Test 7'),
            customcard('Theory Test 8'),
            customcard('Theory Test 9'),
            customcard('Theory Test 10'),
            customcard('Theory Test 11'),
            customcard('Theory Test 12'),
            customcard('Theory Test 13'),
            customcard('Theory Test 14'),
            customcard('Theory Test 15')          
          ]
        ),
      );
    }

这是代码错误。我不知道为什么上下文对我不起作用。

Answer 1

问题（为什么上下文对您不起作用）是因为您的customCard方法中没有BuildContext对象

有几种方法可以实现这一点..

一种方法是在你的方法中添加一个BuildContext参数像这样

  Widget customcard(BuildContext context, String testName) {
    return Padding(
      padding: EdgeInsets.all(10.0),
      child: InkWell(
        onTap: () {
          Navigator.of(context).pushReplacement(
            MaterialPageRoute(
              builder: (context) => GetTestData(),
            ),
          );
        },
        child: Material(
          borderRadius: BorderRadius.circular(50.0),
          elevation: 20.0,
          child: Container(
            child: Column(
              children: <Widget>[
                Padding(
                  padding: EdgeInsets.fromLTRB(5.0, 20.0, 10.0, 20.0),
                  child: Text(
                    testName,
                    style: TextStyle(
                      fontSize: 24.0,
                    ),
                  ),
                ),
              ],
            ),
          ),
        ),
      ),
    );
  }

然后你的 ListView 孩子会像

customCard(context, "Theory Test 1")

另一种方法是创建一个无状态小部件并在 build 方法中返回 customcard

class CustomCard extends StatelessWidget {
  String testName;
  CustomCard(this.testName);
  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: EdgeInsets.all(10.0),
      child: InkWell(
        onTap: () {
          Navigator.of(context).pushReplacement(
            MaterialPageRoute(
              builder: (context) => GetTestData(),
            ),
          );
        },
        child: Material(
          borderRadius: BorderRadius.circular(50.0),
          elevation: 20.0,
          child: Container(
            child: Column(
              children: <Widget>[
                Padding(
                  padding: EdgeInsets.fromLTRB(5.0, 20.0, 10.0, 20.0),
                  child: Text(
                    testName,
                    style: TextStyle(
                      fontSize: 24.0,
                    ),
                  ),
                ),
              ],
            ),
          ),
        ),
      ),
    );
  }
}

然后你的 ListView 孩子会像......

CustomCard("Theory Test 1")

我希望这可以帮助你。