Question

我试图在按下按钮时更改应用程序的背景颜色。但是，当我单击它时会弹出错误。

我尝试将所有东西包装在卡中，放在容器中，放在Material App中，并添加了setState方法。

import 'package:flutter/material.dart';

void main(){
  runApp(
  myStateFulWidget(

  )
  );
}
class myStateFulWidget extends StatefulWidget {
  @override
  _myStateFulWidgetState createState() => _myStateFulWidgetState();
}

class _myStateFulWidgetState extends State<myStateFulWidget> {
   changeColor(){
    setState(() {
      var colorPart = Colors.red;
    });
  }
  @override
  Widget build(BuildContext context) {
  return Card(
    child:Container(
      color: Colors.green,
      child: RaisedButton(
        color: Colors.black,
        child: Text("Ola",textDirection: TextDirection.ltr),
        onPressed: (){
          changeColor();
        },
      ),
    )
  );
  }
}

我一直遇到的错误是：

 ════════ Exception Caught By widgets library ═══════════════════════════════════════════════════════
The following assertion was thrown building InkWell(gestures: [tap], clipped to BoxShape.rectangle, dirty, dependencies: [_FocusMarker], state: _InkResponseState<InkResponse>#6fdbb):
No Directionality widget found.

Answer 1

你得到的理由

No Directionality widget found例外

是因为没有父窗口小部件可以提供与您提供的RaisedButton textDirection值一起使用的方向信息。这可以通过提供一个Directionality小部件或另一个从其上下文中提供TextDirection信息的部件（例如Scaffold）来解决。

请注意，背景色仅在其他小部件未覆盖的部分中可见。

import 'package:flutter/material.dart';

void main(){
  runApp( MyStatefulWidget());
}


class MyStatefulWidget extends StatefulWidget {
  @override
  _MyStatefulWidgetState createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State<MyStatefulWidget> {

  var colorPart = Colors.green;

  changeColor(){
    setState(() {
      colorPart = colorPart == Colors.red ? Colors.green : Colors.red ;
    });
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        backgroundColor: colorPart,
        body: Center(
          child: Card(
              child:Container(
                child: RaisedButton(
                  //color: Colors.black,
                  child: Text("Ola",textDirection: TextDirection.ltr),
                  onPressed: (){
                    changeColor();
                  },
                ),
              )
          ),
        )
      ),
    );
  }
}

Answer 2

Try using this :
import 'package:flutter/material.dart';

void main(){
  runApp(
      myStateFulWidget(

      )
  );
}
class myStateFulWidget extends StatefulWidget {
  @override
  _myStateFulWidgetState createState() => _myStateFulWidgetState();
}

class _myStateFulWidgetState extends State<myStateFulWidget> {
Color col = Colors.green;
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home:new
        Scaffold(
        backgroundColor:col ,
        body:Card(
          child: RaisedButton(
            child: Text("Ola",textDirection: TextDirection.ltr),
            onPressed: (){
              changeColor();
            },
          ),
        )
      )
    );
  }
  changeColor(){
    setState(() {
       col = Colors.red;
    });
  }
}

Answer 3

将var colorPart = Colors.red声明为setstate以外的状态

如何修复“找不到方向性小部件”。问题？

3 个答案: