如何从 VoidCallback 函数返回值

Question

我有一个带有按钮的自定义小部件。我想创建 VoidCallback 派系以从中返回数据。

onDayPressed: (DateTime date, List<Event> events){
   // I want to return date time to original class when the user changes the date 
}

我尝试这样做但不起作用

onDayPressed: (DateTime date, List<Event> events) => widget.onDayChanged,

//关于原始类

CustomCalender(onDayChanged: (){print("HI");}),

我正在使用这个颤振包

flutter_calendar_carousel

Answer 1

如果您需要将数据从子节点传递给父节点，则必须使用 Function(T)，因为 VoidCallback 不支持传递数据。请看下面的代码示例：

// Try adapting this code to work with your code, the principle should be the same.
class MinimalExample extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      // Notice the variable being passed in the function.
      body: ReturnValueToParent( myNumber: (int) => print(int),),
    );
  }
}

// Specify a Function(DateTime) in your case and adapt it to your problem.
class ReturnValueToParent extends StatelessWidget {
  final Function(int) myNumber;
  const ReturnValueToParent({Key key, this.myNumber}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Center(
      child: RaisedButton(
        // Remember the parameter
        onPressed: () => myNumber(5),
      ),
    );
  }
}