I have a Future (async) Date&Time picker function which works fine from within the body of my stateful widget which contains the "Builder" and the function can be called via the onpressed by just this:

onPressed: () {SelectDayAndTimeL();}, 

Code:

Future _selectDayAndTimeL(BuildContext context) async {
    DateTime _selectedDay = await showDatePicker(
        context: context,
        initialDate: DateTime.now(),
        firstDate: DateTime(2021),
        lastDate: DateTime(2030),
        builder: (BuildContext context, Widget child) => child);

    TimeOfDay _selectedTime = await showTimePicker(
      context: context,
      initialTime: TimeOfDay.now(),
    );

    if (_selectedDay != null && _selectedTime != null) {
      //a little check
    }
    setState(() {
      selectedDateAndTime = DateTime(
        _selectedDay.year,
        _selectedDay.month,
        _selectedDay.day,
        _selectedTime.hour,
        _selectedTime.minute,
      );
      // _selectedDate = _selectedDay;
    });
    // print('...');
  }

Now I want to be able to call this function from different dart files/screens which means I have to keep this function on a different dart file which I have tried to do, but because of the setState in the function it needs to be inside a stateful widget. I have tried putting it inside a stateful widget but keeps getting errors.

class Picker extends StatefulWidget {
  @override
  _PickerState createState() => _PickerState();
}

class _PickerState extends State<Picker> {
  @override
  Future<Widget> build(BuildContext context) async { //the error in on the build on this line
    DateTime _selectedDay = await showDatePicker(
        context: context,
        initialDate: DateTime.now(),
        firstDate: DateTime(2021),
        lastDate: DateTime(2030),
        builder: (BuildContext context, Widget child) => child);

    TimeOfDay _selectedTime = await showTimePicker(
      context: context,
      initialTime: TimeOfDay.now(),
    );

    if (_selectedDay != null && _selectedTime != null) {
      //a little check
    }
    setState(() {
      selectedDateAndTime = DateTime(
        _selectedDay.year,
        _selectedDay.month,
        _selectedDay.day,
        _selectedTime.hour,
        _selectedTime.minute,
      );
      // _selectedDate = _selectedDay;
    });
  }
}

How do I properly place the Future Function inside a stateful widget and how to call it on an onpressed?

I don't know if the title I gave this question is actually what it's supposed to be, but I don't know how else to put it.

CodePudding user response：

Create a function which will take datetime as a parameter and setstate of the stateful widget. Write this inside the stateful widget. Pass this function to the other class as an argument. Once the date is picked call this method by passing the datetime selected.

CodePudding user response：

You should pass the setState function itself as a parameter to the method. This way, inside the method you will always be using the correct state setter function. That is especially necessary since you need to keep the variables _selectedDay etc inside the widget, not on the static method. Try this:

Future selectDayAndTimeL(BuildContext context, Function(DateTime) dateTimeSetter) async { //add a function to receive and use the
    DateTime _selectedDay = await showDatePicker(
        context: context,
        initialDate: DateTime.now(),
        firstDate: DateTime(2021),
        lastDate: DateTime(2030),
        builder: (BuildContext context, Widget child) => child);

    TimeOfDay _selectedTime = await showTimePicker(
      context: context,
      initialTime: TimeOfDay.now(),
    );

    if (_selectedDay != null && _selectedTime != null) {
      //a little check
    }
    // Create the variable with the picked date
    DateTime selectedDateAndTime = DateTime(
        _selectedDay.year,
        _selectedDay.month,
        _selectedDay.day,
        _selectedTime.hour,
        _selectedTime.minute,
      );
     //call the function from the parameter, which will be executed on the calling widget
    dateTimeSetter(selectedDateAndTime);
    ....
}

Then, call your function to show the datetime picker passing the context, and a function that receives a DateTime parameter, which will be the parameter picked by the user. When the user picks a date, this function body will be executed, calling setState and setting the pickedTime variable.

class Picker extends StatefulWidget {
  DateTime pickedTime;

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

class _PickerState extends State<Picker> {
  @override
  Future<Widget> build(BuildContext context) async {
     return ...
         _selectDayAndTimeL(context, (DateTime time){
           setState((){
             widget.pickedTime = time;
           });
         });
     ...

You can also extract the function from the parameter into a normal named function, and just use its name in the parameter, but I'll leave it as is for now to make it simpler.

Also, don't forget to make your method public and static if necessary for the scope of your code.

CodePudding user response：

The whole setState inside your method is the problem. Your method should do one thing: get a date and time from the user. And there it's responsibility ends.

Future<DateTime> SelectDayAndTimeL(BuildContext context) async {
    DateTime _selectedDay = await showDatePicker(
        context: context,
        initialDate: DateTime.now(),
        firstDate: DateTime(2021),
        lastDate: DateTime(2030),
        builder: (BuildContext context, Widget child) => child);

    TimeOfDay _selectedTime = await showTimePicker(
      context: context,
      initialTime: TimeOfDay.now(),
    );

    if (_selectedDay != null && _selectedTime != null) {
      //a little check
    }
    return DateTime(
        _selectedDay.year,
        _selectedDay.month,
        _selectedDay.day,
        _selectedTime.hour,
        _selectedTime.minute,
      );
  }

Now your onPressed becomes:

onPressed: () async { 
     final pickedDatetime = await SelectDayAndTimeL(context); 
     setState(() { selectedDateAndTime = pickedDatetime });
},

You have sucessfully divided your code into the function that picks a thing and your widget, which updates after the thing is picked.

The function that picks the date and time can now be reused in every other widget.