The method 'jumpToDay' was called on null. [Flutter] - flutter

Question

In this application, the user will be able to add tasks and display it in a PageView.builder. The user will also be able to scroll through the PageView.builder by swiping left or right. The pageview is mapped to dates (ex: current page maps to today's date, next page maps to tomorrow's date, etc.). I also wanted to implement a jump feature which lets the user move to a new page by specifying a date on a showDatepicker widget.
The PageView.builder was implemented by using this project. this project also has the jump to page feature : https://github.com/ZedTheLed/calendar_views
the showDatepicker is implemented in the method below. it is called by clicking on a Raisedbutton:
_selectDate() async {
final DateTime picker =await showDatePicker(
context: context,
initialDate: DateTime.now(),
firstDate: DateTime(2010),
lastDate: DateTime(2040)
);
if (picker != null) {
print(picker);
return _daysPageController.jumpToDay(picker); // this method jumps the user to a selected date
// Navigator.pop(context);
// print(selectedDate);
// await runJump(selectedDate);
// return selectedDate;
}
}
when the user clicks on a date, the variable DateTime picker successfully returns the user-selected date in the print statement. But when i pass this value to the jumptopage method, it gives his error : The method 'jumpToDay' was called on null.
The PageView.builder is implemented in the code below :
final List<DateTime> days;
Scaffold(
floatingActionButton: new RaisedButton(
child: new Text("Jump To Today"),
onPressed: () {
_selectDate();
},
),
body: new Column(
children: widget.days.map(((day) => Container(
constraints: new BoxConstraints(
maxHeight: MediaQuery.of(context).size.height * 1.00,
maxWidth: MediaQuery.of(context).size.width * 1.00
),
child: Starting_screen(_makeTextString(day)), //this screen displays the tasks added by the user
)
),
).toList()
),
);
the method _makeTextString just modifies a DateTime value and returns it in a desirable format.
Could i get a suggestion on how to handle this error?
full project is available here : https://bitbucket.org/NotAnurag/todolist_restarted/src/master/

Answer 1

When the user clicks on a date, the variable DateTime picker successfully returns the user-selected date in the print statement. But when I pass this value to the jumptopage method, it gives his error: "The method jumpToDay was called on null"
The problem that I see in the code is that _daysPageController is not initialized. IDE helpfully suggests various methods that you can call on DaysPageController, but the fact remains that it is declared, but no value is assigned to it (meaning that it is null):
DaysPageController _daysPageController; // remains null unless assigned a value
Therefore, what the error is attempting to tell is that jumpToDay(DateTime) is called on null (which obviously does not have such a method). If you look at the stack trace a bit more explicit hint is buried in there:
[ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: NoSuchMethodError: The method 'jumpToDay' was called on null.
Try to initialize the controller and see if it helps to resolve the issue.