CODEWITHSUNDEEP
androidflutterwidgetfocusdispose
sazin samin
sazin samin

Reputation: 61

The method 'dispose' was called on null in Flutter

I want to make to do app in flutter, for use of focusNode i write this code ->

FocusNode _titleFocus;
FocusNode _descriptionFocus;
FocusNode _todoFocus;


@override
void initState() {
  // TODO: implement initState
super.initState();
if(widget.task!=null){

  _titleFocus = FocusNode();
  _descriptionFocus = FocusNode();
  _todoFocus = FocusNode();

  }
}

 @override
 void dispose() {
 // TODO: implement dispose
  _titleFocus.dispose();
  _descriptionFocus.dispose();
  _todoFocus.dispose();
  super.dispose();
}

I initiate the FocusNode first below the code, this focusNode work correctly in exiting todo task object but when i want to create new one and passing focus one to another it's not working. I use this code for passing focus...

focusNode: _titleFocus,
_descriptionFocus.requestFocus();

but it goes wrong and show the message ->

The following NoSuchMethodError was thrown while finalizing the widget tree:
The method 'dispose' was called on null.
Receiver: null
Tried calling: dispose()

Upvotes: 1

Views: 2854

Answers (1)

timilehinjegede
timilehinjegede

Reputation: 14043

"When i want to create new one and passing focus one to another it's not working."

The FocusNode doesn't get instantiated because of your condition in the initState method. Hence the error (The method 'dispose' was called on null.).

To fix, you can check for the condition before calling dispose() on the FocusNodes in the dispose method.

 @override
 void dispose() {
 // TODO: implement dispose
if(widget.task!=null){ // check whether it is an existing todo or a new one before calling dispose
_titleFocus.dispose();
  _descriptionFocus.dispose();
  _todoFocus.dispose();
}
  super.dispose();
}

UPDATE: Instead of the IF checks, you could use the null aware operator denoted by ?. :

Added an example below:

 @override
 void dispose() {
 // TODO: implement dispose
  _titleFocus?.dispose();
  _descriptionFocus?.dispose();
  _todoFocus?.dispose();
}
  super.dispose();
}

Upvotes: 5

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