Flutter/Dart: Pass Parameters to a Stateful Widget?

Question

I need to call pass my title and oldtitle parameters to my EditPage Stateful widget. But if I do this;

 class EditPage extends StatefulWidget {
   String title;  
   String oldtitle;
   EditPage({this.title, this.oldtitle})

The strings are not available to the build unless I call it them as widget.title and widget.oldtitle.

But I'm using a textfield within a form that doesn't seem to work right if I use these widgets.

Here's the form code:

      Container(                   
                child: TextField(
                    decoration: new InputDecoration(
                    hintText: widget.oldtitle,
                    contentPadding: new EdgeInsets.all(1.0),
                    border: InputBorder.none,
                    filled: true,
                    fillColor: Colors.grey[300],
                  ),
                  keyboardType: TextInputType.text,
                  autocorrect: false,
                  onChanged: (titleText) {
                    setState(() {
                       widget.title= titleText;
                    });
                  },
                ),
              ),

But then if I do this;

class _EditPageState extends State<EditPage> {
   String title;  
   String oldtitle;  
   EditPage({this.title, this.oldtitle})

I can't pass the title parameter to it from another screen. IE:

`EditPage(title:mytitle, oldtitle:myoldtitle);`

So What's the correct way to pass a parameter to a Stateful widget?

`thistitle` is never declared. You likely meant `this.title`. Static analysis should be showing an error for this. — Christopher Moore, Aug 11 '20 at 13:59
Thanks, this mistake was made as I edited it for Stackoverflow. The full code is quite substantial. I've edited it to read this.title now. — Meggy, Aug 11 '20 at 14:45
`widget.` is the correct method of accessing the arguments of the widget from the state. Please clarify the actual issue with this method. — Christopher Moore, Aug 11 '20 at 14:48

score 11 · Answer 1 · answered Aug 11 '20 at 14:57

You should never pass the variables to the state directly, since it does not guarantee that widget will get rebuilt when state will be updated. You should accept parameters via your stateful widget and access them from the state itself via widget.variable.

Example:

class TestWidget extends StatefulWidget {
  final String variable;

  TestWidget({Key key, @required this.variable}) : super(key: key);

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

class _TestWidgetState extends State<TestWidget> {
  @override
  Widget build(BuildContext context) {
    return Container(
      child: Center(
        // Accessing the variables passed into the StatefulWidget.
        child: Text(widget.variable),
      ),
    );
  }
}

If that's the case I'm guessing my problem is with the form and not with the passing of parameters. I tried your code and still, my form is not working. I'll edit to include the code for the form; — Meggy, Aug 11 '20 at 15:34
this doesnt really seem to work any more. Error says variable cannot be null — nikoss, May 02 '22 at 00:50

score 1 · Accepted Answer · answered Aug 11 '20 at 16:35

Looks like the solution was to separate the title from the oldtitle;

  class EditPage extends StatefulWidget {
     String oldtitle;
     EditPage({this.oldtitle})

and then;

 class _EditPageState extends State<EditPage> {
  String title;

So now for the form;

Container(                   
            child: TextField(
                decoration: new InputDecoration(
                hintText: widget.oldtitle,
                contentPadding: new EdgeInsets.all(1.0),
                border: InputBorder.none,
                filled: true,
                fillColor: Colors.grey[300],
              ),
              keyboardType: TextInputType.text,
              autocorrect: false,
              onChanged: (titleText) {
                setState(() {
                   title= titleText;
                });
              },
            ),
          ),

Flutter/Dart: Pass Parameters to a Stateful Widget?

2 Answers2