[FormBuilderDropdown]: silently ignores an unknown initialValue

[grundid]

Is there an existing issue for this?

• I have searched the existing issues

Package/Plugin version

9.2.1

Platforms

• Android
• iOS
• Linux
• MacOS
• Web
• Windows

Flutter doctor

Latest Flutter

Minimal code example

 FormBuilderDropdown(
                      name: 'weekday',
                      decoration: InputDecoration(
                        labelText: 'Weekday',
                      ),
                      initialValue: DateTime.sunday,
                      allowClear: false,
                      validator: FormBuilderValidators.compose(
                        [FormBuilderValidators.required()],
                      ),
                      items: [
                        DropdownMenuItem<int>(
                          value: DateTime.monday,
                          child: Text("Monday"),
                        )
                      ])

Current Behavior

The dropdown shows an empty entry but still keeps the value in the state. When the user saves the form the value is returned as a valid selection.

Expected Behavior

The dropdown should fail as per design if an unknown option is given.

Steps To Reproduce

see minimal code example

Aditional information

No response

[fatyga]

For first, there is a problem with your code example. It assumes, that underlying DropdownButton can represent a value outside the available ones. It is in a state, that user can't even select.

In case of DropdownButtonFormField from material library, assertion will fire up to show, that you are breaking the rules. Try this:

DropdownButtonFormField<int>(
                hint: Text('Weekday'),
                value: DateTime.sunday,
                items: [
                  DropdownMenuItem<int>(
                    value: DateTime.monday,
                    child: Text("Monday"),
                  ),
                ],
                onChanged: (int? value) {})

It will of course force you to provide correct value and list of values. Then everything will work fine.

I've investigated current FormBuilderDropdown implementation, and it somehow skips assertion on first build. Next ones will fire up an assertion included in didUpdateWidget method.

I think the problem with current implementation is the assumption, that argument provided to value can be possibly outside available values.

[deandreamatias]

I can reproduce this bug with the 10.0.0-dev.1 version