FormBuilderDropdown assertion bug

[kasangasj]

I have two FormBuilderDropdowns which depend on each other, one is for categories and the other is for sub categories. When I change category then sub categories are loaded. This works fine as long as there is no selected subcategory but if I select a category, then select one of its sub categories it throws the following exception:

════════ Exception caught by widgets library ═══════════════════════════════════════════════════════
The following assertion was thrown building FormField-[LabeledGlobalKey<FormFieldState>#3f353](dirty, dependencies: [_FormScope], state: FormFieldState#68c0b):
There should be exactly one item with [DropdownButton]'s value: {id: 3ebc51ba390511eab6a06b0f2e982c39, name: Self Referral, code: 0002, category_id: 3eb329ef390511eab6a029aa47757af9, category_name: User Fee, active: 1, deleted: 0}.
Either zero or 2 or more [DropdownMenuItem]s were detected with the same value
'package:flutter/src/material/dropdown.dart':
Failed assertion: line 805 pos 15: 'items == null || items.isEmpty || value == null ||
items.where((DropdownMenuItem item) {
return item.value == value;
}).length == 1'

Either the assertion indicates an error in the framework itself, or we should provide substantially more information in this error message to help you determine and fix the underlying cause.
In either case, please report this assertion by filing a bug on GitHub:
https://github.com/flutter/flutter/issues/new?template=BUG.md

The relevant error-causing widget was:
FormBuilderDropdown-[<'visit_subcategory'>] file:///home/kasanga/AndroidStudioProjects/mobile/lib/dialogs/client_dialog.dart:119:19
When the exception was thrown, this was the stack:
#2 new DropdownButton (package:flutter/src/material/dropdown.dart:805:15)
#3 _FormBuilderDropdownState.build. (package:flutter_form_builder/src/fields/form_builder_dropdown.dart:118:26)
#4 FormFieldState.build (package:flutter/src/widgets/form.dart)
#5 StatefulElement.build (package:flutter/src/widgets/framework.dart:4334:27)
#6 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4223:15)
...
═════════════════════

How can I clear the subcategories drop down's value when the categories drop down value changes?

[maelfosso]

Hello,

I have the same of error too

List<DropdownMenuItem> items = this.kv.entries
        .map((entry) => DropdownMenuItem(
            value: entry.key,
            child: Text(entry.value)
      )).toList();
return FormBuilderDropdown(
      attribute: this.id,
      decoration: InputDecoration(labelText: this.title),
      // initialValue: value,
      // initialValue: ,
      hint: Text('Select a choice'),
      items: items
    );

I don't know what is the problem.

I set a FormBuilder into a PageView. When It appear at the first time, everything is OK. But if I don't fill it and move forward then I swipe back there, I got that error.

Here is the FormBuilder initialization

return FormBuilder(
      key: _fbKey,
      initialValue: data.map((key, value) {
        KindType p = this.ktypes.firstWhere((k) => k.id == key);
        switch (p.job) {
          case 'student':
            return MapEntry(key, value);
          case 'teacher':
            return MapEntry(key, value);
          case 'administrator':
            return MapEntry(key, DateTime.tryParse(value));
          case 'family':
            return MapEntry(key, value);
          default:
            return null; 
        }
      }),
      autovalidate: true,
      child: Column(
        children: this.ktypes.map((q) => q.build()).toList()
      )
    );

Any clues for me, please?

[danvick]

Hi @kasangasj / @maelfosso,
Flutter expects that the value that's selected on the dropdown button is part of the items to choose from.

Note that if you update the list of DropdownMenuItems that condition may not continue to hold - thus the assertion error.

Therefore if you change the items mid-flight remember to set the value to null. Another alternative is to ignore (though not advisable) because assertion errors don't appear in production.

Sorry for the late response, I thought I had addressed this issue since it's actually a duplicate.

[2shrestha22]

Therefore if you change the items mid-flight remember to set the value to null. Another alternative is to ignore (though not advisable) because assertion errors don't appear in production.

Hi @danvick How to set the value to null, there is not value field like in default dropdownbutton?

[fuzes]

Therefore if you change the items mid-flight remember to set the value to null. Another alternative is to ignore (though not advisable) because assertion errors don't appear in production.

Hi @danvick How to set the value to null, there is not value field like in default dropdownbutton?

Hi @2shrestha22 Did you find a way to change it to null or default value?

[2shrestha22]

I stopped using the package.

[dev-thinks]

probably this might work, @fuzes

formkey.currentState.fields['yourdropdownfieldname'].didChange(null);

[miguelflores1993]

With the official flutter dropdown this does not happen, fix it or I will stop using the library

[deandreamatias]

Fix it or I will stop using the library

Hi @miguelflores1993 . This is a open source package about forms. If you can contribute to solve this problem, will be awesome. If not, we do not seen a problem if you use another package for implement your forms.
The open source does not feel threatened because you stop using something

[gvsakhil]

This issue still exists in 2025... Hope we get a fix soon :(