FormBuilderDropdown assert error with initialValue

[KanybekMomukeyev]

Hi, thanks for sharing source codes!
But FormBuilderDropdown has a serious issue, every time when i am trying to update UI with new items, i have a following issue:

assert(items == null || items.isEmpty || value == null ||
              items.where((DropdownMenuItem<T> item) {
                return item.value == value;
              }).length == 1,
                "There should be exactly one item with [DropdownButton]'s value: "
                '$value. \n'
                'Either zero or 2 or more [DropdownMenuItem]s were detected '
                'with the same value',
              ),

I have allready removed FormBuilderDropdown, and directly used with same source code DropdownButton,
everything is worked like a charm, no problem. By me the problem of FormBuilderDropdown is "initialValue"
the "initialValue" may be not updating, i will try to detail research this issue, but issue is exsists 100%.

[andrewzakhartchouk]

Can you share your code of the FormBuilderDropdown that is causing the problem?

[Chappie74]

This seems to be occurring when the inital value of the dropdown is an empty string, and of course an empty string isn't part of my list for the dropdown. Setting this value to null rather than an empty string fixes the issue.





There are times when my initial value will be empty, because i am using the same form to add/edit. I would expect that if its an empty string it would show the default label text, but it throws the error instead.

[andrewzakhartchouk]

If you declare initialValue, then you can't leave it blank.
An easy fix is using a ternary operator ? to make sure initialValue always has a value. This includes having an empty/null value.

eg:
initialValue: data != null ? data : null

In the case of a FormBuilderDropdown, returning a null value works.
Something like a FormBuilderFilterChip however requires a list [].

[derolf]

Empty string might be a valid drop down value, so empty and null must be treated differently

[YouSour]

anyone can solve this problem ?

[deandreamatias]

This issue still happens in version 7.3.1

[tonypottera24]

Same issue even if the text is not null.

[Chappie74]

I've since opted out of using this. Found a much better and cleaner solution. Those familiar with angular may feel right at home.

https://pub.dev/packages/reactive_forms

[tonypottera24]

I just resolved my issue.
Assume we use int as the value of DropdownMenuItem
i.e.

items = [
DropdownMenuItem<int>(
      value: 100,
      child: Text('Apple'),
),
DropdownMenuItem<int>(
      value: 200,
      child: Text('Orange'),
)
]

The value of FormBuilderDropdown.initialValue must also be an int (100 or 200 or null).

[KanybekMomukeyev]

@Chappie74 why i should use ReactiveForm, what addition required feature it gives me?
I use Native from builder, and everything seems to be ok. Just for interesting.