searchableDropDown: setting selectedItem programmatically does not update UI

[dmoeyers]

Hello,

when updating the selectedItem of a searchableDropDown programmatically

eg via
_formKey.currentState.fields['dropdown'].didChange(newValue);

the state of the form is updated but the previously selected item is still shown in the UI.

[dmoeyers]

Hi Danvick,

I have been looking at this some more and might have found a possible solution (however I am quite new at this so it's just a suggestion):

In DropdownSearchState<T> there's a function that can be used to change the value programmatically: void changeSelectedItem(T selectedItem)

If we then add final dropdownSearchKey = GlobalKey<dropdown_search.DropdownSearchState<T>>(); to _FormBuilderSearchableDropdownState<T>, we can add this key to the dropdown_search created in the builder function

dropdown_search.DropdownSearch<T>(
               key: state.dropdownSearchKey,

Next we can use the function mentioned above in _FormBuilderSearchableDropdownState<T>, either in the didChange override or in a separate method

class _FormBuilderSearchableDropdownState<T>
    extends FormBuilderFieldState<FormBuilderSearchableDropdown<T>, T> {
  final dropdownSearchKey = GlobalKey<dropdown_search.DropdownSearchState<T>>();

  @override
  void didChange(T value) {
    super.didChange(value);
    dropdownSearchKey.currentState.changeSelectedItem(value);
  }
  // void changeSelectedItem(T value) {
  //   dropdownSearchKey.currentState.changeSelectedItem(value);
  // }
}

The didChange has the advantage of keeping the interface uniform (to programmatically change values), but this creates an infinite loop because in the onChanged callback of the dropdown_search (called by the changeSelectedItem), we call back didChange... This loop can be broken by checking whether the value has really changed

onChanged: (val) {
                  state.requestFocus();
                  if(state.value!=val)
                    state.didChange(val); // todo changed
                },

The new separate method does not have this drawback, but then you would need to cast FormBuilderFieldState to _FormBuilderSearchableDropdownState every time or maybe change the interface so didChange is used internally to respond to change and a new function to programmatically change fields would have to be added...

Food for thought!