How to work with Data Model class instead of just Strings?

[aytunch]

I get a list of Products from my backend and I convert the JSON objects in to a Product Model Class and keep them in a List.

Product class has lets say an id field and a name field.
I can display suggestions with product.name however i get an error when i click on the suggestion. Product is not a subclass of String. How can i get the whole product object when user clicks on a suggestion?

[aytunch]

Similar issue is opened in flutter_form_builder which is dependent in this great package

[deakjahn]

suggestionsCallback˛ expects a FutureOr<List<T>>, not a FutureOr<List<String>>. Likewise, onSuggestionSelected passes a T. I have no problems using the package with non-String items.

But I did receive error messages that looked very much like the ones you mention some time ago until I realized that .where(), the filter I used to create my suggestion list, has lazy evaluation and that's not what the widget likes. Isn't this by any chance your problem, too? The solution is easy, just use toList() at the end to evaluate the iterable to a real list. This is a Dart feature, actually, nothing to do with the widget.

[aytunch]

@deakjahn Thanks for your input, can you please share a code snippet so I can try and see if it works. I am still having problems:/

[deakjahn]

I have a POCO, very simple:

class Part {
  String name;
  String number;
  List<int> groups;
  List<int> pages;

  Part({this.name, this.number, this.groups, this.pages});
}

When I create the widget, I just use this type:

Widget _buildSearch() => TypeAheadField<Part>(
      itemBuilder: (context, item) => _buildSuggestion(context, item),
      suggestionsCallback: (pattern) async => await _getMatches(pattern),
      onSuggestionSelected: (suggestion) => _showPart(suggestion),
    );

This calls my functions but there is nothing special about them, _buildSuggestion() just returns a Row with the part name and number. The more interesting one will be _getMatches:

Future<List> _getMatches(String query) async {
  if (query.isEmpty)
    return <Part>[];
  else
    return _parts
      .where((item) => item.name.toLowerCase().contains(query.toLowerCase()))
      .take(20)
      .toList();
}

I return a maximum of 20 matching items. And when I return, I don't just return the result of take() but convert it to a list, forcing the otherwise lazy evaluation to actually happen and all list elements to be ready and finished. I think that's what you missed.

[fabiangruss]

Hi @aytunch ,

I do have the same problem when clicking on a suggestion, which is backed by a custom Model class. Displaying the list of suggestions based on the model is working fine, but clicking on the suggestion always throws the exception "... is not a subtype of type 'String'. Did you solve that issue and if so, how?

Could you post the function behind your onSuggestionSelected @deakjahn ?
That would be a great help. I can't seem to find my error here.

Thank you!

[deakjahn]

I could but you won't find anything interesting there:

void _showPart(Part part) {
  if (part != null)
    // simply use part
    setState(() {
      _name = part.name;
    });
}

Just as you would expect.

If I go in and change the return type of _getMatches() to Future<Iterable> and omit the toList() at the end, I get a similar message but not the same: TakeIterable is not a subtype of type FutureOr<List>. Which is, actually, understandable. But nothing abot Strings. Are you sure you specified your type wherever the generic T is expecting it?