Flutter - Async Validator of TextFormField

Question

In my app the user has to insert a name in the textformfield. While the user is writing a query should be made to the database, that controls if the name already exists. This query returns the number of how many times the name exists. Till now I am able to make it when I press a button.

This is the function that returns the count of the names:

checkRecipe(String name) async{
    await db.create();
    int count = await db.checkRecipe(name);
    print("Count: "+count.toString());
    if(count > 0) return "Exists";
  }

And this is the TextFormField, which should be validated async:

TextField(
    controller: recipeDescription,
    decoration: InputDecoration(
       hintText: "Beschreibe dein Rezept..."
    ),
    keyboardType: TextInputType.multiline,
    maxLines: null,
    maxLength: 75,
    validator: (text) async{ //Returns an error
       int count = await checkRecipe(text);
       if (count > 0) return "Exists";
    },
 )

The error of the code is:

The argument type Future can't be assigned to the parameter type String

I do know what the error means. But I do not know how to work around could look like. It would be awesome if somebody could help me.

I have found a solution.

My Code looks now like this:

//My TextFormField validator
validator: (value) => checkRecipe(value) ? "Name already taken" : null,

//the function
  checkRecipe<bool>(String name) {
    bool _recExist = false;
    db.create().then((nothing){
      db.checkRecipe(name).then((val){
        if(val > 0) {
          setState(() {
            _recExist = true;
          });
        } else {          
          setState(() {
            _recExist = false;
          });
        }
      });
    });
    return _recExist;
  }

[This](https://stackoverflow.com/questions/52584520/flutter-firebase-validation-of-form-field-inputs?rq=1) is the workaround, that did the job for me. — , Nov 07 '18 at 17:35
Possible duplicate of [Flutter firebase validation of form field inputs](https://stackoverflow.com/questions/52584520/flutter-firebase-validation-of-form-field-inputs) — mirkancal, Aug 03 '19 at 14:57
If you came up with your own answer, please add an answer to your question and mark it as correct. This will help other users. — João Soares, Mar 09 '20 at 14:46

score 6 · Answer 1 · answered May 01 '20 at 14:04

6

Perhaps you could run your async check using the onChange handler and set a local variable to store the result.

Something like:

TextFormField(
  controller: recipeDescription,
  decoration: InputDecoration(hintText: "Beschreibe dein Rezept..."),
  keyboardType: TextInputType.multiline,
  maxLines: null,
  maxLength: 75,
  onChanged: (text) async {
    final check = await checkRecipe(text);
    setState(() => hasRecipe = check);
  },
  validator: (_) => (hasRecipe) ? "Exists" : null,
)

answered May 01 '20 at 14:04

Your Friend Ken

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Would this work if a user types quick and the checkRecipe function has a delay? Also, would the `await` block the UI? – Sebastian Roth Jul 23 '20 at 11:20
This is the best answer i found for async validation – Moshe Yamini Mar 27 '22 at 21:45

score 2 · Answer 2 · answered May 05 '21 at 10:39

I wanted a same behavior for one of our apps and ended up writing a widget (which I recently published to pub.dev).

AsyncTextFormField(
    controller: controller,
    validationDebounce: Duration(milliseconds: 500),
    validator: isValidPasscode,
    hintText: 'Enter the Passcode')

You can pass in a Future<bool> function for the validator and set an interval before the text is sent to server.

The code is available on github.

Flutter - Async Validator of TextFormField

I have found a solution.

2 Answers2

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