Flutter async form validation

Question

I am having the same problem as the poster in this question: flutter validate form asynchronously.

However, I'm having trouble implementing this and understand how the validation is working.

First, what does this code return? Does this return a boolean?

Future checkUser() async {
var user = await Firestore.instance
    .collection('users')
    .document(userNameController.text)
    .get();
return user.exists;

Second, what is the userNameValidator in this case? Is this a boolean?

new TextFormField(
              validator: (value) {
                return usernameValidator;
              },

Thanks, for the help.

checkUser() returns Future<bool>

Andrii Turkovskyi
– Andrii Turkovskyi

2018-11-01 15:50:00 +00:00
Commented Nov 1, 2018 at 15:50 — Andrii Turkovskyi
– Andrii Turkovskyi, Commented Nov 1, 2018 at 15:50

Zroq · Accepted Answer · 2018-11-01 18:53:50Z

2

The method checkUser will begin a call to Firebase. The await keyword is telling the compiler that we need the output of that call, but there is no need to block everything else from running. After the call has been made, the function will return a bool indicating if the given user exists.

On the other question checkUser is called via the onPressed call which waits for a return value and assigns it to the usernameValidator variable - therefore making it a bool.

edited Nov 1, 2018 at 18:53

answered Nov 1, 2018 at 16:04

Zroq

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4 Comments

PJQuakJag Over a year ago

Thanks so much for your help Zroq. The problem is that the validator as written above is throwing an error "The return type bool isn't a String as defined by anonymous closure". Any idea what is causing this?

PJQuakJag Over a year ago

I actually think my question is how are you initializing the userNameValidator? After the CheckUser function, how is that set to true or false?

Zroq Over a year ago

You should initialize the variable to false after the State subclass is defined. Like the _isFavorited variable in this example - flutter.io/tutorials/interactive/#step-3

PJQuakJag Over a year ago

Thanks for this, I realized I wasn't using the controller properly to validate the text. Still feeling like a novice with this stuff, but appreciate your help greatly!

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