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Why use Reactive Forms in Flutter?

Joan Pablo on July 20, 2020

Haven't you ever felt that getting data from a Form, validating a field, or even disabling the submit button is tedious and full of boiler...

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Rinzin Wangchuk • Oct 18 '20 • Edited

Thanks for the package. I use angular at work and flutter for my personal projects. I was thinking of making sth like form builder for flutter and found that there was already one🥳🥳🥳. Any way I can contribute to the package although I am not a seasoned developer yet?.

Joan Pablo • Oct 18 '20

Hi Rinzin,

Thank you for your comments. You are welcome to contribute to the package. Your experience is not a problem, together we can improve the package as much as necessary.

John Lester D. Necesito • Oct 22 '20 • Edited

Hello may I ask, how can I convert the date and time format after I select date and time?
like 12-hour format (12:01 AM) for time and YYYY-MM-D for date

Lastly, how can I add validation messages to a reactive textfield v7.0.0+

Joan Pablo • Nov 4 '20 • Edited

Hi John Lester,

You can add a ControlValueAccessor to the reactive text field with the format.
In the Wiki you have an example of how to do that.

To add a validation message you just supply the validationMessages callback method in ReactiveTextField and return a Map with the messages:

ReactiveTextField(
   formControlName: 'email',
   validationMessages: (control) => {
      ValidationMessage.required: 'The email must not be empty',
      ValidationMessage.email: 'The email value must be a valid email'
   },
),

ctechdev • Jan 16 '21

Could you provide a working code example for ReactiveDatePicker?
I am trying but I always get an error "Invalid date format".
My code:
....
var last = DateTime.now ();
var firstDate= DateTime.parse ('2021-01-16');
.....
ReactiveDatePicker (
formControlName: 'birthDate',
firstDate: firstDate,
lastDate: last,
builder: (context, picker, child) {
return IconButton (
onPressed: picker.showPicker,
icon: Icon (Icons.date_range));
}),

Joan Pablo • Apr 14 '21

Hi @ctechdev ,

I have released new versions of the package (v10.2.0). Have you test it? Have you created an issue in the github repo?

Harish Kumar • May 22 '21

Hi John

Your library is life saver :D
One question I wanted to ask is if I wanted to change the decoration around the text fields, how should I do that? like the color of fields and colors of field names that show up the field when a text field is in focus. I understand it is taking defaults from the theme of app but if I wanted to do specific decoration for the text fields how should it be done.

ctechdev • Dec 4 '20

Hi, I would like to use multiple reactive forms. I created a tabbarview with 6 different tabs and each view has a different reactive form. At the top of the appbar I created a button to save the data of all the forms in an Entry object. How can I implement this function without global keys using a provider that collects the data entered in all the tabs? Thanks in advance.

Joan Pablo • Dec 10 '20

Hi ctechdev,

A simple way to create a wizard is for example to wrap all the widget within a ReactiveForm and each TabBarView can contains a ReactiveForm to collect specific data.

John Lester D. Necesito • Sep 28 '20

Hi! Can I ask if it is possible to add a dynamic reactive text field to a form?

Joan Pablo • Sep 29 '20

Hi Jhon,

Right now there is a method FormGroup.addAll() that receives a collection of FormControls and append them as children. But maybe is not what you're asking for.

So I will add that as an issue in the GitHub repo and I will bring the possibility to add a single control FormGroup.add() and that action will trigger an event of type FormControlCollection.collectionChanges.

I will release it in next version.

Thanks again.

Joan Pablo • Oct 1 '20

Hi John Lester,

I've just released v6.0.0.

In this version like in the previous one, you can add controls to a group with the method FormGroup.addAll(). This method receives a Map of controls as arguments. In this version the disrty/pristine state of the group is updated and it also triggers the onCollectionChanges event.

John Lester D. Necesito • Sep 2 '20

Hi may I ask how did you put an initial value coming from firebase?

Joan Pablo • Sep 3 '20

Hi John,

You can just set the value to a control as soon as you get it or you can reset the control to and initial value (release 4.0.0)

// `fb.group` is just a syntax sugar, you can simple use FormGroup if you want.
final form = fb.group({
    'name': 'some init value'
});

_executeFirebaseAsyncMethod().then((newValue) {
    // sets the control init value
    form.value = {'name': newValue};
});

final form = fb.group({
    'name': 'some init value'
});

_executeFirebaseAsyncMethod().then((newValue) {
    // resets the control to untouched and set init value
    form.reset(value: {'name': newValue});
});

John Lester D. Necesito • Sep 3 '20 • Edited

One more thing it is possible to untouch a reactiveTextfield upon editing?

For example, I have an async validation that will check if an email is existing then, when I go to the editing profile screen it automatically validates the value of that field which I don't like. I want to validate it when the value of that field changes.

Lastly, is it possible to add an additional parameter to custom validator?

Joan Pablo • Sep 3 '20 • Edited

Hello John,

Async validators executes after every Sync validator executes without validation errors. That means that if you add for example Validators.required or Validators.email to your ReactiveTextField only when those validators marks the input as valid then the Async Validator excecutes.

But I think you are right about the issue, I will release soon a new version that let you ask inside your validator if the control is "dirty" or not, so you can check if the value has changed or not and request the server in the async validator. Mean while you can implement a workaround by asking inside your async validator if the value of the FormControl is different from the value of your model.

About the Second question, yes you can create a custom validator with additional params, there are two ways of doing this:
1-) Create a function/method that receives arguments and returns a ValidatorFunction. An example of this is the Validators.mustMatch. You can check the README.md.
2-) Extend Validator class.

Creating a function/method

// controlName and matchingControlName as additional arguments
Map<String, dynamic> _mustMatch(String controlName, String matchingControlName) {
  // returns a ValidatorFunction
  return (AbstractControl control) {
    final form = control as FormGroup;

    final formControl = form.control(controlName);
    final matchingFormControl = form.control(matchingControlName);

    if (formControl.value != matchingFormControl.value) {
      matchingFormControl.addError({'mustMatch': true});

      // force messages to show up as soon as possible
      matchingFormControl.touch(); 
    } else {
      matchingFormControl.setErrors({});
    }

    return null;
  };
}

Usage

final form = fb.group({
   'password': ['', Validators.required],
   'passwordConfirmation': ['', Validators.required],
}, [_mustMatch('password', 'passwordConfirmation')]);

Extend Validator class (this is the implementation of Validators.pattern)

/// Validator that requires the control's value to match a regex pattern.
class PatternValidator extends Validator {
  final Pattern pattern;

  /// Constructs an instance of [PatternValidator].
  ///
  /// The [pattern] argument must not be null.
  PatternValidator(this.pattern) : assert(pattern != null);

  @override
  Map<String, dynamic> validate(AbstractControl control) {
    RegExp regex = new RegExp(this.pattern);
    return (control.value == null ||
            control.value == '' ||
            regex.hasMatch(control.value))
        ? null
        : {
            ValidationMessage.pattern: {
              'requiredPattern': this.pattern.toString(),
              'actualValue': control.value,
            }
          };
  }
}

Usage

final form = fb.group({
   'email': ['', PatternValidator('some pattern').validate],
});

Validators.mustMatch and Validators.pattern are already included in Reactive Forms so you don't have to implement them, the above code are just examples to get the idea.

John Lester D. Necesito • Sep 4 '20 • Edited

Thank you so much for your help! I will look forward to the next version of your package! ❤

John Lester D. Necesito • Sep 3 '20

That's great! Thank you so much! 💞

Shaher Yar • Apr 18 '23

Hi, Joan Pablo
Hope you are doing well. I have a question regard reactive forms fields. I have an api in the response of api i got different forms information how i can impliment with this using reactive forms fields?

John Lester D. Necesito • Jan 7 '21 • Edited

Hi Joan,

May I ask how to dynamically add and remove validator in a specific formControl.

For example,

imgur.com/a/ERz7wGa

Joan Pablo • Apr 14 '21

Hi John,

In the recently version 10.2.0 you can add validators dynamically.