textformfield - Flutter Forms Validation on change

Question

Hey maybe someone can help me to figure out how implement proper form validation in Flutter.

So basically in InputDecoration we have

decoration: InputDecoration(
            // focusedBorder: OutlineInputBorder(
            //   borderSide: BorderSide(color: Colors.white, width: 3.0),
            // ),
            errorBorder: OutlineInputBorder(
              borderSide: BorderSide(color: Colors.red, width: 3.0),
            ),
            enabledBorder: OutlineInputBorder(
              borderSide: BorderSide(color: Colors.greenAccent, width: 3.0),
            ),
            focusedErrorBorder: OutlineInputBorder(
              borderSide: BorderSide(color: Colors.red, width: 3.0),
            ),
            border: OutlineInputBorder(
              borderSide: BorderSide(color: Colors.white, width: 3.0),
            ),
            labelText: 'Email',
            // errorText: !_isValid ? "Invalid Email" : null,
            labelStyle: TextStyle(color: Colors.white),
            prefixIcon: Padding(
              padding: const EdgeInsets.only(top: 10, left: 13),
              child: FaIcon(
                FontAwesomeIcons.at,
                color: Colors.white,
                size: 25,
              ),
            ),
          ),

So problem is that I can't understand how to set regular border on form when it is not touched , than when it's touched , on each input it has to validate input and set error if not valid. I know that on TextFormField i can pass onchange function and do the validation

onChanged: (value) {
            if (value.isEmpty || !value.contains('@')) {
              setState(() {
                 _isValid = false;
              });
              print('invalid');
            } else {
              setState(() {
                 _isValid = true;
              });
            }

with this approach I have issue, first I have to set initial value of _isValid and in this case when form is opened and not touched it's already are enabled or with error depending on initial value of _isValid.

I came from web and worked with Angular and there we have reactive forms, maybe someone explain how to achieve similar behavior in flutter?

question from:https://stackoverflow.com/questions/65869808/flutter-forms-validation-on-change

Answer 1

validator: (value) { if (enter code herevalue.isEmpty || !value.contains('@')) { return "incorrect format"; } 1 create a global form key 2 warp your widget inside a Form widget 3 pass your global key to the key parameter of your Form widget 4 and use this line on button click 5 _yourFormKey.CurrentState.Validate();