Show element as soon as form is valid - flutter

Question

I'm trying to show element as soon as my form becomes valid. According to flutter docs I need to use _formKey.currentState.validate() but in the docs it is used on button click, while I'm trying to use it to show/hide element.
Working code (as used in flutter tutorial)
return Form(
key: _formKey,
child: Column(
children: [
TextFormField(
autovalidate: true,
validator: validateName,
),
RaisedButton(
onPressed: () => _formKey.currentState.validate()
? print('valid')
: print('not valid'))
My code with (INVALID MEMER OF NULL: 'validate) error
return Form(
key: _formKey,
child: Column(
children: [
TextFormField(
autovalidate: true,
validator: validateName,
),
_formKey.currentState.validate()
? Container(child: Text('valid'))
: Container(child: Text('not valid'))

Answer 1

The best answer for you will be to use TextFormField onChanged, which is of type ValueChanged, which keeps track of the changes you make in your TextFormField
Advantage
You will be able to keep a track of the text changes, and show/hide content based upon that
Disadvantage
Each TextField should be maintaining the bool for the different TextField to keep a track of the items
It is like a workaround, so can use in this way. I am using a single TextFormField to show how it works, you can then work on ther TextFormField and get it up and running.
FINAL SOLUTION
bool isValid = false;
final TextEditingController _controller = new TextEditingController();
Column(
crossAxisAlignment: CrossAxisAlignment.start,
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
TextFormField(
decoration: InputDecoration(hintText: 'Enter your data'),
controller: _controller,
onChanged: (String val){
setState((){
if(val.length >= 4) isValid = true;
else isValid = false;
});
}
),
SizedBox(height: 20.0),
isValid ? Text('Valid String', textAlign: TextAlign.center) : Text('Name must be more than 3 character', textAlign: TextAlign.center)
]
)
SOLUTION: For various, you must check whether all the different bools are true or not, based upon that, you can show/hide the data.
RESULT
Let me know if is of any use to you :)