Validator for a Custom InputTextField - flutter

Question

I have created my own custom textinputfield, everything do has come up well but the thing is how to give that a validator upon the button click?
This is my custom inputfield,
class CustomInputField extends StatelessWidget {
bool _validate = false;
Icon fieldIcon;
String hintText;
TextInputType textType;
CustomInputField(this.fieldIcon, this.hintText, this.textType);
#override
Widget build(BuildContext context) {
return Container(
width: 300,
child: Material(
elevation: 5.0,
borderRadius: BorderRadius.all(Radius.circular(10.0)),
color: Colors.deepOrange,
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Padding(
padding: const EdgeInsets.all(12.0),
child: fieldIcon,
),
Container(
decoration: BoxDecoration(
color: Colors.white,
borderRadius: BorderRadius.only(topRight: Radius.circular(10.0), bottomRight: Radius.circular(10.0)),
),
width: 250,
child: Padding(
padding: const EdgeInsets.all(8.0),
child: TextField(
controller: _text,
decoration: InputDecoration(
border: InputBorder.none,
hintText: hintText,
fillColor: Colors.white,
errorText: _validate? 'Value can\'t be empty' : null,
filled: true,
),
keyboardType: textType,
style: TextStyle(
fontSize: 15.0,
color: Colors.black,
),
),
),
),
],
)
),
);
}
}
And this is how I'm calling that in different pages
CustomInputField(
Icon(
Icons.lock,
color: Colors.white,
),
'Password',
TextInputType.visiblePassword),
So upon click of the button if the text field is empty, i need to give in the errorText, so could anyone help me out?

Answer 1

You need to do a couple of things.
Create a GlobalKey type FormState for your Stateful Widget.
GlobalKey<FormState> _formKey = GlobalKey<FormState>();
Create a TextFormField with a validator and onSave callback.
Form(
key: _formKey, //Give you form it's key.
child: Column(
children: <Widget>[
TextFormField(
validator: (input) {
if (input.isEmpty) { //Here I check if the field data is empty.
return "Field cannot be empty.;
}
},
//Update what ever variable you want with the validated data.
//Here I picked a variable named foo.
onSaved: (input) => foo = input,
],
),
),
Make a button that uses the _formKey to call the validate function and save function.
RaisedButton(
child: Text("Do Something"),
onPressed: () {
//Validate will run on the TextFormField and return the error provided.
if (_formKey.currentState.validate()) {
_formKey.currentState.save(); //If validated, we will update our foo variable.
}
},
),