How to emptying hint text when focus in TextFormField Flutter - flutter

Question

I want to make the hint text in TextFormField disappear when the field focused. But the hint text won't disappear until I insert a character in the field. I did the following. How can I make the hint text disappear when the field focused? Thanks!
Container buildTextField(bool isObscure, TextEditingController textEditingController, String hintText, bool onlyNumber) {
return Container(
width: double.infinity,
height: 60,
color: MyColors.primary,
alignment: Alignment.center,
child: Padding(
padding: EdgeInsets.only(left: 15, right: 10),
child: TextFormField(
textAlign: TextAlign.center,
keyboardType: onlyNumber ? TextInputType.number : TextInputType.text,
decoration: InputDecoration(
hintText: hintText,
hintStyle: TextStyle(
color: Colors.white,
fontWeight: FontWeight.w600,
),
border: InputBorder.none,
),
style: TextStyle(
color: Colors.white,
decoration: TextDecoration.none,
fontWeight: FontWeight.w600,
),
obscureText: isObscure,
controller: textEditingController,
),
),
);
}

Answer 1

You probably have to add a listener to listen to focus changes:
FocusNode myFocusNode = FocusNode();
myFocusNode.addListener( () {
setState((){});
}
And then, inside your InputDecoration you update the value:
hintText: myFocusNode.hasFocus ? hintText : ''

Answer 2

Use labelText instead,
TextFormField(
controller: fullNameController,
validator: (value) {
if (value.trim().isEmpty) {
return Lang.enterFullName;
}
return null;
},
decoration: InputDecoration(
labelText: Lang.fullName,
prefixIcon: Icon(Icons.person),
),
keyboardType: TextInputType.text,
textInputAction: TextInputAction.next,
),