I am new to the flutter and trying to understand it better.
FormFieldText(
label: "First Name",
initialValue:firstName,
validator: (value) {
if (value.isEmpty) return "Name must be provided";
return null;
},
onChanged: ((value) {
setState(() {
member?.firstName = value;
});
}),
),
3
Answers
Using the function setState forces the ui to rebuild which will show the changes to screen but not using it does nothing
If u want to change something in your screen with that value, you should put it in set state then user can see every change, it is usable in search bar, every word you type will search data base and show result. But if you Don’t use set state in on change, UI doesn’t show any thing until u refresh page. If you don’t want to show every changes in typing, you can use controller and save the value with a button in the last.
You can assign the value directly without
setState(), but then you don’t really require to use the onChanged property at all if you are not willing to display a text or run/callback a function while the user is typing.This property is more used if you need to build a feature that will constantly listen to a user’s input. It will callback a function everytime a user inputs a new character in the formfield.
In your example above, your function is to delete the variable
member?.firstNameand replace it with a new value everytime a user input something. This is useful to show a preview for the user as he is typing for example. You would just need a Text widget displaying somewhere in the screen likeText (member?.firstName.toString). It will visually display the same letters as what the user inputs 1 by 1.The onChanged property is useful for functions like
search, where you show suggestions while the user is typing. Another example is to display the number of characters like200/2000 words, and let the user know how much characters he has left before reaching max.