Flutter, late keyword with declaration

Question

late TextEditingController _controller = TextEditingController();
late String someString = "someString";

TextEditingController _controller = TextEditingController();
String someString = "someString";

Are they still different? or exactly same??? on any circumstances (in performances)

late to field means that the field will be initialized when you use it for the first time. — Jahidul Islam, Sep 24 '21 at 09:50
@JahidulIslam So in the above case, should I use it or not?(there is any benefit?) I know it's good to use it when there is no value assignment. — dontknowhy, Sep 24 '21 at 09:53
@JahidulIslam Null safety is not required if variable declaration and value assignment are made at the same time. But do you think it is right to use "late keyword" nonetheless? — dontknowhy, Sep 24 '21 at 09:56
@JahidulIslam not required means "there is no difference at all in performance"? — dontknowhy, Sep 24 '21 at 09:58
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/237446/discussion-between-jahidul-islam-and-paem-kacit). — Jahidul Islam, Sep 24 '21 at 10:10
If you don't need to use `late`, don't use it. `late` variables have runtime checks to determine if they've been initialized. — jamesdlin, Sep 24 '21 at 14:53
See https://dart.dev/null-safety/understanding-null-safetyhttps://dart.dev/null-safety/understanding-null-safety. — Md. Yeasin Sheikh, Sep 24 '21 at 10:28
`late` is a nice keyword to allow lazy loading initialization, i can get behind that :) — sonjz, May 31 '23 at 16:24

krishnaacharyaa · Answer 1 · 2023-04-25T17:26:06.850

The below statements

late TextEditingController _controller = TextEditingController();
TextEditingController _controller = TextEditingController();

Are both same?

It is just like saying var TextEditingController _controller = TextEditingController();

When to use late ?

In some instances you would not know the value of a variable initially. And the value could possibly be null.

As dart is null safe you have to either use ? or late keyword

var someString;  Flutter doesn't allow this

To overcome this you do either of the following:

   var someString?;  Saying flutter the value is nullable. So that flutter would warn you when you access this variable
   late someString;  You are assuring flutter that you will initialize this in your code before its used.

score 2 · Answer 2 · answered Nov 27 '22 at 09:30

Declare variables that will be initialised later by using the late keyword.

late data_type variable_name;

When a late variable is used before it has been initialised, this error happens. You must keep in mind that although you used some variables or data that were marked as "late," their values were not altered or saved beforehand.

late String name;
@override
Widget build(BuildContext context) {
  return Scaffold(
    body: Text(name)
    //runtime error: 
    //LateInitializationError: Field 'name' has not been initialized.
  );
}

This signifies that the variable name has no value at this time; it will be initialised in the Future. We have used this variable in the Text() widget without first initialising it.

To fix this problem

late String name;

@override
void initState() {
  name = "Flutter Campus";
  super.initState();
}

@override
Widget build(BuildContext context) {
  return Scaffold(
    body: Text(name)
  );
}

score 1 · Answer 3 · answered Jul 21 '23 at 11:28

Scenario 1

late TextEditingController _controller = TextEditingController();

Lazy Initialization:

when you add late before variable declaration then this will initialized when first it will be used.

Scenario 2

late String name;

use of late keyword to make variable non nullable and to initialize variable later so compiler will not give error of non-nullable instance field must be initialized. when we add late keyword we promise that we will initialize this variable before we use it.

Flutter, late keyword with declaration

3 Answers3

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