CODEWITHSUNDEEP
functiondart
Irfan Ganatra
Irfan Ganatra

Reputation: 1398

What is this known in dart?

Actually I am very much confused about this statement in dart and its (_) when does this required and what's difference with () ...What document should I read to make this concept clear like

TextField(
          onSubmitted: (_) {
            onsubmit();
          },

Upvotes: 0

Views: 36

Answers (1)

underwhelmingToaster
underwhelmingToaster

Reputation: 119

The onSubmitted callback function provides the submitted String in the text field as a value, so you can work with it and process it further in the function.

TextField(
  onSubmitted: (String value) { print("Submitted value: $value"); },
),

If you for whatever reason don't need this value, because you do not use it in the function, you can replace the String value with a _, so anyone who reads the code immediately knows that this value is not used.

You can't just leave it out like this:

TextField(
  onSubmitted: () { print("Doing something"); },
),

because you will get the error:

The argument type 'void Function()' can't be assigned to the parameter type 'void Function(String)?'.

So you just assign the value to this variable called _, which you are never going to use.

TextField(
      onSubmitted: (_) { print("Doing something"); },
),

Relevant section in the "Effective Dart" Guide

Upvotes: 2

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