CODEWITHSUNDEEP
flutterdart
user13427040
user13427040

Reputation:

I can't understand this line in dart

class SharedPreferencesDemo extends StatefulWidget {
  SharedPreferencesDemo({Key key}) : super(key: key); <-------- This line

  @override
  SharedPreferencesDemoState createState() => SharedPreferencesDemoState();
}

I can understand the part before and after the colon, but what does the colon at the middle mean? I am talking about the colon sitting in between those two parts of the line. What does the line ultimately mean?

Upvotes: 1

Views: 197

Answers (1)

TheMisir
TheMisir

Reputation: 4279

This is called constructor. Used to create new instance of class by calling new SharedPreferencesDemo() or just SharedPreferencesDemo().

SharedPreferencesDemo({Key key}) : super(key: key);

Here's explanation of each part.

SharedPreferencesDemo - constructor name
(...) - constructor arguments
{Key key} - optional named arguments
: - initializer list, used to call super or initialize variables including final ones
super - calls parent constructor (StatefulWidget.StatefulWidget)
key: key - sets value of optional argument [key] for parent constructor

Initializer list is used to initialize final variables or call constructor with specified arguments. Here's another example:

class AuthClient {
  AuthClient({ String username, String password }) :
    _token = '$username:$password';

  final String _token;
}

Upvotes: 1

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