How do I use Dart extension functions?

by

There is an official video by the Flutter team about extension methods now.

Static extension members

Here is an intuitive example of how extension methods work:

extension FancyNum on num {
  num plus(num other) => this + other;

  num times(num other) => this * other;
}

I simply extend num here and add methods to the class. This could be used like this:

print(5.plus(3)); // Equal to "5 + 3".
print(5.times(8)); // Equal to "5 * 8".
print(2.plus(1).times(3)); // Equal to "(2 + 1) * 3".

Note that the name FancyNum is optional and the following is valid too:

extension on num {}

When you use your extension in another file, you must give it a name.

The extension above will make use of implicit extension member invocations as you do not have to explicitly declare your num to be a FancyNum.

You can also explicitly declare your extension, but this is not needed in most cases:

print(FancyNum(1).plus(2));

Flex childCount

The desired behavior from the question can be achieved by extending Row or Column, or even better: you can extend Flex, which is the super class of Row and Column:

extension ExtendedFlex on Flex {
  int get childCount => this.children.length;
}

this. can also be omitted if children is not defined in the current lexical scope of childCount, which means that => children.length is also valid.

With this static extension of Flex imported, you can call it on any Flex, i.e. also on every Row and Column.
Row(children: const [Text('one'), Text('two')]).childCount will evaluate to 2.

More Related Contents:

  1. How to upload images to server in Flutter?
  2. How to show/hide widgets programmatically in Flutter
  3. What is Null Safety in Dart?
  4. Passing data to StatefulWidget and accessing it in it’s state in Flutter
  5. Force Flutter navigator to reload state when popping
  6. How to use conditional statement within child attribute of a Flutter Widget (Center Widget)
  7. Flutter: Unhandled Exception: ServicesBinding.defaultBinaryMessenger was accessed before the binding was initialized
  8. Flutter: Find the number of days between two dates
  9. How to create GridView Layout in Flutter
  10. Scroll Function In Flutter Web
  11. Flutter: There should be exactly one item with [DropdownButton]’s value
  12. How to open DropdownButton when other widget is tapped, in Flutter?
  13. How to replace deprecated List [duplicate]
  14. Flutter: Filter list as per some condition [closed]
  15. How to listen focus change in flutter?
  16. Flutter: Remove padding in buttons – FlatButton, ElevatedButton, OutlinedButton
  17. Understanding ” ! ” Bang Operator in dart
  18. error in getting data from api in flutter
  19. How can I navigate between 2 classes, one of them requires passing data? in flutter
  20. How can I layout widgets based on the size of the parent?
  21. Why do we use the dispose() method in Flutter Dart code?
  22. What is a NoSuchMethodError and how do I fix it?
  23. Could not open settings generic class cache for settings file ‘
  24. Flutter Zoomable Widget
  25. How to run code after some delay in Flutter?
  26. How to shift focus to the next TextField in Flutter?
  27. The parameter can’t have a value of ‘null’ because of its type in Dart
  28. How to remove hash (#) from URL in Flutter web
  29. Flutter Navigation pop to index 1
  30. How can I detect if my Flutter app is running in the web?

Leave a Comment