List use of double dot (.) in dart?

.. is known as cascade notation. It allows you to not repeat the same target if you want to call several methods on the same object.

List list = [];
list.add(color1);
list.add(color2);
list.add(color3);
list.add(color4);

// with cascade

List list = [];
list
  ..add(color1)
  ..add(color2)
  ..add(color3)
  ..add(color4);

It's the cascade operator of Dart

var l1 = new List<int>()..add(0)..addAll([1, 2, 3]);

results in l1 being a list [0, 1, 2, 3]

var l1 = new List<int>().add(0).addAll([1, 2, 3]);

results in an error, because .add(0) returns void

.. (in the former example) refers to new List(), while . (in the later) refers to the return value of the previous part of the expression.

.. was introduced to avoid the need to return this in all kinds of methods like add() to be able to use an API in a fluent way.

.. provides this out of the box for all classes.

Cascades (..) allow you to make a sequence of operations on the same object. read doc for details

querySelector('#confirm') // Get an object.
  ..text = 'Confirm' // Use its members.
  ..classes.add('important')
  ..onClick.listen((e) => window.alert('Confirmed!'));

The previous example is equivalent to:

var button = querySelector('#confirm');
button.text = 'Confirm';
button.classes.add('important');
button.onClick.listen((e) => window.alert('Confirmed!'));

.. Is known as the cascading operator in dart.

It allows you to use more than one subsequence operation:

Examples:

banerad..load()..show().

List coursename;
coursename..add("java")..add("flutter" )..add("dart");

Here is another example

https://i.stack.imgur.com/Iv4eL.png

Double dots(..) also know as cascade operator

It allows you to not repeat the same target if you want to call several methods on the same object.

e.g without double dots

var paint = Paint();
paint.color = Colors.black;
paint.strokeCap = StrokeCap.round;
paint.strokeWidth = 5.0;

But after using “..”, the above code will be written like this:

var paint = Paint()
..color = Colors.black
..strokeCap = StrokeCap.round
..strokeWidth = 5.0;

Triple dots(…) i.e. Spread Operator

“… ”also known as spread operator which provide a concise way to insert multiple values into a collection. You can use this to insert all the elements of a list into another list:

Normally we use .add() or .addAll() to add data to the list like:

var list = [1, 2, 3];
var list2=[];
list2.addAll(list);

After using “…” we will write code like this:

var list = [1, 2, 3];
var list2 = [0, ...list];