CODEWITHSUNDEEP
flutterdart
baha zou
baha zou

Reputation: 31

The meaning of colon in flutter widgets structure

I have learned Dart and when I started learning Flutter, I got confused by some parts of Flutter code.

Can someone tell me what's the meaning of the colon (:) after child, in the following code:

 const Center(
      child: Text(
        'Hello, world!',
        textDirection: TextDirection.ltr,
      ),

Thanks

Upvotes: 0

Views: 172

Answers (1)

Md. Yeasin Sheikh
Md. Yeasin Sheikh

Reputation: 63809

This is used on named constructor. The textDirection is an optional named parameter on Text widget.

class Foo {
  final int data;
  Foo({
    required this.data,
  });
}

Here Foo class has single integer data field, and using named required constructor to create instance.

final foo = Foo(data: 1);

Now If it was optional as textDirection, we aren't forced to pass it when creating a Foo instance like

class Foo {
  final int? data;
  Foo({
    this.data,
  });
}

void main(List<String> args) {
  final foo = Foo();
}

Now explore the Text, It contains one String position filed and others are optional positional argument.

Here we are forced to pass a String, but data is optional

class Foo {
  final String text;
  final int? data;
  Foo(this.text, {this.data});
}

void main(List<String> args) {
  final foo = Foo("test");
}

The Text widget has been defined like

  const Text(
    String this.data, {
    super.key,
    this.style,
    this.strutStyle,
    this.textAlign,
    this.textDirection,
    this.locale,
    .......

Find more about using constructors and Text

Upvotes: 3

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