I've seen this code and need an explanation for "??". I know ternary operators like "?" and then the true-condition and after ":" the false/else condition. But what means the double "??" ?
Thanks in advance
widget.secondaryImageTop ??
(widget.height / 2) - (widget.secondaryImageHeight / 2); ```
it's the coalesce operator.
a ?? b
means: if a is not null, it resolves to a. if a is null, it resolves to b.
SQL and a few other languages have this operator.
You example:
widget.secondaryImageTop ??
(widget.height / 2) - (widget.secondaryImageHeight / 2);
This will use widget.secondaryImageTop unless it is null, in which case it will use (widget.height / 2) - (widget.secondaryImageHeight / 2).
Source and detail, including dartpad where you can try things out with pre-populated examples: https://dart.dev/codelabs/dart-cheatsheet
An example from that documentation, using the = sign as well.
the ??= assignment operator, which assigns a value to a variable only if that variable is currently null:
int a; // The initial value of a is null.
a ??= 3;
print(a); // <-- Prints 3.
a ??= 5;
print(a); // <-- Still prints 3.