Passing parameters to callback in dart:async's Timer constructor

[Raymond Nürnberger]

For simplicity, I'm rewriting my code to match a more canonical example of what the problem is.

So in dart, the Timer's constructor takes a duration and callback function as parameters. What if you want to pass a parameter to the callback function though?

Example:

Duration duration = const Duration(milliseconds: 3000);
Timer timer = new Timer(duration, callback)

void callback()
{
  //do something...
}

That's an example of how it's worked for me in the past, but this time around what I really need it to do is something like this.

String tmp = document.query("#doc").innerHtml;
.....

...= new Timer(duration, callbackThatTakesAStringAsAParam(tmp));

void callbackThatTakeAStringAsAParam(String contents)
{
  ///do something with contents..
}

Obviously, the compiler throws a warning and the functionality is completely broken. I think the callback needs to be without the parentheses...that way it will defer the evaluation to later...but how would you do that without parentheses?

Thanks.

[Filipe Morgado]

We can't control the arguments of callbacks but closures allow for "variable capture" (something like that).

String myArgument = "pass this";

Duration duration = const Duration(milliseconds: 3000);

Timer timer = new Timer(duration, () => callbackThatTakeAStringAsAParam(myArgument));

[Raymond Nürnberger]

Genius...that seemed to do the trick. Thanks so much....a closure wouldn't have occurred to me if you hadn't mentioned it.