iphone - How can I programmatically pause an NSTimer?

Question

I'm using an NSTimer to do some rendering in an OpenGL based iPhone app. I have a modal dialog box that pops up and requests user input. While the user is providing input I'd like to "pause" i.e. something like this:

[myNSTimer pause];

I'm using this syntax because I've been doing things like:

[myNSTimer invalidate];

when I want it to stop.

How can I programmatically pause the NSTimer?

Answer 1

Just thought of updating minor fixes to kapesoftware's answer:

NSDate *pauseStart, *previousFireDate;

-(void) pauseTimer:(NSTimer *)timer { 

    pauseStart = [[NSDate dateWithTimeIntervalSinceNow:0] retain];

    previousFireDate = [[timer fireDate] retain];

    [timer setFireDate:[NSDate distantFuture]];
}

-(void) resumeTimer:(NSTimer *)timer {

    float pauseTime = -1*[pauseStart timeIntervalSinceNow];

    [timer setFireDate:[previousFireDate initWithTimeInterval:pauseTime sinceDate:previousFireDate]];

    [pauseStart release];

    [previousFireDate release];
}