iPhone SDK: After invalidating a Timer, how can I use it again?

Question

I have set up an animation in Xcode using an NSTimer, and It kept repeating over and over, so i used this command:

else if(gordon.image == pigImage11)
    [animationTimer invalidate];

So, when gordon (a UIImageView) image is set to pigImage11, The timer invalidates, this gave the desired effect of stopping the animation constantly repeating, But stopped the timer being used again, so how would I make the timer usable again, But have it invalidate itself on that frame? For the sake of further clarification here's my entire code:

- (IBAction)startClick:(id)sender{
    animationTimer = [NSTimer scheduledTimerWithTimeInterval:(1.00/30.00) target:self selector:@selector(tick) userInfo:nil repeats:YES];
}
- (void)tick{
    [self animatePig];
}
- (void)animatePig{
    UIImage *pigImage1=[UIImage imageNamed:@"gordonapple0004.png"];
    UIImage *pigImage2=[UIImage imageNamed:@"gordonapple0005.png"];
    UIImage *pigImage3=[UIImage imageNamed:@"gordonapple0006.png"];
    UIImage *pigImage4=[UIImage imageNamed:@"gordonapple0007.png"];
    UIImage *pigImage5=[UIImage imageNamed:@"gordonapple0008.png"];
    UIImage *pigImage6=[UIImage imageNamed:@"gordonapple0009.png"];
    UIImage *pigImage7=[UIImage imageNamed:@"gordonapple0010.png"];
    UIImage *pigImage8=[UIImage imageNamed:@"gordonapple0011.png"];
    UIImage *pigImage9=[UIImage imageNamed:@"gordonapple0012.png"];
    UIImage *pigImage10=[UIImage imageNamed:@"gordonapple0013.png"];
    UIImage *pigImage11=[UIImage imageNamed:@"gordonapple0014.png"];
    UIImage *pigImage12=[UIImage imageNamed:@"gordonapple0015.png"];
    UIImage *pigImage13=[UIImage imageNamed:@"gordonapple0016.png"];


    if(gordon.image == pigImage1)
        gordon.image = pigImage2;
    else if(gordon.image == pigImage2)
        gordon.image = pigImage3;
    else if(gordon.image == pigImage3)
        gordon.image = pigImage4;
    else if(gordon.image == pigImage4)
        gordon.image = pigImage5;
    else if(gordon.image == pigImage5)
        gordon.image = pigImage6;
    else if(gordon.image == pigImage6)
        gordon.image = pigImage7;
    else if(gordon.image == pigImage7)
        gordon.image = pigImage8;
    else if(gordon.image == pigImage8)
        gordon.image = pigImage9;
    else if(gordon.image == pigImage9)
        gordon.image = pigImage10;
    else if(gordon.image == pigImage10)
        gordon.image = pigImage11;
    else if(gordon.image == pigImage11)
        [animationTimer invalidate];
    else
        gordon.image = pigImage1;
}

- (void)stopTimer
{
    [animationTimer invalidate];
    [animationTimer release];
}

Answer 1

How about not invalidating the timer and just setting a "don't animate" flag instead?

Answer 2

[[NSRunLoop currentRunLoop] addTimer:animationTimer
                             forMode:NSDefaultRunLoopMode];

But you must not release the timer after invalidating, of course.

Answer 3

Why not use UIImageView's built in animation:

UIImageView* gordonView = [[UIImage alloc]init];
gordonview.animationImages = [NSArray arrayWithObjects: pigImage1, pigimage2, etc., nil];
gordonView.animationDuration = 0.5f; // about 30fps with your 13 images. 
//Set gordon's frame here
[gordonView startAnimating];

Disclosure, I typed this into SO, not Xcode I'm certain it will not compile but at least you know what to look for in the SDK.

Answer 4

You can reuse a timer like this:

- (void) startTimer {
    if ( myTimer == nil ) {
        myTimer = [NSTimer scheduledTimerWithTimeInterval: 5.0f
                   target: self
                   selector: @selector(myTimerAction:)
                   userInfo: nil
                   repeats: NO];
    }
}

- (void) stopTimer {
    if ( myTimer || [myTimer isValid])
    {
        [myTimer invalidate];
        myTimer = nil;
    }
}