Question

I’m making a game for iOS using XCode however I have run into one problem:

If I use a loop, the graphics do not get updated until the next frame after the loop has finished; so if for example I have something like this:

something.center = CGPointMake(20, something.center.y);
while(something.center.x < 50)
{
    something.center = CGPointMake(something.center.x + 1, something.center.y);
    // Just a delay:
    [NSThread sleepForTimeInterval:0.01];
}

The UIImageView ‘something’ will just go straight from 20 to 50. I know in this occasion I should use an NSTimer but I just made this example to keep things simple.

So is there a function which I can call to update the screen, some kind of VBL?

Answer 1

Since it’s best practice to use the main thread for the UI (like H2CO3 mentioned), I wouldn’t recommend using sleepForTimeInterval, as it clogs up the thread doing arguably the most important job (at least for the user). Instead, you could use a timer like this:

- (void) updatePosition {

    while(something.center.x < 50) {
        something.center = CGPointMake(something.center.x + 1, something.center.y);
    }
}

NSTimer *timer = [NSTimer timerWithTimeInterval:0.05 target:self selector:@selector(updatePosition) userInfo:nil repeats:YES];
[timer fire];

Of course you’ll have to tweak the code and make some modifications, but that’s the gist of what you should do.