Question

Hi Ive got an funny problem.. Forst of all my code:

- (void)viewDidLoad
{

[super viewDidLoad];
didStart=YES;
[NSThread detachNewThreadSelector:@selector(updateGame:) toTarget:self withObject:nil];
}

-(void)updateGame:(id)sender{

while (1) {
    NSLog(@"getting called");
    CGRect frame= self.label.frame;
    frame.origin.y+=1;
    self.label.frame=frame;
    [self.label removeFromSuperview];
    [self.view addSubview:self.label];
    NSLog(@"%f",frame.origin.y);
}


}

Basically I am implementing a game loop. But although I am assured the loop is getting called, somehow the label is not moving on the screen. Any thoughts what could be the problem?

Answer 1

From the UIKit Framework Reference:

Note: For the most part, UIKit classes should be used only from an application’s main thread. This is particularly true for classes derived from UIResponder or that involve manipulating your application’s user interface in any way.

If your game world update code is fast, you can just use an NSTimer to run the game update on the main thread periodically.

If your game world update code is slow, you will want to run it on a background thread, updating model objects. Then you notify the main thread (perhaps using dispatch_async or performSelectorOnMainThread:withObject:waitUntilDone:) to update the UI. But if you can run your update code on the main thread, you will be much less prone to multithreading problems like race conditions.