Dynamically calculate application load time

How can I run a clock that allows me to measure the time to load until appDidFinishLaunching ?

I want to set a sleep call that extends the开发者_运维百科 Defaul.png show time to 3 seconds regardless the speed of the underlying hardware.

First off, you should know that Springboard in iPhone OS is kinda picky about load times. You should never make a sleep call somewhere in the loading process of you application. If Springboard detects that your application is taking too long to launch, your application will be terminated with "failed to launch in time" in the crash log.

Secondly, there is no, as far as I know, way of measuring the time your application took to launch. There are several thing happening when the user taps the Application icon on the springboard, and the iPhone OS provides no good information to your application.

One solution could be to make sure your applicationDidFinishLaunching: is very lightweight, and creating a "fake" Default.png overlay. By trimming down your applicationDidFinishLaunching: method to do only the most essential stuff, and the performing any time consuming tasks in the background, you can ensure that your Default.png overlay is displayed roughly the same time on different hardware.

- (void)applicationDidFinishLaunching:(UIApplication *)application {
    // Create the image view posing with default.png on top of the application
    UIImageView *defaultPNG = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"Default.png"]];
    // Add the image view top-most in the window
    [window addSubview:defaultPNG];

    [window makeKeyAndVisible];

    // Begin doing the time consuming stuff in the background
    [self performSelectorInBackground:@selector(loadStuff) withObject:nil];

    // Remove the default.png after 3 seconds
    [self performSelector:@selector(removeDefaultPNG:) withObject:defaultPNG afterDelay:3.0f];
}

- (void)removeDefaultPNG:(UIImageView *)defaultPNG {
    // We're now assuming that the application is loaded underneath the defaultPNG overlay
    // This might not be the case, so you can also check here to see if it's ok to remove the overlay
    [defaultPNG removeFromSuperview];
    [defaultPNG release];
}

If you add more views (your view controllers etc) in the loadStuff method, you should insert them below the defaultPNG overlay. You should also be aware of problems that could occur by doing these things from another thread. You could use performSelectorOnMainThread:withObject:waitUntilDone: if you encounter problems.