Question

all! I want to create multiple threads in my application. I’ using following code for creating a thread.
This’ buttonPress method where I’m creating a thread:

- (void) threadButtonPressed:(UIButton *)sender {

threadStartButton.hidden = YES;

    threadValueLabel.text = @"0";
threadProgressView.progress = 0.0;

  [NSThread detachNewThreadSelector:@selector(startMethod) toTarget:self withObject:nil];

}

This’ where I’m calling the method for the thread:

- (void)startMethod {

  NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

  [self performSelectorOnMainThread:@selector(threadMethod) withObject:nil waitUntilDone:NO];

  [pool release];

}

 - (void)threadMethod {

float actual = [threadProgressView progress];

    threadValueLabel.text = [NSString stringWithFormat:@"%.2f", actual];
if (actual < 1) {

    threadProgressView.progress = actual + 0.01;
    [NSTimer scheduledTimerWithTimeInterval:0.5 target:self selector:@selector(makeMyProgressBarMoving) userInfo:nil repeats:NO];
}

    else 
    threadStartButton.hidden = NO;  
 }

This thread works properly.
But when I try to create another thread in the same class using the same method, it gets created properly, but at the method “performSelectorOnMainThread”, it doesn’t execute that method. Can anybody please help me?

Answer 1

It seems that you are trying to queue up methods to be executed on the main thread. You might want to look into an NSOperationQueue and NSOperation objects. If you want to proceed on this path, you might consider changing the repeats parameter to YES. The problem seems to be that the main thread is busy when it’s being passed this message. This will cause the main thread to block. You may also consider not using a second threadMethod and calling back to the main thread, but instead wrapping the contents of threadMethod in an @synchronized(self) block. This way, you get the benefits of multi-threading (multiple pieces of code executing at the same time and thus a reactive user interface) without doing some weird stuff with the main thread.