passing variables when calling methon in new thread (iphone) - iphone

Question

i need to pass variables to the thread method when creating a new thread
my code is the follwing
//generating thread
[NSThread
detachNewThreadSelector:#selector(startThread)
toTarget:self withObject:nil];
thread job
- (void)startThread:(NSInteger *)var img:(UIImageView *) Img{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
[NSThread sleepForTimeInterval:var];
[self performSelectorOnMainThread:#selector(threadMethod) withObject:nil waitUntilDone:NO];
//i need to pass Img to threadMethod:
[pool release];
}
thread Method
- (void)threadMethod:(UIImageView *) Img {
//do some coding.
}
so how i can do this (pass parameter to both of methods

Answer 1

The code you provided as I see it is only using the thread to implement a delay. You can do this easily without introducing a thread like this:
[myImageView performSelector:#selector(setImage:)
withObject:image
afterDelay:5.0];
For more complex needs I have written a category on NSInvocation that allow you to easily call any method, independent of the arguments, on any thread.
You have for example this method as I see it:
-(void)doStuffWithImage:(UIImage*)image callbackAfterDelay:(NSTimeInterval)to {
NSAutoreleasePool* pool = [[UIAutoreleasePool alloc] init];
// ... do stuff
[NSThread sleepForTimeInterval:ti];
[self performSelectorOnMainThread:#selector(callbackWithImage:)
withObject:image
waitUntilDone:NO];
[pool release];
}
This is easy enough, but spawning this method on a secondary thread is not that easy. My category allow you to do it with this simple code:
[[NSInvocation invocationWithTarget:self
selector:#selector(doStuffWithImage:callbackAfterDelay:)
retainArguments:YES, image, 5.0] invokeInBackground];
This is where you can find the code and a blog post elaborating on why and how it was implemented:
http://blog.jayway.com/2010/03/30/performing-any-selector-on-the-main-thread/

Answer 2

You can pass only one argument by using withObject:, change your code as follows
[self performSelectorOnMainThread:#selector(threadMethod)
withObject:image
waitUntilDone:NO];
If you need to pass more than one value make it as a array, and then pass it.
And UIComponents are not thread safe, so be careful while passing UIcomponents to threads.

Answer 3

I'm reasonably certain UIImage isn't thread safe, so you may be out of luck there. In general though, any of these:
Make the object an instance variable
Make the object a global
Capture the variable in a block and use dispatch_async to do your threaded work instead of NSThread
Send the object to the thread using NSConnection
etc...
Remember though, just because you have a reference to the object doesn't mean it's safe to use. Consider thread-safety guarantees (main thread only vs one thread only vs one writer only vs thread safe), and consider where you need to use locks or queues to guard resources shared between threads.