How does multithreading work in Objective-C on iPhone?

Question

I got confused about the concept of “streams” in the development of the iPhone:

• Why are threads necessary / useful?
• How to use streams in Objective-C?

Answer 1

You need multithreading in object c, because sometimes you need functions / code to run "in the background" (read: in another thread). For example (but not explicitly) you may need to download a large amount of data from the Internet (image or video).

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: NSURLConnection [self performSelector:onThread:...]

Answer 2

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Answer 3

Apple , ; it Concurrency :
http://developer.apple.com/library/mac/#documentation/General/Conceptual/ConcurrencyProgrammingGuide/Introduction/Introduction.html#//apple_ref/doc/uid/TP40008091

Answer 4

The recommended way to implement concurrency is to use queues.

For those who just want to execute a method / block in a separate thread, use this code:

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(queue, ^{
   [self longMehtod];
});

read Apple's Concurrency Programming Guide for more information