how to run code in the UI thread calling it from the others ones

Question

In Android there are several ways to run some code in the main thread from others ones:

 1. Activity.runOnUiThread(Runnable r)  2. new Handler.post(Runnable r);  3. View.post 

What are the analogues in iOS?

 dispatch_async(dispatch_get_main_queue(), ^{      }); 

Something else?

Thanks in advance.

Answer 1

The preferred way nowadays is using GCD, with the code you quoted in your question:

dispatch_async(dispatch_get_main_queue(), ^{     // Your code to run on the main queue/thread }); 

If you prefer using a more Object-Oriented approach than GCD, you may also use an NSOperation (like an NSBlockOperation) and add it to the [NSOperationQueue mainQueue].

[[NSOperationQueue mainQueue] addOperationWithBlock:^{     // Your code to run on the main queue/thread  }]; 

This does quite the same thing as dispatch_async(dispatch_get_main_queue(), …), has the advantage of being more Objective-C/POO oriented that the plain C GCD function, but has the drawback of needing to allocate memory for creating the NSOperation objects, whereas you can avoid it using plain C and GCD.

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I recommend using GCD, but there are other ways, like those two which allow you to call a selector (method) on a given object from the main thread:

• - (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait (method of NSObject so it can be called on any object)
• Send - (void)performSelector:(SEL)aSelector target:(id)target argument:(id)anArgument order:(NSUInteger)order modes:(NSArray *)modes on the [NSRunLoop mainRunLoop]

But those solutions are not as flexible as the GCD or NSOperation ones, because they only let you call existing methods (so your object has to have a method that already exists and does what you want to perform), whereas GCD or -[NSOperationQueue addOperationWithBlock:] allows you to pass arbitrary code (using the block).