Yes, you can do this. Note, however, that the block will retain self. If you end up storing this block in an ivar, you could easily create a retain cycle, which means neither would ever get deallocated. To get around this, you can do: – (void) someMethodWithAParameter:(id)aParameter { __block MySelfType *blocksafeSelf = self; void (^tempFunction)(void) … Read more
I’d like to explain this a bit more, with a more complete answer. First let’s consider this code: #import <Foundation/Foundation.h> int main(int argc, char *argv[]) { void (^block)() = nil; block(); } If you run this then you’ll see a crash on the block() line that looks something like this (when run on a 32-bit … Read more
Edit: updated for ARC typedef void(^MyCustomBlock)(void); @interface MyClass : NSObject @property (nonatomic, copy) MyCustomBlock customBlock; @end @implementation MyClass @end MyClass * c = [[MyClass alloc] init]; c.customBlock = ^{ NSLog(@”hello…..”); } c.customBlock();
1) Define your own completion block, typedef void(^myCompletion)(BOOL); 2) Create a method which takes your completion block as a parameter, -(void) myMethod:(myCompletion) compblock{ //do stuff compblock(YES); } 3)This is how you use it, [self myMethod:^(BOOL finished) { if(finished){ NSLog(@”success”); } }];
From the docs about __block __block variables live in storage that is shared between the lexical scope of the variable and all blocks and block copies declared or created within the variable’s lexical scope. Thus, the storage will survive the destruction of the stack frame if any copies of the blocks declared within the frame … Read more
There’s no built-in way to do that, but it’s not too bad to add via a category: @implementation NSObject (PerformBlockAfterDelay) – (void)performBlock:(void (^)(void))block afterDelay:(NSTimeInterval)delay { block = [[block copy] autorelease]; [self performSelector:@selector(fireBlockAfterDelay:) withObject:block afterDelay:delay]; } – (void)fireBlockAfterDelay:(void (^)(void))block { block(); } @end Credit to Mike Ash for the basic implementation.
The pattern of “run on whatever queue the caller was on” is appealing, but ultimately not a great idea. That queue could be a low priority queue, the main queue, or some other queue with odd properties. My favorite approach to this is to say “the completion block runs on an implementation defined queue with … Read more
– ( void )myMethodTakingPredicate: ( BOOL ( ^ )( int ) )predicate
The type of a block varies depending on its arguments and its return type. In the general case, block types are declared the same way function pointer types are, but replacing the * with a ^. One way to pass a block to a method is as follows: – (void)iterateWidgets:(void (^)(id, int))iteratorBlock; But as you … Read more
Ultimately, use whichever pattern you want to use and comes more naturally in the context. While for(… in …) is quite convenient and syntactically brief, enumerateObjectsUsingBlock: has a number of features that may or may not prove interesting: enumerateObjectsUsingBlock: will be as fast or faster than fast enumeration (for(… in …) uses the NSFastEnumeration support … Read more