How to store blocks in properties in Objective-C?
Objective CObjective C-BlocksObjective C Problem Overview
I'd like to store objective-c block in a property for later use. I wasn't sure how to do it so I googled a bit and there is very little info about the subject. But I've managed to find the solution eventually and I've thought that it might be worth sharing for other newbies like me.
Initially I've thought that I would need to write the properties by hand to use Block_copy & Block_release.
Fortunately I've found out that blocks are NSObjects and - copy/- release is equivalent to Block_copy/Block_release. So I can use @property (copy) to auto generate setters & getters.
Objective C Solutions
Solution 1 - Objective C
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();
Solution 2 - Objective C
Alternatively, without the typedef
@property (copy, nonatomic) void (^selectionHandler) (NSDictionary*) ;
Solution 3 - Objective C
You can find a very good explanation of this in WWDC 2012 session 712 starting in page 83. The correct way of saving a block under ARC is the following:
@property(strong) my_block_type work;
Be careful with the retain cycles. A good way to solve is set the block to nil when you do not need it anymore:
self.work = nil;