Can I use Objective-C blocks as properties?

Question

Is it possible to have blocks as properties using the standard property syntax?

Are there any changes for ARC?

Answer 1

@property (nonatomic, copy) void (^simpleBlock)(void); @property (nonatomic, copy) BOOL (^blockWithParamter)(NSString *input); 

If you are going to be repeating the same block in several places use a type def

typedef void(^MyCompletionBlock)(BOOL success, NSError *error); @property (nonatomic) MyCompletionBlock completion; 

Answer 2

Here's an example of how you would accomplish such a task:

#import <Foundation/Foundation.h> typedef int (^IntBlock)();  @interface myobj : NSObject {     IntBlock compare; }  @property(readwrite, copy) IntBlock compare;  @end  @implementation myobj  @synthesize compare;  - (void)dealloc  {    // need to release the block since the property was declared copy. (for heap    // allocated blocks this prevents a potential leak, for compiler-optimized     // stack blocks it is a no-op)    // Note that for ARC, this is unnecessary, as with all properties, the memory management is handled for you.    [compare release];    [super dealloc]; } @end  int main () {     @autoreleasepool {         myobj *ob = [[myobj alloc] init];         ob.compare = ^         {             return rand();         };         NSLog(@"%i", ob.compare());         // if not ARC         [ob release];     }      return 0; } 

Now, the only thing that would need to change if you needed to change the type of compare would be the typedef int (^IntBlock)(). If you need to pass two objects to it, change it to this: typedef int (^IntBlock)(id, id), and change your block to:

^ (id obj1, id obj2) {     return rand(); }; 

I hope this helps.

EDIT March 12, 2012:

For ARC, there are no specific changes required, as ARC will manage the blocks for you as long as they are defined as copy. You do not need to set the property to nil in your destructor, either.

For more reading, please check out this document: http://clang.llvm.org/docs/AutomaticReferenceCounting.html