//
// TYPEDEFS
//
typedef int (^MyBlockTypeWithArgs)(int, int);
typedef int (^MySimpleBlockType)();
// Obj-C object argument/return types are ok too of course...

//
// LOCAL VARS
//
int (^multiply)(int, int) = ^int(int a, int b) { return a*b; };
int (^multiply)(int, int) = ^(int a, int b) { return a*b; };        // same as above
MyBlockTypeWithArgs multiple = ^(int a, int b) { return a*b; };
MySimpleBlockType doSomething = ^{ [self _doSomething]; }; 

//
// PROPERTIES (same as local vars)
//
@property (nonatomic, copy) int (^multiply)(int, int);
@property (nonatomic, strong) MyBlockTypeWithArgs callbackBlock;

//
// METHOD ARGUMENTS
//
@interface MyClass
- (void)doItWithBlock:(int(^)(int, int))blockTakingArgs;
- (void)doItWithBlock3:(void (^)())simpleBlock;
- (void)doItWithBlock:(MyBlockTypeWithArgs)block;
@end

@property (nonatomic, copy) void (^cbPlaybackFinished)();
@property (nonatomic, copy) void (^cbPlaybackDidOccur)(NSUInteger frame, NSTimeInterval time);

// Or if you prefer
typedef BOOL (^TesterCallbackType)();
//...
@property (nonatomic, copy) TesterCallbackType cbAllowPlaybackActionCallback;

typedef NSString *(^MyBlockTypeName)(NSInteger, NSString *);

@interface MyClass

- (void)doItWithBlock:(MyBlockTypeName)block;
- (void)doItWithBlock2:(NSString *(^)(NSNumber *, double))blockTakingArgs;
- (void)doItWithBlock3:(void (^)())simpleBlock;

@end

- (void)setupNotification {

    // Prevents a circular reference. Otherwise dealloc will never be called
    __weak SWAnalytics *weakSelf = self;

    [[NSNotificationCenter defaultCenter]
     addObserverForName:UIApplicationDidEnterBackgroundNotification
     object:nil
     queue:[NSOperationQueue mainQueue]
     usingBlock:^(NSNotification *n) {

        [weakSelf doSomething];

     }];
}

- dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

// Nothing to do if it's already the active one
if (activeIndex == theIdx)
    return;    

// Hide immediately all lagging animations and
// fade out the visible one if any
for (int i=0; i