Question

I have a very simple class (currently used as a testing class), which uses delegate/protocol methods to interface with it’s parent class. However, I would really like to convert this to use blocks. Yet I can’t find a good resource or tutorial out there to help me figure out how to do this. All the blocks tutorials are just way to complicated, and I would really just like a small, concise example of how to do this.

I currently have the class:

#import <Foundation/Foundation.h>

@protocol TestObjectDelegate <NSObject>

@optional
-(void)testObjectSucceeded:(BOOL)passedTest;
-(void)testObjectedFailed:(NSError *)error;
@end

@interface TestObject : NSObject {
    id<TestObjectDelegate> _delegate;
}
-(void)compare:(NSString *)stringA with:(NSString *)stringB;

@end


#import "TestObject.h"



@implementation TestObject 

- (id)initWithDelegateController:(id<TestObjectDelegate>)delegate {
    self = [super init];
    if (self) {
        _delegate = delegate;
    }
    return self;
}

-(void)compare:(NSString *)stringA with:(NSString *)stringB {
    if ([stringA isEqualToString:stringB]) {
        if(_delegate && [_delegate respondsToSelector:@selector(testObjectSucceeded:)]) {
            [_delegate testObjectSucceeded:YES];
        }
        else {
            [_delegate testObjectSucceeded:NO];
        }
    }
    else {
        if(_delegate && [_delegate respondsToSelector:@selector(testObjectedFailed:)]) {
            [_delegate testObjectedFailed:nil];
        }
    }
}
@end

How could I begin to convert this to a blocks based function? Also, I know ‘retain cycles’ are something to watch out for when implementing a blocks function. What would I need to watch out for when converting this class to use blocks instead of delegate/protocols? Googling ‘retain cycles’ also gives some overly complicated answers.

Any starting pointers would be much appreciated?

Answer 1

Maybe this example gives you an idea:

typedef void (^MyCallbackBlock)(BOOL);

@interface TestObject : NSObject {

}
@property (nonatomic, copy) MyCallbackBlock myBlock;
@end




#import "TestObject.h"

@implementation TestObject 

-(void) yourMethod
{
    ...
        self.myBlock(YES); // call block with argument
    ...
}

- (void)dealloc 
{
    [myBlock release];   
    myBlock = nil;
    [super dealloc];
}

@end

When using the object you can then define the block like this:

TestObject* theTestObject = [[TestObject alloc] init];
theTestObject.myBlock = ^(BOOL theParameter){
    NSLog(@"foo");
};