ios store ^block in dictionary or array?

Question

Can I store ^block in a dictionary or an array?

I need to listen to a server notification which I need to provide a block to handle the notification, and in my project several view controllers all want to hear the notification, so I made a generic notification manager, which has its own block for handling server notification and it has an array of delegates, so in the manager's block:

- (^)(NSString *message){
    for (delegate in allDelegates)
    {
        delegate.handlerBlock(message);
    }
}

but can I store blocks in a collection?

Indeed you can. Blocks are objective c objects, just remember to copy them off of the stack first. — Richard J. Ross III
– Richard J. Ross III, Commented Oct 24, 2012 at 4:52

Ted · Accepted Answer · 2015-09-15 16:42:11Z

12

You can store object into collection. But take care of the scope: Copy them when they will be kept out of a function scope. This is your case since you are storing them in a array.

[NSArray arrayWithObject: 
[[^{ NSLog(@"block 1"); } copy] autorelease],
[[^{ NSLog(@"block 2"); } copy] autorelease], nil]

On ARC, you still need to tell it you absolutely needs to copy your block. It should release the block when the array is freed.

  [NSArray arrayWithObject: 
    [^{ NSLog(@"block 1"); } copy],
    [^{ NSLog(@"block 2"); } copy], nil]

edited Sep 15, 2015 at 16:42

Ted

23.9k11 gold badges102 silver badges113 bronze badges

answered Oct 24, 2012 at 7:38

Mr Bonjour

3,4203 gold badges28 silver badges47 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

hzxu Over a year ago

But I am using ARC, so I cannot use autorelease?

Mr Bonjour Over a year ago

hzxu, if you use ARC, then forget autorelease. I have updated my example.

newacct · Accepted Answer · 2012-10-24 18:45:14Z

5

Blocks are special in that they should be copied in most cases when other objects should be retained. As you must have read by now, this is because blocks start out on the stack (a "stack block"), and is only valid in the local scope where they were defined. Copying a stack block gives you a heap block, and that will have a dynamic lifetime like normal objects. Copying a heap bock will simply retain it, so it is always right to copy a block when you need to keep it around for longer.

Now, functions that take a block argument generally take responsibility for copying blocks as necessary. So you don't need to do anything special when passing a block to these functions. However, in this case you're passing your block to [NSArray arrayWithObject:], which takes a normal object argument. Since it doesn't take a block argument, it doesn't know to copy the argument, so it will just retain it. So when you pass a block to a method that takes a normal object argument, you need to copy it first.

answered Oct 24, 2012 at 18:45

newacct

123k29 gold badges168 silver badges227 bronze badges

1 Comment

Abhi Beckert Over a year ago

Blocks are not "special", copy should be used in almost all cases instead of retain. For most objects where retain is the "right" thing to do, copy will in fact just retain and return self.

Paul de Lange · Accepted Answer · 2012-10-24 07:33:56Z

-1

You will find how to do this if you read the very good article here. And take particular note of the "copy them off the stack first" idiom mentioned there.

answered Oct 24, 2012 at 7:33

Paul de Lange

10.6k10 gold badges44 silver badges56 bronze badges

1 Comment

Thomas Tempelmann Over a year ago

The link is dead

Collectives™ on Stack Overflow

ios store ^block in dictionary or array?

3 Answers 3

2 Comments

1 Comment

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related