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Questions tagged [objective-c-blocks]

Blocks are Apple’s implementation of closures for C, which are also available for Objective-C and C++.

Blocks are an Apple extension to C, often used in conjunction with Objective-C. When used from Objective-C, blocks also function as full Objective-C objects.
They are more traditionally known as closures. As closures, they can capture variables from the surrounding scope, be passed to functions, and be stored in variables. The syntax of a Block type is nearly identical to a function pointer, with * being replaced by ^.

An example of block definition is the following one:

int (^minusOne)(int);

minusOne = ^(int anInt) {
    return anInt - 1;
};

For more examples regarding how to declare various types of blocks, see How Do I Declare A Block In Objective-C?, and for more in-depth information, see Blocks Programming Topics.

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Is there an easy way to autocomplete block variables in xcode?

Usually Xcode autocomplete works really well for me but when tabbing through method signatures with blocks and block variables I always have to retype the variable types and names. Here's an example: The animation block is easy to complete since it…
Nick
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Cocoa blocks as strong pointers vs copy

I did work several times with blocks as with pointers to which i had strong reference I heard that you should use copy, but what is the implication in working with blocks as pointers and not with the raw object? I never got a complain from the…
Peter Lapisu
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Possible to pass [self anyFunction] in blocks without __weak object (iOS 5 + ARC)

Is it possible to pass [self anyFunction] in blocks without a __weak object from self? As an example this is valid code from the System Framework: [UIView animateWithDuration:0.8 animations:^{ //Do animationStuff }…
andreschneider
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avoiding "expression result unused" warning in a block

The following code is returning an expression unused warning on the assignment operation in the block. The code isn't very practical, but there is a lot more code in the excluded section and that code has to run on a particular queue. __block…
Mark Lilback
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How can I retrieve a return value from a completion block?

Is it possible to run a completion block on the main thread? For example, I have one method which returns a value: - (int)test { /* here one method is called with completion block with return type void */ [obj…
Elegant Microweb
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Having trouble with BOOL return type in Objective-C blocks

I stumbled over a curious problem with BOOL return type in blocks. Having the following definition: typedef BOOL (^BoolBlock)(void); …this code passes: BoolBlock foo = ^{ return YES; }; …but this fails to compile: BoolBlock bar = ^{ return YES ||…
zoul
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Grand Central Dispatch (GCD) with CoreData

I'm using Grand Central Dispatch (GCD) in my application to do some heavy lifting. The application is using Core-Data for data storage purposes. Here's my scenario (along with relevant question): dispatch_queue_t main_queue =…
Mustafa
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Have you noticed that dispatch_after runs ~10% too slow on iOS devices?

Lately I've been using dispatch_after instead of performSelector:withObject:afterDelay when I want to trigger some code after a delay. The code is cleaner, it has access to the enclosing scope, I can put the code in-line instead of writing a…
Duncan C
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recursive block and retain cycles in ARC

EDIT2: No. The suggested answer is about async calls. I want & need synchronous calls, like in a normal, standard recursive call. EDIT: while __unsafe_unretained void (^unsafe_apply)(UIView *, NSInteger) ; compiles without warning or errors, it…
verec
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What will happen if I have nested dispatch_async calls?

It may be a dumb question but I need to ask and clear this up for myself. To submit a block onto a queue for execution, use the functions dispatch_sync and dispatch_async. They both take a queue and a block as parameters. dispatch_async returns…
tranvutuan
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using completion with animateWithDuration causes exc_bad_access

I am trying to animate 2 UIButtons in a UITableViewCell called addToPlaylist and removeFromPlayList (they animate off to the right after being swiped on) and am using a block as follows [UIView animateWithDuration:0.25 animations:^{ …
craigk
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Capturing 'self' strongly in this block is likely to lead to a retain cycle

I have reqest with block. But the compiler issues a warning "Capturing 'self' strongly in this block is likely to lead to a retain cycle" __weak typeof(self) weakSelf = self; [generalInstaImage setImageWithURLRequest:[NSURLRequest…
Alexander
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How do I create an objective-c method that return a block

-(NSMutableArray *)sortArrayByProminent:(NSArray *)arrayObject { NSArray * array = [arrayObject sortedArrayUsingComparator:^(id obj1, id obj2) { Business * objj1=obj1; Business * objj2=obj2; NSUInteger prom1=[objj1…
user4951
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Objective C - How to implement custom callback method but enforce specific parameter?

In my app I have a custom UITableViewCell subclass that pops up a picker when pressed. from now on I'll refer to this class as PickerCell. I'm using several of instances of PickerCell in the same UITableView. I don't want the cell to respond to the…
Avi Shukron
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What is the property block declaration equivalent in swift of the following block property?

In Objective-C I do this: @property (nonatomic, copy) void(^completion)(MyObject * obj); What is the correct way to do this in swift?
zumzum
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