As I believe you correctly diagnosed, using self will not necessarily cause strong reference cycle in this scenario. But this will retain the view controller while the network operation completes, and in this case (as in most cases), there’s no need to. Thus, it may not be necessary to do use weakSelf, but probably prudent … Read more
You don’t need to make two sets of weak references. What you want to avoid with blocks is a retain cycle—two objects keeping each other alive unnecessarily. If I have an object with this property: @property (strong) void(^completionBlock)(void); and I have this method: – (void)doSomething { self.completionBlock = ^{ [self cleanUp]; }; [self doLongRunningTask]; } … Read more
You should only use a weak reference to self, if self will hold on to a reference of the block. In your example, you are not keeping a reference to your block in self, you are only using blocks inline with the UIView animateWithDuration:, and as such there is no need to use __weak myViewController … Read more
A block is a lot like an anonymous function. So you can use return to exit from the function with return type void.
Sure. typedef void(^MyCustomBlockType)(void); @interface MyCustomObject { MyCustomBlockType block; } @property (nonatomic, copy) MyCustomBlockType block; //note: this has to be copy, not retain – (void) executeBlock; @end @implementation MyCustomObject @synthesize block; – (void) executeBlock { if (block != nil) { block(); } } – (void) dealloc { [block release]; [super dealloc]; } @end //elsewhere: MyCustomObject * … Read more
To block the execution of the main thread until the operation completes, you could do [operation waitUntilFinished] after it’s added to the operation queue. In this case, you wouldn’t need the return in the block; setting the __block variable would be enough. That said, I’d strongly discourage forcing asynchronous operations to synchronous methods. It’s tricky … Read more
I always use this when I want to write a block: http://fuckingblocksyntax.com EDIT If you are writing Swift then use this: http://fuckingswiftblocksyntax.com If the above links are not opening because of the obscene language, use this one. http://goshdarnblocksyntax.com/
Excerpt From: Apple Inc. “Using Swift with Cocoa and Objective-C.” iBooks: “Swift closures and Objective-C blocks are compatible, so you can pass Swift closures to Objective-C methods that expect blocks. Swift closures and functions have the same type, so you can even pass the name of a Swift function. Closures have similar capture semantics as … Read more
See Declaring a Block Reference in “Blocks Programming Topics”: Block variables hold references to blocks. You declare them using syntax similar to that you use to declare a pointer to a function, except that you use ^ instead of *. So typedef void (^myBlock) (int a); defines a the type of a block using the … Read more
You must use the __block specifier when you modify a variable inside a block, so the code you gave should look like this instead: __block NSString *textString; dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, (unsigned long)NULL), ^(void) { textString = [self getTextString]; }); Blocks capture the state of the variables referenced inside their bodies, so the captured variable must be declared … Read more