The compiler complains on var completionHandler: (Float)->Void = {} because the right-hand side is not a closure of the appropriate signature, i.e. a closure taking a float argument. The following would assign a “do nothing” closure to the completion handler: var completionHandler: (Float)->Void = { (arg: Float) -> Void in } and this can be … Read more
Strictly speaking, the fact that it’s a const copy has nothing to do with this problem. Blocks will retain any obj-c values that are captured when they are created. It just so happens that the workaround for the const-copy issue is identical to the workaround for the retain issue; namely, using the __block storage class … Read more
Use dispatch groups: see here for an example, “Waiting on Groups of Queued Tasks” in the “Dispatch Queues” chapter of Apple’s iOS Developer Library’s Concurrency Programming Guide Your example could look something like this: dispatch_group_t group = dispatch_group_create(); dispatch_group_async(group,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ { // block1 NSLog(@”Block1″); [NSThread sleepForTimeInterval:5.0]; NSLog(@”Block1 End”); }); dispatch_group_async(group,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ { // … Read more
Short answer Instead of accessing self directly, you should access it indirectly, from a reference that will not be retained. If you’re not using Automatic Reference Counting (ARC), you can do this: __block MyDataProcessor *dp = self; self.progressBlock = ^(CGFloat percentComplete) { [dp.delegate myAPI:dp isProcessingWithProgress:percentComplete]; } The __block keyword marks variables that can be modified … Read more
List of Block Declaration Syntaxes Throughout, let return_type be the type of object/primitive/etc. you’d like to return (commonly void) blockName be the variable name of the block you’re creating var_type be the type object/primitive/etc. you’d like to pass as an argument (leave blank for no parameters) varName be the variable name of the given parameter … Read more
@property (nonatomic, copy) void (^simpleBlock)(void); @property (nonatomic, copy) BOOL (^blockWithParamter)(NSString *input); If you are going to be repeating the same block in several places use a type def typedef void(^MyCompletionBlock)(BOOL success, NSError *error); @property (nonatomic) MyCompletionBlock completion;
You need to use this line of code to resolve your problem: __block Person *aPerson = nil; For more details, please refer to this tutorial: Blocks and Variables
It tells the compiler that any variable marked by it must be treated in a special way when it is used inside a block. Normally, variables and their contents that are also used in blocks are copied, thus any modification done to these variables don’t show outside the block. When they are marked with __block, … Read more
I think you’re looking for dispatch_after(). It requires your block to accept no parameters, but you can just let the block capture those variables from your local scope instead. int parameter1 = 12; float parameter2 = 144.1; // Delay execution of my block for 10 seconds. dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 10 * NSEC_PER_SEC), dispatch_get_main_queue(), ^{ NSLog(@”parameter1: %d parameter2: … Read more