Objective-C Blocks are very powerful but often under-used or badly abused! Continuing on from my previous post on how to declare a block, here is a quick-fire list of 5 experience-earned tips that every developer should know.
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GCD
There are 3 posts filed in GCD (this is page 1 of 1).
How to declare a block
Are you really sure on how to declare a block? How about all 4 variations? On iOS and macOS, it can be easy to forget Objective-C block syntax as it isn’t the most intuitive, especially now Swift is becoming the main language of new projects. Remembering the syntax is actually just a short click away but here are easy-to-read example uses with nullability tips and things to watch out for when declaring a block.
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How to call a block after a delay
On iOS and on OS X you sometimes need the User Interface to update after a short delay. The old way of doing it was calling the performSelector:withObject:afterDelay: selector on any NSObject subclass but that requires defining a new method in your class and you can only pass one object as a parameter.
Instead, you can use dispatch_after from the Grand Central Dispatch APIs to execute code within a block after a certain time interval. Don’t be afraid, it might be low-level C but you can cut and paste and just put your code inside and it will retain the variable scope that blocks usually do!
double delayInSeconds = 0.5;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
// Your code here
});