Question

What’s the best way to make a synchronous version of an asynchronous method in Objective-C (for iOS, in case it matters)?

Say you have a class with these two methods:

- (void) asyncDoSomething; // Starts an asynchronous task. Can't be changed.
- (void) onFinishDoSomething; // Called when the task is finished 

How would you implement a synchronous doSomething that does not return until the task is finished?

Answer 1

Ok, so you can declare a global boolean that will tell you to continue or wait, just before calling your - (void)asyncDoSomething; method you set your BOOL wait to YES and after the method you do

while (wait) {
    [NSThread sleepForTimeInterval:1];
}

to wait for your response, and in you async callback - (void)onFinishDoSomething; you set your boolean to NO;

This way, your method is still called asynchronous but the code after is not executed before the response. It will wait like if it was synchronous.