Question

I have an object which takes a long time to do some stuff (it downloads data from a server).

How can I write my own completion block so that I can run…

[downloader doSomeLongThing:^(void) {
    //do something when it is finished
}];

I’m not sure how to save this block in the downloader object.

Answer 1

You can copy the block then invoke it:

typedef void (^CallbackBlk)();

@property (copy) CallbackBlk cb;

- (void)doSomething:(CallbackBlk)blk
{
    self.cb = blk;

    // etc.
}

// when finished:
self.cb();