On 29/08/2013, at 5:18 AM, Rick C. <rickcort...@gmail.com> wrote:
> But this is an unreliable way to do this I know because I have problems. Can
> someone please help me with the right way? Because I need for it to wait
> before advancing or else it will cause problems in following code. Really
> appreciate the time thanks!
You should state what your goals are and why it's not meeting them. I'm
guessing what you're trying to do is to download an image from a server which
takes time, but your program can't do anything until you have it.
You need to design your app for asynchronous work like this - just spinning the
run loop 'inline' is no good.
As a general solution, I usually follow this outline:
1. Design an object that is responsible for supplying the data you need (image,
whatever).
2. Allow the above object to return nil to its client (caller) if the data is
not yet available, but use that call to trigger the asynchronous fetch. That
fetch can be performed using any of the asynchronous techniques available -
GCD, threads, runloop queues, etc.
3. The client must be ready to deal with the nil and defer the task that needs
the data until later, returning to the normal run loop while it waits, or get
on with something else.
4. When the fetcher has the data, it notifies the client that the data is
ready, so that the client can ask for it again, this time with a positive
result.
5. The notification in step 4 can use any reasonable method - e.g. an actual
notification, an explicit callback to the client, KVO, etc.
The fetcher object wraps up all the functionality relating to the actual fetch
and caches the result data so it can return it when required. This general
outline works whether the data to be fetched comes from the web, off disk,
wherever you need the client to remain responsive while a lengthy background
load takes place.
The client code looks like this:
- (void) getData
{
// call initially when you require something
myData = [fetcher getData];
if( myData )
[self processData];
}
- (void) fetchNotification
{
// called by fetcher when it finishes
[self getData];
}
--Graham
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