Question

Here’s my situation: I am making synchronous HTTP requests to collect data but before hand I want to place a loading view within the navigation bar title view. After the request is over I want to return the titleView back to nil.

[self showLoading];        //Create loading view and place in the titleView of the nav bar.
[self makeHTTPconnection]; //Creates the synchronous request
[self endLoading];         //returns the nav bar titleView back to nil.

I know the loading view works because after the request is over the loading view is shown.

My Problem: It should be obvious at this point but basically I want to delay the
[self makeHTTPconnection] function until the [self showLoading] has completed.

Thanks for you time.

Answer 1

You can’t do that in a synchronous approach.
When you would send [self showLoading] message, the UI wouldn’t be updated until the entire method finishes, so it would already finish the other two tasks (makeHTTPConnection and endLoading). As a result, you would never see the loading view.

A possible solution for this situation would be working concurrently:

[self showLoading];
NSOperationQueue *queue = [[[NSOperationQueue alloc] init] autorelease];
NSInvocationOperation *operation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(_sendRequest) object:nil];
[queue addOperation:operation];
[operation release];

Then you must to add the *_sendRequest* method:

- (void)_sendRequest
{
    [self makeHTTPConnection];
    //[self endLoading];
    [self performSelectorOnMainThread:@selector(endLoading) withObject:nil waitUntilDone:YES];
}