Question

I am creating a MKMapView in a method named “generateMap”. From inside viewDidLoad, this works:

[self generateMap];

but this causes the map to quickly load and then disappear, leaving only the blank grey grid:

[NSThread detachNewThreadSelector:@selector(generateMap) toTarget:self withObject:nil];

Any ideas why this might be happening when I call the method through a thread?

---

I ended up doing this:

-(void)viewDidLoad {
[NSThread detachNewThreadSelector:@selector(spinTheSpinner) toTarget:self withObject:nil];
[self performSelectorOnMainThread:@selector(generateMap) withObject:nil waitUntilDone:NO];
[super viewDidLoad];
}

This allows me to have a spinner (UIActivityIndicator) and load the MKMapView as I want. I set “waitUntilDone:No]” so that the screen switches the MapView before it is done with generateMap. Otherwise, we would not see the spinner and would only see a blank screen until generateMap was done.

Answer 1

I don’t think it is advisable to try to update the UI through anything but the main thread.

What happens when you try to run -generateMap on the main thread with -performSelectorOnMainThread:withObject:waitUntilDone:?

For example:

[self performSelectorOnMainThread:@selector(generateMap) withObject:nil waitUntilDone:YES];