iPhone 3.0 Compass: how to get a heading?

Question

I'm relatively new to Objective-C and really don't know much about it yet, so I apologise for what is probably a really amateurish question.

I'm trying to get the magnetic heading from CLHeading and CLLocationDirection. However I'm getting compile errors for this line of code:

locationLabel.text = [[[location course] magneticHeading] stringValue];

The errors are:

warning: invalid receiver type 'CLLocationDirection'  
error: cannot convert to a pointer type

I don't really understand what I'm doing wrong here. Please help!

Answer 1

Here are the steps needed to use the compass.

1) check the availability: if the headingAvailable property of the location manager is YES, then you can use the compass.

2) use the location manager method -(void) startUpdatingHeading to begin receiving the information you are searching for

3) actually retrieve this information using the delegate method (do not forget to set yourself as the delegate)

 - (void)locationManager:(CLLocationManager *)manager didUpdateHeading:(CLHeading *)newHeading

Hope this helps.

Answer 2

magneticHeading is of CLLocationDirection type, which is simply a typedef for the primitive data type "double". In your example you are trying to send a message to something that is not an object ! You should simply format the double like so:

locationLabel.text = [NSString stringWithFormat:@"Heading %.3f", [[location course] magneticHeading]];

Answer 3

How are you allocating and initializing location? Make sure location is defined as a (CLLocationDirection *) and not just a (CLLocationDirection).