Objective-C - Errors when passing a variable into function - iphone

Question

What is the easiest way to pass a var into another function ?
- (void)locationManager:(CLLocationManager *)manager
didUpdateToLocation:(CLLocation *)newLocation
fromLocation:(CLLocation *)oldLocation {
NSLog(#"%#", started);
}
I tried:
Defined a global vars:
extern NSString *started;
When I set the NSString directly and passing into another function, it works well:
-(void) startTracking:(CDVInvokedUrlCommand*)command {
started = #"testing";
}
But it doesn't work:
-(void) startTracking:(CDVInvokedUrlCommand*)command {
NSString* myarg = [command.arguments objectAtIndex:0]; // http://docs.phonegap.com/en/2.5.0/guide_plugin-development_ios_index.md.html#Developing%20a%20Plugin%20on%20iOS_writing_an_ios_cordova_plugin
started = myarg;
}
(I'm a objective-C beginner, don't understand it well)
EDIT: Seems like it only crashed when I put the app into background.

Answer 1

Depending on wether you are using ARC, you have to retain the object. You'll probably want to use a property on your class:
in your header:
#property(strong) NSString *started;
in implementation:
-(void)locationManager:(CLLocationManager *)manager
didUpdateToLocation:(CLLocation *)newLocation
fromLocation:(CLLocation *)oldLocation {
NSLog(#"%#", self.started);
}
-(void) startTracking:(CDVInvokedUrlCommand*)command {
self.started = #"testing";
}
-(void) startTracking:(CDVInvokedUrlCommand*)command {
NSString* myarg = [command.arguments objectAtIndex:0];
self.started = myarg;
}

Answer 2

Mate, seems like you want to track the date you started receiving location information.
How about doing it like this:
// Your .h file
#interface MyClass <CLLocationManagerDelegate>
{
BOOL hasStartedUpdatingLocation;
NSDate *startDate;
CLLocationManager *locationManager;
}
...
// Your .m file
- (void)locationManager:(CLLocationManager *)manager
didUpdateToLocation:(CLLocation *)newLocation
fromLocation:(CLLocation *)oldLocation
{
// ---------------------------------------------------------------
// if has NOT started updating location, record start date
// otherwise, do not execute this if statement
// ---------------------------------------------------------------
if(!hasStartedUpdatingLocation)
{
hasStartedUpdatingLocation = YES;
// this if statement should only execute once
startDate = [NSDate date]; // get the current date and time
}
else
{
// do something else
}
}