persisting launchOptions NSURL as global variable - iphone

Question

I have associated my app with a UTI so that users can launch KML attachments. In the iPad app delegate of my universal app I can see the launchOptions and from these I get an NSURL for the file being launched. I want to store this as a global so that I can access it from elsewhere in my app, I am doing this using a singleton called Engine. This is my App Delegate:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
Engine *myEngine=[Engine sharedInstance];
StormTrackIpad *newVC=[[StormTrackIpad alloc] initWithNibName:#"StormTrackIpad" bundle:nil];
[window addSubview:newVC.view];
NSURL *launchFileURL=(NSURL *)[launchOptions valueForKey:#"UIApplicationLaunchOptionsURLKey"];
myEngine.launchFile=launchFileURL;
/* Show details of launched file
NSString *message =launchFileURL.absoluteString;
NSString *title = [NSString stringWithFormat:#"Opening file"];
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:title message:message delegate:self cancelButtonTitle:#"OK" otherButtonTitles:nil];
[alert show];
[alert release];
*/
[window makeKeyAndVisible];
return YES;
}
My Engine class looks like this:
// Engine.h
#import <Foundation/Foundation.h>
#interface Engine : NSObject {
NSURL *launchFile;
}
+ (Engine *) sharedInstance;
#property (nonatomic, retain) NSURL *launchFile;
#end
// Engine.m
#import "Engine.h"
#implementation Engine
#synthesize launchFile;
static Engine *_sharedInstance;
- (id) init
{
if (self = [super init])
{
// custom initialization
}
return self;
}
+ (Engine *) sharedInstance
{
if (!_sharedInstance)
{
_sharedInstance = [[Engine alloc] init];
}
return _sharedInstance;
}
#end
My problem is that when I try to access the launchFile variable from the Engine elsewhere in my app (from a View Controller) the debugger shows the value of Engine.launchFile to be . I am accessing the variable like this:
- (void)viewDidLoad {
[super viewDidLoad];
Engine *myEngine=[Engine sharedInstance];
NSURL *launchFile=myEngine.launchFile;
NSString *title = [NSString stringWithFormat:#"Opening file"];
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:title message:launchFile.absoluteString delegate:self cancelButtonTitle:#"OK" otherButtonTitles:nil];
[alert show];
[alert release];
}
Any help?

Answer 1

Your code looks OK at first glance - can you set a breakpoint on myEngine.launchFile = just to see what myEngine is pointing at? This should make sure that your singleton code is working.
Also, have you checked that [launchOptions valueForKey:#"UIApplicationLaunchOptionsURLKey"] definitely returns an object? Did you mean to type this :
[launchOptions valueForKey:UIApplicationLaunchOptionsURLKey];
Sam
P You should read the answer to this question on creating singleton objects, there's a few overrides that you should put into your Engine class ;)