Objective C - deallocated variable - objective-c

Question

I have this static/singelton class that has a member variable.
Everything works just fine, however, when I quit the app, and the come back, that member variable is causing the app to crash.
I tried reinitializing the member variable, but doesn't seem to do the trick.
I am including samples of my code below, has anyone seen this before?
The header (.h) file:
#interface Metrics : NSObject {
Metrics *metrics;
Distance *distance;
}
The implementation (.m) file:
#implementation Metrics
static Metrics *metrics = nil;
+ (Metrics *)sharedInstance {
#synchronized(self) {
if (metrics == nil) {
metrics = [[Metrics alloc] init];
}
}
return metrics;
}
- (id)init {
self = [super init];
if (self) {
}
return self;
}
-(void) setupDistance
{
distance = [[Distance alloc] init];
distance.test; // it dies here after I quit the app and come back
}
And where it is used, AppDelegate.m
- (void)applicationDidBecomeActive:(UIApplication *)application
{
[[Metrics sharedInstance] setupDistance];
}
Thank you,
Tee

Answer 1

When you say "quit the app" you almost certainly mean "send the app to the background." This does not terminate your application. When you become active again, you're leaking distance and assigning a new one. I suspect that something in test is actually the problem.
First, don't access your ivars directly, except in init and dealloc. Use accessors. This will make most of your problems go away.
Second, don't call setupDistance in applicationDidBecomeActive. You mean to call it in applicationDidFinishLaunchingWithOptions:. But better yet, just initialize it during Metrics init. Why have this internal Metrics detail in the app delegate?

Answer 2

applicationDidBecomeActive will get called when it comes back from sleep calling to setup in the distance again. It's wierd that you're calling a property (.test) and not assigning. Is test doing work? Should it be a method? What's it doing?
Also, in a singleton you have to overload quite a few things. Here's a good template for a singleton that I use.
static MySingleton *sharedInstance = nil;
#implementation MySingleton
#pragma mark -
#pragma mark class instance methods
#pragma mark -
#pragma mark Singleton methods
+ (MySingleton*)sharedInstance
{
#synchronized(self)
{
if (sharedInstance == nil)
sharedInstance = [[MySingleton alloc] init];
}
return sharedInstance;
}
+ (id)allocWithZone:(NSZone *)zone {
#synchronized(self) {
if (sharedInstance == nil) {
sharedInstance = [super allocWithZone:zone];
return sharedInstance;  // assignment and return on first allocation
}
}
return nil; // on subsequent allocation attempts return nil
}
- (id)copyWithZone:(NSZone *)zone
{
return self;
}
- (id)retain {
return self;
}
- (unsigned)retainCount {
return UINT_MAX;  // denotes an object that cannot be released
}
- (void)release {
//do nothing
}
- (id)autorelease {
return self;
}
#end