CODEWITHSUNDEEP
iosobjective-cnsdatenscalendar
kas-kad
kas-kad

Reputation: 3764

Can't init static calendar in initialize method of NSDate category

I've created a helpers category for NSDate (NSDate+Helpers). Here is a caching for the calendar object I'm going to use inside the category implementation:

static NSCalendar* currentCalendar = nil;
@implementation NSDate (Helpers)

+(void)initialize{
    currentCalendar = [NSCalendar currentCalendar];
}
@end

The problem is that my application doesn't starts anymore. I see only black screen. I would like to know what I am doing wrong. You can get same problem on clean test project.

Upvotes: 0

Views: 191

Answers (1)

Greg
Greg

Reputation: 9168

When you use a category to override an existing method, you overwrite the original implementation, so NSDate's original +initialize method never gets executed. In this case, it looks like it's doing something in that method that's necessary for its own internal functionality, and this is breaking your app.

Even if this is not the issue, overriding the +initialize method is a bad idea, and doing any custom object instantiation there is an especially bad idea.

Try initialising the calendar object somewhere else, e.g. in applicationDidFinishLaunchingWithOptions: in your app's delegate.

Another thing you can do is implement the calendar as a singleton in your category, like so:

@implementation NSDate (Helpers)

- (NSCalendar *)myCurrentCalendar {
    static NSCalendar *currentCalendar; // static property
    static dispatch_once_t onceToken;   // token for dispatch
    dispatch_once(&onceToken, ^{
        currentCalendar = [NSCalendar currentCalendar]; // initialise
    });
    return currentCalendar; // return the calendar
}

Then, when you need to use it, you access it as [NSDate myCurrentCalendar]. This will initialise the calendar the first time you call this method, and on subsequent calls to the method will simply immediately return the calendar.

Upvotes: 2

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