CODEWITHSUNDEEP
iphoneobjective-cioscocoa-touch
Sergey Grishchev
Sergey Grishchev

Reputation: 12051

Unable to access @property on another class

A really noob question here. I have 2 VCs. One is called SGPlayer and another is SGDownloader. Basically I want to change the property of SGDownloader from the first class. I import the SGDownloader class like this:

//  SGPlayer.h

#import <UIKit/UIKit.h>
#import "SGDownloader.h"

@interface SGPlayer : UIViewController

@property (nonatomic, retain) SGDownloader *downloaderClass;

SGPlayer.m is like this:

//  SGPlayer.m

#import "SGPlayer.h"

@interface SGPlayer ()

@end

@implementation SGPlayer
@synthesize downloaderClass;

I then set the downloadUrl property form the SGDownloader class in an action triggered by UIButton like that:

- (IBAction)loadURLButton:(id)sender {

    [self performSegueWithIdentifier:@"loadMyData" sender:nil];
    downloaderClass.downloadURL = [NSURL URLWithString:@"http://www.google.com"];
}

NSLog gives me (null) on my URL. If I use prepareForSegue method all is fine:

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {

    if ([[segue identifier] isEqualToString:@"loadMyData"])
    {
        SGDownloader *vc = [segue destinationViewController];

        vc.downloadURL = [NSURL URLWithString:@"http://www.google.com"];
    }
}

The thing is I don't want to use prepareForSegue here.

I assume I might be misunderstanding the whole concept of how do you transfer the data between classes in Obj-C.

Edit:

I do have a synthesised property in the SGDownloader class:

@interface SGDownloader : UIViewController

@property (nonatomic, retain) NSURL *downloadURL;

@end

Upvotes: 1

Views: 447

Answers (6)

Hermann Klecker
Hermann Klecker

Reputation: 14068

Unfortunately yo do not show the full code. I guess that if your self.downloaderClass is not nil, as suggested before, then it is a different instance of oyur view controller than segue.destinationViewController. You may have created an instance but that does not stop storyboard from creating its own.

I'd rather suggest to use prepareForSegue when using storyboard. Simply because this method is designed for exactly this purpose.

BTW, downloaderClass is not the smartest name for that object, because it does not refer to a class (that would be a property of type Class*) but to an acutal instance. downloadViewController or so would be more appropriate in terms of "speaking code". However, this does not cause your problem.

And, of course, downloadURL must be accessible from outside that class. That needs to be a property too. On the other hand it seems to be derrived from a constant string value. If that is true and remains true while your project carries on, then there is no point in setting the value from outside. You could as well set it in an appropriate init method within the class.

Upvotes: 2

Martin
Martin

Reputation: 747

As mentioned above your downloaderClass is nil when you try and set the property. So before you set it you can use self.downloaderClass = [[SGDownloader alloc] init....].

You then have to make sure when you switch view controllers that you are using this instance and not one instantiated by the storyboard (cant help here as i havent used storyboards).

Upvotes: 3

YogiAR
YogiAR

Reputation: 2237

Either create property of downloadURL and synthesize it or you can use delegate to pass values between class

Upvotes: 3

Levi
Levi

Reputation: 7343

It seems that your downloaderClass property is nil, not just it's downloadURL. That is why you get null. In the prepareForSegue it is instantiated for you from the storyboard, I recommend you use it there.

Hope this helps!

Upvotes: 2

zahreelay
zahreelay

Reputation: 1742

You need to provide memory to your SGDownloader *downloaderClass before you assign a property. Use alloc before you use that downloaderClass.

Upvotes: -1

Rajneesh071
Rajneesh071

Reputation: 31091

Hi make property of downloadURL

@property (nonatomic, retain) NSUrl * downloadURL;

Upvotes: 3

Related Questions