Public Properties Loses Value When Accessed From Functions - ios

Question

I am very new to iPhone programming and I have a very basic problem which just confuses me. I declare a public UIScrollView in my header file like this.
#property UIScrollView *scroller;
Then in my implementation file I synthesize it;
#synthesize scroller;
And in the
- (id)initWithFrame:(CGRect)frame
method I allocate my object.
if (self) {
scroller = [[UIScrollView alloc] initWithFrame:CGRectMake(23, 99, 280, 300)];
}
( The class is extended from UIView )
But when I try to access this property in a method I always get nil value which just does not make sense.
- (void)DeselectAll{
scroller.hidden = YES;
}
( The scroller is always returning nil here. )
I also try accessing it with self.scroller but the value is still nil. I am sure that I am missing a very simple point but just couldn't figure it out.
( By the way this problem is happening for all my public properties )
Any help is very much appreciated.
Thank you.

Answer 1

First of all, declare the property like below
#property(strong,nonatomic) UIScrollView *scroller;
Now you initialize as
if (self) {
self.scroller = [[UIScrollView alloc] initWithFrame:CGRectMake(23, 99, 280, 300)];
}

Answer 2

Create the UIScrollView in your header file like so :
#interface MyViewController : UIViewController {
UIScrollView * scrollView;
}
#property (nonatomic, retain) IBOutlet UIScrollView * scrollView;
#end
Then initialize it in viewDidLoad:
#synthesize scrollView;
- (void)viewDidLoad {
[super viewDidLoad];
self.scrollView = [[UIScrollView alloc]init(WithFrame:)];
[self.scrollView addSubview:...];
self.scrollView.contentSize = ...;
}

Answer 3

If you are using ARC, I think the properties are getting released.
Just use strong property at the time of declaration.
#property(strong, nonatomic)UIScrollView *scroller;

Answer 4

Ya you have correct. But you had missed memory management to property. Take a look at this.
For example, if you need to hold your created object. you should do this.
For ARC,
#property(strong,nonatomic) UIScrollView *scroller;
withour ARc
#property(retain,nonatomic) UIScrollView *scroller;
Update:
You must assign it using self. Otherwise it will not set via setter method. like as below
if (self) {
self.scroller = [[UIScrollView alloc] initWithFrame:CGRectMake(23, 99, 280, 300)];
}

Answer 5

Ok, here is how i solved this problem. I created these controls in my nib file and assigned the variables as outlets to these objects. In that case the objects are retained and I can access them from my methods. (I tried defining the variables as IBOutlets without assigning to the controls in the nib file and in that case values were returned as nil again. Only after I link them to controls, the objects are retained. ) Although I solved this problem I have difficulty understanding this behaviour. I tried everything recommended in the answers but weirdly I kept getting nil for the object in my method.
Thanks to everyone that has taken time to write a reply to my question. Maybe someone can explain and help me understand this weird behaviour?
Cheers.

Answer 6

Have you checked that initWithFrame: is being called?
If you are creating your UIView subclass in a NIB file then that method won't be called, but initWithCoder: is called instead.