IOS Issue Accessing Class Properties

Question

I have a view that is loaded as a subview programmatically. The view has a three properties defined in the .h and synthesized in the .m. The view is loaded by creating an object of the view in the parent controller and then calling it's initialization function. In the initialization function I set a number of values to the their respective properties. For some reason I am not able to access the properties outside of the initialization function. My first thought was that the properties were defined incorrectly but after messing around with their strong and weak attributes nothing changed.

The UIView's .h

#import <UIKit/UIKit.h>
#import <QuartzCore/QuartzCore.h>
#import <Parse/Parse.h>

@protocol subViewDelegate
- (void)photoFromSubview:(NSInteger *)imageId;
- (void)downloadData;
@end

@interface ImageViewer : UIView

@property (nonatomic, assign) id <subViewDelegate> delegate;
//three properties
@property (nonatomic, copy) UIImage *mainImage;
@property (nonatomic, copy) UIViewController *parentView;
@property (nonatomic) NSInteger imageId;

- (void)removeImageViewer;
- (void)captureImage:(id)sender;
- (void)uploadPhoto:(id)sender;
- (UIImage *)addBackground;

- (ImageViewer *)loadImageIntoViewer:(UIViewController *)superView imageToLoad:(UIImage *)imageToLoad imageId:(NSInteger *)imageId;

@end

The relevant functions in the UIViews .m

//implementation of the properties 
#import "ImageViewer.h"
#import "SpinnerView.h"

@implementation ImageViewer : UIView
{

}

@synthesize mainImage = _mainImage;
@synthesize parentView = _parentView;
@synthesize imageId = _imageId;

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self)
    {

    }
    return self;
}

//initialization function
- (ImageViewer *)loadImageIntoViewer:(UIViewController *)superView imageToLoad:(UIImage *)imageToLoad imageId:(NSInteger *)imageId
{
    //create a new view with the same frame size as the superView
    ImageViewer *imageViewer = [[ImageViewer alloc] initWithFrame:superView.view.bounds];
    imageViewer.delegate = superView;

    //three properties assigning values 
    _mainImage = imageToLoad;
    _parentView = superView;
    _imageId = imageId;

    //if something's gone wrong, abort!
    if(!imageViewer)
    {
        return nil;
    }

    //add all components and functionalities to the program
    //when I use _mainImage bellow it works with the correct value 
    UIImageView *background = [[UIImageView alloc] initWithImage:[imageViewer addBackground]];
    background.alpha = 0.85;
    [imageViewer addSubview:background];
    [imageViewer addSubview:[imageViewer addImageToView:_mainImage superView:superView.view]];
    [imageViewer addSubview:[imageViewer addButtonToView:(superView.view.bounds.origin.x + 10.0) yPos:(superView.view.bounds.origin.x + 10.0) buttonAction:@selector(back:) buttonTitle:@"Back"]];
    [imageViewer addSubview:[imageViewer addButtonToView:(superView.view.bounds.origin.x + 10.0) yPos:((superView.view.center.y/2) + 270.0) buttonAction:@selector(captureImage:) buttonTitle:@"Camera"]];
    [imageViewer addSubview:[imageViewer addButtonToView:(superView.view.bounds.origin.x + 105.0) yPos:((superView.view.center.y/2) + 270.0) buttonAction:@selector(uploadPhoto:) buttonTitle:@"Upload"]];
    [superView.view addSubview:imageViewer];

    return imageViewer;
}

The above code allows you to access the values assigned to _mainImage, _parentView and _imageId. But when I try to access them through a private function defined in the .m the return the initialized value as can be seen below.

- (void)uploadPhoto:(id)sender
{
   //These all return as empty or uninitialized
   NSLog(@"%@", _mainImage);
   NSLog(@"%d", _imageId);
}

Why is this? Am I defining the properties incorrectly in the .h or is it because self doesn't refer to the instance of ImageView defined in loadImageIntoViewer? How can I fix this?

One question if you declare them as strong instead of copy does it work in the private method? — Radu, May 09 '13 at 14:16
I believe you don't want a copy of UIViewController - you want a weak reference to it. — Rok Jarc, May 09 '13 at 14:21

score 1 · Accepted Answer · answered May 09 '13 at 14:21

Some thoughts:

Firstly, you don't need to declare the @synthesize statements anymore, assuming you're working on a recent version of XCode. The compiler will automatically insert the synthesize statements for you, and create instance variables appended with a underscore (as you've done).

Secondly, when you say you are 'not able to access the properties outside of the initialization function' - do you mean when you try to access the properties you get a bad access, or they simply return nil? I'm not sure if you mean what you say, because looking at your current initialization method you don't currently access the properties at all, only their instance variables.

I think you might be getting instance variables and properties mixed up. A property in Objective-C looks like this:

NSLog(@"%@", self.mainImage);

...your app structure is also a little confusing to me. Your initialisation method is an instance, rather than class, method, so you create one ImageViewer only to then have it create another ImageViewer. I'd suggest you try and create a true init method, one that calls out to initWithFrame. I think maybe you might find it helpful to look through Apple's intro Objective-C documentation, as I don't think the structure of your app is helping you debug the issue.

I read into the documentation for the UIView. I see exactly what you mean with the confusion between class and instance. I was unaware that the initWithFrame was the initializer method for the UIView. I have essentially copied the code from load image into view to the initWithFrame method. Now I have a couple of questions, the documentation said that the initWithFrame method could be customized or overdid can I add my ow parameters to the initWithFrame method? Also does the initWithFrame method get called when I add the view from my main view controller with addSubview? @lxt — ScottOBot, May 09 '13 at 18:31

IOS Issue Accessing Class Properties

1 Answers1