Question

I am trying to create a sort of ‘settings’ page, and I am having a hard time switching the background image of my original view. The code, so far, is:

-(IBAction)switchBackground:(id)sender {
ViewController *mainView = [[ViewController alloc] initWithNibName:nil bundle:nil];
mainView.displayedImage.image = [UIImage imageNamed:@"image.png"];;
}

Perhaps I can get some pointers?

Thanks, all.

Answer 1

You are creating a new mainView object each time you call switchBackground method. You must change the background of an existing object to see the change happen.

From your code it is hard to say where switchBackground method is located. ViewController?

If it is located in the view controller then all you have to do is:

self.displayedImage.image = [UIImage imageNamed:@"image.png"];

EDIT

As per your comment.

When you want to change the image of an object of class A from class B you can do it in two different ways:

1. Through reference to an object

this is the settings initializer which on creation gets the pointer to your existing mainView

@property(nonatomic,assign)ViewController *mainView;

- (id)initWithMainViewController:(ViewController*)vc {
    self = [super init];
    if (self) {
        self.mainView = vc;
    }
    return self;
}

-(IBAction)switchBackground:(id)sender {
    mainView.displayedImage.image = [UIImage imageNamed:@"image.png"];
}

2. By posting local notification through NSNotificationCenter.

-(IBAction)switchBackground:(id)sender {
      [[NSNotificationCenter defaultCenter] postNotificationName: @"changeImage" object: [UIImage imageNamed:@"image.png"]];
}

Now in your ViewController listen to the notification and react

in the init method in ViewController

- (id)initWithMainViewController:(ViewController*)vc {
    self = [super init];
    if (self) {
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(changeImage:) name:@"changeImage" object:nil];
    }
    return self;
}

-(void)changeImage:(NSNotification*)notification{
    self.displayedImage.image = (UIImage*) notification.object;
}