Question

I have made this ImageView (UIImageView) programmatically in the viewDidLoad method.

  UIImageView *imageview = [[UIImageView alloc]initWithFrame:CGRectMake(110, 200, 100, 100)];
  imageview.image = [UIImage imageNamed:@"imageviewImage.png"];
  [self.view addSubview:imageview];

But when I create the button like this in the viewDidLoad method I can’t reference it in other methods in the same class. Let’s say I want to change the ImageView alpha to 0.0f in an IBAction method in the same class. I can’ just reference to imageview like this:

  -(IBAction) button {
  imageview.alpha = 0.0f;
  }

What is the easiest thing to do with the ImageView if I want to reference it in another method?

PS: The ImageView has to be made programmatically.

Answer 1

The issue is scope. The imageView pointer you create in viewDidLoad is only accessible there. Either create a property or use a tag.

1) Create a property:

// top of the .m file
@interface MyClass () /* replace MyClass with your class name */
@property(strong, nonatomic) UIImageView *imageView;
@end

// in viewDidLoad, don't declare UIImageView *imageView, just replace
// all mentions of it with self.imageView;

2) Or use a tag:

// top of the .m file
#define kIMAGE_VIEW_TAG   128

// in viewDidLoad
UIImageView *imageview = [[UIImageView alloc]initWithFrame:CGRectMake(110, 200, 100, 100)];
imageview.image = [UIImage imageNamed:@"imageviewImage.png"];
imageView.tag = kIMAGE_VIEW_TAG;
[self.view addSubview:imageview];

// elsewhere in the code, when you want the image view
UIImageView *imageView = (UIImageView *)[self.view viewWithTag:kIMAGE_VIEW_TAG];