UIImage PNG Opacity adjustment - ios

Question

I have created a custom button using a .png image that has transparency. However, when I implement it as a UIImage, the transparency is lost. Here's the code that I'm using:
- (void)setMyCustomBackButton;
{
UIImage *backButtonImage = [UIImage imageNamed:#"Back Button.png"];
UIButton *backButton = [UIButton buttonWithType:UIButtonTypeCustom];
[backButton setBackgroundImage:backButtonImage forState:UIControlStateNormal];
[backButton addTarget:self action:#selector(popCurrentViewController) forControlEvents:UIControlEventTouchUpInside];
backButton.frame = CGRectMake(0, 0, backButtonImage.size.width, backButtonImage.size.height);
UIView *backButtonView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 63, 33)];
backButtonView.bounds = CGRectOffset(backButtonView.bounds, -12, -2);
[backButtonView addSubview:backButton];
UIBarButtonItem *finalBackButton = [[UIBarButtonItem alloc] initWithCustomView:backButtonView];
self.navigationItem.leftBarButtonItem = finalBackButton;
}
Is there a UIImage property for transparency? Does it have to do with opacity?

Answer 1

If you're creating the PNG in an image editing software, please make sure you've encoded the transparency while creating the image. Sometimes some image editors have an option for 'saving transparency' that's unchecked by default, when you're exporting something as a PNG.
Other than that, any transparency on a PNG will show up on a UIButtonTypeCustom. You don't need to do anything special to preserve transparency on a UIImage that's loading up a PNG.
Before you use the image in the code, please open it in Preview to make sure the transparency is present.
Oh and to answer your other question, UIImage does not have any properties relating to transparency. The closest thing you have is the alpha property for a UIView but even that simply changes the overall opacity of your UIView.
EDIT: Missed this the first time I read your question. Try:
UIBarButtonItem *finalBackButton = [[UIBarButtonItem alloc] initWithCustomView:backButton];
No need to have the backButtonView. You can pass in the UIButton as the custom view. I use this to create custom bar button items. This should fix your problem.
EDIT 2: The UIBarButtonItem class does not have an alpha property you can set. Also, modifying the alpha property of the UIButton that you set as the UIBarButtonItem's custom view won't affect the transparency of the UIBarButtonItem.
The only way you can do this is to modify the transparency of the source image being used for the UIButton.
Modify your original PNG to have the desired transparency you want (and based on your comments, you need a very low transparency). Use an image editing software / preview to fine tune the transparency before you export the PNG.