BarButtonItem resizing for unknown reason - objective-c

Question

I have a button that is initialized like that>
self.button = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemDone
target:self
action:#selector(doAction)];
Later, I am attaching a custom background to it, like that>
[self.button setBackgroundImage:[UIImage imageNamed:#"customNavBar_button_right_enabled"]
forState:UIControlStateNormal
barMetrics:UIBarMetricsDefault];
and puting it onto navbar.
[self.navigationItem setRightBarButtonItem:self.button
animated:NO];
This image has fixed size. I want that button to have fully custom background image with no "intelligent" resizing with UIEdgeInsets.I don't want any resizing. But for some reason, it behaves like its insets would be active and it is resized to have bigger width, with roughly the middle half of picture considerably stretched to provide for the wider button.
Why is this happening? How can I prevent this to happen?

Answer 1

The easiest way to achieve a bar button item with a custom image is by:
Drag a UIButton onto the storyboard.
Set the button Type to Custom and set your image for that button.
Drag the button onto your Toolbar.
The storyboard automatically creates a UIBarButtonItem and adds your UIButton as a subview. Or if you do NOT want to use storyboards you could implement the following:
// Initialize the UIButton
UIImage *buttonImage = [UIImage imageNamed:#"buttonImage.png"];
UIButton *aButton = [UIButton buttonWithType:UIButtonTypeCustom];
[aButton setImage:buttonImage forState:UIControlStateNormal];
aButton.frame = CGRectMake(0.0, 0.0, buttonImage.size.width, buttonImage.size.height);
// Initialize the UIBarButtonItem
UIBarButtonItem aBarButtonItem = [[UIBarButtonItem alloc] initWithCustomView:aButton];
// Set the Target and Action for aButton
[aButton addTarget:self action:#selector(aButtonClicked:) forControlEvents:UIControlEventTouchUpInside];
Hope it helps!
EDIT: Do not forget to add the aBarButtonItem to the UIToolbar.