Change the font of a UIBarButtonItem

To be precise, this can be done as below

[buttonItem setTitleTextAttributes:[NSDictionary dictionaryWithObjectsAndKeys: 
    [UIFont fontWithName:@"Helvetica-Bold" size:26.0], NSFontAttributeName,
    [UIColor greenColor], NSForegroundColorAttributeName,
    nil] 
                          forState:UIControlStateNormal];

Or with object literal syntax:

[buttonItem setTitleTextAttributes:@{
     NSFontAttributeName: [UIFont fontWithName:@"Helvetica-Bold" size:26.0],
     NSForegroundColorAttributeName: [UIColor greenColor]
} forState:UIControlStateNormal];

For convenience, here's the Swift implementation:

buttonItem.setTitleTextAttributes([
        NSAttributedStringKey.font: UIFont(name: "Helvetica-Bold", size: 26.0)!,
        NSAttributedStringKey.foregroundColor: UIColor.green],
    for: .normal)

For those interested in using UIAppearance to style their UIBarButtonItem's fonts throughout the app, it can be accomplished using this line of code:

Objective C:

NSDictionary *barButtonAppearanceDict = @{NSFontAttributeName : [UIFont fontWithName:@"HelveticaNeue-Light" size:12.0], NSForegroundColorAttributeName: [UIColor whiteColor]};
[[UIBarButtonItem appearance] setTitleTextAttributes:barButtonAppearanceDict forState:UIControlStateNormal];

Swift 2.3:

UIBarButtonItem.appearance().setTitleTextAttributes(
[
    NSFontAttributeName : UIFont(name: "HelveticaNeue-Light", size: 12)!,
    NSForegroundColorAttributeName : UIColor.white
],
for: .normal)

Swift 3

UIBarButtonItem.appearance().setTitleTextAttributes(
[
    NSFontAttributeName : UIFont(name: "HelveticaNeue-Light", size: 12)!,
    NSForegroundColorAttributeName : UIColor.white,
], for: .normal)

Swift 4

UIBarButtonItem.appearance().setTitleTextAttributes(
[
    NSAttributedStringKey.font : UIFont(name: "HelveticaNeue-Light", size: 12)!,
    NSAttributedStringKey.foregroundColor : UIColor.white,
], for: .normal)

Or for a single UIBarButtonItem (not for all app wide), if you have a custom font for one button in particular:

Swift 3

let barButtonItem = UIBarButton()
barButtonItem.setTitleTextAttributes([
    NSFontAttributeName : UIFont(name: "FontAwesome", size: 26)!,
    NSForegroundColorAttributeName : UIColor.white,
], for: .normal)
barButtonItem.title = "\u{f02a}"

Swift 4

let barButtonItem = UIBarButton()
barButtonItem.setTitleTextAttributes([
    NSAttributedStringKey.font : UIFont(name: "FontAwesome", size: 26)!,
    NSAttributedStringKey.foregroundColor : UIColor.white,
], for: .normal)
barButtonItem.title = "\u{f02a}"

Of course, you can change the font & size to whatever you'd like. I prefer to put this code in the AppDelegate.m file in the didFinishLaunchingWithOptions section.

Available attributes (just add them to the NSDictionary):

• NSFontAttributeName: Change font with a UIFont
• NSForegroundColorAttributeName: Change color with a UIColor
• NSShadow: Add a drop shadow (see NSShadow class reference)

(Updated for iOS7+)

Because UIBarButtonItem inherits from UIBarItem, you can try

- (void)setTitleTextAttributes:(NSDictionary *)attributes
                  forState:(UIControlState)state

but this is for iOS5 only. For iOS 3/4, you will have to use a custom view.

In Swift you would do this as followed:

backButtonItem.setTitleTextAttributes([
        NSFontAttributeName : UIFont(name: "Helvetica-Bold", size: 26)!,
        NSForegroundColorAttributeName : UIColor.blackColor()],
    forState: UIControlState.Normal)

These are great answers above. Just updating for iOS7:

NSDictionary *barButtonAppearanceDict = @{NSFontAttributeName : [UIFont fontWithName:@"HelveticaNeue-Thin" size:18.0] , NSForegroundColorAttributeName: [UIColor whiteColor]};
    [[UIBarButtonItem appearance] setTitleTextAttributes:barButtonAppearanceDict forState:UIControlStateNormal];