Preventing a UITabBar from applying a gradient to its icon images

Question

When I make icons for a UITabBar, it applies a gradient to the images. I need to know how to prevent it from having this gradient.

Answer 1

Apple added tab bar customization in iOS 5, and now this kind of stuff is trivial. Prior to this it was a huge hack, and not recommended.

Here's how to do a completely custom tab bar:

// custom icons
UITabBarItem *item = [[UITabBarItem alloc] init];
item.title = @"foo";
// setting custom images prevents the OS from applying a tint color
[item setFinishedSelectedImage:[UIImage imageNamed:@"tab1_active.png"] withFinishedUnselectedImage:[UIImage imageNamed:@"tab1_image_deselected.png"]];
tab1ViewController.tabBarItem = item;

    // tab bar

    // set background image - will be used instead of glossy black
    tabBarController.tabBar.backgroundImage = [UIImage imageNamed:@"tab_bar_bg.png"];
    // optionally set the tint color - setting this ti nil will result in the standard, blue tint color. tint color is ignored when custom icons are set as above.
    tabBarController.tabBar.selectedImageTintColor = nil;
    // remove the highlight around the selected tab - or provide an alternate highlight image. If you don't do this the iOS default is to draw a highlighted box beneath the selected tab icon.
    tabBarController.tabBar.selectionIndicatorImage = [[UIImage alloc] init];

Answer 2

This is surprisingly difficult as the UITabBar doesn't provide access to it's selected/unselected images. It can be achieved with a private API though:

@interface UITabBar (ColorExtensions)
- (void)recolorItemsWithColor:(UIColor *)color shadowColor:(UIColor *)shadowColor shadowOffset:(CGSize)shadowOffset shadowBlur:(CGFloat)shadowBlur;
@end

@interface UITabBarItem (Private)
@property(retain, nonatomic) UIImage *selectedImage;
- (void)_updateView;
@end

@implementation UITabBar (ColorExtensions)
- (void)recolorItemsWithColor:(UIColor *)color shadowColor:(UIColor *)shadowColor shadowOffset:(CGSize)shadowOffset shadowBlur:(CGFloat)shadowBlur
{
    CGColorRef cgColor = [color CGColor];
    CGColorRef cgShadowColor = [shadowColor CGColor];
    for (UITabBarItem *item in [self items])
        if ([item respondsToSelector:@selector(selectedImage)] &&
            [item respondsToSelector:@selector(setSelectedImage:)] &&
            [item respondsToSelector:@selector(_updateView)])
        {
            CGRect contextRect;
            contextRect.origin.x = 0.0f;
            contextRect.origin.y = 0.0f;
            contextRect.size = [[item selectedImage] size];
            // Retrieve source image and begin image context
            UIImage *itemImage = [item image];
            CGSize itemImageSize = [itemImage size];
            CGPoint itemImagePosition; 
            itemImagePosition.x = ceilf((contextRect.size.width - itemImageSize.width) / 2);
            itemImagePosition.y = ceilf((contextRect.size.height - itemImageSize.height) / 2);
            UIGraphicsBeginImageContext(contextRect.size);
            CGContextRef c = UIGraphicsGetCurrentContext();
            // Setup shadow
            CGContextSetShadowWithColor(c, shadowOffset, shadowBlur, cgShadowColor);
            // Setup transparency layer and clip to mask
            CGContextBeginTransparencyLayer(c, NULL);
            CGContextScaleCTM(c, 1.0, -1.0);
            CGContextClipToMask(c, CGRectMake(itemImagePosition.x, -itemImagePosition.y, itemImageSize.width, -itemImageSize.height), [itemImage CGImage]);
            // Fill and end the transparency layer
            CGContextSetFillColorWithColor(c, cgColor);
            contextRect.size.height = -contextRect.size.height;
            CGContextFillRect(c, contextRect);
            CGContextEndTransparencyLayer(c);
            // Set selected image and end context
            [item setSelectedImage:UIGraphicsGetImageFromCurrentImageContext()];
            UIGraphicsEndImageContext();
            // Update the view
            [item _updateView];
        }
}
@end

One can even create some pretty cool effects:

_{(source: booleanmagic.com)}

It is very possible that Apple will reject an application for doing this. If the private API is removed in a future OS update,
-[UITabBar recolorItemsWithColor:shadowColor:shadowOffset:shadowBlur:] will do nothing instead of crashing.