防止UITabBar对其图标图像应用渐变

Question

当我为UITabBar制作图标时,它会对图像应用渐变.我需要知道如何防止它有这个渐变.

Answer 1

Apple在iOS 5中添加了标签栏自定义,现在这种东西是微不足道的.在此之前它是一个巨大的黑客,不推荐.

以下是完全自定义标签栏的方法:

// 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

这是非常困难的,因为UITabBar它不提供对其选择/未选择图像的访问.它可以通过私有API实现:

@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

甚至可以创造一些非常酷的效果:

Red Tab Bar http://booleanmagic.com/uploads/RedTabBar.png

苹果很可能会拒绝这样做的申请.如果在将来的操作系统更新中删除了私有API,则
-[UITabBar recolorItemsWithColor:shadowColor:shadowOffset:shadowBlur:]不会执行任何操作而不会崩溃.