将此添加到应用程序：didFinishLaunchingWithOptions：

UIColor *backgroundColor = [UIColor greenColor];

// set the bar background color
[[UITabBar appearance] setBackgroundImage:[AppDelegate imageFromColor:backgroundColor forSize:CGSizeMake(320, 49) withCornerRadius:0]];

// set the text color for selected state
[[UITabBarItem appearance] setTitleTextAttributes:[NSDictionary dictionaryWithObjectsAndKeys:[UIColor whiteColor], UITextAttributeTextColor, nil] forState:UIControlStateSelected];
// set the text color for unselected state
[[UITabBarItem appearance] setTitleTextAttributes:[NSDictionary dictionaryWithObjectsAndKeys:[UIColor whiteColor], UITextAttributeTextColor, nil] forState:UIControlStateNormal];

// set the selected icon color
[[UITabBar appearance] setTintColor:[UIColor whiteColor]];
[[UITabBar appearance] setSelectedImageTintColor:[UIColor whiteColor]];
// remove the shadow
[[UITabBar appearance] setShadowImage:nil];

// Set the dark color to selected tab (the dimmed background)
[[UITabBar appearance] setSelectionIndicatorImage:[AppDelegate imageFromColor:[UIColor colorWithRed:26/255.0 green:163/255.0 blue:133/255.0 alpha:1] forSize:CGSizeMake(64, 49) withCornerRadius:0]];

添加一个helper函数以将UIColor转换为UIImage
您可以将此代码放在AppDelegate或其他任何位置：

+ (UIImage *)imageFromColor:(UIColor *)color forSize:(CGSize)size withCornerRadius:(CGFloat)radius
{
    CGRect rect = CGRectMake(0, 0, size.width, size.height);
    UIGraphicsBeginImageContext(rect.size);

    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetFillColorWithColor(context, [color CGColor]);
    CGContextFillRect(context, rect);

    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    // Begin a new image that will be the new image with the rounded corners
    // (here with the size of an UIImageView)
    UIGraphicsBeginImageContext(size);

    // Add a clip before drawing anything, in the shape of an rounded rect
    [[UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:radius] addClip];
    // Draw your image
    [image drawInRect:rect];

    // Get the image, here setting the UIImageView image
    image = UIGraphicsGetImageFromCurrentImageContext();

    // Lets forget about that we were drawing
    UIGraphicsEndImageContext();

    return image;
}

我找到了解决方法，无需添加其他图像

class TabBarController: UITabBarController {
override func viewDidLoad() {
    super.viewDidLoad()
    // update first item
    dispatch_async(dispatch_get_main_queue()) {
        self.setSelection(self.tabBar.selectedItem!)
    }
}

// MARK: - UITabBarDelegate handlers

override func tabBar(tabBar: UITabBar, didSelectItem item: UITabBarItem) {
    clearSelections()
    setSelection(item)
}

// MARK: - Selection Methods

func setSelection(item:UITabBarItem) {
    dispatch_async(dispatch_get_main_queue()) {
        for i in 0..<self.tabBar.items!.count {
            let ii = self.tabBar.items![i]
            if(item == ii) {
                let sv = self.tabBar.subviews[i+1]
                let label:UILabel =  sv.subviews[1] as! UILabel
                print("didSelectItem \(label.text) = \(ii.title)")
                sv.backgroundColor = UIColor() // Selection color
            }
        }
    }
}

func clearSelections() {
    for s in tabBar.subviews {
        s.backgroundColor = UIColor.clearColor()
    }
}
}

在结果中，我可以设置所选选项卡

的背景颜色

如何更改单个选项卡栏项目的选定背景颜色
选项卡栏项没有“选定的背景色”。它们有一个selectedImage，您 * 可以 * 设置它。通过将其设置为呈现模式为.AlwaysOriginal的图像，您可以指定整个选项卡栏项图像在被选中时的外观，而不是在未被选中时的外观。

我给你一个最完美和最简单的方法（开个玩笑）。你可以在AppDelegate中设置TabBar外观的selectionIndicatorImage为默认值，如下所示：

let screenWidth = UIScreen.main.bounds.width
    let tabSelectedBGImage = R.image.tabSelectedBg()?.resize(toWidth: screenWidth/3)
    UITabBar.appearance().selectionIndicatorImage = tabSelectedBGImage

我不得不调整图片的大小，以正确的宽度，因为我有3个标签，我需要划分屏幕宽度为3当然。如果你不这样做，图像将不会填写您的标签项的宽度。* 我张贴在我的博客 *：D

在Swift 5中

class SceneDelegate: UIResponder, UIWindowSceneDelegate {

    var window: UIWindow?

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {

          let imageTabSelected = UIImage(named: "my_bg")
          UITabBar.appearance().selectionIndicatorImage = imageTabSelected
        }
    }
}

一个好的方法是使用AlamofireImage库并根据需要调整图像大小，然后在UITabBarViewController类的viewDidLoad方法中设置它：

override func viewDidLoad() {
    super.viewDidLoad()

    let screenWidth = UIScreen.main.bounds.width
    let tabSelectedBGImage = UIImage(named:"tab_selector")
    let size = CGSize(width: screenWidth/5, height: (tabSelectedBGImage?.size.height)!)
    let aspectScaledToFitImage = tabSelectedBGImage?.af_imageAspectScaled(toFill: size)

    UITabBar.appearance().selectionIndicatorImage = aspectScaledToFitImage

}

我找到的最简单的方法。

快速4

1.choose selectionIndicationImage.
2.Set tabar clipstobounds = true
3.Set insets for image.
4.Enjoy