I recommend you taking a look at the following article. It explains how to customise a tab bar raising the main button.

我建议你看看下面的文章。它解释了如何自定义提升主按钮的标签栏。

Code:

代码：

UIButton* button = [UIButton buttonWithType:UIButtonTypeCustom];
button.frame = CGRectMake(0.0, 0.0, buttonImage.size.width, buttonImage.size.height);
[button setBackgroundImage:buttonImage forState:UIControlStateNormal];
[button setBackgroundImage:highlightImage forState:UIControlStateHighlighted];

CGFloat heightDifference = buttonImage.size.height - self.tabBar.frame.size.height;
if (heightDifference < 0)
   button.center = self.tabBar.center;
else
{
 CGPoint center = self.tabBar.center;
 center.y = center.y - heightDifference/2.0;
 button.center = center;
}

[self.view addSubview:button];

Guide: https://github.com/boctor/idev-recipes/tree/master/RaisedCenterTabBar

指南：https: //github.com/boctor/idev-recipes/tree/master/RaisedCenterTabBar

2017 Answer - With Just Xcode

2017 答案 - 仅使用 Xcode

Click the tab bar button within the view controller of the particular tab bar item you want to make prominent,

单击要突出显示的特定标签栏项目的视图控制器中的标签栏按钮，

Remove the text, just set the image inset top to -25 of the tab bar button.

删除文本，只需将图像插入顶部设置为标签栏按钮的 -25。

Like Below image

喜欢下图

After that

在那之后

goto assets,
select the image you set in tab bar button,
set the property Rendering As to Original Image(in case if you have a colourful button or else it would render as one colour)
Like below,

转到资产，
选择您在标签栏按钮中
设置的图像，将属性渲染为原始图像（如果您有彩色按钮，否则它将呈现为一种颜色）
如下所示，

Now, You will get it like you wanted,

现在，你会得到你想要的，

EDIT: To make upper half clickable, inherit UITabBar

编辑：要使上半部分可点击，请继承 UITabBar

class ProminentTabBar: UITabBar {
    var prominentButtonCallback: (()->())?

    override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
        guard let items = items, items.count>0 else {
            return super.hitTest(point, with: event)
        }

        let middleItem = items[items.count/2]
        let middleExtra = middleItem.imageInsets.top
        let middleWidth = bounds.width/CGFloat(items.count)
        let middleRect = CGRect(x: (bounds.width-middleWidth)/2, y: middleExtra, width: middleWidth, height: abs(middleExtra))
        if middleRect.contains(point) {
            prominentButtonCallback?()
            return nil
        }
        return super.hitTest(point, with: event)
    }
}

And in TabBarController add this

在 TabBarController 添加这个

override func viewDidLoad() {
    super.viewDidLoad()

    let prominentTabBar = self.tabBar as! ProminentTabBar
    prominentTabBar.prominentButtonCallback = prominentTabTaped
}

func prominentTabTaped() {
    selectedIndex = (tabBar.items?.count ?? 0)/2
}

And remmber there is no nice solution when it comes to UITabBar :-)

并且记住，当涉及到 UITabBar 时，没有好的解决方案 :-)

Swift 3, 4:

斯威夫特 3、4：

I use this code in the viewDidLoadof my subclass of UITabBarController:

我在viewDidLoad我的子类中使用此代码UITabBarController：

let button = UIButton()
button.setImage(UIImage(named: "home"), for: .normal)
button.sizeToFit()
button.translatesAutoresizingMaskIntoConstraints = false

tabBar.addSubview(button)
tabBar.centerXAnchor.constraint(equalTo: button.centerXAnchor).isActive = true
tabBar.topAnchor.constraint(equalTo: button.centerYAnchor).isActive = true

Sometimes I also set button.adjustsImageWhenHighlighted = falseto mimic the behavior of the other items, or change the constraint constantproperty to move the button up or down.

有时我也设置button.adjustsImageWhenHighlighted = false模仿其他项目的行为，或更改约束constant属性以向上或向下移动按钮。

Here's the ported Swift 3 version of @Kakashi's answer (and +1 to them), which I put in my custom UITabBarController subclass:

这是@Kakashi 答案的移植 Swift 3 版本（并对他们 +1），我将其放入我的自定义 UITabBarController 子类中：

override func viewDidLoad() {
        if let newButtonImage = UIImage(named: "new__button") {
            self.addCenterButton(withImage: newButtonImage, highlightImage: newButtonImage)
        }
 }

 func handleTouchTabbarCenter(sender : UIButton)
 {
    if let count = self.tabBar.items?.count
    {
        let i = floor(Double(count / 2))
        self.selectedViewController = self.viewControllers?[Int(i)]
    }
 }

func addCenterButton(withImage buttonImage : UIImage, highlightImage: UIImage) {

        let paddingBottom : CGFloat = 10.0

        let button = UIButton(type: .custom)
        button.autoresizingMask = [.flexibleRightMargin, .flexibleTopMargin, .flexibleLeftMargin, .flexibleBottomMargin]
        button.frame = CGRect(x: 0.0, y: 0.0, width: buttonImage.size.width / 2.0, height: buttonImage.size.height / 2.0)
        button.setBackgroundImage(buttonImage, for: .normal)
        button.setBackgroundImage(highlightImage, for: .highlighted)

        let rectBoundTabbar = self.tabBar.bounds
        let xx = rectBoundTabbar.midX
        let yy = rectBoundTabbar.midY - paddingBottom
        button.center = CGPoint(x: xx, y: yy)

        self.tabBar.addSubview(button)
        self.tabBar.bringSubview(toFront: button)

        button.addTarget(self, action: #selector(handleTouchTabbarCenter), for: .touchUpInside)

        if let count = self.tabBar.items?.count
        {
            let i = floor(Double(count / 2))
            let item = self.tabBar.items![Int(i)]
            item.title = ""
        }
    }

For hide UITabbar, I make custom UITabbarController and insert this method.

为了隐藏 UITabbar，我制作了自定义 UITabbarController 并插入了这个方法。

- (void)viewDidLoad
{
    [super viewDidLoad];
    [self addCenterButtonWithImage:[UIImage imageNamed:@"logo"] highlightImage:[UIImage imageNamed:@"logo"]];
}

- (void)addCenterButtonWithImage:(UIImage*)buttonImage highlightImage:(UIImage*)highlightImage
{
    float paddingBottom = 10;

    UIButton* button = [UIButton buttonWithType:UIButtonTypeCustom];
    button.autoresizingMask = UIViewAutoresizingFlexibleRightMargin | UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleBottomMargin | UIViewAutoresizingFlexibleTopMargin;
    button.frame = CGRectMake(0.0, 0.0, buttonImage.size.width, buttonImage.size.height);
    [button setBackgroundImage:buttonImage forState:UIControlStateNormal];
    [button setBackgroundImage:highlightImage forState:UIControlStateHighlighted];

    CGRect rectBoundTabbar = [self.tabBar bounds];
    float xx = CGRectGetMidX(rectBoundTabbar);
    float yy = CGRectGetMidY(rectBoundTabbar) - paddingBottom;
    button.center = CGPointMake(xx, yy);

    [self.tabBar addSubview:button];
    [self.tabBar bringSubviewToFront:button];

    // add handle
    [button addTarget:self action:@selector(handleTouchTabbarCenter:) forControlEvents:UIControlEventTouchUpInside];

    // hide title item menu
    NSInteger count = [self.tabBar.items count];
    NSInteger i = floor(count / 2.0);
    UITabBarItem *item = [self.tabBar.items objectAtIndex:i];
    [item setTitle:nil];

}

- (void)handleTouchTabbarCenter:(id)sender
{
    // go to some view
}

I've taken Manuel's example (the accepted answer) and added an adjustment for the bottom safe area insets due to issues with iPhone X.

由于 iPhone X 的问题，我以 Manuel 的示例（已接受的答案）为例，并添加了对底部安全区域插图的调整。

UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
button.frame = CGRectMake(0.0, 0.0, buttonImage.size.width, buttonImage.size.height);
[button setBackgroundImage:buttonImage forState:UIControlStateNormal];
[button setBackgroundImage:highlightImage forState:UIControlStateHighlighted];

CGFloat heightDifference = buttonImage.size.height - self.tabBar.frame.size.height;
CGPoint center = self.tabBar.center;
if (heightDifference >= 0) {
    center.y = center.y - heightDifference/2.0;
}

if (@available(iOS 11.0, *)) {
    UIWindow *window = UIApplication.sharedApplication.keyWindow;
    CGFloat bottomPadding = window.safeAreaInsets.bottom;
    center.y = center.y - bottomPadding;
}

[self.view addSubview:button];

For Swift

对于斯威夫特

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (Int64)(2.0)), dispatch_get_main_queue(), {
            let button: UIButton = UIButton(type: .Custom)
            let win:UIWindow = UIApplication.sharedApplication().delegate!.window!!

            button.frame = CGRectMake(0.0, win.frame.size.height - 65, 55, 55)
            button.center = CGPoint(x:win.center.x , y: button.center.y)

            button.setBackgroundImage(UIImage(named: "Camera") , forState: .Normal)
            button.setBackgroundImage(UIImage(named: "Camera"), forState: .Highlighted)
            win.addSubview(button)
        });

I followed @Michael Dautermann answer but the button never registers the tap so I modified it to make it work:

我遵循了@Michael Dautermann 的回答，但该按钮从未注册过水龙头，因此我对其进行了修改以使其正常工作：

  func handleTouchTabbarCenter()
{
    if let count = self.tabBar.items?.count
    {
        let i = floor(Double(count / 2))
        self.selectedViewController = self.viewControllers?[Int(i)]
    }
}

func addCenterButton(withImage buttonImage : UIImage, highlightImage: UIImage) {

    self.centerButton = UIButton(type: .custom)
    self.centerButton?.autoresizingMask = [.flexibleRightMargin, .flexibleTopMargin, .flexibleLeftMargin, .flexibleBottomMargin]
    self.centerButton?.frame = CGRect(x: 0.0, y: 0.0, width: buttonImage.size.width, height: buttonImage.size.height)
    self.centerButton?.setBackgroundImage(buttonImage, for: .normal)
    self.centerButton?.setBackgroundImage(highlightImage, for: .highlighted)
    self.centerButton?.isUserInteractionEnabled = true

    let heightdif: CGFloat = buttonImage.size.height - (self.tabBar.frame.size.height);

    if (heightdif < 0){
        self.centerButton?.center = (self.tabBar.center)
    }
    else{
        var center: CGPoint = (self.tabBar.center)
        center.y = center.y - 24
        self.centerButton?.center = center
    }

    self.view.addSubview(self.centerButton!)
    self.tabBar.bringSubview(toFront: self.centerButton!)

    self.centerButton?.addTarget(self, action: #selector(handleTouchTabbarCenter), for: .touchUpInside)

    if let count = self.tabBar.items?.count
    {
        let i = floor(Double(count / 2))
        let item = self.tabBar.items![Int(i)]
        item.title = ""
    }
}