在 Swift 中向 UITabbarItem 添加一行作为选择指示器

Question

我想在 UITabbarItems 的底部使用粗线作为选择指示器。由于该应用程序必须在不同的 phone 大小上运行，我不能使用图像作为选择指示器。这就是为什么我认为我必须使用 Swift 来执行此操作。（线必须是页面宽度的 1/3）。

我尝试使用 UITabBarItem.appearance() 但没有成功。

Answer 1

您可以通过添加将在您的代码中创建的自定义图像到 UITabBar 对象上的 selectionIndicatorImage 来实现。例如，您可以像这样为 UIImage class 创建 extension：

extension UIImage {
    func createSelectionIndicator(color: UIColor, size: CGSize, lineWidth: CGFloat) -> UIImage {
        UIGraphicsBeginImageContextWithOptions(size, false, 0)
        color.setFill()
        UIRectFill(CGRectMake(0, size.height - lineWidth, size.width, lineWidth))
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return image
    }
}

然后在你第一次加载时调用它 ViewController 像这样：

class FirstViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let tabBar = self.tabBarController!.tabBar
        tabBar.selectionIndicatorImage = UIImage().createSelectionIndicator(UIColor.blueColor(), size: CGSizeMake(tabBar.frame.width/CGFloat(tabBar.items!.count), tabBar.frame.height), lineWidth: 2.0)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

在这种情况下，结果将是这样的：

Answer 2

我解决了我的问题。

这个小代码片段的特点：

宽度是动态的
它是动画的

未来功能的可定制性要高得多

class FirstViewController: UIViewController {

let rectShape = CAShapeLayer()
let indicatorHeight: CGFloat = 5
var indicatorWidth: CGFloat!
let indicatorBottomMargin: CGFloat = 2
let indicatorLeftMargin: CGFloat = 2

override func viewDidLoad() {
    super.viewDidLoad()

    // setup tabbar indicator
    rectShape.fillColor = UIColor.redColor().CGColor
    indicatorWidth = view.bounds.maxX / 2 // count of items
    self.tabBarController!.view.layer.addSublayer(rectShape)
    self.tabBarController?.delegate = self

    // initial position
    updateTabbarIndicatorBySelectedTabIndex(0)
}

func updateTabbarIndicatorBySelectedTabIndex(index: Int) -> Void
{
    let updatedBounds = CGRect( x: CGFloat(index) * (indicatorWidth + indicatorLeftMargin),
                                y: view.bounds.maxY - indicatorHeight,
                                width: indicatorWidth - indicatorLeftMargin,
                                height: indicatorHeight)

    let path = CGPathCreateMutable()
    CGPathAddRect(path, nil, updatedBounds)
    rectShape.path = path
}
}

extension FirstViewController: UITabBarControllerDelegate {

func tabBarController(tabBarController: UITabBarController, didSelectViewController viewController: UIViewController) {
    updateTabbarIndicatorBySelectedTabIndex(tabBarController.selectedIndex)
}
}

Answer 3

Swift 3:

extension UIImage {
    func createSelectionIndicator(color: UIColor, size: CGSize, lineHeight: CGFloat) -> UIImage {
        UIGraphicsBeginImageContextWithOptions(size, false, 0)
        color.setFill()
        UIRectFill(CGRect(origin: CGPoint(x: 0,y :size.height - lineHeight), size: CGSize(width: size.width, height: lineHeight)))
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return image!
    }
}

override func viewDidLoad() {
    super.viewDidLoad()
    let tabBar = self.tabBarController!.tabBar
    tabBar.selectionIndicatorImage = UIImage().createSelectionIndicator(color: UIColor.blue, size: CGSize(width: tabBar.frame.width/CGFloat(tabBar.items!.count), height: tabBar.frame.height), lineHeight: 2.0)
}

Answer 4

Swift 4.x
Xcode10.x

extension UIImage {
    func createSelectionIndicator(color: UIColor, size: CGSize, lineWidth: CGFloat) -> UIImage {
        UIGraphicsBeginImageContextWithOptions(size, false, 0)
        color.setFill()
        UIRectFill(CGRect(x: 0, y: size.height - lineWidth, width: size.width, height: lineWidth))
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return image!
    }
}

使用

tabBar.selectionIndicatorImage = UIImage().createSelectionIndicator(color: BLUE, size: CGSize(width: tabBar.frame.width/CGFloat(tabBar.items!.count), height:  tabBar.frame.height), lineWidth: 2.0)

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