Set background color of active tab bar item in Swi

问题:

I'm hoping to accomplish this without the use of images, if at all possible. Is there a way to create the effect shown in the image programmatically without have to render each tab out as an image?

Every question I've reviewed on SO has the tabs saved as JPGs, which is more work than I feel it should be.

Any ideas?

回答1:

I took a similar approach to @matcartmill but without the need for a special image. This solution is just based on your color.

// set red as selected background color
let numberOfItems = CGFloat(tabBar.items!.count)
let tabBarItemSize = CGSize(width: tabBar.frame.width / numberOfItems, height: tabBar.frame.height)
tabBar.selectionIndicatorImage = UIImage.imageWithColor(color: UIColor.red, size: tabBarItemSize).resizableImage(withCapInsets: UIEdgeInsets.zero)

// remove default border
tabBar.frame.size.width = self.view.frame.width + 4
tabBar.frame.origin.x = -2

I'm making use of the following extension of UIImage:

extension UIImage {

    class func imageWithColor(color: UIColor, size: CGSize) -> UIImage {
        let rect: CGRect = CGRectMake(0, 0, size.width, size.height)
        UIGraphicsBeginImageContextWithOptions(size, false, 0)
        color.setFill()
        UIRectFill(rect)
        let image: UIImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return image
    }

}

I hope this helps!

for swift 4

extension UIImage {

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

回答2:

Update to SWIFT 3:

let numberOfItems = CGFloat((tabBarController?.tabBar.items!.count)!)

let tabBarItemSize = CGSize(width: (tabBarController?.tabBar.frame.width)! / numberOfItems,
                            height: (tabBarController?.tabBar.frame.height)!)

tabBarController?.tabBar.selectionIndicatorImage
    = UIImage.imageWithColor(color: UIColor.black,
                             size: tabBarItemSize).resizableImage(withCapInsets: .zero)

tabBarController?.tabBar.frame.size.width = self.view.frame.width + 4
tabBarController?.tabBar.frame.origin.x = -2

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

回答3:

So here's what I ended up doing. It's a mix of using a 640x49 PNG that's the color of the blue "highlighted" background I need.

In AppDelegate.swift:

var selectedBG = UIImage(named:"tab-selected-full")?.resizableImageWithCapInsets(UIEdgeInsetsMake(0, 0, 0, 0))
UITabBar.appearance().selectionIndicatorImage = selectedBG

And then in the first View Controller that gets loaded, I have:

tabBarController?.tabBar.frame.size.width = self.view.frame.width+4
tabBarController?.tabBar.frame.origin.x = -2

The reason for the above two lines is that, by default, Apple has a 2px border between the left and right sides of the tab bar and the tab bar items.

In the above I simply make the tab bar 4px wider, and then offset it so the border on the left falls just outside of the view, thus the border on the right will also fall outside of the view.