[iOS] App 引导页的简单实现 (Swift 3)

** 转载请注明出处：http://www.jianshu.com/p/024dd2d6e6e6#**

已更新至 Xcode8.2、Swift3

在第一次打开App或者App更新后通常用引导页来展示产品特性

我们用NSUserDefaults类来判断程序是不是第一次启动或是否更新，在 AppDelegate.swift中加入以下代码：

 func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {

    // 得到当前应用的版本号
    let infoDictionary = Bundle.main.infoDictionary
    let currentAppVersion = infoDictionary!["CFBundleShortVersionString"] as! String
        
    // 取出之前保存的版本号
    let userDefaults = UserDefaults.standard
    let appVersion = userDefaults.string(forKey: "appVersion")
        
    let storyboard = UIStoryboard(name: "Main", bundle: nil)
        
    // 如果 appVersion 为 nil 说明是第一次启动；如果 appVersion 不等于 currentAppVersion 说明是更新了
    if appVersion == nil || appVersion != currentAppVersion {
        // 保存最新的版本号
        userDefaults.setValue(currentAppVersion, forKey: "appVersion")
            
        let guideViewController = storyboard.instantiateViewController(withIdentifier: "GuideViewController") as! GuideViewController
        self.window?.rootViewController = guideViewController
    }
        
    return true
}

在GuideViewController中，我们用UIScrollView来装载我们的引导页:

class GuideViewController: UIViewController {
    
    @IBOutlet weak var pageControl: UIPageControl!
    @IBOutlet weak var startButton: UIButton!
    
    fileprivate var scrollView: UIScrollView!
    
    fileprivate let numOfPages = 3

    override func viewDidLoad() {
        super.viewDidLoad()

        let frame = self.view.bounds
        
        scrollView = UIScrollView(frame: frame)
        scrollView.isPagingEnabled = true
        scrollView.showsHorizontalScrollIndicator = false
        scrollView.showsVerticalScrollIndicator = false
        scrollView.scrollsToTop = false
        scrollView.bounces = false
        scrollView.contentOffset = CGPoint.zero
        // 将 scrollView 的 contentSize 设为屏幕宽度的3倍(根据实际情况改变)
        scrollView.contentSize = CGSize(width: frame.size.width * CGFloat(numOfPages), height: frame.size.height)
        
        scrollView.delegate = self
        
        for index  in 0..<numOfPages {
            let imageView = UIImageView(image: UIImage(named: "GuideImage\(index + 1)"))
            imageView.frame = CGRect(x: frame.size.width * CGFloat(index), y: 0, width: frame.size.width, height: frame.size.height)
            scrollView.addSubview(imageView)
        }
        
        self.view.insertSubview(scrollView, at: 0)
        
        // 给开始按钮设置圆角
        startButton.layer.cornerRadius = 15.0
        // 隐藏开始按钮
        startButton.alpha = 0.0
    }
    
    // 隐藏状态栏
    override var prefersStatusBarHidden : Bool {
        return true
    }
}

最后我们让GuideViewController遵循UIScrollViewDelegate协议，在这里判断是否滑动到最后一张以显示进入按钮：

// MARK: - UIScrollViewDelegate
extension GuideViewController: UIScrollViewDelegate {
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        let offset = scrollView.contentOffset
        // 随着滑动改变pageControl的状态
        pageControl.currentPage = Int(offset.x / view.bounds.width)
        
        // 因为currentPage是从0开始，所以numOfPages减1
        if pageControl.currentPage == numOfPages - 1 {
            UIView.animate(withDuration: 0.5, animations: {
                self.startButton.alpha = 1.0
            }) 
        } else {
            UIView.animate(withDuration: 0.2, animations: {
                self.startButton.alpha = 0.0
            }) 
        }
    }
}

在上面的代码中，为了显得自然我们给进入按钮加入了一点动画 :]

最终效果如下：

Github地址：https://github.com/GuiminChu/JianshuExample