WWDC20: 更新 iOS 14 pickers, actions 及 menu 等控件

iOS 14 很多原生控件的样式和功能都做了更新，带来了更好的体验，如新的 UIPageControl 特性支持不限数量、自定义背景等，新增的 UIColorPickerViewController 和 PHPickerViewController，以及更新后的 UIDatePicker 和 menu 等。

几个比较突出的更新：

UIPageControl 

• 无限制数量
• 自定义背景样式
• 自定义图标

let pageControl = UIPageControl()
pageControl.numberOfPages = 5

pageCcontrol.backgroundStyle = .prominent

pageControl.preferredIndicatorImage = UIImage(systemName: "bookmark.fill")

pageControl.setIndicatorImage(UIImage(system: "heart.fill", forPage: 0)

New UIColorPickerViewController 

• 滴管选择器
• 网格布局
• 色盘
• 饱和度等调整
• 收藏颜色（可以在不同应用间共享使用）

var color = UIColor.blue
var colorPicker = UIColorPickerViewController

func pickColor() {
    colorPicker.supportsAlpha = true
    colorPicker.selectedColor = color
    self.present(colorPicker, animated: true, completion: nil)
}

// Color picker delegates

func colorPickerViewControllerDidSelectColor(_ viewController: UIColorPickerViewController) {
    color = viewController.selectedColor
}

func colorPickerViewControllerDidFinish(_ viewController: UIColorPickerViewController) {
    //
}

UIDatePicker 

精简样式用于显示，模态窗口可以选择日期、时间

let datePicker = UIDatePicker()
datePicker.date = Date(timeIntervalSinceReferenceDate:timeInterval)

// 设置为精简样式
datePicker.preferredDatePickerStyle = .compact

datePicker.calendar = Calendar(idnetifier: .japanese)
datePicker.datePickerMode = .date

New Photos Picker

• 支持搜索
• 多选
• 放大缩小

var configuration = PHPickerConfiguration()

// "unlimited" selection by specifying 0, default is 1
configuration.selectionLimit = 0

// Only show images (including Live Photos)
configuration.filter = .images
// Only videos or Live Photos (for their video complement), but no images
configuration.filter = .any(of: [.videos, .livePhotos])

let picker = PHPickerViewController(configuration: configuration)

picker.delegate = self

present(picker, animated: true)

// Handling results
func picker(_ picker: PHPickerViewController, didFinishPicking results: [PHPickerResult]) {
	// The client is responsible for presentation and dismissal
    picker.dismiss(animated: true)
    
    // Get the first item provider from the results
    let itemProvider = results.first?.itemProvider
    
    // Access the UIImage representation for the result
    if let itemProvider = itemProvider, itemProvider.canLoadObject(ofClass: UIImage.self) {
        itemProvider.loadObject(ofClass: UIImage.self) { image, error in
			if let image = image {
                // Got the image
            }
		}
    }
}

Menu

默认为长按触发

// 按钮添加菜单
button.menu = UIMenu(...)
// 自定义立即触发
button.showsMenuAsPrimaryAction = true

// UIBarButtonItem 添加菜单
barButtonItem.menu = UIMenu(...)
// 自定义触发
UIBarButtonItem(systemItem: .save, primaryAction: saveAction, menu: saveMenu)
UIBarButtonItem(image: optionsImage, menu: optionsMenu)
UIBarButtonItem(primaryAction: revertAction)