SwiftUI中ObservableObject搭配DatePicker的实现优化咨询

实现方案 #

第一步：改造DateHandler直接遵守ObservableObject #

不需要额外的包装类，只要在存储属性的didSet中手动发送视图更新通知即可，兼容你已有的自定义getter/setter逻辑：

import SwiftUI

class DateHandler: ObservableObject {
    var date1 : Date {
        didSet{
            objectWillChange.send() // 手动通知视图属性变更
            print("StartDate: \(date1)")
        }
    }
    var date2 : Date {
        didSet{
            objectWillChange.send() // 手动通知视图属性变更
            print("EndDate: \(date2)")
        }
    }
    
    var startDate:Date {
        get{
            return date1
        }
        set(newValue){
            let adjustedDate = toLocalTime(date: newValue)
            // 直接把日期校验逻辑内聚到这里，不用放到视图层
            guard adjustedDate < endDate else { return }
            date1 = adjustedDate
        }
    }
    
    var endDate:Date {
        get{
            return date2
        }
        set(newValue){
            let adjustedDate = addOneDay(date: toLocalTime(date: newValue))
            guard adjustedDate > startDate else { return }
            date2 = adjustedDate
        }
    }
    
    init(){
        self.date1 = Date()
        self.date2 = addOneDay(date: toLocalTime(date: Date())) // 初始化默认结束日期比开始晚一天
    }
    
    //Customize time zone
    func toLocalTime(date : Date) -> Date {
        let calendar = Calendar.current
        let timezone = TimeZone.current
        let seconds = TimeInterval(timezone.secondsFromGMT(for: date))
        let newDate = calendar.date(bySettingHour: 00, minute: 00, second: 00, of: date)
        let dateLocalTimezone = Date(timeInterval: seconds, since: newDate!)
        return dateLocalTimezone
    }
    
    func addOneDay(date : Date) -> Date {
        let tomorrow = Calendar.current.date(byAdding: .day, value: 1, to: date)
        return tomorrow!
    }
}

第二步：简化视图代码，省略中转State变量 #

现在可以直接把DatePicker绑定到DateHandler的属性，不需要额外的辅助变量和onChange/onAppear逻辑：

struct ContentView: View {
    // iOS14+用@StateObject，低版本用@ObservedObject即可
    @StateObject var dateHandler = DateHandler()

    var body: some View {
        VStack(spacing: 20) {
            DatePicker("Date1", selection: Binding(
                get: { dateHandler.startDate },
                set: { dateHandler.startDate = $0 }
            ), displayedComponents: .date)
            
            DatePicker("Date2", selection: Binding(
                get: { dateHandler.endDate },
                set: { dateHandler.endDate = $0 }
            ), displayedComponents: .date)
        }
        .padding()
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

方案说明 #

• 直接让DateHandler遵守ObservableObject，利用objectWillChange.send()手动触发变更通知，解决了自定义getter/setter无法使用@Published的问题，完全省略了冗余的DateHandlerHelper包装类
• 直接通过Binding构造器绑定DatePicker到DateHandler的属性，不再需要中转的辅助State变量
• 把开始日期不能晚于结束日期的校验逻辑内聚到DateHandler内部，逻辑更聚合，视图层更干净

内容的提问来源于stack exchange，提问作者Jorge Reich