这个时间这部分真的太难了。再练习一遍。增强熟练度。

时间选择器样式

时间选择器隐藏文本标签,时间选择器只显示小时和分钟。

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DatePicker(selection: $wakeUp, displayedComponents: .hourAndMinute, label: { Text("Please enter a date") })
.labelsHidden()
.datePickerStyle(WheelDatePickerStyle())

读取和写入时间的特定部分

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var components = DateComponents()
components.hour = 8
components.minute = 0
let date = Calendar.current.date(from: components)

有可能出错的情况下使用 do catch 结构抓取错误

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do {
let sleepTime = try model.prediction(wake: time, estimatedSleep: Double(self.sleepTimeLength), coffee: Double(self.coffeeCups))

let bestSleepTime = self.wakeDate - sleepTime.actualSleep

let formatter = DateFormatter()
formatter.timeStyle = .short
let dateString = formatter.string(from: bestSleepTime)

self.alertTitle = "您的睡眠时间应该在"
self.alertMessage = "\(dateString)"
self.alertShow.toggle()
}catch{
self.alertTitle = "出现了未知错误"
self.alertMessage = "无法计算出推荐睡眠时间"
self.alertShow.toggle()

第二遍练习代码

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//
// ContentView.swift
// Practise2-4for2
//
// Created by 张洪Hoo on 2020/4/3.
// Copyright © 2020 张洪Hoo. All rights reserved.
//

import SwiftUI

struct ContentView: View {
@State private var wakeDate = compDate
@State private var sleepTimeLength: Double = 8
@State private var coffeeCups = 1

@State private var alertShow = false
@State private var alertTitle = ""
@State private var alertMessage = ""

static var compDate: Date {
var com = DateComponents()

com.hour = 8
com.minute = 0

return Calendar.current.date(from: com) ?? Date()
}

var body: some View {
NavigationView {
Form {
VStack(alignment: .leading) {
Text("你什么时候想起床?")
.bold()

DatePicker(selection: $wakeDate,displayedComponents: .hourAndMinute, label: { Text("你什么时候想起床?") })
.labelsHidden()
.datePickerStyle(WheelDatePickerStyle())
}

VStack(alignment: .leading) {
Text("期望睡眠时长")
.bold()
Stepper(value: $sleepTimeLength, in: 4...12, step: 0.25) {
Text("\(self.sleepTimeLength, specifier: "%.2f") 小时")
}
}

VStack(alignment: .leading) {
Text("每日饮用咖啡杯数")
.bold()
Stepper(value: $coffeeCups, in: 1...20) {
Text("\(self.coffeeCups) 杯")
}
}
}
.navigationBarTitle(Text("最佳睡眠时间计算"))
.navigationBarItems(trailing: Button(action: {
//do something

let model = SleepCalculator()

let wakeTime = Calendar.current.dateComponents([.hour,.minute], from: self.wakeDate)

let hour = (wakeTime.hour ?? 0) * 60 * 60

let minute = (wakeTime.minute ?? 0) * 60

let time = Double(hour + minute)

do {
let sleepTime = try model.prediction(wake: time, estimatedSleep: Double(self.sleepTimeLength), coffee: Double(self.coffeeCups))

let bestSleepTime = self.wakeDate - sleepTime.actualSleep

let formatter = DateFormatter()
formatter.timeStyle = .short
let dateString = formatter.string(from: bestSleepTime)

self.alertTitle = "您的睡眠时间应该在"
self.alertMessage = "\(dateString)"
self.alertShow.toggle()
}catch{
self.alertTitle = "出现了未知错误"
self.alertMessage = "无法计算出推荐睡眠时间"
self.alertShow.toggle()
}
}) {
Text("计算")
})
}
.alert(isPresented: $alertShow){
Alert(---
title: Text(alertTitle), message: Text(alertMessage), dismissButton: .default(Text("确定")))
}
}
}

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

-w1792

SwiftPlayground 进度

-w1792