Swift学习备忘
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SwiftUI 变量触发界面刷新
1.关于ObservableObject，Published和EnvironmentObject三个关键字的含义理解
2.两种方法触发界面刷新，方法一，如下
class UserOnboard: ObservableObject {
@Published var onboardComplete : Bool = false
}方法二：不带关键字 Published，在属性发生变化是，该属性的类调用objectWillChange.send()，通知界面刷新
触发刷新的代码：
struct StartOnboardView: View {
@EnvironmentObject var userOnboard: UserOnboard
var body: some View {
let contentView = StartView()
let settings = UserSettings()
if userOnboard.onboardComplete {
return AnyView(contentView.environmentObject(settings))
} else {
if UserDefaults.standard.bool(forKey: "Loggedin") {
settings.loggedIn = true
return AnyView(TabbarVC())
} else {
settings.loggedIn = false
return AnyView(OnboardingView())
}
}
}
}相关问题可以参考Stack Overflow：NSManagedObject changes do not trigger objectWillChange，I'm trying to use “objectWillChange.send()” in an protocol extension but it's not working, any idea why?，SwiftUI ObservableObject used as EnvironmentObject odd behaviour
仅以此做个记录，备忘
PS，像这种刚刚（也不叫刚刚）出来的技术和属性，国内很少有说明和解释的博客，估计过几年各种博客搬运，都要泛滥了
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List在 UIKit 中对应的是UITableView -
闭包相关
List {
Text("Static row 1")
Text("Static row 2")
ForEach(0..<5) {
Text("Dynamic row \($0)")
}
Text("Static row 3")
Text("Static row 4")
}举例说明list的简单用法，顺便引出闭包的相关问题
上面的ForEach 可以理解为简单的闭包
List {
Text("Static row 1")
Text("Static row 2")
ForEach(0..<5) {(index:int)->void in
Text("Dynamic row \(index)")
}
Text("Static row 3")
Text("Static row 4")
}Another example:
let array = ["1", "2", "3", "4", "5"]
array.forEach { (element) in
print(element)
}闭包表达式的一般格式
{ (parameters) -> (return type) in
statements
}几种简写
/* 原始闭包写法 */
//从数组中筛选指出合适的数据组成新的数组
func getList(score:[Int], con:(Int)->Bool) -> [Int]{
var newScore:[Int] = [Int]()
for item in score {
if con(item) {
newScore.append(item)
}
}
return newScore
}
let newAarray = getList(score: [75,60,95,45,85], con:{(s:Int)->Bool in return s>80})
print(newAarray)
/* 简写一 */
let newAarray = getList(score: [75,60,95,45,85], con:{(s:Int) in return s>80})
/* 简写二 */
let newAarray = getList(score: [75,60,95,45,85], con:{s in return s>80})
/* 简写三 */
let newAarray = getList(score: [75,60,95,45,85], con:{s in s>80})
/* 简写四 */
let newAarray = getList(score: [75,60,95,45,85], con:{$0>80})-
Swift解包
var num: Int?这是Optional的声明，意思不是"我声明了一个Optional的Int值"，而是”我声明了一个Optional类型值，它可能包含一个Int值，也可能什么都不包含”，也就是说实际上我们声明的是Optional类型，而不是声明了一个Int类型!
//if let 解包
func getHeight(_ height: Float?) -> Float? {
if let unwrapedHeight = height {
return unwrapedHeight / 100
}
return nil
}
//guard let解包
func getHeight(_ height: Float?) -> Float? {
guard let unwrapedHeight = height else {
return nil
}
return unwrapedHeight / 100
}