swift 错误处理do catch try try!使用详解

在swift中 如果我们要定义一个表示错误类型非常简单,只要遵循Error协议就可以了,我们通常用枚举或者结构体来表示错误类型,枚举可能用的多些,因为他能更直观的表达当前错误类型的每种错误细节。

//
// AboutError.swift
// learn_swiftUi
//
// Created by liuan on 2020/9/4.
// Copyright © 2020 liuan. All rights reserved.
//

import Foundation
enum VendingMachingError:Error{
 case invalideSelection
 case insufficientFunds(coinsNeeded:Int)
 case outOfStock
}

函数、方法和初始化器都可以抛出错误。需要在参数列表后面,返回值加throws 关键字。

简化版

func canThrowErrors() throws -> String
//
// AboutError.swift
// learn_swiftUi
//
// Created by liuan on 2020/9/4.
// Copyright © 2020 liuan. All rights reserved.
//

import Foundation
enum VendingMachingError:Error{
 case invalideSelection
 case insufficientFunds(coinsNeeded:Int)
 case outOfStock
}
struct Item {
 var price: Int
 var count: Int
}

class VendingMathine{
 var inventory=[
 "Candy bar":Item(price: 12, count: 7),
 "Chips":Item(price: 10, count: 4),
 "Pretzels":Item(price: 7, count: 11),
 ]
 
 var coinsDeposited = 0
 func vend(itemNaamed name:String) throws{
 guard let item = inventory[name] else{
 throw VendingMachingError.invalideSelection
 }
 
 guard item.count > 0 else{
 throw VendingMachingError.outOfStock
 }
 guard item.price <= coinsDeposited else{
 throw VendingMachingError.insufficientFunds(coinsNeeded: item.price - coinsDeposited)
 }
 
 coinsDeposited -= item.price
 var newItem = item
 newItem.count -= 1
 inventory[name]=newItem
 print("Dispensing \(name)")
 
 }
}


let vm=VendingMathine()

vm.coinsDeposited=2
try vm.vend(itemNaamed: "Pretzels")

抛出异常

Playground execution terminated: An error was thrown and was not caught:
▿ VendingMachingError
 ▿ insufficientFunds : 1 element
 - coinsNeeded : 5

在Swift中我们使用do-catch块对错误进行捕获,当我们在调用一个throws声名的函数或方法时,我们必须把调用语句放在do语句块中,同时do语句块后面紧接着使用catch语句块

swift 错误处理do catch try try! defer_ci

do里面执行调用语句

后面跟着catch 第一种错误 在第一种错误里面做处理

第二种错误需要符合一定的条件

然后做错误处理

第三种是没有捕获到的错误 然后在第三个语句里面做处理

swift 错误处理do catch try try! defer_ide_02

如果你确信一个函数或者方法不会抛出错误,可以使用try! 来中断错误的传播,但是如果错误真的发生了。你会得到一个运行时错误

//
// AboutError.swift
// learn_swiftUi
//
// Created by liuan on 2020/9/4.
// Copyright © 2020 liuan. All rights reserved.
//

import Foundation
let photo = try! 5/0
warning: BlackMyPlayground.playground:10:19: warning: no calls to throwing functions occur within 'try' expression
let photo = try! 5/0
 ^

warning: BlackMyPlayground.playground:10:19: warning: no calls to throwing functions occur within 'try' expression
let photo = try! 5/0
 ^

error: BlackMyPlayground.playground:10:19: error: division by zero
let photo = try! 5/0
 ^

defer关键字:defer block 例的代码会在函数return之前执行,无论函数是从哪个分之return的,还有throw,还是自然而然走到最后一样。

//
// File.swift
// learn_swiftUi
//
// Created by liuan on 2020/9/4.
// Copyright © 2020 liuan. All rights reserved.
//

import Foundation

func processFile(fileName: String)throws{
 defer{
 print("JIESHU")
 }
 print("KAISHI ")
 
}
作者:mp624183768原文地址:https://blog.51cto.com/u_14523369/6124034

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