Swift Error的处理方法说明

蒙岳清 發表於 2022-8-24 09:00:21

<div id="navCategory"><h5 class="catalogue">目录</h5><ul class="first_class_ul"><li>错误类型</li><ul class="second_class_ul"><li>自定义错误</li></ul><li>处理Error</li><ul class="second_class_ul"><li>try?与try!</li><li>rethrows</li><li>defer</li></ul></ul></div><p class="maodian"></p><h2>错误类型</h2>
<p>1、开发过程常见的错误</p>
<ul><li>语法错误（编译报错）</li><li>逻辑错误</li><li>运行时错误（可能会导致闪退，一般也叫做异常），也是我们今天讲的重点</li></ul>
<p class="maodian"></p><h3>自定义错误</h3>
<p>1、Swift中可以通过Error协议自定义运行时的错误信息</p>
<div class="jb51code"><pre class="brush:java;">enum SomeError: Error {
case illegalArg(String)
case outOfBounds(Int, Int)
case outOfMemory
}</pre></div>
<p>2、函数内部通过throw抛出自定义Error，可能会抛出Error的函数必须加上throws声明</p>
<div class="jb51code"><pre class="brush:java;">func divide(_ num1: Int, _ num2: Int) throws -> Int {
if num2 == 0 {
   throw SomeError.illegalArg("0不能作为除数")
}
return num1 / num2
}</pre></div>
<p>3、需要使用try调用可能会抛出Error的函数</p>
<p>4、可以使用do-catch捕捉Error</p>
<div class="jb51code"><pre class="brush:java;">func test() {
do {
   try divide(20, 0)
} catch let SomeError.illegalArg(msg) {
   print("参数异常：", msg)
} catch let SomeError.outOfBounds(size, index) {
   print("下标越界：", "size = \(size), index = \(index)")
} catch SomeError.outOfMemory {
   print("内存溢出")
} catch {
   print("其他错误")
}
}</pre></div>
<p>5、抛出Error后，try下一句直到作用域结束的代码都停止运行</p>
<p class="maodian"></p><h2>处理Error</h2>
<p>1、处理Error的2种方式</p>
<p>a、通过do-catch捕捉Error</p>
<p>b、不捕捉Error，在当前函数增加throws声明，Error将自动抛给上层函数</p>
<div class="jb51code"><pre class="brush:java;">func test() throws {
print(try divide(200, 0))
}</pre></div>
<p>如果最顶层函数（main函数）依然没有捕捉Error，那么程序将终止</p>
<p>以下是几种error的处理方法：</p>
<div class="jb51code"><pre class="brush:java;">func test() throws {
do {
   print(try divide(200, 0))
} catch let error as SomeError {
   print(error)
}
}</pre></div>
<div class="jb51code"><pre class="brush:java;">func test() throws {
do {
   print(try divide(200, 0))
} catch is SomeError {
   print("SomeError")
}
}</pre></div>
<div class="jb51code"><pre class="brush:java;">do {
try divide(20, 0)
} catch let error {
switch error {
case let SomeError.illegalArg(msg):
   print("参数异常：", msg)
default:
   print("其他异常")
}
}</pre></div>
<p>我们通过一个例子来总结一下处理Error的2种方式：</p>
<div class="jb51code"><pre class="brush:java;">override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
try test0()
}
func test0() throws -> Void {
try test1()
}
func test1() throws -> Void {
try test2()
}
func test2() throws -> Void {
do {
   print(try divide(200, 0))
} catch is SomeError {
   print("This is SomeError")
}
}</pre></div>
<p class="maodian"></p><h3>try?与try!</h3>
<p>1、可以使用try?、try!调用可能会抛出Error的函数，这样就不用去处理Error</p>
<div class="jb51code"><pre class="brush:java;">func test() -> Void {
print("1")
var result1 = try? divide(20, 10) // Optional(2), Int?
var result2 = try? divide(20, 0) // nil
var result3 = try! divide(20, 10) // 2, Int
print("2")
}</pre></div>
<p>2、a、b是等价的</p>
<div class="jb51code"><pre class="brush:java;">var a = try? divide(20, 0)
var b: Int?
do {
b = try divide(20, 0)
} catch {
b = nil
}</pre></div>
<p class="maodian"></p><h3>rethrows</h3>
<p>1、rethrows表明：函数本身不会抛出错误，但调用闭包参数抛出错误，那么它会将错误向上抛</p>
<div class="jb51code"><pre class="brush:java;">func exec(_ fn: (Int, Int) throws -> Int, _ num1: Int, _ num2: Int) rethrows -> Void {
print(try fn(num1, num2))
}</pre></div>
<p class="maodian"></p><h3>defer</h3>
<p>1、defer语句：用来定义以任何方式（抛错误、return等）离开代码块前必须要执行的代码</p>
<p>defer语句将延迟到当前作用域结束之前执行</p>
<div class="jb51code"><pre class="brush:java;">func open(_ filename: String) -> Int {
print("open")
return 1
}
func close(_ file: Int) -> Void {
print("close")
}
func processFile(_ filename: String) throws -> Void {
let file = open(filename)
defer {
   close(file)
}
try divide(20, 0)
}</pre></div>
<p>2、defer语句的执行顺序与定义顺序相反</p>
<div class="jb51code"><pre class="brush:java;">func fn1() -> Void {
print("fn1")
}
func fn2() -> Void {
print("fn2")
}
func testDefer() -> Void {
defer {
   fn1()
}
defer {
   fn2()
}
} //fn2 fn1</pre></div>
<p>到此这篇关于Swift Error的处理方法说明的文章就介绍到这了,更多相关Swift Error内容请搜索琼殿技术社区以前的文章或继续浏览下面的相关文章希望大家以后多多支持琼殿技术社区！</p>

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Swift Error的处理方法说明