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137 lines
3.1 KiB
Markdown
137 lines
3.1 KiB
Markdown
# Swift 错误处理
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```swift
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enum SomeError: Error {
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case illegalArg(String)
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case outOfBounds(Int, Int)
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case outOfMemory
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}
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func divide(_ num1: Int, _ num2: Int) throws -> Int {
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if num2 == 0 {
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throw SomeError.illegalArg("分母不能为0")
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}
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return num1/num2
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}
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func testErrorCapture() {
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print("1")
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do {
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print("2")
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print(try divide(20, 0))
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print("3")
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} catch let SomeError.illegalArg(msg) {
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print("参数异常：", msg)
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} catch let SomeError.outOfBounds(size, index) {
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print("下标越界： size = \(size), index = \(index)")
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} catch SomeError.outOfMemory {
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print("内存溢出")
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} catch {
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print("其他异常")
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}
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print("4")
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}
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testErrorCapture()
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// console
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1
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2
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参数异常： 分母不能为0
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4
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```
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如果 `try divide(20, 0)` 则输出： 1 、2、参数异常： 分母不能为0、4
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如果 `try divide(20, 2)` 则输出： 1 、2、10、3、4
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说明：如果 do 抛出异常，则作用域内的后续的其他代码都不会被执行
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## Error 处理方式
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- 通过 do-catch 捕捉 Error
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- 不捕捉 Error，在当前函数增加 throws 声明，Error 继续向上层调用函数抛
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```swift
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func divide(_ num1: Int, _ num2: Int) throws -> Int {
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if num2 == 0 {
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throw SomeError.illegalArg("分母不能为0")
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}
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return num1/num2
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}
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func safeDivide(_ num1: Int, _ num2: Int) -> Int {
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var result:Int = 0
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do {
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result = try divide(num1, num2)
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} catch let SomeError.illegalArg(msg) {
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print("参数异常：", msg)
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} catch let SomeError.outOfBounds(size, index) {
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print("下标越界： size = \(size), index = \(index)")
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} catch SomeError.outOfMemory {
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print("内存溢出")
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} catch {
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print("其他异常")
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}
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return result
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}
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print("1")
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print(safeDivide(8, 2))
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print("3")
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// console
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1
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4
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3
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```
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- 如果有些错误不需要向上抛，可以用 `try?` ` try!` 调用可能会抛出 Error 的函数，这样就不需要去处理 Error
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```swift
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func testIgnoreError () {
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print("1")
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print(try? divide(10, 0))
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print("2")
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}
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testIgnoreError()
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// console
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1
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nil
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2
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```
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## rethrows
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如果一个函数本身不会抛出错误，但某个参数是闭包，且闭包抛出错误，那么函数需要用 `rethrows` 向上抛出错误
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```swift
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func exec(_ fn: (Int, Int) throws -> Int, _ num1: Int, _ num2: Int) rethrows {
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print(try fn(num1, num2))
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}
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func testCaptureClouserError () {
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do {
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try exec(divide, 20, 0)
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} catch let error {
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switch error {
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case let SomeError.illegalArgs(msg):
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print("参数异常：", msg)
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break
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case let SomeError.outOfBounds(size, index):
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print("下标越界： size = \(size), index = \(index)")
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break
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case SomeError.outOfMemory :
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print("内存溢出")
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break
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default:
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print("其他异常")
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}
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}
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}
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testCaptureClouserError() // 参数异常： 分母不能为0
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```
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