Swift try try! Try? Use and differences

swift exception handling in the History

• Swift1.0 Cocoa Touch version of NSError, Swift does not really have its own exception handling mechanism
• Swift2.0 version added ErrorType protocol
• Swift3.0 version renamed Error protocol

Use of Swift3.0 Error protocol

First, the definition of an enumerated, integration protocol Error (Swift 2.0 protocol is called ErrorType, 3.0 renamed Protocol Error)

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enum MyError : Error { case one case two case three }

Use throws and throw the

Throws back the parameter list used in a method of indicating an exception is thrown, the standard format: func 方法名字 (参数列表) throws -> 返回值类型using throw thrown in the method

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func testFunc(str: String) throws -> String { if str == "one" { throw MyError.one } else if str == "two" { throw MyError.two } else if str == "three" { throw MyError.three } return "ok" }

Using the do-catch handle exceptions

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do { var str = try testFunc(str: "three") } catch MyError.one { print( "MyError.one") } catch MyError.two { print( "MyError.two") } catch let error as MyError { print(error) }

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try?的使用

Swift2.0 后加入了新的关键字 try? , 如果不想处理异常那么可以用这个关键字,使用这个关键字返回一个可选值类型,如果有异常出现,返回nil.如果没有异常,则返回可选值.例子如下

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enum MyError : Error { case one case two case three } func testFunc(str: String) throws -> String { if str == "one" { throw MyError.one } else if str == "two" { throw MyError.two } else if str == "three" { throw MyError.three } return "ok" } var str = try? testFunc(str: "three") print(str)

控制台输出

`nil
Program ended with exit code: 0`

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try!的使用

如果不想处理异常,而且不想让异常继续传播下去,可以使用try!.这有点儿类似NSAssert().但是一旦使用try!后,在可能抛出异常的方法中抛出了异常,那么程序会立刻停止.例子如下

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enum MyError : Error { case one case two case three } func testFunc(str: String) throws -> String { if str == "one" { throw MyError.one } else if str == "two" { throw MyError.two } else if str == "three" { throw MyError.three } return "ok" } var str = try! testFunc(str: "three")

控制台:程序奔溃掉~

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try try? try! 的区别

• try 出现异常处理异常
• try? not handle the exception, an optional return value type, abnormal returns nil
• try! prevent abnormal continue to spread, once the program appears to stop abnormal, similar NSAssert ()