Learn the Swift from the Start learning Note (Day--cocoa) error handling mode

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Swift error handling mode, in swift1.x and the Swift 2.0 are two different modes.

Swift 1.x Code error handling mode uses Cocoa Frame error Handling mode, up to now objective-c This processing mode is also used, and Swift2.0 then adopted the Do-try-catch error handling mode.

The following example code reads a string from a file into memory if you use the Swift 1.x The error handling mode code is as follows:

Import Foundation var err:nserror? Define optional nserror? variable let contents =nsstring (Contentsoffile:filepath, encoding:nsutf8stringencoding, error: & ERR) If err! = Nil {//To determine if the ERR variable is still nil//error handling}

nserror? must be an optional variable, because you want to initialize it to a Nil .

Judging Err whether the variable is still Nil , if it is still Nil in the Code

Let contents =nsstring (Contentsoffile:filepath, encoding:nsutf8stringencoding, error: &err)

No error occurred during method call, otherwise an error occurred.

The constructor of the above code, its Swift The syntax is defined as follows:

Init? (Contentsofurl url:nsurl, encoding enc:uint, error error:nserrorpointer)

the last parameter of the constructor is Nserrorpointer (i.e. Nserror pointer), then in the actual call we need to pass Err variable address (that is, &err ), & is a fetch address character. The ERR variable is assigned a value if there is an error after the method call is complete .

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Learn the Swift from the Start learning Note (Day--cocoa) error handling mode