Swift 2(executeFetchRequest):错误处理 [英] Swift 2 ( executeFetchRequest ) : error handling

问题描述

我遇到了我无法弄清楚的代码问题.安装Xcode 7 Beta并将我的Swift代码转换为Swift 2之后

I got some issue with the code that I can't figure out. After I installed Xcode 7 beta and convert my swift code to Swift 2

代码:

override func viewDidAppear(animated: Bool) {

    let appDelegate: AppDelegate = UIApplication.sharedApplication().delegate as! AppDelegate

    let context: NSManagedObjectContext = AppDel.managedObjectContext
    let request = NSFetchRequest(entityName: "PlayerList")

    list = Context.executeFetchRequest(request)

    tableView.reloadData()
}

屏幕截图:

推荐答案

从Swift 2开始，将产生错误的Cocoa方法转换为引发错误的Swift函数.

As of Swift 2, Cocoa methods that produce errors are translated to Swift functions that throw an error.

代替 Swift 1.x 中的可选返回值和错误参数:

Instead of an optional return value and an error parameter as in Swift 1.x:

var error : NSError?
if let result = context.executeFetchRequest(request, error: &error) {
    // success ...
    list = result
} else {
    // failure
    println("Fetch failed: \(error!.localizedDescription)")
}

在 Swift 2 中，该方法现在返回非可选值并引发错误 在错误情况下，必须使用try-catch进行处理:

in Swift 2 the method now returns a non-optional and throws an error in the error case, which must be handled with try-catch:

do {
    list = try context.executeFetchRequest(request)
    // success ...
} catch let error as NSError {
    // failure
    print("Fetch failed: \(error.localizedDescription)")
}

有关更多信息，请参见采用可可粉"中的错误处理"设计模式" 在将Swift与Cocoa和Objective-C结合使用" 文档.

For more information, see "Error Handling" in "Adopting Cocoa Design Patterns" in the "Using Swift with Cocoa and Objective-C" documentation.

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