Question

我试图转换这段ojb-c代码：

MPMovieFinishReason finishReason = [notification.userInfo[MPMoviePlayerPlaybackDidFinishReasonUserInfoKey] integerValue];

快点，因此我有这个：

var finishReason: MPMovieFinishReason = notification.userInfo[MPMoviePlayerPlaybackDidFinishReasonUserInfoKey.integerValue];

然而，这给了我标题中的错误。我在这里做错了什么？

Answer 1

您有一些问题，首先是您的直接翻译：

var finishReason: MPMovieFinishReason = notification.userInfo[MPMoviePlayerPlaybackDidFinishReasonUserInfoKey.integerValue];

]位置错误，因此您尝试在integerValue上调用MPMoviePlayer...而不是字典查找。

var finishReason: MPMovieFinishReason = notification.userInfo[MPMoviePlayerPlaybackDidFinishReasonUserInfoKey].integerValue;

这仍然失败，因为userInfo是一个NSDictionary而不是一个Dictionary，所以它被映射到[AnyObject:AnyObject]似乎自动变形让你失败了，所以它又回到了CFString不能映射到AnyObject。

如果我们进一步分解，这个过程就会变得更加清晰：

// Recover the original dictionary, and cast is by input and output, to it
//  all makes sense.  This will allow String as a parameter and return an NSNumber
//  as a result.
let userInfo = notification.userInfo as [String:NSNumber]

// From the userInfo, let's extract the raw NSNumber using lookup
let reason = userInfo[MPMoviePlayerPlaybackDidFinishReasonUserInfoKey]

// Convert the NSNumber into an MPMovieFinishReason enum.  Note that it's 
// 0215 and I'm on ambien so I don't care about the force unwrapping that
// should be optional unwrapping
let finishReason = MPMovieFinishReason.fromRaw(reason!.integerValue)

如果您一次只采取一个步骤，许多问题可以分解为更简单的问题。现代编译器甚至不会受到太多的困扰，因为它可以识别变量何时不再使用并进行适当的回收。另请注意，对这些临时值使用let而不是var，因为它们不应该被重用。

Answer 2

尝试使用类型转换函数Int（）

即，

var finishReason = Int(notification.userInfo[MPMoviePlayerPlaybackDidFinishReasonUserInfoKey]) as MPMovieFinishReason;

Swift Int不能转换为DictionaryIndex？

2 个答案: