ios - 类型NSArray不能隐式向下转换

我正在尝试将我的应用转换为Swift，但遇到了我不太了解的Swift错误。

在Obj-c中，我在这里有一个for in循环:

for (MYVisitor *visitor in visitors) {
    if (visitor.boxState == MYVisitorBoxStateChatting) {
        [self.chattingVisitors addObject:visitor];
    }
    else {
        [self.unknownVisitors addObject:visitor];
    }
}

我迅速:

for visitor: MYVisitor in visitors {
        if visitor.boxState == MYVisitorBoxStateChatting {
            self.chattingVisitors.addObject(visitor)
        }
        else {
            self.unknownVisitors.addObject(visitor)
        }
    }

我在迅速遇到一个错误，说:NSArray cannot be implicitly downcast to MYVisitor, did you mean to use as to force downcast?
Xcode建议此更改:for visitor: FHVisitor in visitors as MYVisitor {...然后给我这个错误:MYVisitor does not conform to protocol SequenceType

最佳答案

如果visitors是NSArray，并且保证其所有元素都是MYVisitor类型，则可以将数组转换为[MYVisitor]:

for visitor in visitors as [MYVisitor] {
    // ...
}

请注意，如果任何数组元素不是MYVisitor，这将在运行时崩溃。

或者，您可以使用

if let theVisitors = visitors as? [MYVisitor] {
    for visitor in theVisitors {
        println(visitor.name)
    }
} else {
    // This is not an array of MYVisitor objects.
}

或者，您可以检查每个数组元素:

for item in visitors {
    if let visitor = item as? MYVisitor {
        // ...
    } else {
        // This is not a MYVisitor.
    }
}