我在Swift(XCode beta 5)中遇到泛型类和NSCoding问题.具体来说,这个示例代码很好地工作：
class Foo : NSObject,NSCoding
{
let bar: String
init(bar: String){
self.bar = bar;
}
func encodeWithCoder(aCoder: NSCoder!){
aCoder.encodeObject(bar,forKey: "bar")
}
required init(coder aDecoder: NSCoder!){
self.bar = aDecoder.decodeObjectForKey("bar") as String
super.init()
}
}
let foo = Foo(bar: "hello,world")
NSKeyedArchiver.archiveRootObject(foo,toFile: "test.dat")
但是,当我尝试相同的代码,并添加一个泛型参数;当我尝试编码对象;我收到一个’无法识别的选择器发送到实例’错误：
class Foo<T> : NSObject,forKey: "bar")
}
required init(coder aDecoder: NSCoder!){
self.bar = aDecoder.decodeObjectForKey("bar") as String
super.init()
}
}
let foo = Foo<String>(bar: "hello,toFile: "test.dat")
以下是错误详细信息和堆栈跟踪：
[_TtC6SafeId14ArrayContainer00007F8893418E58 encodeWithCoder:]: unrecognized selector sent to instance 0x7f8890ee4080
2014-08-16 10:43:54.632 SafeId[1778:32501] *** Terminating app due to uncaught exception 'NSinvalidargumentexception',reason: '-[_TtC6SafeId14ArrayContainer00007F8893418E58 encodeWithCoder:]: unrecognized selector sent to instance 0x7f8890ee4080'
*** First throw call stack:
(
0 CoreFoundation 0x0000000103a6e3e5 __exceptionPreprocess + 165
1 libobjc.A.dylib 0x000000010371e967 objc_exception_throw + 45
2 CoreFoundation 0x0000000103a754fd -[NSObject(NSObject) doesNotRecognizeSelector:] + 205
3 CoreFoundation 0x00000001039cd5ff ___forwarding___ + 495
4 CoreFoundation 0x00000001039cd388 _CF_forwarding_prep_0 + 120
5 Foundation 0x00000001032eaa75 _encodeObject + 1120
6 Foundation 0x0000000103326bf5 +[NSKeyedArchiver archiveRootObject:toFile:] + 241
当我读到这一点,当类是通用的时,Swift无法调用encodeWithCoder的实现.它是否正确 ？为了在泛型类上使用NSCoding,我该如何解决这个问题？
当您将类泛型化时,它变得与Objective-C不兼容. NSCoder的东西都发生在不能再访问你的类的Objective-C中.
注意还有其他的后果,使类通用.例如,如果要添加描述属性,则还会收到编译时错误：
// Error: '@objc' getter for non-'@objc' property
override var description: String {
return "Foo: \(bar)"
}