如何在Swift中的泛型类上实现NSCoding？ [英] How to implement NSCoding on a generic class in Swift?
问题描述
我在Swift（XCode beta 5）中遇到了泛型类和NSCoding问题。具体来说，这个示例代码很好用：
class Foo：NSObject，NSCoding
{
let bar：字符串
init（bar：String）{
self.bar = bar;
$ b func encodeWithCoder（aCoder：NSCoder！）{
aCoder.encodeObject（bar，forKey：bar）
}
所需的init（编码器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通用参数时;当我尝试编码对象时;我得到一个'无法识别的选择器发送到实例'错误：
class Foo< T> ：NSObject，NSCoding
{
let bar：String
init（bar：String）{
self.bar = bar;
$ b func encodeWithCoder（aCoder：NSCoder！）{
aCoder.encodeObject（bar，forKey：bar）
}
所需的init（编码器aDecoder：NSCoder！）{
self.bar = aDecoder.decodeObjectForKey（bar）as String
super.init（）
}
）
let foo = Foo< String>（bar：hello，world）
NSKeyedArchiver.archiveRootObject（foo，toFile：test.dat）
以下是错误详细信息和堆栈跟踪：
<$无法识别的选择器发送到实例0x7f8890ee4080
2014-08-16 10：43：54.632 SafeId [1778：32501] ***由于未被捕获的终止应用程序异常'NSInvalidArgumentException'，原因：' - [_TtC6SafeId14ArrayContainer00007F8893418E58 encodeWithCoder：]：无法识别的选择器发送到实例0x7f8890ee4080'
***第一次抛出调用堆栈：
（
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
当我读到这个时，当类是通用类时，Swift无法调用encodeWithCoder的实现。它是否正确 ？我怎样才能解决这个问题，以便在泛型类上使用NSCoding？
与Objective-C不兼容。 NSCoder的所有东西都发生在Objective-C中，它不能再访问你的类。
请注意，还有其他一些使类为通用的结果。例如，如果您要添加description属性，则还会收到编译时错误：
//错误：'@objc'获取非'@ objc'属性
覆盖var description：String {
returnFoo：\（bar）
}
I am having trouble with generic classes and NSCoding in Swift (XCode beta 5). Specifically, this example code works nicely:
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")
However, when I try the same code, and add a generic parameter; when I try to encode the object; I get a 'unrecognized selector sent to instance' error:
class Foo<T> : 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<String>(bar: "hello, world")
NSKeyedArchiver.archiveRootObject(foo, toFile: "test.dat")
Here is the error details and stack trace:
[_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
As I read this, Swift is unable to call the implementation of encodeWithCoder when the class is generic. Is this correct ? How can I work around this in order to use NSCoding on generic classes ?
The moment you make the class generic, it becomes non-compatible with Objective-C. The NSCoder stuff all happens in Objective-C which can no longer access your class.
Note there are other consequences of making the class generic as well. For example, if you were to add a description property, you'll also get a compile-time error:
// Error: '@objc' getter for non-'@objc' property
override var description: String {
return "Foo: \(bar)"
}
这篇关于如何在Swift中的泛型类上实现NSCoding？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
