所以我只是在处理我正在处理的状态机类型,并且大多想要尝试使用Activator.CreateInstance方法来查看它是什么样的,我遇到了一个问题,我似乎无法使用where子句正如我想的那样.如果我只是个白痴,我会提前道歉,大家都会把我从这里拉出来.所以我有2个小班.
public class TransitionContainer<TTransition,TStateTo> :
ITransitionContainer<TTransition,TStateTo>
where TTransition : ITransition
where TStateTo : IState
{
public TransitionContainer()
{
StateTo = typeof(TStateTo);
Transition = Activator.CreateInstance<TTransition>();
}
public Type StateTo { get; private set; }
public TTransition Transition { get; private set; }
}
以及
public class StateContainer<T> : IStateContainer<T> where T : IState
{
private Dictionary<Type,TransitionContainer<ITransition,IState>> _transitions =
new Dictionary<Type,IState>>();
public StateContainer()
{
State = Activator.CreateInstance<T>();
}
public T State { get; private set; }
public int TransitionCount
{
get { return _transitions.Count; }
}
public void AddTransition<TTransition,TStateTo>() where TTransition : ITransition,new()
where TStateTo : IState,new()
{
var transitionContainer= new TransitionContainer<TTransition,TStateTo>();
_transitions.Add(typeof(TTransition),transitionContainer);
}
所以就行_transitions.Add(typeof(TTransition),transitionContainer);我收到一个无法转换的TransitionContainer< TTransition,TStateTo>表达式类型TransitionContainer< ITransition,IState>错误.
如果我将通用参数更改为
var transitionContainer= new TransitionContainer<ITransition,IState>();
它工作正常,但我想使用new()的继承类型,所以我可以确定我可以实例化它们.
我再次道歉,如果我做了一件令人难以置信的错事,我只是碰到了一堵砖墙而且我的谷歌搜索引导我走向了不好的方向.我没有包含任何其他接口或类,因为它们似乎不是问题的一部分,但如果需要我可以附加它们.谢谢你的帮助！
解决方法
出现此问题是因为：
> ITransitionContainer不是类型参数的covariant interface.
> AddTransition方法泛型参数是not constrained为reference types.
> _transitions不是具有ITransitionContainer值的字典,因此不将其更改为Dictionary< Type,ITransitionContainer< ITransition,IState>>我们仍然无法添加适当的resticted协变转换.
简化示例
考虑以下简化案例：
public interface ITransition
{
}
public class SomeTransition : ITransition
{
}
public interface ITest<TTransition>
where TTransition : ITransition
{
TTransition Value { get; }
}
public class SomeTest<TTransition> : ITest<TTransition>
where TTransition : ITransition
{
public TTransition Value
{
get
{
throw new NotImplementedException();
}
}
}
两者都会失败
public static void Do<TTransition>()
where TTransition : ITransition
{
ITest<ITransition> item = new SomeTest<TTransition>();
}
和
ITest<ITransition> item = new SomeTest<SomeTransition>();
如果你使ITest协变
public interface ITest<out TTransition>
,那么它只会在通用方法中失败.因为这里TTransition可以是结构和co /(contra)方差doesn’t work with value types：
public static void Do<TTransition>()
where TTransition : ITransition
{
ITest<ITransition> item = new SomeTest<TTransition>();
}
但是,如果您使用该方法constrained to only reference types,那么它将在两种情况下都有效：
public static void Do<TTransition>()
where TTransition : class,ITransition
{
ITest<ITransition> item = new SomeTest<TTransition>();
}
将相同的原则(out和class)应用于您的两个通用参数,它将完成这项工作.
针对您具体案例的完整解决方案
public interface IState
{ }
public interface ITransition
{ }
// !!!!! - Here we add out specifier
public interface ITransitionContainer<out TTransition,out TStateTo>
where TTransition : ITransition
where TStateTo : IState
{
Type StateTo
{
get;
}
TTransition Transition
{
get;
}
}
public interface IStateContainer<T> where T : IState
{
T State
{
get;
}
}
public class TransitionContainer<TTransition,TStateTo> : ITransitionContainer<TTransition,TStateTo>
where TTransition : ITransition
where TStateTo : IState
{
public TransitionContainer()
{
StateTo = typeof(TStateTo);
Transition = Activator.CreateInstance<TTransition>();
}
public Type StateTo { get; private set; }
public TTransition Transition { get; private set; }
}
public class StateContainer<T> : IStateContainer<T> where T : IState
{
private Dictionary<Type,ITransitionContainer<ITransition,IState>>();
public StateContainer()
{
State = Activator.CreateInstance<T>();
}
public T State { get; private set; }
public int TransitionCount
{
get { return _transitions.Count; }
}
public void AddTransition<TTransition,TStateTo>()
// !!!!!! - Here we add class constraints
where TTransition : class,ITransition,new()
where TStateTo : class,IState,new()
{
var transitionContainer = new TransitionContainer<TTransition,transitionContainer);
}
}
