无法从泛型类型转换接口 [英] Cannot convert from generic type to interface

问题描述

>

其可能与协变和逆变，但我不知道如何工作的;

我试图仿制对象添加到列表<时，得到一个错误解决这个问题。我试着使用来限制我的泛型类型的其中T：IRegister 的

我要代表名册的接口，然后两个类其中。 。代表ByteRegister和DoubleWordRegister

 公共接口IRegister 
 {
字符串名称{;设置; } 
} 
 
公共类ByteRegister：IRegister 
 {
：
} 
 
公共类DoubleWordRegister：IRegister 
 {
：
} 
  

然后我有另一个类。它代表了这些寄存器的块中的所有相同类型的

 公共类RegisterBlock< T>其中T：IRegister 
 {
私人的IList< T> _registers; 
 
 ...构造，性能等
 
公共无效AddRegister（T寄存器）
 {
 _registers.Add（注册）; 
} 
} 
  

最后我有一个用于将RegisterMap类定义寄存器块列表和块内的每个注册。

 公共类RegisterMap 
 {
私人清单< RegisterBlock< IRegister>> _blocks; 
 
公共RegisterMap（）
 {
 _blocks =新的List< RegisterBlock< IRegister>>（）; 
 
 RegisterBlock< ByteRegister>块1 =新RegisterBlock&所述; ByteRegister>（块1，0）; 
 block1.AddRegister（新ByteRegister（REG1））; 
 block1.AddRegister（新ByteRegister（REG2））; 
 _blocks.Add（块1）; 
 
 RegisterBlock< D​​oubleWordRegister>块2 =新RegisterBlock&所述; DoubleWordRegister>（块2，10）; 
 block2.AddRegister（新DoubleWordRegister（REG3））; 
 block2.AddRegister（新DoubleWordRegister（REG4））; 
 block2.AddRegister（新DoubleWordRegister（REG5））; 
 _blocks.Add（块2）; 
} 
} 
  

但是我收到以下错误

错误20参数1：不能从转换'RegisterBlock< ByteRegister>'到'RegisterBlock< IRegister> 上线_blocks.Add（块1）同样对_blocks.Add（块2）;

解决方案

这的确是一个的 **方差问题。你需要为你的 RegisterBlock 类，也许 IRegisterBlock 其它接口：

 公共类RegisterBlock< T> ：IRegisterBlock 
，其中T：IRegister 
  

然后您可以创建<$ C $名单C> IRegisterBlock ：

 私人列表< IRegisterBlock> _blocks; 
  

其实我上周曾在我们的代码库类似的情况，而这正是我该怎么解决吧。

I'm getting an error when trying to add generic object to a List<>.

Its probably related to Covariance and Contravariance but I not sure how to work around this. I've tried to restrict my generic types using where T: IRegister.

I have an interface to represent a register and then two classes which represent a ByteRegister and a DoubleWordRegister.

public interface IRegister
{
    string Name {get;set;}
}

 public class ByteRegister : IRegister
{
...
}

public class DoubleWordRegister : IRegister
{
...
}

I then have another class which represents a block of these registers all of the same type.

public class RegisterBlock<T> where T:IRegister
{
   private IList<T> _registers;

 ... constructors, properties etc

    public void AddRegister(T register)
    {
        _registers.Add(register);
    }
}

And finally I have a RegisterMap class which is used to define the list of register blocks and each register within the block.

public class RegisterMap
{
    private List<RegisterBlock<IRegister>> _blocks;

    public RegisterMap()
    {
        _blocks = new List<RegisterBlock<IRegister>>();

        RegisterBlock<ByteRegister> block1= new RegisterBlock<ByteRegister>("Block1", 0);
        block1.AddRegister(new ByteRegister("Reg1"));
        block1.AddRegister(new ByteRegister("Reg2"));
        _blocks.Add(block1);

        RegisterBlock<DoubleWordRegister> block2= new RegisterBlock<DoubleWordRegister>("Block2", 10);
        block2.AddRegister(new DoubleWordRegister("Reg3"));
        block2.AddRegister(new DoubleWordRegister("Reg4"));
        block2.AddRegister(new DoubleWordRegister("Reg5"));
         _blocks.Add(block2);
    }
}

However I'm getting the following error:

Error 20 Argument '1': cannot convert from 'RegisterBlock<ByteRegister>' to 'RegisterBlock<IRegister>' on the line _blocks.Add(block1) and similarly on _blocks.Add(block2);

解决方案

This is indeed a **variance problem. You will need another interface for your RegisterBlock class, maybe IRegisterBlock:

public class RegisterBlock<T> : IRegisterBlock
    where T : IRegister

Then you can create a list of IRegisterBlock:

private List<IRegisterBlock> _blocks;

I actually had a similar situation in our code-base last week, and this is exactly how I resolved it.

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