在类型为< T>的类型T的成员变量上调用扩展方法 [英] Calling an extension method on a member variable of type T of class<T>

问题描述

给定扩展方法如下：

  public static class Ext 
 {
 public static void Serialize这Guid guid_，StringWriter sw_）
 {
 sw_.Write（guid_.ToString（B））; 
 
 
 $ / code $ / pre 
 
 和类：
 
 
  public class Field< T> 
 {
公共T值; 
 
 public void Serialize（StringWriter sw_）
 {
 value.Serialize（sw_）; 
 
 
 
 
 $ b我想要做以下事情， t相当数字：
 
 
  public class Foo 
 {
 public Field< Guid> UID; 
 
 public Foo（）
 {
 //假定StringWriter对象sw; 
 uid.Serialize（sw）; 
 
 
 $ / code> 
显然现实生活中的情况比较复杂，这是只是一个简单的例子。
 
 
 编辑 
 
 
 
编译错误： p> 
 
 
错误CS1928：'T'不包含'Serialize'的定义，并且最佳扩展方法重载'Ext.Serialize（System.Guid，StringWriter）'有一些无效参数
 
 
 
错误CS1929：实例参数：无法从'T'转换为'System.Guid'
 
解决方案 
这是不可能的，因为 T 在编译时并不知道它是否是 Guid  
 
 
但你可以这样做
 公共类GuidField：Field< Guid> 
 {
 public override void Serialize（StringWriter sw _）//假设我们已经使基类方法变为虚拟
 {
 value.Serialize（sw_）; 
 
 
 
 
 $ b $ p 
 $ b 
这样做可以，因为c＃编译器知道 value 在编译时是 Guid 。 
 
 
以下方法可行，但它会打败泛型的观点。不建议也。 
举例说明如何做一个例子 
 
 
  public void Serialize（StringWriter sw_）
 {
 if（typeof（T）== typeof（Guid））
 {
（（Guid）（object）value）.Serialize（sw_）; 
} 
} 
  
 
Given extension method below:
public static class Ext
{
    public static void Serialize(this Guid guid_, StringWriter sw_)
    {
        sw_.Write(guid_.ToString("B"));
    }
}
and the class:
public class Field<T>
{
    public T value;

    public void Serialize(StringWriter sw_)
    {
        value.Serialize(sw_);
    }
}
I would like to do the following, but can't quite figure it out:
public class Foo
{
    public Field<Guid> uid;

    public Foo()
    {
        // assume StringWriter object sw;
        uid.Serialize(sw);
    }
}
Obviously real-life situation is more complicated, this is just a bare-bones example.

EDIT

Compiler errors:

error CS1928: 'T' does not contain a definition for 'Serialize' and the best extension method overload 'Ext.Serialize(System.Guid, StringWriter)' has some invalid arguments

error CS1929: Instance argument: cannot convert from 'T' to 'System.Guid'
解决方案
It is not possible because T is not certainly known at compile time whether it is Guid or not.

But you can do something like this
public class GuidField : Field<Guid>
{
    public override void Serialize(StringWriter sw_)//Assume we have made base class method virtual
    {
        value.Serialize(sw_);
    }
}
This works, since c# compiler knows value is Guid at compile time.

Following way will work but it will defeat the point of "Generics". Not recommended also.
To show how to do I give an example
public void Serialize(StringWriter sw_)
{
    if (typeof (T) == typeof (Guid))
    {
        ((Guid)(object)value).Serialize(sw_);
    }
}


                        
这篇关于在类型为&lt; T&gt;的类型T的成员变量上调用扩展方法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！