从C#中的未知类型进行强制转换 [英] Cast from unknown type in c#

问题描述

我有一个对象，其中包含一个字符串值和一个字段中的原点类型.

I have a object that contain a value in string and a origin Type that is in a field.

class myclass
{
   public string value;
   public Type type;
}
myclass s=new myclass();
s.value = "10";
s.type = typeof(int);
Type tt = s.type;
row.Value[ind]= s[0].value as tt; //i have error here

如何通过该类型转换值.

How can i cast an value by that's type.

推荐答案

基本上，您的方案是要使用存储在变量中的类型进行类型转换.您只能像这样在运行时这样做:

Basically your scenario is that you want to type cast with the type stored in a variable. You can only do that at runtime like this :

    myclass s=new myclass();
    s.value = "10";
    s.type = typeof(int);

    var val = Convert.ChangeType(s.value, s.type);

但是由于转换是在运行时完成的，因此您不能将变量val存储在任何整数集合中，即 List< int> ，甚至不能进行 int another = val ，在编译时是coz，类型未知，由于同样明显的原因，您也会遇到编译错误.

but since the conversion is done at runtime, you cannot store the variable val in any integeral collection i.e. List<int> or even you cannot do int another = val, coz at complie time, the type is not known yet, and you will have compilation error, again for same obvious reason.

在稍微复杂的情况下，如果必须强制转换为 User-Defined dataType ，并且想要访问其不同的属性，则不能照原样进行.让我来演示一下您的代码:

In a little complex scenario, if you had to typecast to a User-Defined dataType and you wanted to access its different properties, you cannot do it as is. Let me demonstrate with few modifications to your code :

class myclass
{
    public object value;
    public Type type;
}

还有另一个:

    class myCustomType
    {
        public int Id { get; set; }
    }

现在您要做:

 myclass s = new myclass();
 s.value = new myCustomType() { Id = 5 };
 s.type = typeof(myCustomType);
 var val = Convert.ChangeType(s.value, s.type);

现在，如果您执行 val.Id ，它将无法编译.您必须使用动态关键字或通过如下所示的反射来检索它:

now if you do val.Id, it won't compile. You must retrieve it either by using dynamic keyword or by reflection like below:

 var id = val.GetType().GetProperty("Id").GetValue(val);

您可以遍历customType(类)的所有可用属性并检索它们的值.

you can iterate over all the available properties of your customType (class) and retrieve their values.

要通过 dynamic 关键字进行检索，请直接执行以下操作:

for retrieving it through dynamic keyword, directly do this:

dynamic val = Convert.ChangeType(s.value, s.type);
int id = val.Id;

并且编译器不会哭.(是的，但是不会有任何智能感知).

and compiler won't cry. (Yes there won't be any intellisense though)

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