获取通用类的属性 [英] Get property of generic class

问题描述

我有一个通用类，还有一个对象值，其中 obj.GetType（）。GetGenericTypeDefinition（）== typeof（Foo<>）。

I have a generic class, and an object value where obj.GetType().GetGenericTypeDefinition() == typeof(Foo<>).

class Foo<T>
{
    public List<T> Items { get; set; }
}

如何获取 Items <的值/ code>来自 obj ？记住， obj 是一个 Object ，我不能转换 obj 为 Foo ，因为我不知道 T 是什么。

How do I get the value of Items from obj? Remember, obj is an Object, I can't cast obj as Foo because I don't know what T is.

我希望对此使用反射，但是每次我执行 GetProperty（ Items）时，它都会返回null。但是，如果有人知道一种无需反思的好方法，就一定可以。

I was hoping to use reflection for this, but each time I do GetProperty("Items") it returns null. However, if someone knows a good way to do this without reflection, by all means.

让我们说我的代码如下：

Let's say my code looks like this:

//just to demonstrate where this comes from
Foo<int> fooObject = new Foo<int>();
fooObject.Items = someList;
object obj = (object)fooObject;

//now trying to get the Item value back from obj
//assume I have no idea what <T> is
PropertyInfo propInfo = obj.GetType().GetProperty("Items"); //this returns null
object itemValue = propInfo.GetValue(obj, null); //and this breaks because it's null

推荐答案

可以使用：

Type t = obj.GetType();

PropertyInfo prop = t.GetProperty("Items");

object list = prop.GetValue(obj);

您将无法转换为 List< T> T ，所以直接使用code>，但是您仍然应该能够获得的值项目。

You will not be able to cast as a List<T> directly, of course, as you don't know the type T, but you should still be able to get the value of Items.

编辑：

下面是一个完整的示例，以演示此工作：

The following is a complete example, to demonstrate this working:

// Define other methods and classes here
class Foo<T>
{
    public List<T> Items { get; set; }
}

class Program
{
    void Main()
    {   
        //just to demonstrate where this comes from
        Foo<int> fooObject = new Foo<int>();
        fooObject.Items = new List<int> { 1, 2, 3};
        object obj = (object)fooObject;

        //now trying to get the Item value back from obj
        //assume I have no idea what <T> is
        PropertyInfo propInfo = obj.GetType().GetProperty("Items"); //this returns null
        object itemValue = propInfo.GetValue(obj, null);

        Console.WriteLine(itemValue);
                    // Does not print out NULL - prints out System.Collections.Generic.List`1[System.Int32]


        IList values = (IList)itemValue;
        foreach(var val in values)
            Console.WriteLine(val); // Writes out values appropriately
    }
}

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