我需要获取特定对象属性的值，但不知道 object 的类型

Question

I have got an c# object and I don't know the type of this object. (ie object o) What I know is that this object has a member called 'ID' of type int.

I wanted to get the value of this property but I am not good enough with reflection...

I can get a type and members of this object:

Type type = obj.GetType();
System.Reflection.MemberInfo[] member = type.GetMember("ID");

...but don't know what to do next:-)

Thanks for help in advance Mariusz

Answer 1

You can use:

Type type = obj.GetType();
PropertyInfo property = type.GetProperty("ID");
int id = (int) property.GetValue(obj, null);

• Use PropertyInfo because you know it's a property, which makes things easier
• Call GetValue to get the value, passing in obj as the target of the property and null for indexer arguments (as it's a property, not an index)
• Cast the result to int as you already know it's going to be an int

Jared's suggestion of using dynamic is good too, if you're using C# 4 and .NET 4, although to avoid all the brackets I'd probably write it as:

dynamic d = obj;
int id = d.ID;

(unless you needed it in a single expression for some reason).

Answer 2

Is this a public property? Is so then the easiest route is to use dynamic

int value = ((dynamic)obj).ID;

Answer 3

Can you use C# 4? In that case, you can use dynamic :

dynamic dyn = obj;
int id = dyn.ID;

Answer 4

public class TestClass
{
    public TestClass()
    {
        // defaults
        this.IdField = 1;
        this.IdProperty = 2;
    }

    public int IdField;
    public int IdProperty { get; set; }
}

// here is an object obj and you don't know which its underlying type
object obj = new TestClass();
var idProperty = obj.GetType().GetProperty("IdProperty");
if (idProperty != null)
{
    // retrieve it and then parse to int using int.TryParse()
    var intValue = idProperty.GetValue(obj, null);
}

var idField = obj.GetType().GetField("IdField");
if (idField != null)
{
    // retrieve it and then parse to int using int.TryParse()
    var intValue = idField.GetValue(obj);
}