C# Set Property in unknown object

Question

I have to set a property inside an unknown object. The structure looks like this:

        ObjA.ObjB().ObjC.PropA = propValue;

ObjA is from a referenced class. ObjB() is of type object and therefore ObjC is unknown. I thought about using Reflection but don't know how to use it correctly in this case.

        object objB = ObjA.ObjB();
        Type objBType = objB.GetType();
        System.Reflection.XXXInfo objCInfo = objBType.GetXXX("ObjC");

        Type objCType = objCInfo.GetType();
        System.Reflection.PropertyInfo PropAInfo = objCType.GetProperty("PropA");
        PropAInfo.SetValue(PropAInfo, propValue, null);

Answer (Thanks to BigM):

        dynamic objAB = ObjA.ObjB(); 
        objAB.ObjC.PropA = propValue;

Answer 1

This should probably work for you.

object objB = ObjA.ObjB();
Type objBType = objB.GetType();
System.Reflection.PropertyInfo objCInfo = objBType.GetProperty("ObjC");
object val = objCInfo.GetValue(objB);

Type objCType = val.GetType();
System.Reflection.PropertyInfo PropAInfo = objCType.GetProperty("PropA");
PropAInfo.SetValue(val, propValue, null);

However, I think a bit of re-architecting could be done here to make life a bit easier. For example, if you don't know anything about the types then you might consider using dynamic and returning dynamic types from ObjC and PropA - but there is a performance hit there.

On the other hand, if there is any way that you can use generics, that would make your life a lot easier. For example, the code here that sets the property value, if that method were generic it might likely be able to define the type of ObjC - but I can't really infer that with the current snippet.

Answer 2

Here are a couple of generic extension methods to help you get and set "unknown" properties by name:

public static class ReflectionHelpers
{
    public static bool TrySetProperty<TValue>(this object obj, string propertyName, TValue value)
    {
        var property = obj.GetType()
            .GetProperties()
            .Where(p => p.CanWrite && p.PropertyType == typeof(TValue))
            .FirstOrDefault(p => p.Name == propertyName);

        if (property == null)
        {
            return false;
        }

        property.SetValue(obj, value);
        return true;
    }

    public static bool TryGetPropertyValue<TProperty>(this object obj, string propertyName, out TProperty value)
    {
        var property = obj.GetType()
            .GetProperties()
            .Where(p => p.CanRead && p.PropertyType == typeof(TProperty))
            .FirstOrDefault(p => p.Name == propertyName);

        if (property == null)
        {
            value = default(TProperty);
            return false;
        }

        value = (TProperty) property.GetValue(obj);
        return true;
    }
}

And a usage example:

public class Program
{
    public static void Main()
    {
        var foo = new Foo
        {
            Bar = new Bar
            {
                HelloReflection = "Testing"
            }
        };

        string currentValue;
        if (foo.Bar.TryGetPropertyValue("HelloReflection", out currentValue))
        {
            Console.WriteLine(currentValue); // "Testing"
        }

        if (foo.Bar.TrySetProperty("HelloReflection", "123..."))
        {
            foo.Bar.TryGetPropertyValue("HelloReflection", out currentValue)

            Console.WriteLine(currentValue); // "123.."
        }
        else
        {
            Console.WriteLine("Failed to set value");
        }
    }
}

public class Foo
{
    public object Bar { get; set; }
}

public class Bar
{
    public string HelloReflection { get; set; }
}