Is there a way to set properties on struct instanc

Question

I'm trying to write some code that sets a property on a struct (important that it's a property on a struct) and it's failing:

System.Drawing.Rectangle rectangle = new System.Drawing.Rectangle();
PropertyInfo propertyInfo = typeof(System.Drawing.Rectangle).GetProperty("Height");
propertyInfo.SetValue(rectangle, 5, null);

The Height value (as reported by the debugger) never gets set to anything - it stays at the default value of 0.

I have done plenty of reflection on classes before and this has worked fine. Also, I know that when dealing with structs, you need to use FieldInfo.SetValueDirect if setting a field, but I don't know of an equivalent for PropertyInfo.

Answer 1

Ever heard of SetValueDirect? There's a reason they made it. :)

struct MyStruct { public int Field; }

static class Program
{
    static void Main()
    {
        var s = new MyStruct();
        s.GetType().GetField("Field").SetValueDirect(__makeref(s), 5);
        System.Console.WriteLine(s.Field); //Prints 5
    }
}

There's other methods than the undocumented __makeref which you could use (see System.TypedReference) but they're more painful.

Answer 2

The value of rectangle is being boxed - but then you're losing the boxed value, which is what's being modified. Try this:

Rectangle rectangle = new Rectangle();
PropertyInfo propertyInfo = typeof(Rectangle).GetProperty("Height");
object boxed = rectangle;
propertyInfo.SetValue(boxed, 5, null);
rectangle = (Rectangle) boxed;