C# Reflection issue | Tech Off

Zeus
Why is the caption missing??

Hi guys and gals.

I am having a problem with reflection, and accessing sub-classes. Let's take a look at this structure:

public class Master { 
    public int ID { get; set; } 
    public string Name { get; set; } 
    public Child FirstChild { get; set; } 
} 
 
public class Child { 
    public int ID { get; set; } 
    public string Name { get; set; } 
}

If I want to get the value of the Name property on the master class I can do this:

string name = item.GetType().GetProperty("Name").GetValue(item, null).ToString();

But If I want to access the value of the Name property of the FirstChild, I am stuck. I have read StackOverflow from cover to cover trying to find out how to do this ... do you have any insights ?

And I know reflection is performance heavy, but it's used in very few cases in our system, but getting this to work would simplify things a great deal.

TommyCarlier
I want my scalps!

object child =
  item
    .GetType()
    .GetProperty("FirstChild")
    .GetValue(item, null);

if (child != null)
{
  string childName =
    child
      .GetType()
      .GetProperty("Name")
      .GetValue(child, null) as string;
}

Zeus
Why is the caption missing??

In reply to TommyCarlier

#Oct 19th @ 4:15 AM

thx Tommy ... found one bug though:

// YOURS:
if (child != null)
{
  string childName =
    child
      .GetType()
      .GetProperty("Name")
      .GetValue(item, null) as string;
}
// MINE:
if (child != null)
{
  string childName =
    child
      .GetType()
      .GetProperty("Name")
      .GetValue(child, null) as string;
}

Thanks for the help .... I kept getting null exceptions doing something similar.

Now all I have to do is make this dynamic and I am good to go .... Smiley

TommyCarlier
I want my scalps!

In reply to Zeus

#Oct 19th @ 4:29 AM

Thanks for the bug fix, I corrected my code. That's what happens when you improvize in the C9 editor. Smiley

Maybe it's easier to make a method to do this (so you can reuse it):

public static object GetPropertyValue(object item, string propertyName)
{
  return item != null
    ? item
        .GetType()
        .GetProperty(propertyName)
        .GetValue(item, null)
    : null;
}

Which you can the use like this:

var childName = 
  GetPropertyValue(
    GetPropertyValue(item, "FirstChild"),
    "Name") as string;

Yggdrasil
Pour me a cab, 'cause I can't drink no more.

In reply to TommyCarlier

#Oct 19th @ 4:37 AM

I'm with Tommy here - if you're going to do any serious work with reflection, building a set of easy-access methods is essential, otherwise you'll get bogged down in tedious syntax and methods with 5-6 parameters, half of which are usually null or identical from call to call. Make your life easier, make a ReflectionHelper class with some helper methods.

spivonious

Wait I'm confused. Why can't you just say

var childName = parent.FirstChild.Name;

?

wkempf

In reply to spivonious

#Oct 19th @ 6:34 AM

Because he's in a scenario where he doesn't know the types at compile time.

public void DoSomething(object parent)

{

}

There are lots of scenarios where reflection is very handy, if not essential. It comes at a heavy price in runtime performance, but that's a trade off that is often worth the price.

Zeus
Why is the caption missing??

In reply to Yggdrasil

#Oct 19th @ 6:26 AM

That is exactly what I did, I made the thing pretty friggin' dynamic. Now I can crawl down endless child and sub classes to find the value of my property.

ODIN => Simplified ! (with your help of course) .... thx guys Smiley

stevo_
Human after all

In reply to Zeus

#Oct 19th @ 9:36 AM

I wouldn't go nuts Tongue Out

Zeus
Why is the caption missing??

In reply to stevo_

#Oct 19th @ 9:44 AM

I like nuts ... peanuts that is .... salted, mmmm, very nice ...

spivonious

In reply to wkempf

#Oct 19th @ 6:53 AM

Ah that makes sense then.

I think VB's late binding would take care of that for me. Runtime error if the property doesn't exist.

Sven Groot
My name has 9 letters. Coincidence? I think not...

In reply to Zeus

#Oct 19th @ 10:02 AM

Peanuts aren't nuts. Tongue Out

Sven Groot
My name has 9 letters. Coincidence? I think not...

In reply to spivonious

#Oct 19th @ 10:20 AM

VB's late binding won't help you if you don't know the name of the property apriori.

spivonious

In reply to Sven Groot

#Oct 19th @ 7:03 PM

But if Zeus doesn't know the name of the property he's after, the function Tommy gave won't help him either.

In VB I can compile


Public Sub(parent as Object)

   Dim name as String = parent.FirstChild.Name

End Sub

If parent doesn't have a FirstChild property then an exception is thrown at runtime.

Sven Groot
My name has 9 letters. Coincidence? I think not...

In reply to spivonious

#Oct 20th @ 1:30 PM

For your VB snippet, you need to know the property's name at compile time.

For Tommy's function (and reflection in general), it's sufficient to know the property's name at run time, you don't need to know it at compile time.

That's the difference.

spivonious

In reply to Sven Groot

#Oct 20th @ 6:58 PM

*light bulb moment*

Gotcha. I fail to see when I would ever need this, but I understand this thread now.