Get an object value using a string

MrEyes

Hello all, Odd title, not an easy one to summarise. Basically I am trying to find a way of access an object value from a string that contains that objects name. So, lets assume I have the following basic class

class NoddyClass
{
public string foo;
public string bar;
}

Which is used by the following

class NoddyProcess
{
private NoddyClass nc;

public NoddyProcess()
{
this.nc = new NoddyClass()
this.nc.foo = "thingys";
this.nc.bar = "doodars";
}

public void GetValueFromString(string value)
{
//A miracle occurs here
}
}

class AnotherNoddyProcess
{
private void DoSomething()
{
NoddyProcess np = new NoddyProcess();
np.GetValueFromString("foo");
}
}

So putting all this together in the GetValueFromString method I need to access this.nc and using the passed string retrieve the value of this.nc.foo and return it to the caller. I am assuming that this can be done with reflection, however I seem to have hit a wall on this and could do with a prod in the right direction. P.S. I realise that in the examples given above none of this is actually necessary, however these are extemely simplfied versions of a much more complex framework.

TJoe

Since you are accessing fields, check out this[^]. It has an example that should get you started. For properties, check out this[^].

Take care, Tom ----------------------------------------------- Check out my blog at http://tjoe.wordpress.com

led mike

MrEyes wrote:

however these are extemely simplfied versions of a much more complex framework.

This "much more complex framework" is what? Or is it what you are developing?

MrEyes

Basically I have a library that has an encrypted XML file sat underneath it, when the library object is created it reads in, decrypts and deserialises the XML to an class level object. This object is then used within the library to drive various things. This library exposes a COM interface to allow none .NET applications to interact with it, and until today these external applications did not require the ability to directly extract data from the XML file. Today however, this functionality is now a requirement. The XML itself while structurally simple, contains alot of elements. In fact it looks something like this:

Due to the volume of elements it isnt really feasible to create an externally accessible property for every single one, i.e:

public string GetElement1Value
{
return this.myXmlObject.Element1
}

There was also the option of not using the current XML object in memory, re-reading, re-decrypting it, and then using XmlDocument and Xpath to get the value, however I belive the overhead here would be greater than using reflection. So this is where the idea of using reflection comes in. In fact since posting I have found a solution, so this is what I am currently trying out:

public string GetConfigurationValue(string key)
{
Type itemType = typeof(MyXmlObject);

PropertyInfo property = itemType.GetProperty(key);

if (property == null)
{
    throw new ArgumentException("Invalid XML element key", key);
}

return property.GetValue(this.myXmlObject, null).ToString();

}

Which as you can see is alot shorter than using 1000+ property accessor/methods. Maybe I am barking up the wrong tree here, so feel free to point out something that I have considered as I have to admit using reflection doesnt sit very well with me.

led mike

MrEyes wrote:

In fact it looks something like this:

WOW... I am sorry but using XML in that way crosses my threshold of acceptability. I am afraid I cannot assist you any further.

Kasdoffe

This appeared to work for me, and I think it's what you want, using reflection. Note the Main method and GetValueFromString method. (Sorry for the formatting) using System; using System.Collections.Generic; using System.Text; using System.Reflection; namespace ConsoleApplication1 { class Program { static void Main(string [] args) { NoddyProcess p = new NoddyProcess(); object o = p.GetValueFromString("foo"); Console.WriteLine(o.ToString()); o = p.GetValueFromString("bar"); Console.WriteLine(o.ToString()); Console.Read(); } } class NoddyClass { public string foo; public string bar; } class NoddyProcess { private NoddyClass nc; public NoddyProcess() { this.nc = new NoddyClass(); this.nc.foo = "thingys"; this.nc.bar = "doodars"; } public object GetValueFromString(string value) { FieldInfo info = nc.GetType().GetField(value,BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Public ); return info.GetValue(nc); } } class AnotherNoddyProcess { private void DoSomething() { NoddyProcess np = new NoddyProcess(); np.GetValueFromString("foo"); } } }

Patrick Etc

Ack.. you may want to reconsider this approach. Did you know that you can use XPath queries in XML documents using the XmlDocument class in .NET? This might serve your purpose alot better than attempting to manually extract fields in this manner.

The early bird who catches the worm works for someone who comes in late and owns the worm farm. -- Travis McGee