Dynamically assign values to instance

Stevo Z

Hi Guys, I'd like to dynamically assign values to a known class instance based on the Property name. An example describes perfectly what I want to do: There is a class

public class AClass
{
public string _aValue;

    public string AValue
    {
        get { return \_aValue; }
        set { \_aValue = value; }
    }
}

and I want to assing value to AClass.AValue without actually explicitly writing:

AClass aInstance = new AClass();
aInstance.AValue = "value";

and now comes the best part. I'd like to avoid reflection as much as possible, because performance matters. I could go and look for a property named "AValue" and do

typeof(AClass).GetProperty("AValue").SetValue(aInstance, "value", null);

however that's veery slow. It's got to be possible to do that some other way, Linq works like this and it's not slow. any ideas?

zilo

musefan

Could try creating a method in the class that takes param name and value, then do a switch and assign the value to the property required

If only MySelf.Visible was more than just a getter... A person can produce over 5 times there own body weight in excrement each year... please re-read your questions before posting

Stevo Z

thanks for the idea, for now something like that is my workaround solution. However I wanted to avoid writing special code into the AClass itself as well. I was thinking of something generic that could either AClass inherit from or a Wrapper class.

zilo

S Senthil Kumar

Zilo(svk) wrote:

and I want to assing value to AClass.AValue without actually explicitly writing

It's difficult to answer without knowing why. Is it because you don't know the type at compile time?

Regards Senthil [MVP - Visual C#] _____________________________ My Home Page |My Blog | My Articles | My Flickr | WinMacro

DaveyM69

If it's only the one property you could use an implicit operator overload.

public class AClass
{
public AClass() : this(string.Empty) { }
private AClass(string aValue)
{
AValue = aValue;
}
public static implicit operator AClass(string aValue)
{
return new AClass(aValue);
}
public string AValue
{
get;
set;
}
}

AClass aInstance = "Test String";
Console.WriteLine(aInstance.AValue);

Dave
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
Visual Basic is not used by normal people so we're not covering it here. (Uncyclopedia)

Stevo Z

Interesting idea, but... It's not only one, there will be many properties like this within AClass. And it needs to be done outside of constructor.

zilo

Stevo Z

Yes. I'm loading the class from dll as

Assembly.LoadFile(string file);

And I'd like to keep AClass as simple as possible, without any specific code to read or write values into it. It's just a data container.

zilo

Calin Tatar

Basically, you are searching for an alternative to Reflection, right? Calin

Stevo Z

Kind of. Something that does the job but keeps the speed on same level as direct access.

zilo

Calin Tatar

I think you could try by using Dynamic Invocation. Calin

Stevo Z

Do you suggest to create a method using reflection on the fly:

void AssingAValue(AClass aInstance, object value)
{
aInstance.AValue = value;
}

and then just call this method?

zilo

Calin Tatar

yes, so you can dynamically change the AValue property. Calin

S Senthil Kumar

Well, LINQ knows the types of data objects at compile time, so there's no similarity there. Without reflection, I guess your best bet is emitting the IL directly[^].

Regards Senthil [MVP - Visual C#] _____________________________ My Home Page |My Blog | My Articles | My Flickr | WinMacro

DaveyM69

Maybe extension methods could work. Create an extension method ToAClass for each type, and also pass the AClass instance.

public static class ExtensionMethods
{
static public void SetAClass(this string value, AClass instance)
{
instance.AString = value;
}

static public void SetAClass(this int value, AClass instance)
{
    instance.AInt = value;
}

}
public class AClass
{
public string AString
{
get;
set;
}
public int AInt
{
get;
set;
}
}

AClass aInstance = new AClass();
"Test string".SetAClass(aInstance);
123.SetAClass(aInstance);

Dave
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
Visual Basic is not used by normal people so we're not covering it here. (Uncyclopedia)

Stevo Z

Anyhow, whether is it extension methods or not, I'll have to create them dynamically using reflection and then just call those methods. I think I have a better idea now, thanks

zilo

Stevo Z

It doesn't have to, I'm using those classes to work with linq as well and it's working fine. Thanks for the suggestion, that looks to be the only way to go.

zilo

S Senthil Kumar

Zilo(svk) wrote:

I'm using those classes to work with linq as well and it's working fine

Now I'm curious - can you paste a snippet of code that does that? I can't imagine LINQ working without you specifying the type somewhere (unless it's an anonymous type, of course).

Regards Senthil [MVP - Visual C#] _____________________________ My Home Page |My Blog | My Articles | My Flickr | WinMacro

Stevo Z

I ment the classes are not present withing the same solution or assembly when compiling the code. When working with linq, I'm using strong types. This is a sample of one of the classes:

[Table(Name = "Books")]
public partial class Book : IDALEntity
{
private int _BookId;
private string _Title;
private int _Price;
private int _PublisherID;

    public Book()
    {   }

    \[Column(Storage = "\_BookId", AutoSync = AutoSync.OnInsert, DbType = "Int NOT NULL", IsPrimaryKey = true)\]
    public int BookId
    {
        get
        {
            return this.\_BookId;
        }
        set
        {
           this.\_BookId = value;                 
        }
    }

...
}

zilo

S Senthil Kumar

Well, LINQ uses reflection to read the custom attributes you provide for each property, so that it can map them to database columns. I guess they do it just once and then generate dynamic code to do the actual translation from SQL results to object property assignments.

Regards Senthil [MVP - Visual C#] _____________________________ My Home Page |My Blog | My Articles | My Flickr | WinMacro

Calin Tatar

Also, you can use TypeDescriptor, and PropertyDescriptor. Calin