CODEWITHSUNDEEP
c#c#-4.0razordynamic-language-runtime
Daniel A. White
Daniel A. White

Reputation: 190944

Dynamic property evaluation

With the DLR, i would like to do something like this:

class MyClass {
   int MyProperty { get; set; }
}

In razor, I would do something like this. (InstanceOfMyClass is some dynamic object that looks at an instance of MyClass)

@InstanceOfMyClass.MyProperty

This would output the string representation of MyProperty.

Now if I do this.

@InstanceOfMyClass.MyMissingProperty

I would like it to output "Missing: MyMissingProperty". I would love to capture the whole expression, like so.

@InstanceOfMyClass.MyMissingProperty.MoreMissing

Could potentially output "Missing: MyMissingProperty.MoreMissing", but that might be asking a lot of the DLR.

Will the ExpandoObject allow me to do this? If not, what do I have to do to implement this?

Upvotes: 4

Views: 494

Answers (3)

Bassam Mehanni
Bassam Mehanni

Reputation: 14944

You could achieve that by creating your own version of DynamicObject then over-write the TryGetMember

http://haacked.com/archive/2009/08/26/method-missing-csharp-4.aspx

Upvotes: 0

Ivo
Ivo

Reputation: 8352

Extend DynamicObject.TryGetMember in this way:

If the member exists, return the value. If the member doesn't exist, return a new instance of a class that will handle both the string representation of the missing property and also the chain. Something like this

public class MissingPropertyChain : DynamicObject
{
    private string property;

    public MissingPropertyChain(string property)
    {
        this.property = property;
    }

    public override bool TryGetMember(GetMemberBinder binder, out object result) 
    {
        if(binder.Name == "ToString")
            result = "Missing property: " + property;
        else
            result = new MissingPropertyChain( property + "." + binder.Name;

        return true;
    }
}

I didn't try it, but I think it will give you the idea of how to solve the problem.

Hope it helps.

Upvotes: 3

Wiktor Zychla
Wiktor Zychla

Reputation: 48230

I am not sure about the Expando, it's rather used when you want to set the property and then get it. From what you write, however, it seems that you'd like to be able to read any value which hasn't been set before.

For this, the DynamicObject could be used. You just override the TryGetMember.

Upvotes: 0

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