Get property from local variable by string

Question

Inside a method i make a few web service calls to get data, like so:

public void SomeMethod()
{
    var user = userWS.GetUsers();
    var documents = documentWS.GetDocuments();
}

I also have an XML file in which a user can tell what property to map. The XML sort of looks like this:

<root>
  <item id="username" mapper="user.username.value" />
  <item id="document1" mapper="documents.document1.value" />
</root>

So what i basically want to do is execute to string that is inside the mapper attribute. So that i have something like this:

public void SomeMethod()
{
    var user = userWS.GetUsers();
    var documents = documentWS.GetDocuments();

    // returns: "user.username.value"
    string usernameProperty = GetMapperValueById ( "username" );

    var value = Invoke(usernameProperty);
}

So it should act as if i was calling var value = user.username.value; manually in my code.

But how can i invoke this action from a string?

I've provided GetPropertyValue method that will suit your needs in this answer — Konrad Kokosa
– Konrad Kokosa, Commented Dec 10, 2013 at 9:27
I'm not sure if that is the answer i'm looking for. This is about a local variable from inside a method that i need to execute. I think i need more of an Eval function for this. But unfortunately that isn't as easy as i thought it would be — Vivendi
– Vivendi, Commented Dec 10, 2013 at 9:40
it will be enough, I'm going to provide an answer with proper example. — Konrad Kokosa
– Konrad Kokosa, Commented Dec 10, 2013 at 9:48
@Vivendi the only way to execute dynamic code would be via CodeDOM. However, you could do this using reflection - it just won't be as simple as you would like it to be. — James
– James, Commented Dec 10, 2013 at 10:00

Community · Accepted Answer · 2017-05-23 12:07:40Z

3

In general, you can't get values of local variables at runtime (see this question for reference), but based on my own answer from another question, you can use method GetPropertyValue to workaround this problem creating a local object with desired properties:

public void SomeMethod()
{
    var container = new 
    {
        user = userWS.GetUsers(),
        documents = documentWS.GetDocuments()
    }

    // returns: "user.username.value"
    string usernameProperty = GetMapperValueById ( "username" );

    var value = GetPropertyValue(container, usernameProperty);
}

static object GetPropertyValue(object obj, string propertyPath)
{
    System.Reflection.PropertyInfo result = null;
    string[] pathSteps = propertyPath.Split('.');
    object currentObj = obj;
    for (int i = 0; i < pathSteps.Length; ++i)
    {
        Type currentType = currentObj.GetType();
        string currentPathStep = pathSteps[i];
        var currentPathStepMatches = Regex.Match(currentPathStep, @"(\w+)(?:\[(\d+)\])?");
        result = currentType.GetProperty(currentPathStepMatches.Groups[1].Value);
        if (result.PropertyType.IsArray)
        {
            int index = int.Parse(currentPathStepMatches.Groups[2].Value);
            currentObj = (result.GetValue(currentObj) as Array).GetValue(index);
        }
        else
        {
            currentObj = result.GetValue(currentObj);
        }

    }
    return currentObj;
}

edited May 23, 2017 at 12:07

CommunityBot

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answered Dec 10, 2013 at 10:07

Konrad Kokosa

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2 Comments

James Over a year ago

+1 the idea of the container is a nice touch. This could be further improved by making GetPropertyValue generic.

Vivendi Over a year ago

Thanks alot, this seems to be doing the trick! I changed both result.GetValue(currentObj) to result.GetValue(currentObj, null) in my code, since it expects two params.

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