Question

I have a set of user controls on a page that are dynamically loaded based on condition to run a variety reports (the condition driver). Each control has one or more properties exposed that will be used to get data from my database query. Because the controls vary for each report I wrote a procedure to access the appropriate control’s property by name so I can send it to the database query in the code behind (C#). I got it all setup to access the public property like this:

stringVal = userControl.Attributes[stringName].ToString();

and it is telling me that I need to new up an object. I don’t understand how I need to access that property dynamically by string name. In my immediate window I can see the property I want; but, it is not an “Attribute” as control.Attributes.Count = 0. So, how do I need to set this up properly so I can access it by string name? Do I need to decorate the property with something?

Thank you in advance.

Answer 1

Below, I’ve written a wrapper class you can use to set/get public fields or properties of the wrapped class by string name.

First, let’s look at how you could use it on a class that had the public fields or properties StartDate and SocialSecurityNumber.

// First create the instance we'll want to play with
MyUserControl myControlInstance = new MyUsercontrol();
// MyUserContol has two properties we'll be using
// DateTime StartDate
// int SocialSecurityNumber

// Now we're creating a map to facilitate access to the properties
// of "myControlInstance" using strings
PropertyMap<MyUserControl> map = 
             new PropertyMap<MyUserControl>(myControlInstance);

// Since the map is directed toward "myControlInstance"
// this line is equivalent to:
// myControlInstance.StartDate = Datetime.Now;
map.Set<DateTime>("StartDate", DateTime.Now);

// This line is equivalent to:
// ssn = myUsercontrol.SocialSecurityNumber;
int ssn = map.Get<int>("SocialSecurityNumber");

And now on to how it’s implemented:

public class PropertyMap<T>
{
    readonly T Instance;

    public PropertyMap(T instance)
    {
        Instance = instance;
    }

    public U Get<U>(string PropertyName)
    {
        // Search through the type's properties for one with this name
        // Properties are things with get/set accessors
        PropertyInfo property = typeof(T).GetProperty(PropertyName);
        if (property == null)
        {
            // if we couldn't find a property, look for a field.
            // Fields are just member variables, but you can only
            // manipulate public ones like this.
            FieldInfo field = typeof(T).GetField(PropertyName);
            if (field == null)
                throw new Exception("Couldn't find a property/field named " + PropertyName);
            return (U)field.GetValue(Instance);
        }
        return (U)property.GetValue(Instance, null);
    }

    public void Set<U>(string PropertyName, U value)
    {
        // Search through the type's properties for one with this name
        PropertyInfo property = typeof(T).GetProperty(PropertyName);
        if (property == null)
        {
            // if we couldn't find a property, look for a field.
            FieldInfo field = typeof(T).GetField(PropertyName);
            if (field == null)
                throw new Exception("Couldn't find a property/field named " + PropertyName);
            field.SetValue(Instance, value);
            return;
        }
        property.SetValue(Instance, value, null);
    }
}