How do I get the name of a property from a property in C# (2.0)

Question

I know I could have an attribute but that's more work than I want to go to... and not general enough.

I want to do something like

class Whotsit
{
    private string testProp = "thingy";

    public string TestProp 
    {
        get { return testProp; }
        set { testProp = value; }
    }

}

...

Whotsit whotsit = new Whotsit();
string value = GetName(whotsit.TestProp); //precise syntax up for grabs..

where I'd expect value to equal "TestProp"

but I can't for the life of me find the right reflection methods to write the GetName method...

EDIT: Why do I want to do this? I have a class to store settings read from a 'name', 'value' table. This is populated by a generalised method based upon reflection. I'd quite like to write the reverse...

/// <summary>
/// Populates an object from a datatable where the rows have columns called NameField and ValueField. 
/// If the property with the 'name' exists, and is not read-only, it is populated from the 
/// valueField. Any other columns in the dataTable are ignored. If there is no property called
/// nameField it is ignored. Any properties of the object not found in the data table retain their
/// original values.
/// </summary>
/// <typeparam name="T">Type of the object to be populated.</typeparam>
/// <param name="toBePopulated">The object to be populated</param>
/// <param name="dataTable">'name, 'value' Data table to populate the object from.</param>
/// <param name="nameField">Field name of the 'name' field'.</param>
/// <param name="valueField">Field name of the 'value' field.</param>
/// <param name="options">Setting to control conversions - e.g. nulls as empty strings.</param>

public static void PopulateFromNameValueDataTable<T>
        (T toBePopulated, System.Data.DataTable dataTable, string nameField, string valueField, PopulateOptions options)
    {
        Type type = typeof(T);
        bool nullStringsAsEmptyString = options == PopulateOptions.NullStringsAsEmptyString;

        foreach (DataRow dataRow in dataTable.Rows)
        {
            string name = dataRow[nameField].ToString();
            System.Reflection.PropertyInfo property = type.GetProperty(name);
            object value = dataRow[valueField];

            if (property != null)
            {
                Type propertyType = property.PropertyType;
                if (nullStringsAsEmptyString && (propertyType == typeof(String)))
                {
                    value = TypeHelper.EmptyStringIfNull(value);
                }
                else
                {
                    value = TypeHelper.DefaultIfNull(value, propertyType);
                }

                property.SetValue(toBePopulated, System.Convert.ChangeType(value, propertyType), null);
            }
        }
    }

FURTHER EDIT: I am just in code, have an instance of Whotsit and I want to get the text string of the 'TestProp' property. It seems kind of weird I know, I can just use the literal "TestProp" - or in the case of my class to datatable function I'd be in a foreach loop of PropertyInfos. I was just curious...

The original code had string constants, which I found clumsy.

Answer 1

No, there's nothing to do this. The expression whotsit.TestProp will evaluate the property. What you want is the mythical "infoof" operator:

// I wish...
MemberInfo member = infoof(whotsit.TestProp);

As it is, you can only use reflection to get the property by name - not from code. (Or get all the properties, of course. It still doesn't help you with your sample though.)

One alternative is to use an expression tree:

Expression<Func<string>> = () => whotsit.TestProp;

then examine the expression tree to get the property.

If none of this helps, perhaps you could tell us more about why you want this functionality?

Answer 2

It is possible (without reflection) but only with latest C# 3.0

quick & very very dirty

class Program
{
    static void Main()
    {
        string propertyName = GetName(() => AppDomain.CurrentDomain);
        Console.WriteLine(propertyName); // prints "CurrentDomain"
        Console.ReadLine();
    }

    public static string GetName(Expression<Func<object>> property)
    {
        return property.Body.ToString().Split('.').Last();
    }
}

Update: I've just realized that Jon Skeet (anyone surprised? :) has covered this possibility already but I'll keep my answer here just in case someone is interested in some example to start with.