Question

Possible Duplicate:
How can I code a C# function to accept a variable number of parameters?

I have the following class:

public class Product : AuditableTable  
{
    public string Position { get; set; }
    public string Quantity { get; set; }
    public double Location { get; set; }
}

What I need is to be able to update fields in the class with the following function.

Parameters:

• ac and pr define the keys and enable me to get an instance of the class.
• fld is the field name of the class to update. It could be “Position”, “Quantity” or “Location” or ??
• val is the value. It could be something like “London” or “1.234”

How can I arrange for the field name to be set dynamically without using a case statement to
check each value of fld and many different setters. Also if there’s some way of setting the field
dynamically how do I deal with casting it to the correct object type for that field?

    public void Update(string ac, string pr, string fld, string val) 
    { 
        try 
        { 
            vm.Product = _product.Get(ac, pr);
            vm.Product. xxx = fld 
        }
        catch (Exception e) { log(e); }
    }

Update

Here’s the solution proposed by Pieter:

public void Update(string ac, string pr, string fld, string val) { 
            try { 
                vm.Product = _product.Get("0000" + ac, pr);
                if (vm.Product != null)
                {
                    var property = vm.Product.GetType().GetProperty(fld);
                    var type = Nullable.GetUnderlyingType(property.PropertyType) ?? property.PropertyType;
                    val = Convert.ChangeType(val, type);
                    property.SetValue(vm.Product, val, null); 
                } 
                _product.AddOrUpdate(vm.Product);
            }
            catch (Exception e) { log(e); }
        }

Answer 1

You can use reflection:

vm.Product.GetType().GetProperty(field).SetValue(vm.Product, val, null);

SetValue requires that the value is of the correct type. If this isn’t the case, you can convert it with the following:

var property = vm.Product.GetType().GetProperty(field);

// Convert.ChangeType does not work with nullable types, so we need
// to get the underlying type.

var type = Nullable.GetUnderlyingType(property.PropertyType) ?? property.PropertyType;

object convertedValue = Convert.ChangeType(val, type);

property.SetValue(vm.Product, convertedValue, null);

This automatically converts val to the type of the property before assigning it.

Note however that both using reflection and Convert.ChangeType are horribly slow. If you do this a lot, you should have a look at DynamicMethod.