ToString() for a class property?

Question

Supposing I have a class "Item", which has three member variables: string name, decimal quantity and string unit. I have got public get/set properties on all three.

Sometimes, I want to display quantity as text along with correct unit, eg. 10m or 100 feet.

My question is, is it possible to have some sort of ToString() function for properties too, so that their text output can be customized?

Thanks,

Saurabh.

Answer 1

You could implement the IFormatable interface to have different ToString's

public class Item : IFormattable
{
    public string Name;
    public decimal Quantity;
    public string Unit;

    public override string ToString(string format, IFormatProvider provider)
    {
        switch(format)
        {
            case "quantity": return Quantity + Unit;
            default: return Name;
        }
    }
}

This can be used like this:

Item item = new Item();
Console.WriteLine(item.ToString());
Console.WriteLine("Quantity: {0:quantity}", item);

Answer 2

It sounds like your object model isn't correctly factored. What you probably want to do is abstract Unit and Quantity into another object and then you can override ToString for that. This has the advantage of keeping dependent values together, and allowing you to implement things such as conversions between units in the future (e.g. conversion from inchest to feet etc.), e.g.

public struct Measure
{
    public Measure(string unit, decimal quantity)
    {
        this.Unit = unit;
        this.Quantity = quantity;
    }

    public string Unit { get; private set; }
    public decimal Quantity { get; private set; }

    public override string ToString() 
    { 
        return string.Format("{0} {1}", this.Quantity, this.Unit);
    }
}

public class Item
{
    public string Name { get; set; }
    public Measure Measure { get; set; }

    public override string ToString() 
    { 
        return string.Format("{0}: {1}", this.Name, this.Measure);
    }
}

Note that I made Measure a struct here as it probably has value semantics. If you take this approach you should make it immutable and override Equals/GetHashCode as is appropriate for a struct.

Answer 3

What you can do is to make a new (readonly) property returning a formatted version:

public string QuantityAsString
{
    get
    {
        return string.Format("{0} {1}", this.Quantity, this.Unit);
    }
}