String.Format isn't working

Question

public override string ToString()
{
    string token = "something";
    foreach (something item in this)
    {
        something = something + "Some_Point({0},{1}),";
        string.Format(something, item.X, item.Y);
    }
    return something+= "anything";
}

This is the overridden ToString() method of a custom collection. The problem here is that String.Format isn't substituting the values of X and Y. It does substitute whenever I add return before String.Format. I am just starting to learn C# and have no idea what is causing this strange behaviour.

Answer 1

string.Format returns formatted string, you have to assign it back to your variable:

something = string.Format("Some_Point({0},{1}),", item.X, item.Y);

Answer 2

If you have lots of strings to append in a single result, you should use StringBuilder class from System.Text namespace. That is a good pratice because a string object is immutable and every time you change something, a new instance is create on the heap. Try to do something like this:

using System.Text;

...

public override string ToString()
{
    StringBuilder s = new StringBuilder("something initial if you need");
    foreach (something item in this)
    {
        s.AppendFormat("Some_Point({0},{1}),", item.X, item.Y);
    }
    s.Append("something else");

    return s.ToString();
}

If you want know more about why avoid string concatenation, look this article: http://msdn.microsoft.com/en-us/library/ms182272(v=vs.80).aspx

Answer 3

string.Format returns a string, so:

something = string.Format(something, item.X, item.Y);