How do I create my own custom ToString() format?

Question

I would like to specify the format of the ToString format, but I am not sure of the best way to handle this.

For example if I have the following specifiers

• EE = equipment
• ED = equipment description
• EI = equipment ID

so that if I used the ToString as such:

eqp.ToString("EE-EI (ED)")

the output might be:

"CAT994-61 (Front end loader)"

Would the best way be to search for the substrings and do a token replacement? Does any one have an example of doing this?

I'm currently doing sequential string.Replace, which works nicely.

public class Equipment
{
    // (other class code)

    public string ToString(string format)
    {
        string output = format;
        output = output.Replace("EE", _EquipID);
        output = output.Replace("ED", _EquipDescription);
        output = output.Replace("DI", _DepartID);
        return output;
    }

    public override string ToString()
    {
        return _EquipID;
    }
}

Answer 1

Combining string format, and overloading the ToString you can do this:

public override string ToString(string myFormat)
{
    myFormat = myFormat.Replace("EE", "{0}");
    myFormat = myFormat.Replace("EI", "{1}");
    myFormat = myFormat.Replace("ED", "{2}");
    return String.Format(myFormat, this.equipment, this.description, this.id);
}

You can also use regular expressions to make the Replace functions nicer.

---

This can be used as follows:

oProd.ToString("EE,ED,EI");
oProd.ToString("EE-ED (EI)"); // change order
oProd.ToString("ED-EE,EE,EE (EI)"); // multiple times
oProd.ToString("ED:EI"); // have some missing
etc

The String.Format gives you the flexibility to position the format variables any way like, have them multiple times, or drop some.

Answer 2

First override ToString()

Then if you want it to be dynamic you would have to parse the format string a token at a time and add the appropriate string to your output string. Using single letter format specifiers would make it a little simpler since you could parse it a character at a time. If it is a special character you output the appropriate data else output the character.

So something like this

public override string ToString(string format)
{
  StringBuilder s = new StringBuilder();

  foreach (char c in format)
  {
    switch (c)
    {
      case 'E':
        s.Append(EquipID);
        break;
      case 'D':
        s.Append(EquipDesc);
        break;
      case 'I':
        s.Append(DepartID);
        break;
      default:
        s.Append(c);
        break;
    }
  }

  return s.ToString();
}

This has the relatively minor advantage of doing it in one pass which is more efficient than multiple string replace calls.