How to Conditionally Format a String in .Net?

Question

I would like to do some condition formatting of strings. I know that you can do some conditional formatting of integers and floats as follows:

Int32 i = 0;
         


        

Answer 1

I hoped this could do it:

return String.Format(items.ToString(itemList + " ;;") + "Values: {0}", valueList);

Unfortunately, it seems that the .ToString() method doesn't like the blank negative and zero options or not having a # or 0 anywhere. I'll leave it up here in case it points someone else to a better answer.

Answer 2

Well, you can simplify it a bit with the conditional operator:

string formatString = items.Count > 0 ? "Items: {0}; Values: {1}" : "Values: {1}";
return string.Format(formatString, itemList, valueList);

Or even include it in the same statement:

return string.Format(items.Count > 0 ? "Items: {0}; Values: {1}" : "Values: {1}",
                     itemList, valueList);

Is that what you're after? I don't think you can have a single format string which sometimes includes bits and sometimes it doesn't.

Answer 3

While not addressing the OP directly, this does fall under the question title as well.

I frequently need to format strings with some custom unit, but in cases where I don't have data, I don't want to output anything at all. I use this with various nullable types:

/// <summary>
/// Like String.Format, but if any parameter is null, the nullOutput string is returned.
/// </summary>
public static string StringFormatNull(string format, string nullOutput, params object[] args)
{
    return args.Any(o => o == null) ? nullOutput : String.Format(format, args);
}

For example, if I am formatting temperatures like "20°C", but encounter a null value, it will print an alternate string instead of "°C".

double? temp1 = 20.0;
double? temp2 = null;

string out1 = StringFormatNull("{0}°C", "N/A", temp1); // "20°C"
string out2 = StringFormatNull("{0}°C", "N/A", temp2); // "N/A"

Answer 4

This is probably not what you're looking for, but how about...

formatString = (items.Count > 0) ? "Items: {0}; Values: {1}" : "Values: {1}";

Answer 5

Not within String.Format(), but you could use C#'s inline operators, such as:

return items.Count > 0 
       ? String.Format("Items: {0}; Values: {1}", itemList, valueList)
       : String.Format("Values: {0}", valueList);           

This would help tidy-up the code.

Answer 6

string.Format(  (items.Count > 0 ? "Items: {0}; " : "") + "Values {1}"
              , itemList
              , valueList);