Scott Hanselman

Three years ago I postulated about a ToString implementation for C# that seemed useful to me and a few days later I threw it out on the blog. We used in at my old company for a number of things.

Just now I realized that it'd be even more useful (or more evil) with Extension Methods, so I opened up the old project, threw in some MbUnit tests and changed my implementation to use extension methods.

So, like bad take-out food, here it is again, updated as ToString() overloads:

[Test]
public void MakeSimplePersonFormattedStringWithDoubleFormatted()
{
	Person p = new Person();
	string foo = p.ToString("{Money:C} {LastName}, {ScottName} {BirthDate}");
	Assert.AreEqual("$3.43 Hanselman, {ScottName} 1/22/1974 12:00:00 AM", foo);
}

[Test]
public void MakeSimplePersonFormattedStringWithDoubleFormattedInHongKong()
{
	Person p = new Person();
	string foo = p.ToString("{Money:C} {LastName}, {ScottName} {BirthDate}",new System.Globalization.CultureInfo("zh-hk"));
	Assert.AreEqual("HK$3.43 Hanselman, {ScottName} 1/22/1974 12:00:00 AM", foo);
}

It's moderately well covered for all of the hour it took to write it, and I find it useful.

Here's all it is.

public static class FormattableObject 
{
    public static string ToString(this object anObject, string aFormat)
    {
        return FormattableObject.ToString(anObject, aFormat, null);
    }

    public static string ToString(this object anObject, string aFormat, IFormatProvider formatProvider)
	{
		StringBuilder sb = new StringBuilder();
		Type type = anObject.GetType();
		Regex reg = new Regex(@"({)([^}]+)(})",RegexOptions.IgnoreCase);
		MatchCollection mc = reg.Matches(aFormat);
		int startIndex = 0;
		foreach(Match m in mc)
		{
			Group g = m.Groups[2]; //it's second in the match between { and }
			int length = g.Index - startIndex -1;
			sb.Append(aFormat.Substring(startIndex,length));
			
			string toGet = String.Empty;
			string toFormat = String.Empty;
			int formatIndex = g.Value.IndexOf(":"); //formatting would be to the right of a :
			if (formatIndex == -1) //no formatting, no worries
			{
				toGet = g.Value;
			}
			else //pickup the formatting
			{
				toGet = g.Value.Substring(0,formatIndex);
				toFormat = g.Value.Substring(formatIndex+1);
			}

			//first try properties
			PropertyInfo retrievedProperty = type.GetProperty(toGet);
			Type retrievedType = null;
			object retrievedObject = null;
			if(retrievedProperty != null)
			{
				retrievedType = retrievedProperty.PropertyType;
				retrievedObject  = retrievedProperty.GetValue(anObject,null);
			}
			else //try fields
			{
				FieldInfo retrievedField = type.GetField(toGet);
				if (retrievedField != null)
				{
					retrievedType = retrievedField.FieldType;
					retrievedObject = retrievedField.GetValue(anObject);
				}
			}

			if (retrievedType != null ) //Cool, we found something
			{
				string result = String.Empty;
				if(toFormat == String.Empty) //no format info
				{
					result = retrievedType.InvokeMember("ToString",
						BindingFlags.Public | BindingFlags.NonPublic | 
						BindingFlags.Instance | BindingFlags.InvokeMethod | BindingFlags.IgnoreCase
						,null,retrievedObject,null) as string;
				}
				else //format info
				{
					result = retrievedType.InvokeMember("ToString",
						BindingFlags.Public | BindingFlags.NonPublic | 
						BindingFlags.Instance | BindingFlags.InvokeMethod | BindingFlags.IgnoreCase
						,null,retrievedObject,new object[]{toFormat,formatProvider}) as string;
				}
				sb.Append(result);
			}
			else //didn't find a property with that name, so be gracious and put it back
			{
				sb.Append("{");
				sb.Append(g.Value);
				sb.Append("}");
			}
			startIndex = g.Index + g.Length +1 ;
		}
		if (startIndex < aFormat.Length) //include the rest (end) of the string
		{
			sb.Append(aFormat.Substring(startIndex));
		}
		return sb.ToString();
	}
}

Enjoy.

About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. I am a failed stand-up comic, a cornrower, and a book author.

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