Using the ConvertAll function with a converter delegate is the easiest way to convert a list of generic objects into specific types. As you might have inferred from its name, a converter delegate is yet another incarnation of anonymous delegates, but one that performs the conversion of each item in a list from a generic object to a specific class.

To see ConvertAll in action, let’s convert a list of DateTime values to a list of other types. First let’s build up a quick List:

Predicates.aspx.cs (excerpt)

List dates = new List();

for (DateTime d = DateTime.Now;

d < DateTime.Now.AddMonths(10);

d.AddDays(2)

) { dates.Add(d); }

Now we’ll call dates.ConvertAll with a few different converter delegates to show how easy this approach to converting objects is:

Predicates.aspx.cs (excerpt)

// Convert date list to short date (string) list

List strings = dates.ConvertAll(

delegate(DateTime value)

{ return value.ToShortDateString(); }

);

// Convert date list to day of year (int) list

List ints = dates.ConvertAll(

delegate(DateTime value)

{ return value.DayOfYear; }

);

// Convert date list to daylight savings time (bool) list

List bools = dates.ConvertAll(

delegate(DateTime value)

{ return value.IsDaylightSavingTime(); }

);

Note that we’re taking advantage of type inference to simplify the syntax a little. You can define the converter source and destination types explicitly if you want, like this:

Predicates.aspx.cs (excerpt)

List strings = dates.ConvertAll

(new Converter

(

delegate(DateTime d) { return d.ToShortDateString(); }

)

);

However, as the compiler can see what you’re converting from and to, it will infer those types for you.