I have seen a few samples of code involving the three timer classes provided with the .Net framework over the years.  Juval has such a sample, which he is updating to use ISynchronizeInvoke.InvokeRequired.  Even within the MSDN documentation, however, I have never seen much guidance between when to use System.Threading.Timer and System.Timers.Timer.  I decided to put together a table that outlines the characteristics of all three.

Feature description	System.Timers.Timer	System.Threading.Timer	System.Windows.Forms.Timer
Support for adding and removing listeners after the timer is instantiated.	Yes	No	Yes
Supports call backs on the user-interface thread	Yes	No	Yes
Calls back from threads obtained from the thread pool	Yes	Yes	No
Supports drag-and-drop in the Windows Forms Designer	Yes	No	Yes
Suitable for running in a server multi-threaded environment	Yes	Yes	No
Includes support for passing arbitrary state from the timer initialization to the callback.	No	Yes	No
Implements IDisposable	Yes	Yes	Yes
Supports one-off callbacks as well as periodic repeating callbacks	Yes	Yes	Yes
Accessible across application domain boundaries	Yes	Yes	Yes
Supports IComponent – hostable in an IContainer	Yes	No	Yes

Using the System.Windows.Forms.Timer is a relatively obvious choice for user interface programming.  Choosing between the other two options is less obvious and generally the choice between the two is insignificant.  If hosting within an IContainer is necessary then obviously System.Timers.Timer is the right choice.  However, if no specific System.Timers.Timer feature is required, then I suggest choosing System.Threading.Timer by default, simply because it is a slightly lighter weight implementation.

UPDATE - October 5, 2005

Thanks to Stephen Toub for pointing out that System.Timers.Timer can be used in the Windows Forms designer (although it does not appear in the toolbox by default) and that, using SynchronizationObject, on System.Timers.Timer, there is support for calling back on the UI thread.

Saturday, February 19, 2005 9:20:02 PM (Pacific Standard Time, UTC-08:00)      Comments [3]  Computer Related | .Net