Refreshing Windows program when other users make changes?

Scenario:

• 4 users launch separate instances of the same client program (Winforms) that is connected to a database based To-Do list.
• The first user selects the 3rd To-Do list item.

How do I update/refresh the other 3 users screens to reflect that开发者_JS百科 item #3 is no longer available?

My thought was a table that contains the last update date-time stamp. Then a timer would check every few seconds to see if there have been any changes.

UPDATE1:

Thanks to all - there are definitely a number of valid answers.

I went with simpler version of the scenario that Icemanind recommended.

As Lucas suggested you can implement a 'Push' style system that whenever an entity is modified it is 'Pushed' to the other connected users. This can be a bit complex. Working with a legacy system the way we handle this is through a 'Change Number' column but really it can be anything that is updated each time the record is modified.

When a user attempts to modify an entity we query the database to row-lock that entity where the 'Change Number' reflects the 'Change Number' the user currently has.

If the lock is successful the user is able to update/delete the entity. When they are done they 'Save/Commit' and 'Change Number' on the entity is increased.

If they fail to get the row-lock and the 'Change Number' was the same, we display a message that the entity they requested is in use by another user. If the 'Change Number' was different then the message states they must refresh their view.

Yes. The best way to do this is to implement a "push" type system. Here is how it would work. Whenever someone clicks something on the client end, the client would send a message to the server. The server would need to receive this signal and then the server would send out a refresh message to all clients connected to the server.

I don't know your client or server is coded, but you'll want to create a thread on the server that "listens" for incoming messages from clients and once it receives a message, puts it into a queue, the returns to listening for more messages. A second thread on the server needs to process the messages in the queue.

On the client side, you'll also want a second thread that listens for incoming messages from the server. Once a message is received, it can process the message and take whatever action is necessary.

A pretty decent tutorial on client/server and socket programming can be found here: http://www.codeproject.com/KB/IP/serversocket.aspx

Of course, it is a guide. You will need to modify it as you see fit.

Hope this makes sense and good luck!

You could implement a 'Push' system where when 1 user updates something, the server sends an update message to all connected clients.

I'd opt for an isDirty timestamp/flag on the items. No need to get all the items again and no need to create a difficult push system. Reread the items since last call every now and then.

If you're using SQL Server as your store, and ADO.NET or something on top of that for your data access, you should also check into SQL Dependency.

Basically, you can create a query from a table, and you can instruct SQL Server to notify you if any of the data in that query result changes.

See some intro articles on the topic:

• Using SqlDepedency for data change events
• SqlDepedency: creating a smarter cache
• Using SqlDependency to monitor SQL Database changes
• Query notifications in ADO.NET 2.0

It requires a bit of initial setup effort, but the huge advantage here is: you'll be notified automagically when something you're interested in (which is part of your query result set) changes, and you can react to that. No messy polling or anything....