Which .Net Timer() to use

问题:

I have a legacy WinForms Mdi App in VB.Net 2.0 which I am adding functionality to. One of the additions is a warning which needs to be raised when the current time nears a specified value (a deadline). My intention is to check the time once an hour until there is less than an hour until the deadline, then display warnings at specified intervals until the time's up.

The user needs to be able to continue to use the app up to and even after the deadline, but they need to periodically be made aware of the deadline's proximity.

The app does not use System.Threading yet and my knowledge of it is limited at this time. I do know that there are 3 different Timer() methods available:

• System.Threading.Timer(),
• Windows.Forms.Timer() and
• System.Timers.Timer()

My question is, which is the best way to go with this? I attempted to use the threaded timer, but since WinForms are not thread safe I got a run time error trying to access another class. Is it worth making the class/form thread safe? Am I completely off track?

Thanks.

回答1:

I would just use the Forms timer. I think I read that it's not as accurate, but it sounds like you don't need it to be.

回答2:

This article explains pretty well:

Comparing the Timer Classes in the .NET Framework Class Library

It sounds like System.Windows.Forms.Timer is the one for you.

My guideline: If you want the timer to run on your main GUI thread, stick with Windows.Forms.Timer. If it's okay for your timer to be called asynchronously on a thread pool thread, or if you don't want to experience the small delays that System.Windows.Forms.Timer tends to suffer, use System.Timers.Timer. System.Threading.Timer has a different interface from the other two and is not thread-safe; personally, I'm not a fan.

回答3:

I agree that Windows.Forms.Timer() is the best for this case as it handles the cross thread marshalling issues.

Some useful related links:

• Windows Presentation Foundation Threading Model
• WinForms UI Thread Invokes: An In-Depth Review of Invoke/BeginInvoke/InvokeRequred

回答4:

The System.Forms.Timer actually works on the main thread using the windows message queue. This makes it somewhat inacurate but since you don't really need ms precision it's good enough. You could use one of the other timers that work on a separate thread but since you need to activate a winforms component that work in the main you'll need to use Form.Invoke or some other way to pass the event to the main thread - which would cause some latency as well. In conclusion use the System.Forms.Timer when you need to activate a winforms based component.

回答5:

Ok, first things first...

If you want to show the user a form and do something in the background I would use the BackgroundWorker class, it worked for me before. Also, you need invoke methods as mentioned before and as Chris said, it sounds harder than what it actually is.

Here's a link which I think will help you out.
http://msdn.microsoft.com/en-us/library/ms171728(VS.80).aspx