First time multithreader

Question

I am trying to use threading for the first time, and came up with this:

Thread myThread  = new Thread(() =>
  {
    test = Class1.getNumbers(param1, param 2);
    MessageBox.Show(test.toString());
  });

This doesn't do anything for me though. What did I do wrong?

You're missing the call to `Start`. Try adding `myThread.Start()` after you define `myThread`. — M.Babcock, Apr 12 '12 at 20:28
You are trying to show a message box from a worker thread. UI elements can only be created on the main thread. — Lubo Antonov, Apr 12 '12 at 20:28
For learning threading in the .NET platform, I highly recommend reading through this: http://www.yoda.arachsys.com/csharp/threads/index.shtml — Katie Kilian, Apr 12 '12 at 20:29
@lucas1024 : But `MessageBox.Show()` is a thread-safe static method. — H H, Apr 12 '12 at 20:34
What do I do if I want to add some data from the thread to the UI? Do I have to pass the data from the thread to the main thread? — TheGateKeeper, Apr 12 '12 at 20:42
@TheGateKeeper : _What do I do if I want to add some data from the thread to the UI?_ That's a separate question and it has been asked & answered here many times already. — H H, Apr 12 '12 at 20:46

score 6 · Answer 1 · answered Apr 12 '12 at 20:29

6

You didn't start the thread.

myThread.Start();

(You also have a syntax error on the MessageBox call...)

answered Apr 12 '12 at 20:29

jhenderson2099

956
8
17

score 4 · Answer 2 · answered Apr 12 '12 at 20:36

4

I am trying to use threading for the first time

Try to avoid using the Thread class directly. That is rarely needed.
Look into:

Backgroundworker
Task Parallel Library
ThreadPool

More or less in that order.

They all provide layers on top of threading to help you.

answered Apr 12 '12 at 20:36

H H

263,252
30
330
514

I think in the mind of a beginner this might confuse because avoiding the "Thread class" and avoiding "Multi threading" are distinct but sound the same... just a thought - another thought - it might be a bad thing to skip the Thread class along the same lines as learning EF without ever learning rdbms/sql... (i'm not trying to critisize, just thinking..) – Aaron Anodide Apr 12 '12 at 20:38
@Gabriel: Yes, a good learning track would be to use the Thread _in a Console App_. And then use the Bgw in WinForms. – H H Apr 12 '12 at 20:45

score 3 · Accepted Answer · answered Apr 12 '12 at 20:44

3

Read this free chapter from a very good book (honest plug - no inscentive here):

It's consice and gives you the know-how you want in an incremental way so you don't go too high level too fast. The answer your question is in the first few paragraphs...

answered Apr 12 '12 at 20:44

Aaron Anodide

16,906
15
62
121

Maybe I am going at this the wrong way... I just want to update a progress bar while executing a method. – TheGateKeeper Apr 12 '12 at 20:45
if you don't give a hoot about threads, then go for http://stackoverflow.com/questions/1259949/how-do-i-implement-a-progress-bar-in-c – Aaron Anodide Apr 12 '12 at 20:46
This is what I needed. I obviously need to learn more before attempting this! – TheGateKeeper Apr 12 '12 at 20:58

Brian Gideon · Answer 4 · 2012-04-13T13:10:33.327

You need to start the thread by calling Start.

Also, it is important to note that MessageBox.Show pumps messages. That is why it is working correctly¹ without an explicit call to Application.Run on that thread. Most UI forms and controls do not work this way though. In general do not attempt to access or create any UI elements from a worker thread.

¹A MessageBox can technically work from a thread other than the main UI thread, but it can cause some weird problems. For example, this message box could get stuck behind a modal dialog displayed by the UI thread. It is for this reason, among others, that it is not advised to display UI elements from a worker thread even if they are done so with self pumping calls like Form.ShowDialog or MessageBox.Show.

First time multithreader

4 Answers4