8

In Watin's source code, there is this piece of code:

    public void NavigateToNoWait(Uri url)
    {
        var thread = new Thread(GoToNoWaitInternal);
        thread.SetApartmentState(ApartmentState.STA);
        thread.Start(url);
        thread.Join(500);
    }

    [STAThread]
    private void GoToNoWaitInternal(object uriIn)
    {
        var uri = (Uri)uriIn;
        NavigateTo(uri);
    }

Since the thread created has its apartment state set, why is the [STAThread] attribute added to the method? I am not interested in the specific piece of code, but I am wondering if STAThread attribute is needed at all.

Notes:

  • The method GoToNoWaitInternal isn't used elsewhere.
  • The whole watin project is about manipulating WebBrowser objects (Internet explorer windows in general). Thus, we are manipulating a COM Object.
Daniel A. White
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Odys
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2 Answers2

8

Just read the documentation for STAThreadAttribute (emphasis mine):

Apply this attribute to the entry point method (the Main() method in C# and Visual Basic). It has no effect on other methods. To set the apartment state of threads you start in your code, use the Thread.SetApartmentState method before starting the thread.

So, in this case, the attribute should have no effect.

svick
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  • There must be a reason [Jeroen van Menen](http://stackoverflow.com/users/52173/jeroen-van-menen) added it – Odys Nov 28 '12 at 11:28
  • @odyodyodys You'd have to ask him about that. – svick Nov 28 '12 at 11:47
  • Note that `STAThreadAttribute` only effects `main()` because it's only used in [ApplicationActivator.CreateInstance](https://msdn.microsoft.com/en-us/library/ms146108%28v=vs.110%29.aspx), you can see how this attribute is used in the [Reference Source](https://referencesource.microsoft.com/#mscorlib/system/applicationactivator.cs,104) (in an `internal` method, `ApplicationActivator.ExecuteAsAssembly()`) – jrh May 04 '17 at 14:31
3

It should be noted that the STA (Single Threaded Apartment) is the threading model used by pre-.Net Visual Basic. It should only be used on the Main method of components that will be exposed to COM. The author of the code that you are trying to understand, appearantly did not understand how it is supposed to be used.

Kevin
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