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Asked: 2026-05-12T10:50:19+00:00

I am learning C# 3.5 and I want to know what [STAThread] does in

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I am learning C# 3.5 and I want to know what [STAThread] does in our programs?

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  1. Editorial Team

    The STAThreadAttribute is essentially a requirement for the Windows message pump to communicate with COM components. Although core Windows Forms does not use COM, many components of the OS such as system dialogs do use this technology.

    MSDN explains the reason in slightly more detail:

    STAThreadAttribute indicates that the
    COM threading model for the
    application is single-threaded
    apartment. This attribute must be
    present on the entry point of any
    application that uses Windows Forms;
    if it is omitted, the Windows
    components might not work correctly.
    If the attribute is not present, the
    application uses the multithreaded
    apartment model, which is not
    supported for Windows Forms.

    This blog post (Why is STAThread required?) also explains the requirement quite well. If you want a more in-depth view as to how the threading model works at the CLR level, see this MSDN Magazine article from June 2004 (Archived, Apr. 2009).

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