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STAThreadAttribute Class

Indicates that the COM threading model for an application is single-threaded apartment (STA).

System.Object
  System.Attribute
    System.STAThreadAttribute

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

[AttributeUsageAttribute(AttributeTargets.Method)]
[ComVisibleAttribute(true)]
public sealed class STAThreadAttribute : Attribute

The STAThreadAttribute type exposes the following members.

  NameDescription
Public methodSTAThreadAttributeInitializes a new instance of the STAThreadAttribute class.
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  NameDescription
Public propertyTypeIdWhen implemented in a derived class, gets a unique identifier for this Attribute. (Inherited from Attribute.)
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  NameDescription
Public methodEqualsInfrastructure. Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetHashCodeReturns the hash code for this instance. (Inherited from Attribute.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodIsDefaultAttributeWhen overridden in a derived class, indicates whether the value of this instance is the default value for the derived class. (Inherited from Attribute.)
Public methodMatchWhen overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
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  NameDescription
Explicit interface implemetationPrivate method_Attribute.GetIDsOfNamesMaps a set of names to a corresponding set of dispatch identifiers. (Inherited from Attribute.)
Explicit interface implemetationPrivate method_Attribute.GetTypeInfoRetrieves the type information for an object, which can be used to get the type information for an interface. (Inherited from Attribute.)
Explicit interface implemetationPrivate method_Attribute.GetTypeInfoCountRetrieves the number of type information interfaces that an object provides (either 0 or 1). (Inherited from Attribute.)
Explicit interface implemetationPrivate method_Attribute.InvokeProvides access to properties and methods exposed by an object. (Inherited from Attribute.)
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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.

NoteNote

In the .NET Framework versions 1.0 and 1.1, set the Thread.ApartmentState property before starting the thread.

COM threading models only pertain to applications that use COM interop. Using this attribute in an application that does not use COM interop has no effect.

The COM threading model can be set to single-threaded apartment or multithreaded apartment. The application thread is only initialized for COM interop if the thread actually makes a call to a COM component. If COM interop is not used, then the thread is not initialized.

In the .NET Framework versions 1.0 and 1.1, use this attribute on Main() instead of setting the Thread.ApartmentState property on the first line of code, to ensure that the threading model is set before any startup code is executed.

Important noteImportant

In the .NET Framework version 2.0, new threads are initialized as ApartmentState.MTA if their apartment state has not been set before they are started. The main application thread is initialized to ApartmentState.MTA by default. You can no longer set the main application thread to ApartmentState.STA by setting the Thread.ApartmentState property on the first line of code. Use the STAThreadAttribute instead.

In the .NET Framework version 2.0, you can also specify the COM threading model for a C++ application using the /CLRTHREADATTRIBUTE (Set CLR Thread Attribute) linker option.

ASP.NET applications should set the ASPCompat attribute of the @ Page directive to true, to force the page to be serviced by the STA thread pool.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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