.NET Framework Class Library
MTAThreadAttribute Class

Indicates that the COM threading model for an application is multithreaded apartment (MTA).

Inheritance Hierarchy
SystemObject
   SystemAttribute
    SystemMTAThreadAttribute

Namespace:   System
Assembly:  mscorlib (in mscorlib.dll)
Syntax
<[%$TOPIC/77y997f0_en-us_VS_110_2_0_0_0_0%]([%$TOPIC/77y997f0_en-us_VS_110_2_0_0_0_1%].Method)> _
<[%$TOPIC/77y997f0_en-us_VS_110_2_0_0_0_2%](True)> _
Public NotInheritable Class MTAThreadAttribute _
	Inherits [%$TOPIC/77y997f0_en-us_VS_110_2_0_0_0_3%]
[[%$TOPIC/77y997f0_en-us_VS_110_2_0_1_0_0%]([%$TOPIC/77y997f0_en-us_VS_110_2_0_1_0_1%].Method)]
[[%$TOPIC/77y997f0_en-us_VS_110_2_0_1_0_2%](true)]
public sealed class MTAThreadAttribute : [%$TOPIC/77y997f0_en-us_VS_110_2_0_1_0_3%]
[[%$TOPIC/77y997f0_en-us_VS_110_2_0_2_0_0%]([%$TOPIC/77y997f0_en-us_VS_110_2_0_2_0_1%]::Method)]
[[%$TOPIC/77y997f0_en-us_VS_110_2_0_2_0_2%](true)]
public ref class MTAThreadAttribute sealed : public [%$TOPIC/77y997f0_en-us_VS_110_2_0_2_0_3%]
[<[%$TOPIC/77y997f0_en-us_VS_110_2_0_3_0_0%]>]
[<[%$TOPIC/77y997f0_en-us_VS_110_2_0_3_0_1%]([%$TOPIC/77y997f0_en-us_VS_110_2_0_3_0_2%].Method)>]
[<[%$TOPIC/77y997f0_en-us_VS_110_2_0_3_0_3%](true)>]
type MTAThreadAttribute =  
    class 
        inherit [%$TOPIC/77y997f0_en-us_VS_110_2_0_3_0_4%] 
    end
public final class MTAThreadAttribute extends [%$TOPIC/77y997f0_en-us_VS_110_2_0_4_0_0%]

The MTAThreadAttribute type exposes the following members.

Constructors
  NameDescription
Public method MTAThreadAttributeInitializes a new instance of the MTAThreadAttribute class.
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Properties
  NameDescription
Public property TypeIdWhen implemented in a derived class, gets a unique identifier for this Attribute. (Inherited from Attribute.)
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Methods
  NameDescription
Public method EqualsInfrastructure. Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute.)
Public method GetHashCodeReturns the hash code for this instance. (Inherited from Attribute.)
Public method GetTypeGets the Type of the current instance. (Inherited from Object.)
Public method IsDefaultAttributeWhen overridden in a derived class, indicates whether the value of this instance is the default value for the derived class. (Inherited from Attribute.)
Public method MatchWhen overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute.)
Public method ToStringReturns a string that represents the current object. (Inherited from Object.)
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Explicit Interface Implementations
  NameDescription
Explicit interface implemetation Private method _AttributeGetIDsOfNamesMaps a set of names to a corresponding set of dispatch identifiers. (Inherited from Attribute.)
Explicit interface implemetation Private method _AttributeGetTypeInfoRetrieves the type information for an object, which can be used to get the type information for an interface. (Inherited from Attribute.)
Explicit interface implemetation Private method _AttributeGetTypeInfoCountRetrieves the number of type information interfaces that an object provides (either 0 or 1). (Inherited from Attribute.)
Explicit interface implemetation Private method _AttributeInvokeProvides access to properties and methods exposed by an object. (Inherited from Attribute.)
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Remarks

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 ThreadSetApartmentState or ThreadTrySetApartmentState method before starting the thread.

NoteNote

For an overview of COM threading models, see Understanding and Using COM Threading Models.

COM threading models only apply to applications that use COM interop. 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, and the MTAThreadAttribute attribute, if it is present, has no effect.

Starting with the .NET Framework version 2.0, the default threading model for COM interop depends on the language in which you are developing your application, as the following table shows.

Language

COM apartment model

C#

Multithreaded apartment

C++

Multithreaded apartment

Visual Basic

Single-threaded apartment

To change these defaults, you use the MTAThreadAttribute attribute to set the threading model for the application, or call the ThreadSetApartmentState or ThreadTrySetApartmentState method before starting the thread to set the threading model for a particular thread. In C++, you can also use the /CLRTHREADATTRIBUTE linker option to specify the apartment model.

Some of the cases in which you want to use the MTAThreadAttribute attribute to explicitly set the threading model to multithreaded apartment include the following:

  • You're developing a Visual Basic app that calls to a C# library that in turn relies on COM interop. Because the multithreaded apartment model is the default for C#, you should change your app's threading model to multithreaded by using the MTAThreadAttribute attribute.

  • Your application makes calls to COM components that use the multithreaded apartment model.

Version Information

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
Thread Safety
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.