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Thread.TrySetApartmentState Method

Sets the apartment state of a thread before it is started.

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

[HostProtectionAttribute(SecurityAction.LinkDemand, Synchronization = true, 
	SelfAffectingThreading = true)]
public bool TrySetApartmentState(
	ApartmentState state
)

Parameters

state
Type: System.Threading.ApartmentState

The new apartment state.

Return Value

Type: System.Boolean
true if the apartment state is set; otherwise, false.

ExceptionCondition
ArgumentException

state is not a valid apartment state.

ThreadStateException

The thread has already been started.

NoteNote:

The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: Synchronization | SelfAffectingThreading. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

New threads are initialized as ApartmentState.MTA if their apartment state has not been set before they are started. Apartment state must be set before a thread is started.

NoteNote:

The main application thread is initialized to ApartmentState.MTA by default. The only way to set the apartment state of the main application thread to ApartmentState.STA is to apply the STAThreadAttribute attribute to the entry point method.

The TrySetApartmentState method, along with the GetApartmentState method and the SetApartmentState method, replaces the ApartmentState property.

The following code example demonstrates the GetApartmentState, SetApartmentState, and TrySetApartmentState methods. The code example creates a thread. Before the thread is started, GetApartmentState displays the initial ApartmentState.Unknown state and SetApartmentState changes the state to ApartmentState.STA. The TrySetApartmentState method then returns false when attempting to change the state to ApartmentState.MTA because the apartment state is already set. If the same operation had been attempted with SetApartmentState, InvalidOperationException would have been thrown.

After the thread is started, the TrySetApartmentState method is used again. This time it throws ThreadStateException because the thread has already been started.

using System;
using System.Threading;

class Example
{
    public static void Main()
    {
        Thread t = new Thread(ThreadProc);
        Console.WriteLine("Before setting apartment state: {0}", 
            t.GetApartmentState());

        t.SetApartmentState(ApartmentState.STA);
        Console.WriteLine("After setting apartment state: {0}", 
            t.GetApartmentState());

        bool result = t.TrySetApartmentState(ApartmentState.MTA);
        Console.WriteLine("Try to change state: {0}", result);

        t.Start();

        Thread.Sleep(500);

        try
        {
            t.TrySetApartmentState(ApartmentState.STA);
        }
        catch (ThreadStateException)
        {
            Console.WriteLine("ThreadStateException occurs " +
                "if apartment state is set after starting thread.");
        }

        t.Join();
    }

    public static void ThreadProc()
    {
        Thread.Sleep(2000);
    }
}

/* This code example produces the following output:

Before setting apartment state: Unknown
After setting apartment state: STA
Try to change state: False
ThreadStateException occurs if apartment state is set after starting thread.
 */

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

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

.NET Framework

Supported in: 3.5, 3.0, 2.0

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