C (WinForm) the current thread is not in a single threaded unit, so ActiveX controls cannot be instantiated

Reprint ：https://blog.csdn.net/qq_37508511/article/details/82770349
1、 Instantiate this in the main thread ActiveX Control
2、 This will be created Active The thread of the control is set to single thread .
Thread.ApartmentState Gets or sets the cell state of this thread .

thread = new Thread(Mehtod);
thread.SetApartmentState(System.Threading.ApartmentState.STA);
thread.Start();

Or thread pool
ThreadPool.QueueUserWorkItem(new WaitCallback(functionname),obj);

If not in a single threaded unit , Then declare it as a single threaded unit
to Main Function plus [STAThread]

static class Program
    {
    
        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {
    
 
        }
}

        stay .NET Framework 1.0 Version and 1.1 Version of the ,ApartmentState  Property marks the thread as indicating that it will execute in a single threaded unit or a multi-threaded unit . When the thread is in  Unstarted  or  Running  In thread state , You can set this property ; But a thread can only set this property once . If this property has not been set , It will return  Unknown.

       stay .NET Framework 2.0 Version of the , If their unit state has not been set before starting new threads , Then these new threads will be initialized to ApartmentState.MTA. By default , The main application thread is initialized to  ApartmentState.MTA. You can no longer set  System.Threading.ApartmentState  Property sets the main application thread to  ApartmentState.STA. Should be used instead  STAThreadAttribute.

      stay .NET Framework 1.0 and 1.1 Version of the , By using System.Threading.ApartmentState Property sets the unit state after the thread runs ; This will create a race condition . stay .NET Framework 2.0 Version of the , This is not allowed .

COM Components use units to synchronize access to resources . In contrast , Managed objects use synchronization zones 、 Synchronize primitives and context to ensure that all shared resources are used in a thread safe manner , Where synchronous primitives refer to mutexes 、 Lock and completion port and other objects . of .NET Other information about the threading model , See managed thread processing .

For interoperability , The common language runtime will call COM Object to create a unit and initialize it . Managed threads can create and enter single threaded units that contain only one thread (STA) Or a multithreaded unit containing one or more threads (MTA). When COM When the unit is compatible with the unit generated by the thread ,COM Will allow the calling thread to call directly COM object . If the two units are incompatible ,COM A compatible unit will be created and all calls will be marshaled in the new unit through the proxy .

Runtime calls  CoInitializeEx  take COM Unit initialized to MTA or STA unit . stay .NET Framework 2.0 Version of the , If the unit state of the managed thread is not set before starting the thread , Then the managed thread will be initialized to MTA. Before starting the thread, you can use SetApartmentState or TrySetApartmentState Method to set the unit state .

stay .NET Framework 2.0 Version of the , Unless STAThreadAttribute Apply to entry point processes , Otherwise, the main application thread will be initialized to MTA.

The following table lists  ApartmentState  Enumerate values and display comparable COM Unit initialization call .

ApartmentState Enumerated values	COM Unit initialization
MTA	CoInitializeEx(NULL, COINIT_MULTITHREADED)
STA	CoIntializeEx(NULL, COINIT_APARTMENTTHREADED)
Unknown	CoInitializeEx(NULL, COINIT_MULTITHREADED)