Why does the process return null if we use Process.Start of a file in C# ?

Question

I'm using Windows 10 Enterprise in Administrator user

I have a program that receives the file stored in binary form in SQL Server and puts it in a folder in the TEMP path. For example: there is a photo in the database, I select it and WriteAllBytes
in the temp, then using Process.Start(C:\Users\ADMINI~1\AppData\Local\Temp.myiamge.png)
I run that photo through the Windows Photo Viewer.

so for control the process has started to know when that would be ended I use this : MyProcess.WaitForExit(); but I get this error because MyProcess is null but it stated process successfully !

full code and info :

Answer 1

You can start the Photos App using the ApplicationActivationManager. Refer to https://stackoverflow.com/questions/12925748/iapplicationactivationmanageractivateapplication-in-c.

Adapting the code in the above SO answer, the following C# .Net Framework console application will start the Photos App with a file and wait for it to be closed. Error checking has been omitted.

   static void Main(string[] args)  
   {  
       Guid clsidActivationManager = new Guid("45BA127D-10A8-46EA-8AB7-56EA9078943C");  
       Type ta = Type.GetTypeFromCLSID(clsidActivationManager);  
       IApplicationActivationManager iAppMgr = (IApplicationActivationManager)Activator.CreateInstance(ta);  
       uint pid;  
       IShellItemArray array = GetShellItemArray(@"C:\Users\RLWA32\Pictures\propget.png");  
       iAppMgr.ActivateForFile("Microsoft.Windows.Photos_8wekyb3d8bbwe!App", array, "Open",  
           out pid);  
       Console.WriteLine("Photos App activated for file");  
       Process Photos = Process.GetProcessById((int)pid);  
       Photos.WaitForExit();  
       Console.WriteLine("Photos App has exited");  
   }  

Answer 2

The Windows API function that is ultimately called by Process.Start with UseShellExecute=true is ShellExecuteEx. The documentation for calling this function includes the following -

"Note: ShellExecuteEx does not always return an hProcess, even if a process is launched as the result of the call. For example, an hProcess does not return when you use SEE_MASK_INVOKEIDLIST to invoke IContextMenu."

Consequently, the call to Process.Start is not guaranteed to return a non-null Process reference.