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

Mojtaba_Hakim 281 Reputation points
2022-10-17T08:29:24.097+00:00

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 :

Windows Presentation Foundation
Windows Presentation Foundation
A part of the .NET Framework that provides a unified programming model for building line-of-business desktop applications on Windows.
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Accepted answer
  1. RLWA32 41,046 Reputation points
    2022-10-17T12:12:58.207+00:00

    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");  
       }  
    
    1 person found this answer helpful.

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  1. RLWA32 41,046 Reputation points
    2022-10-17T09:52:01.097+00:00

    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.

    1 person found this answer helpful.