Question

For a project I have to start an application in C#, rip out the AutomationElement tree related to the process, and then close the application and output the tree. I’m doing this by opening the application using Process.Start. Then I’m finding the AutomationElements related to the spawned process and walking the tree using a combination of TreeWalker and AutomationElement’s FindFirst and FindAll methods.

This runs fine on my computer and runs correctly using NUnit locally. It also runs on the other people in my groups computers. The problem is that it never runs on our central testing server that’s running Hudson. After some hours of debugging, I had a test on Hudson start the application and then print the first level of the AutomationTree. On my computer, this prints all of the windows I have on my desktop. On Hudson, this only prints the Desktop.

Thinking there might be multiple desktops, I tried using TreeWalker’s GetNextSibling function on the RootElement. It still only reported one desktop.

Here’s the code I’m using to start a process.

public bool connect(string[] args)
{
    if (this.process != null) {
        Console.WriteLine("ERROR: Process already connected");
        return false;
    }

    if (!File.Exists(sApplicationPath)) {
        Console.WriteLine(sApplicationPath + " does not exist");
        return false;
    }

    // Turn the command arguments into a single string
    string arguments = "";
    foreach (string arg in args) {
        arguments += arg + " ";
    }

    try {
        // Start the application
        ProcessStartInfo processStartInfo =
            new ProcessStartInfo(sApplicationPath);
        processStartInfo.Arguments = arguments;
        this.process = Process.Start(processStartInfo);

        // Must be a positive integer (non-zero)
        if ( !( iInitialDelay > 0 )  ) {
            Console.WriteLine("Invalid initial delay. " +
                              "Defaulting to 5 seconds.");
            this.iInitialDelay = 5000;
        }

        Thread.Sleep(this.iInitialDelay);
    } catch (Exception ex) {
        Console.WriteLine("WGApplication.connect: " + ex.Message);
        return false;
    }

    // Check if the process still exists
    try {
        /** This part does not return an error, so I think that means the process exists and is started */
        Process check = Process.GetProcessById(process.Id);
    } catch (ArgumentException ex) {
        Console.WriteLine("The process expired before connection was complete");
        Console.WriteLine("Make sure the process is not open anywhere else");
        Console.WriteLine("and that it is able to execute on the host machine.");
        return false;
    }

    // Check if the base automation element exists to verify open
    AutomationElement rootWindow =
        AutomationElement.RootElement.FindChildProcessById(process.Id);
    /** This part returns null, so it can't find the window associated with this process id */

    if (this.process == null) {
        return false;
    } else if (rootWindow == null) {
        // A root window with this process id has not been found
        Console.WriteLine("Cannot find the root window of the created " +
                          "process. Unknown error.");
        return false;
    } else {
        // Everything is good to go
        return true;
    }
}

sApplicationPath is set to the absolute path of the executable. iInitialDelay is a delay to make sure the application has time to start. I’m running this on ‘C:\Windows\System32\notepad.exe’ on Windows Vista SP2 and compiling it with the v3.5 C# compiler.

FindChildProcessById is defined as follows:

public static AutomationElement FindChildProcessById(
    this AutomationElement element, int processId)
{
    var result = element.FindChildByCondition(
        new PropertyCondition(AutomationElement.ProcessIdProperty,
                              processId));

    return result;
}

Remember that this compiles and works on my computer. My test program on Hudson said that the RootElement had no children at all.

So I start the application, confirm it exists, and then I can’t find any windows associated with the process. I can’t find any windows associated with anything except the desktop.

Is this a problem with Hudson? Does Hudson work in some specific way that this code wouldn’t work on it? Is it a problem with my code? The Hudson server is running on a Windows Server 2003 computer. Any help would be appreciated. I know this is a very specific problem which is a reason why I can’t find any solutions online.

Answer 1

Is Hudson running as a service? If so, it may not have the necessary rights to show windows.