Process still starts when application is told to exit

Question

4.00/5 (1 vote)

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I have written some code to check that all required files are present before starting a process. This is the code:

C#

public void LaunchServices()
        {
            string LaunchConfig = "C:/Users/Henry/AppData/Local/WeatherLink/LaunchConfig.xml";
            if (File.Exists(LaunchConfig))
            {
                XmlDocument config = new XmlDocument();
                config.Load(LaunchConfig);

                string MainExecutable = "";
                string ExceptionModule = "";
                string FilesystemModule = "";

                try
                {
                    MainExecutable = config.SelectSingleNode("//MainExecutable").InnerText;
                    ExceptionModule = config.SelectSingleNode("//ExceptionModule").InnerText;
                    FilesystemModule = config.SelectSingleNode("//FilesystemModule").InnerText;
                }
                catch (NullReferenceException)
                { MessageBox.Show("Weather Link cannot start because the module reference file is corrupted"); Application.Exit(); }

                if (File.Exists(ExceptionModule)) { Process.Start(ExceptionModule); }
                else { MessageBox.Show("Weather Link cannot start because the exception module does not exist or is corrupted"); Application.Exit(); }
                if (File.Exists(FilesystemModule)) { Process.Start(FilesystemModule); }
                else { MessageBox.Show("Weather Link cannot start because the filesystem watcher module does not exist or is corrupted"); Application.Exit(); }
                if (File.Exists(MainExecutable)) { Process.Start(MainExecutable); }
                else { MessageBox.Show("Weather Link cannot start because the main executable file does not exist or is corrupted"); Application.Exit(); }
            }
            else { MessageBox.Show("Weather Link cannot start because the module reference file is missing"); Application.Exit(); }
        }

At the moment, the message box for the exception module is the only one that shows but in my XML file the only thing that is correct is the path to the main executable, the other 2 are empty. The real problem is that it is not exiting after dismissing the message box. If I click OK, the main executable starts but it shouldn't because I have told it to close after all message boxes. What is wrong? I cannot seem to solve it.

Posted 14-Nov-13 11:18am

Henry Hunt

Updated 14-Nov-13 12:16pm

Sergey Alexandrovich Kryukov

v2

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Comments

Sergey Alexandrovich Kryukov 14-Nov-13 18:36pm

I up-voted this answer with my 4, despite pretty naive attempt to solve the problem. It makes quite an interesting question, because solving it helps to understand some delicate mechanism of event-oriented architecture. I mean, if you consider Solution 3. :-)
—SA

2 solutions

Solution 3

This is not a very trivial issue, but you can do it very easily.

Here is one trick: you should do it somewhere when the System.Windows.Forms.Application.Run(System.Windows.Forms.Form) is already called, say, somewhere in the code of the main window. If you call it from its constructor, it will certainly work. Let's say, it is called withing the form constructor.

C#

internal MyForm() {

    //...

    if (/* ... */) {
        //...
    } else {
        MessageBox.Show("Weather Link cannot start because the module reference file is missing");
        //Application.Exit(); //remove it, won't work
        BeginInvoke(new System.Action(() => { System.Windows.Forms.Application.Exit(); })); //that's the real trick!
    } //if

} //MyForm (constructor)

[EDIT]

On second though, this can work in even funnier situation, right in the entry point of the application:

C#

using System.Windows.Forms;
//...

void Main() {

    Form mainForm = // create your main form    

    if (/* ... */) {
        //...
    } else {
        MessageBox.Show("Weather Link cannot start [...] is missing");
        mainForm.BeginInvoke(new System.Action(() => {
            System.Windows.Forms.Application.Exit();
        })); 
        // practically, you can simply exit here... :-)
    } //if

    Application.Run(mainForm); // application will perform full event cycle
    // you will get all side-effect of starting and closing in place...

} //Main

[END EDIT]

Note, it should be BeginInvoke, not Invoke. Why? Why BeginInvoke works? I would leave it as the exercise for your homework. It will really help you to understand a lot about how event-oriented programming works. :-)

And this is one of the relatively rare example when BeginInvoke is useful even when no multithreading is involved!

—SA

Posted 14-Nov-13 12:32pm

Sergey Alexandrovich Kryukov

Updated 14-Nov-13 13:07pm

v6

Comments

Ron Beyer 14-Nov-13 21:01pm

Another good solution, +5!

Sergey Alexandrovich Kryukov 14-Nov-13 23:22pm

Thank you, Ron.
—SA

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Ron Beyer · Accepted Answer · 2013-11-14T11:37:00

Ok, first you have to learn to properly format your code, having everything on a single line is very difficult to read, and even more difficult to debug.

Does this look easier to read?

C#

if (File.Exists(ExceptionModule)) 
{ 
    Process.Start(ExceptionModule); 
}
else
{
    MessageBox.Show("Weather Link cannot start because the exception module does not exist or is corrupted"); 
    Application.Exit(); 
}

if (File.Exists(FilesystemModule)) 
{ 
    Process.Start(FilesystemModule); 
}
else 
{ 
    MessageBox.Show("Weather Link cannot start because the filesystem watcher module does not exist or is corrupted"); 
    Application.Exit(); 
}
                
if (File.Exists(MainExecutable)) 
{ 
    Process.Start(MainExecutable); 
}
else 
{ 
    MessageBox.Show("Weather Link cannot start because the main executable file does not exist or is corrupted"); 
    Application.Exit(); 
}

Ok, the first thing you should do is check if all the module exists, and only start the processes if they all exist:

C#

if (!File.Exists(ExceptionModule) || !File.Exists(FilesystemModule) || !File.Exists(MainExecutable))
{
     //One of the modules don't exist, show an error and exit the application
}

//Start the modules here

On top of that, if you start a process with Process.Start, exiting your application will not stop the processes. You have to hold a reference to the ProcessInfo object using Process.Start so you can explicitly close them. Application.Exit will not do it for you.