Question

I’m in to a loop defined dynamically the function that will run onClick of control.

the function is the following:

   public static void TryOpenFile(string filename, EventHandler callback)
        {

                Process proc;
                proc = Process.Start(filename);

             if (callback != null)
                {
                    proc.EnableRaisingEvents = true;
                    proc.Exited += (a, b) =>
                        {
                            callback(a, b);
                        };
                }
}

And then:

for(int i = 0; i < numberOfControls; i++)
{

            controlImg.SetFileToOpen(file, 
                delegate
                {
                    //exited!
                });

}

Answer 1

The documentation for this overload of Process.Start explains what is happening (emphasis mine):

Use this overload to start a process resource by specifying its file
name. The overload associates the resource with a new Process
component. If the process is already running, no additional process
resource is started. Instead, the existing process resource is reused
and no new Process component is created. In such a case, instead of
returning a new Process component, Start returns null to the calling
procedure.

A new process may not be started if you are using ShellExecute to start a file using it’s association, rather than running an executable. For instance, if filename is (for example) “C:\Test.xls”, it might start Excel. But if Excel was already running, it might open the file in the existing running instance, rather than starting a new process. In that case, the value of proc would be null.