I noticed that on the Smart Client developer site on MSDN that Jonathan Wells answered the question regarding ensuring a single instance of a Windows Forms application. Awhile back I wrote a custom ApplicationContext class using ideas I read in an article I can't now locate. Anyway, here is the C# code for that class that allows you to pass a form and a flag to the Run method to disallow multiples. The default behavior is to disallow. This class uses the Mutex object as Jonathan mentions.
using System;
using System.Windows.Forms;
using System.Diagnostics;
using System.Threading;
using System.Runtime.InteropServices;
namespace AppContext
{
public class AppCtx : ApplicationContext
{
[DllImport("user32")]
private static extern bool SetForegroundWindow(IntPtr hwnd);
private AppCtx()
{}
private static Mutex s_Mutex;
public static void Run(Form mainForm)
{
run(mainForm,false);
}
public static void Run()
{
run(null,false);
}
public static void Run(Form mainForm, bool allowMultiples)
{
run(mainForm,allowMultiples);
}
private static void run(Form mainForm, bool allowMultiples)
{
if (!allowMultiples)
{
s_Mutex = new Mutex(true, Process.GetCurrentProcess().ProcessName);
if (s_Mutex.WaitOne(0,false))
{
if (mainForm == null)
Application.Run();
else
Application.Run(mainForm);
}
else
{
Process[] ps = Process.GetProcessesByName(
Process.GetCurrentProcess().ProcessName);
for (int i=0; i < ps.Length;i++)
{
if (ps[i].Id != Process.GetCurrentProcess().Id)
{
SetForegroundWindow(ps[i].MainWindowHandle);
}
}
}
}
else
Application.Run(mainForm);
}
public static void Exit()
{
Application.Exit();
}
}
}
The Main method would then look like so to disallow multiple instances of the app. Another great use of a custom app context would be to populate a custom IPrincipal object.
using System;
namespace AppContext
{
public class app
{
[STAThread]
static void Main()
{
Form1 f = new Form1();
AppCtx.Run(f,false);
}
}
}
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