How can i set the focus to application which is already in running state?

I have developed a C# Windows application & created a exe of it.

What I want is that when ever I try to run the application, if it is already in running state, then activate that application instance, else start new application.

Th开发者_StackOverflowat means I don't want to open same application more than one time

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Use the following code to set focus to the current application:

        [DllImport("user32.dll")]
        internal static extern IntPtr SetForegroundWindow(IntPtr hWnd);

        [DllImport("user32.dll")]
        internal static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);
        ... 
        Process currentProcess = Process.GetCurrentProcess();
        IntPtr hWnd = currentProcess.MainWindowHandle;
        if (hWnd != IntPtr.Zero)
        {
            SetForegroundWindow(hWnd);
            ShowWindow(hWnd, User32.SW_MAXIMIZE);
        }

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You can PInvoke SetForegroundWindow() and SetFocus() from user32.dll to do this.

[DllImport("user32.dll")]
static extern bool SetForegroundWindow(IntPtr hWnd);

// SetFocus will just focus the keyboard on your application, but not bring your process to front.
// You don't need it here, SetForegroundWindow does the same.
// Just for documentation.
[DllImport("user32.dll")]
static extern IntPtr SetFocus(HandleRef hWnd);

As argument you pass the window handle of the process you want to bring in the front and focus.

SetForegroundWindow(myProcess.MainWindowHandle);

SetFocus(new HandleRef(null, myProcess.Handle)); // not needed

Also see the restrictions of the SetForegroundWindow Methode on msdna.

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Use the following code part for multiple Instance checking of an exe, and if its true return at form load. For running this functionality in your app include using System.Diagnostics; namespace

private bool CheckMultipleInstanceofApp()
        {
            bool check = false;
            Process[] prc = null;
            string ModName, ProcName;
            ModName = Process.GetCurrentProcess().MainModule.ModuleName;
            ProcName = System.IO.Path.GetFileNameWithoutExtension(ModName);
            prc = Process.GetProcessesByName(ProcName);
            if (prc.Length > 1)
            {
                MessageBox.Show("There is an Instance of this Application running");
                check = true;
                System.Environment.Exit(0);
            }
            return check;
        }

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Use Mutex to launch single instance of the application. Also, you can use Process class to find your application and SetFocus on it. Here http://social.msdn.microsoft.com/Forums/da-DK/csharpgeneral/thread/7fd8e358-9709-47f2-9aeb-6c35c7521dc3