What is the correct way to create a single-instance WPF application?

Question

Using C# and WPF under .NET (rather than Windows Forms or console), what is the correct way to create an application that can only be run as a single instance?

I kno

Answer 1

This code should go to the main method. Look at here for more information about the main method in WPF.

[DllImport("user32.dll")]
private static extern Boolean ShowWindow(IntPtr hWnd, Int32 nCmdShow);

private const int SW_SHOWMAXIMIZED = 3;

static void Main() 
{
    Process currentProcess = Process.GetCurrentProcess();
    var runningProcess = (from process in Process.GetProcesses()
                          where
                            process.Id != currentProcess.Id &&
                            process.ProcessName.Equals(
                              currentProcess.ProcessName,
                              StringComparison.Ordinal)
                          select process).FirstOrDefault();
    if (runningProcess != null)
    {
        ShowWindow(runningProcess.MainWindowHandle, SW_SHOWMAXIMIZED);
       return; 
    }
}

Method 2

static void Main()
{
    string procName = Process.GetCurrentProcess().ProcessName;
    // get the list of all processes by that name

    Process[] processes=Process.GetProcessesByName(procName);

    if (processes.Length > 1)
    {
        MessageBox.Show(procName + " already running");  
        return;
    } 
    else
    {
        // Application.Run(...);
    }
}

Note : Above methods assumes your process/application has a unique name. Because it uses process name to find if any existing processors. So, if your application has a very common name (ie: Notepad), above approach won't work.