c#设计应用程序单实例运行

[DllImport("user32.dll", EntryPoint = "ShowWindow", CharSet = CharSet.Auto)]
public static extern int ShowWindow(IntPtr hwnd, int nCmdShow);
[DllImport("User32.dll")]
private static extern bool SetForegroundWindow(IntPtr hWnd);

static SingleInstanceManager manager;
/// <summary>
/// 应用程序的主入口点。
/// </summary>
[STAThread]
static void Main(string[] args)
{
    Application.EnableVisualStyles();
    Application.SetCompatibleTextRenderingDefault(false);
    manager = new SingleInstanceManager(new Form5());
    manager.Run(args);
}

public static void ShowForm(Form Nform, bool closeOldOne = true)
{
    manager.ChangeForm(Nform, closeOldOne);
}

public class SingleInstanceManager : WindowsFormsApplicationBase
{
    ApplicationContext app;

    public SingleInstanceManager(Form mainForm)
    {
        this.IsSingleInstance = true;
        app = new ApplicationContext();
        app.MainForm = mainForm;
    }

    protected override bool OnStartup(Microsoft.VisualBasic.ApplicationServices.StartupEventArgs e)
    {
        Application.Run(app);
        return false;
    }

    protected override void OnStartupNextInstance(StartupNextInstanceEventArgs eventArgs)
    {
        base.OnStartupNextInstance(eventArgs);
        SetForegroundWindow(app.MainForm.Handle);
        ShowWindow(app.MainForm.Handle, 4);
    }

    public void ChangeForm(Form newForm, bool closeOldOne = true)
    {
        if (app.MainForm == newForm) return;
        Form tem = app.MainForm;
        tem.Hide();
        app.MainForm = newForm;
        newForm.Show();
        if (closeOldOne) tem.Close();
    }
}

private void button1_Click(object sender, EventArgs e)
{
    Program.ShowForm(new Form6());
}