program.cs中自动生成的代码是用来在启动窗口关闭时终止应用程序的。您需要调整它，使其仅在没有更多窗口时终止。这样地：

[STAThread]
    static void Main() {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        var main = new Form1();
        main.FormClosed += new FormClosedEventHandler(FormClosed);
        main.Show();
        Application.Run();
    }

    static void FormClosed(object sender, FormClosedEventArgs e) {
        ((Form)sender).FormClosed -= FormClosed;
        if (Application.OpenForms.Count == 0) Application.ExitThread();
        else Application.OpenForms[0].FormClosed += FormClosed;
    }

默认情况下，第一个窗体控制windows窗体应用程序的生存期。如果需要多个独立的windows窗体，则应用程序上下文应该是与窗体分离的上下文。

public class MyContext : ApplicationContext
{
   private List<Form> forms;     

   private static MyContext context = new MyContext();

   private MyContext()
   {
      forms = new List<Form>();
      ShowForm1();
   }

   public static void ShowForm1()
   {
      Form form1 = new Form1();
      context.AddForm(form1);
      form1.Show();
   }

   private void AddForm(Form f)
   { 
      f.Closed += FormClosed;
      forms.Add(f);
   }

   private void FormClosed(object sender, EventArgs e)
   {
      Form f = sender as Form;
      if (form != null)
          forms.Remove(f);
      if (forms.Count == 0)
         Application.Exit();
   }          
}

要使用上下文，请将其传递给application.run（而不是表单）。如果要创建另一个form1，请调用mycontext.showform1（）等。

public class Program
{
   public void Main()
   {
      Application.Run(new MyContext());
   }
}

你可以这样做：

form2 f2=new form2()
this.Hide();
f2.Show();

希望有帮助。

将其写入您的方法中，该方法在 FormClosing 事件发生。

private void Form1_Closing(object sender, System.ComponentModel.CancelEventArgs e)
{
      // Display a MsgBox asking the user if he is sure to close
      if(MessageBox.Show("Are you sure you want to close?", "My Application", MessageBoxButtons.YesNo) 
         == DialogResult.Yes)
      {
         // Cancel the Closing event from closing the form.
         e.Cancel = false;
         // e.Cancel = true would close the window
      }
}