WinForm 更换主窗体的例子

做一个登录窗口，登录成功时关闭form1，展示from2界面

1.主界面Login

 namespace WindowsFormsApplication1
 {
     public partial class Login : Form
     {
         public string username;//定义一个变量给子窗体传值
         public Login()
         {
             InitializeComponent();
         }

         private void button1_Click(object sender, EventArgs e)
         {
             //取出用户名和密码
             string uid = txtuid.Text;
             string pwd = txtpwd.Text;

             if (uid != "" && pwd != "")
             {
                 LoginDA da = new LoginDA(); //连接数据库
                 if (da.DengLu(uid, pwd)) //登录查询
                 {

                     //将用户名赋值给成员变量username
                     username = uid;
                     //将该窗体的返回值变为OK
                     this.DialogResult = DialogResult.OK;
                     //将该窗体关闭
                     this.Close();

                 }
                 else
                 {
                     MessageBox.Show("用户名或密码错误！");
                 }
             }
             else
             {
                 MessageBox.Show("用户名和密码不能为空！");
             }
         }

         private void Login_Load(object sender, EventArgs e)
         {

         }
     }
 }

2.Program.cs 修改主主窗体Login变为Main

namespace WindowsFormsApplication1
{
    static class Program
    {
        /// <summary>
        /// 应用程序的主入口点。
        /// </summary>
        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);

            //造一个登录窗体
            Login log = new Login();

            if (log.ShowDialog() == DialogResult.OK)
            {
                Application.Run(new Main(log.username));//main窗体的构造方法
            }
        }
    }
}

3.Main窗体

namespace WindowsFormsApplication1
{
    public partial class Main : Form
    {
        private string uid;//造一个变量接收Login窗体的值
        private ChinaDA cda;
        public Main()
        {
            InitializeComponent();
        }
        public Main(string username)
        {
            InitializeComponent();
            uid = username;

            cda = new ChinaDA();//连接数据库
        }

        private void Main_Load(object sender, EventArgs e)
        {
            label1.Text = uid;//把接收到的值传给label1显示一下

            //填充省的下拉列表
            FillSheng();

            //填充市的下拉列表
            FillShi();

            //填充区的下拉列表
            FillQu();

        }

        private void cmbsheng_SelectedIndexChanged(object sender, EventArgs e)
        {
            //填充市的下拉列表
            FillShi();

            //填充区的下拉列表
            FillQu();
        }

        private void cmbshi_SelectedIndexChanged(object sender, EventArgs e)
        {
            //填充区的下拉列表
            FillQu();
        }

        //填充省的方法
        public void FillSheng()
        {
            List<China> list = cda.Select("");

            cmbsheng.DataSource = list;
            cmbsheng.DisplayMember = "Name";
            cmbsheng.ValueMember = "Code";
        }

        //填充市的方法
        public void FillShi()
        {
            List<China> list = cda.Select(cmbsheng.SelectedValue.ToString());

            cmbshi.DataSource = list;
            cmbshi.DisplayMember = "Name";
            cmbshi.ValueMember = "Code";
        }

        //填充区的方法
        public void FillQu()
        {
            List<China> list = cda.Select(cmbshi.SelectedValue.ToString());

            cmbqu.DataSource = list;
            cmbqu.DisplayMember = "Name";
            cmbqu.ValueMember = "Code";
        }

        private void button1_Click(object sender, EventArgs e)
        {
            MessageBox.Show(cmbsheng.SelectedValue.ToString());
        }
    }
}