如何用C#写一个简单的Login窗口

最近，看到网上经常会问如何进行窗口跳转，大多数的问题都是牵扯到Login窗口。其实，在Visual Studio 6以来，比较正确的做法，是判断Login窗口的返回值，然后决定是否打开主窗体，那么在C#中也是一样的。
具体做法如下：
首先，创建Login窗口，然后添加相应的输入框和按钮，设置窗口的AcceptButton为窗体的确认按钮，而CancelButton为窗体的取消按钮。例如：
this.AcceptButton = this.btnOK;this.CancelButton = this.btnCancel;定义确定按钮以及取消按钮事件，如下：
private void btnOK_Click(object sender, System.EventArgs e){// Here is to use fixed username and password// You can check username and password from DBif( txtUserName.Text == "Admin" && txtPassword.Text == "nopassword" ){// Save login user infouiLogin.UserName = txtUserName.Text;uiLogin.Password = txtPassword.Text;// Set dialog result with OKthis.DialogResult = DialogResult.OK;}else{// Wrong username or passwordnLoginCount++;if( nLoginCount == MAX_LOGIN_COUNT )// Over 3 timesthis.DialogResult = DialogResult.Cancel;else{MessageBox.Show( "Invalid user name and password!" );txtUserName.Focus();}}}private void btnCancel_Click(object sender, System.EventArgs e){// Set dialog result with Cancelthis.DialogResult = DialogResult.Cancel;}然后，在Login窗体的Closing事件中，要进行处理，如下：
private void frmLogin_Closing(object sender, System.ComponentModel.CancelEventArgs e){// Check whether form is closed with dialog resultif( this.DialogResult != DialogResult.Cancel &&this.DialogResult != DialogResult.OK )e.Cancel = true;}除此外，Login窗体一些辅助代码如下：
private int nLoginCount = 0;private const int MAX_LOGIN_COUNT = 3;private UserInfo uiLogin;public frmLogin( ref UserInfo ui ){//// Required for Windows Form Designer support//InitializeComponent();// Set login info to class memberuiLogin = ui;}调用的时候，要修改程序的Main函数，如下：
/// <summary>/// The main entry point for the application./// </summary>[STAThread]static void Main() {UserInfo ui = new UserInfo();frmLogin myLogin = new frmLogin( ref ui );if( myLogin.ShowDialog() == DialogResult.OK ){//Open your main form hereMessageBox.Show( "Logged in successfully!" );}else{MessageBox.Show( "Failed to logged in!" );}}而附加的UserInfo类如下：
/// <summary>/// User info class/// </summary>public class UserInfo{private string strUserName;private string strPassword;public string UserName{get{ return strUserName;}set{ strUserName = value; }}public string Password{get{ return strPassword;}set{ strPassword = value;}}public UserInfo(){strUserName = "";strPassword = "";}}