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 DB




if( txtUserName.Text == "Admin" && txtPassword.Text == "nopassword" )






...{




// Save login user info




uiLogin.UserName = txtUserName.Text;




uiLogin.Password = txtPassword.Text;








// Set dialog result with OK




this.DialogResult = DialogResult.OK;




}




else






...{




// Wrong username or password




nLoginCount++;




if( nLoginCount == MAX_LOGIN_COUNT )




// Over 3 times




this.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 Cancel




this.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 result




if( 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 member




uiLogin = 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 here




MessageBox.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 = "";




}




}