如何用C#写一个简单的Login窗口

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;

this.DialogResult = DialogResult.OK;

}

else

{

nLoginCount++;

if( nLoginCount == MAX_LOGIN_COUNT )

this.DialogResult = DialogResult.Cancel;

else

{

MessageBox.Show( "Invalid user name and password!" );

txtUserName.Focus();

}

}

}

private void btnCancel_Click(object sender, System.EventArgs e)

{

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)

{

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 = "";

}

}