ASP.NET私有成员字段在回发时损失价值 [英] ASP.NET private member field loses value on postback

问题描述

考虑以下代码:

    public partial class TeacherControlPanel : System.Web.UI.Page
    {
        protected string username = string.Empty;

        protected void Page_Load(object sender, EventArgs e)
        {
            username = (string)Request.QueryString["username"];

            Ice_Web_Portal.BO.Teacher teacher = Ice_Web_Portal.BO.Teacher.GetTeacherByUsername(username);

            if (teacher != null)
            {
                labUsername.Text = username;
                labName.Text = teacher.TeacherName;
                labTeacherCode.Text = teacher.TeacherCode;

                Dept dept = teacher.Department;

                if (dept != null)
                {
                    labDepartment.Text = dept.DeptName;
                }
            }
            else
            {
                //labErrorMessage.Text = "No teacher found";
            }
        }

        protected void btnSendMail_Click(object sender, EventArgs e)
        {
            Response.Redirect(@"~/Teacher/TeacherComposeMail.aspx?username=mahabub" + username);            
        }
}

在此代码中，当我将用户名"声明为私有时，在后续发回信息后，它会初始化为null.

In this code, when I am declaring 'username' as private, it is initialized to null after subsequent post backs.

为什么?

秘密是什么?

推荐答案

因为ASP.NET是无状态的，所以它不会保持其状态在发回之间.将用户保存到视图状态，会话或应用程序以在回发到回发时查看它.

Because ASP.NET is stateless meaning it does not keep it state from post back to postback. Save the user to the viewstate, session, or application to see it on postback to postback.

#region UserName
public string UserName
{
    get
    {
        if (this.ViewState["UserName"] == null)
            return string.Empty;

        return (string)this.ViewState["UserName"];
    }
    set { this.ViewState["UserName"] = value; }
}
#endregion

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