我正在制作在线表格。我在开头的代码中初始化了4个变量。当我选择一个下拉列表时，会触发一个事件（DropDownList4_SelectedIndexChanged），然后调用Availability（）。这里我的布尔变量 avail_bus 被赋值。但是，当我单击提交按钮（Button1_Click1）时，变量 avail_bus 将重新初始化为false。我调试了这个，发现在点击提交（Button1_Click1）后，控件首先进入页面中代码的顶部
public partial class Appform : System.Web.UI.Page
{
private bool isNotDup = true;
private bool avail_bus ;
private int max_capacity_bus;
private int realAvailability;
}
然后转到 Button1_click1 。 我怎样才能防止这种情况发生？如果在调用可用性时avail_bus的状态更改为true，则在单击“提交”时不应将其重新初始化为true。
以下是我的代码：
namespace eTransport
{
public partial class Appform : System.Web.UI.Page
{
private bool isNotDup = true;
private bool avail_bus ;
private int max_capacity_bus;
private int realAvailability;
protected void Page_Load (object sender, EventArgs e)
{
if (!this.IsPostBack)
{
BindDropDown();
}
}
//Method called when dropdown is selected in Bus Stop. It helps to populate Bus Number
protected void DropDownList4_SelectedIndexChanged (object sender, EventArgs e)
{
AutoPopulateBusStop();
Availability();
}
//Method to load drop down values in Bus Stop. These are populated from database
protected void BindDropDown ()
{
//some code here
}
//Method to autopopulate Bus Number based on selection of Bus Stop. The mapping is in the database in the table named -> dropdownlist
protected void AutoPopulateBusStop ()
{
//some code here
}
protected void Availability ()
{
string constr5 = ConfigurationManager.ConnectionStrings["myConnectionString"].ConnectionString;
using (SqlConnection con5 = new SqlConnection(constr5))
{
try
{
using (SqlCommand cmd5 = new SqlCommand("select count(*) from etms where BusNo='" + TextBox6.Text.ToString() + "'"))
{
cmd5.CommandType = CommandType.Text;
cmd5.Connection = con5;
con5.Open();
int capacity_from_db = Convert.ToInt16(cmd5.ExecuteScalar());
realAvailability = max_capacity_bus - capacity_from_db;
if (realAvailability > 0)
{
avail_bus = true;
TextBox2.Text = realAvailability.ToString() + " seats available ";
TextBox2.ForeColor = System.Drawing.ColorTranslator.FromHtml("#008000");
}
else
{
TextBox2.Text = "Seats Not available. Please choose another Stop";
TextBox2.ForeColor = System.Drawing.ColorTranslator.FromHtml("#ff1919");
}
}
}
catch (Exception ex)
{
Response.Write(ex);
}
}
}
protected void Button1_Click1 (object sender, EventArgs e)
{
if (isNotDup)
{
if (avail_bus)
{
// Submit the Form
}
else
{
Label14.Text = "Bus Seats not available!";
Label15.Text = null;
}
}
}
protected void PhoneNumberValidatation (object source, ServerValidateEventArgs args)
{
//some code here
}
}
}
答案 0 :(得分：1)
每次有页面请求时，都会创建该页面类的新实例来处理该请求。因此，任何字段都会重新初始化。
您可以在ViewState中存储值以记住各种请求的值：
namespace eTransport
{
public partial class Appform : System.Web.UI.Page
{
private bool isNotDup
{
set { ViewState["isNotDup "] = value; }
get
{
if (ViewState["isNotDup "] == null)
return true;
return (bool )ViewState["isNotDup "];
}
}
private bool avail_bus
{
set { ViewState["avail_bus"] = value; }
get
{
if (ViewState["avail_bus"] == null)
return true;
return (bool )ViewState["avail_bus"];
}
}
private int max_capacity_bus
{
set { ViewState["max_capacity_bus "] = value; }
get
{
if (ViewState["max_capacity_bus "] == null)
return 0;
return (int)ViewState["max_capacity_bus "];
}
}
private int realAvailability
{
set { ViewState["realAvailability"] = value; }
get
{
if (ViewState["realAvailability"] == null)
return 0;
return (int)ViewState["realAvailability"];
}
}
protected void Page_Load (object sender, EventArgs e)
{
if (!this.IsPostBack)
{
BindDropDown();
}
}
//Method called when dropdown is selected in Bus Stop. It helps to populate Bus Number
protected void DropDownList4_SelectedIndexChanged (object sender, EventArgs e)
{
AutoPopulateBusStop();
Availability();
}
//Method to load drop down values in Bus Stop. These are populated from database
protected void BindDropDown ()
{
//some code here
}
//Method to autopopulate Bus Number based on selection of Bus Stop. The mapping is in the database in the table named -> dropdownlist
protected void AutoPopulateBusStop ()
{
//some code here
}
protected void Availability ()
{
string constr5 = ConfigurationManager.ConnectionStrings["myConnectionString"].ConnectionString;
using (SqlConnection con5 = new SqlConnection(constr5))
{
try
{
using (SqlCommand cmd5 = new SqlCommand("select count(*) from etms where BusNo='" + TextBox6.Text.ToString() + "'"))
{
cmd5.CommandType = CommandType.Text;
cmd5.Connection = con5;
con5.Open();
int capacity_from_db = Convert.ToInt16(cmd5.ExecuteScalar());
realAvailability = max_capacity_bus - capacity_from_db;
if (realAvailability > 0)
{
avail_bus = true;
TextBox2.Text = realAvailability.ToString() + " seats available ";
TextBox2.ForeColor = System.Drawing.ColorTranslator.FromHtml("#008000");
}
else
{
TextBox2.Text = "Seats Not available. Please choose another Stop";
TextBox2.ForeColor = System.Drawing.ColorTranslator.FromHtml("#ff1919");
}
}
}
catch (Exception ex)
{
Response.Write(ex);
}
}
}
protected void Button1_Click1 (object sender, EventArgs e)
{
if (isNotDup)
{
if (avail_bus)
{
// Submit the Form
}
else
{
Label14.Text = "Bus Seats not available!";
Label15.Text = null;
}
}
}
protected void PhoneNumberValidatation (object source, ServerValidateEventArgs args)
{
//some code here
}
}
}
答案 1 :(得分：1)
您可以将可用性状态存储在隐藏的输入字段中，该字段稍后会在Button1单击事件上发布。
在button1点击事件而不是从变量访问avail值从hiddenField的值
访问它另一个选项是在button1的click事件中再次调用Availability（）作为第一行，以便在avail_bus变量中设置正确的值
答案 2 :(得分：1)
这个问题有三种可能的解决方案。
Static - 这将创建一个可供所有页面访问的实例（全局）。
private static avail_bus = true;
Session State - 这使您可以在用户导航时存储和检索用户的值。
// Get...
private bool avail_bus = (bool)Session["avail_bus"];
// Set
Session["avail_bus"] = true;
Control.ViewState - 获取状态信息字典，允许您跨同一页面的多个请求保存和恢复服务器控件的视图状态。
public bool avail_bus
{
get { return ViewState["avail_bus"] == null ? false : (bool)ViewState["avail_bus"]; }
set { ViewState["avail_bus"] = value; }
}