C# ASP.NET - 存储当前值的下拉列表

Question

当我使用我的下拉列表并尝试存储我想要存储的值时。它只是像默认值一样存储（例如，我有一个从 2015 年到 2020 年的下拉列表。如果我选​​择 2018 年，它将传递回 2015 年的原始值）。

然后我尝试将我拥有的所有三个下拉列表（日月和年）合并到一个 DateTime 变量中。然而，一切都会回到默认状态。

protected void Page_Load(object sender, EventArgs e)
{
    int[] days = new int[31];

    for (int i = 0; i < days.Length; i++)
    {
        days[i] = i + 1;
    }
    //Binding the information to drop downlist.
    ddlDayCI.DataSource = days;
    ddlDayCI.DataBind();
    ddlDayCO.DataSource = days;
    ddlDayCO.DataBind();

    int[] months = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 };
    ddlMonthCI.DataSource = months;
    ddlMonthCI.DataBind();
    ddlMonthCO.DataSource = months;
    ddlMonthCO.DataBind();

    int[] years = new int[] { 2015, 2016, 2017, 2018, 2019, 2020 };

    ddlYearCI.DataSource = years;
    ddlYearCI.DataBind();
    ddlYearCO.DataSource = years;
    ddlYearCO.DataBind();
}
protected void CheckAvailability_Click(object sender, EventArgs e)
{
    int yearCI = Convert.ToInt32(ddlYearCI.SelectedItem.Value);
    int monthCI = Convert.ToInt32(ddlMonthCI.SelectedItem.Value);
    int dayCI = Convert.ToInt32(ddlDayCI.SelectedItem.Value);
    DateTime dateOfCheckIn = new DateTime(yearCI, monthCI, dayCI);

    int yearCO = Convert.ToInt32(ddlYearCO.SelectedItem.ToString());
    int monthCO = Convert.ToInt32(ddlMonthCO.SelectedItem.ToString());
    int dayCO = Convert.ToInt32(ddlDayCO.SelectedItem.ToString());
    DateTime dateOfCheckOut = new DateTime(yearCO, monthCO, dayCO);

    testing.Text = dateOfCheckIn.ToString();
}

有人能帮助我解决这个问题吗？ testing.Text 只是一个输出我输入内容的标签，以防我忘记设置断点。

签入和签出值都会出现此问题。

谢谢

Answer 1

在page_load 中使用IsPostBack 事件

尝试：

protected void Page_Load(object sender, EventArgs e)
{
    if(!IsPostBack)
     {
        FillDropDowns();
     }
}

protected void FillDropDowns()
{
   int[] days = new int[31];

    for (int i = 0; i < days.Length; i++)
    {
        days[i] = i + 1;
    }
    //Binding the information to drop downlist.
    ddlDayCI.DataSource = days;
    ddlDayCI.DataBind();
    ddlDayCO.DataSource = days;
    ddlDayCO.DataBind();

    int[] months = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 };
    ddlMonthCI.DataSource = months;
    ddlMonthCI.DataBind();
    ddlMonthCO.DataSource = months;
    ddlMonthCO.DataBind();

    int[] years = new int[] { 2015, 2016, 2017, 2018, 2019, 2020 };

    ddlYearCI.DataSource = years;
    ddlYearCI.DataBind();
    ddlYearCO.DataSource = years;
    ddlYearCO.DataBind();
}