C＃ASP.NET-下拉列表存儲當前值

Question

當我使用下拉列表並嘗試存儲我要存儲的值時。 它只像默認值那樣存儲（例如，我有一個下拉列表，其中包含從2015年到2020年的年份。如果選擇2018年，它將返回到2015年的原始值）。

然后，我嘗試將我擁有的所有三個下拉列表（日月和年）合並到一個DateTime變量中。 但是，然后一切都恢復為默認設置。

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();
}

有人可以幫助我解決此問題嗎？ testing.Text只是輸出我輸入內容的標簽，以防萬一我忘記放置斷點。

簽入和簽出值均會出現此問題。

謝謝

Answer 1

在page_load使用IsPostBack事件

嘗試：

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();
}