DROPDOWNLIST将更新面板后不更新 [英] Dropdownlist does not update after adding update panel

查看：210 发布时间：2016/6/15 22:21:56 c# asp.net drop-down-menu updatepanel

本文介绍了DROPDOWNLIST将更新面板后不更新的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我有多个的dropdownlist框所有查询同一列，同一个表，并从相同的数据库。例如下MEMBERID列我有以下的ID。

12345

23456

34567

和我有3个不同的DropDownList框，如下图所示。

 ＆LT; ASP：DropDownList的ID =memberID3=服务器可见=假OnSelectedIndexChanged =ddlpid3_SelectedIndexChanged＆GT;
    ＆LT; / ASP：DropDownList的＆GT;
    ＆LT; ASP：DropDownList的ID =memberID1=服务器可见=假OnSelectedIndexChanged =ddlpid1_SelectedIndexChanged＆GT;
    ＆LT; / ASP：DropDownList的＆GT;
    ＆LT; ASP：DropDownList的ID =memberID2=服务器可见=假OnSelectedIndexChanged =ddlpid2_SelectedIndexChanged＆GT;
    ＆LT; / ASP：DropDownList的＆GT;

我添加DropDownList中的更新面板，以便使我的DropDownList于任何更新/选择刷新。

 ＆LT; ASP：的UpdatePanel ID =UpdatePanel1=服务器＆GT;
  ＆LT;＆的ContentTemplate GT;
  ＆LT; /＆的ContentTemplate GT;
  ＆LT; / ASP：的UpdatePanel＆GT;

有关例如，当memberID1选择12345，其他2的dropdownlist（memberID2和3）将不显示该ID 12345反之亦然，当memberID1选择的dropdownlist的默认值，该ID重现中的其他2下拉框。我添加了一个默认值所有DDL的。

  memeberID（数字）.Items.Insert（0，新的ListItem（请选择一个会员ID，））;
 memeberID（数）.SelectedIndex = 0;

如果我没有看错更新面板的财产，是不是能够使此功能工作的？

这里是绑定code的要求。

 保护无效ddllocation_SelectedIndexChanged（对象发件人，EventArgs的发送）
    {        使用（VAR connAdd =新的SqlConnection（数据源=本地主机;初始目录= MajorProject;集成安全性= SSPI））
        {
            connAdd.Open（）;            VAR SQL =从PoliceAccount选择policeid在那里的地位='可用'和处理='offcase和postedto ='+ ddllocation.SelectedValue +';
            使用（VAR cmdAdd =新SqlDataAdapter的（SQL，connAdd））
            {
                数据集DS2 =新的DataSet（）;
                cmdAdd.Fill（DS2）;                memberID1.Items.Clear（）;
                memberID1.DataSource = DS2;
                memberID1.DataTextField =MEMBERID;
                memberID1.DataValueField =MEMBERID;
                memberID1.DataBind（）;
                memberID1.Items.Insert（0，新的ListItem（请选择一个会员ID，））;
                memberID1.SelectedIndex = 0;                memberID2.Items.Clear（）;
                memberID2.DataSource = DS2;
                memberID2.DataTextField =MEMBERID;
                memberID2.DataValueField =MEMBERID;
                memberID2.DataBind（）;
                memberID2.Items.Insert（0，新的ListItem（请选择一个会员ID，））;
                memberID2.SelectedIndex = 0;                memberID3.Items.Clear（）;
                memberID3.DataSource = DS2;
                memberID3.DataTextField =MEMBERID;
                memberID3.DataValueField =MEMBERID;
                memberID3.DataBind（）;
                memberID3.Items.Insert（0，新的ListItem（请选择一个会员ID，））;
                memberID3.SelectedIndex = 0;            }

更新的

有关现在我能够让我的其他DDL来重新绑定，并选择默认值时，缓存中的其他DropDownList中选定的值。然而，当我选择其他的ID，这个ID被删除，它不会重新绑定其他DDL。

 保护无效FillddlLocations（）
    {
        FillDropdown（ddlpid1）;
        FillDropdown（ddlpid2）;
        FillDropdown（ddlpid3）;
        FillDropdown（ddlpid4）;
        FillDropdown（ddlpid5）;
        ddlpid1.Visible = FALSE;
        ddlpid2.Visible = FALSE;
        ddlpid3.Visible = FALSE;
        ddlpid4.Visible = FALSE;
        ddlpid5.Visible = FALSE;
    }    保护无效FillDropdown（DropDownList的DDL）
    {        使用（VAR connAdd =新的SqlConnection（数据源=本地主机;初始目录= MajorProject;集成安全性= SSPI））
        {
            connAdd.Open（）;            VAR SQL =从PoliceAccount选择policeid在那里的地位='可用'和处理='offcase和postedto ='+ ddllocation.SelectedValue +';
            使用（VAR cmdAdd =新SqlDataAdapter的（SQL，connAdd））
            {
                数据集DS2 =新的DataSet（）;
                cmdAdd.Fill（DS2）;                ddl.Items.Clear（）;
                ddl.DataSource = DS2;
                ddl.DataBind（）;
                ddl.Items.Insert（0，新的ListItem（警察ID，））;
                ddl.SelectedIndex = 0;            }        }
    }    保护无效ddlpid1_SelectedIndexChanged（对象发件人，EventArgs的发送）
    {        如果（ddlpid1.SelectedIndex大于0）
        {            会话[PID1] = ddlpid1.SelectedValue;            列表项removeItem2 = ddlpid2.Items.FindByValue（ddlpid1.SelectedValue）;
            ddlpid2.Items.Remove（removeItem2）;
            列表项removeItem3 = ddlpid3.Items.FindByValue（ddlpid1.SelectedValue）;
            ddlpid3.Items.Remove（removeItem3）;
            列表项removeItem4 = ddlpid4.Items.FindByValue（ddlpid1.SelectedValue）;
            ddlpid4.Items.Remove（removeItem4）;
            列表项removeItem5 = ddlpid5.Items.FindByValue（ddlpid1.SelectedValue）;
            ddlpid5.Items.Remove（removeItem5）;
        }        其他        如果（ddlpid1.SelectedItem.Text.Equals（警察ID））
        {
            FillDropdown（ddlpid1）;
            FillDropdown（ddlpid2）;
            FillDropdown（ddlpid3）;
            FillDropdown（ddlpid4）;
            FillDropdown（ddlpid5）;
            ddlpid2.SelectedValue =（字符串）会议[PID2];
            ddlpid2_SelectedIndexChanged（这一点，EventArgs.Empty）;            ddlpid3.SelectedValue =（字符串）会议[PID3];
            ddlpid3_SelectedIndexChanged（这一点，EventArgs.Empty）;            ddlpid4.SelectedValue =（字符串）会议[PID4];
            ddlpid4_SelectedIndexChanged（这一点，EventArgs.Empty）;            ddlpid5.SelectedValue =（字符串）会议[PID5];
            ddlpid5_SelectedIndexChanged（这一点，EventArgs.Empty）;
        }    }    保护无效ddlpid2_SelectedIndexChanged（对象发件人，EventArgs的发送）
    {        如果（ddlpid2.SelectedIndex大于0）
        {            会话[PID2] = ddlpid2.SelectedValue;
            列表项removeItem1 = ddlpid1.Items.FindByValue（ddlpid2.SelectedValue）;
            ddlpid1.Items.Remove（removeItem1）;
            列表项removeItem3 = ddlpid3.Items.FindByValue（ddlpid2.SelectedValue）;
            ddlpid3.Items.Remove（removeItem3）;
            列表项removeItem4 = ddlpid4.Items.FindByValue（ddlpid2.SelectedValue）;
            ddlpid4.Items.Remove（removeItem4）;
            列表项removeItem5 = ddlpid5.Items.FindByValue（ddlpid2.SelectedValue）;
            ddlpid5.Items.Remove（removeItem5）;
        }
        否则，如果（ddlpid2.SelectedItem.Text.Equals（警察ID））
        {
            FillDropdown（ddlpid1）;
            FillDropdown（ddlpid2）;
            FillDropdown（ddlpid3）;
            FillDropdown（ddlpid4）;
            FillDropdown（ddlpid5）;            ddlpid1.SelectedValue =（字符串）会议[PID1];
            ddlpid1_SelectedIndexChanged（这一点，EventArgs.Empty）;            ddlpid3.SelectedValue =（字符串）会议[PID3];
            ddlpid3_SelectedIndexChanged（这一点，EventArgs.Empty）;            ddlpid4.SelectedValue =（字符串）会议[PID4];
            ddlpid4_SelectedIndexChanged（这一点，EventArgs.Empty）;            ddlpid5.SelectedValue =（字符串）会议[PID5];
            ddlpid5_SelectedIndexChanged（这一点，EventArgs.Empty）;
        }
    }    保护无效ddlpid3_SelectedIndexChanged（对象发件人，EventArgs的发送）
    {
        如果（ddlpid3.SelectedIndex大于0）
        {            会话[PID3] = ddlpid3.SelectedValue;
            列表项removeItem1 = ddlpid1.Items.FindByValue（ddlpid3.SelectedValue）;
            ddlpid1.Items.Remove（removeItem1）;
            列表项removeItem2 = ddlpid2.Items.FindByValue（ddlpid3.SelectedValue）;
            ddlpid2.Items.Remove（removeItem2）;
            列表项removeItem4 = ddlpid4.Items.FindByValue（ddlpid3.SelectedValue）;
            ddlpid4.Items.Remove（removeItem4）;
            列表项removeItem5 = ddlpid5.Items.FindByValue（ddlpid3.SelectedValue）;
            ddlpid5.Items.Remove（removeItem5）;
        }
    否则，如果（ddlpid3.SelectedItem.Text.Equals（警察ID））
        {
            FillDropdown（ddlpid1）;
            FillDropdown（ddlpid2）;
            FillDropdown（ddlpid3）;
            FillDropdown（ddlpid4）;
            FillDropdown（ddlpid5）;            ddlpid1.SelectedValue =（字符串）会议[PID1];
            ddlpid1_SelectedIndexChanged（这一点，EventArgs.Empty）;            ddlpid2.SelectedValue =（字符串）会议[PID2];
            ddlpid2_SelectedIndexChanged（这一点，EventArgs.Empty）;            ddlpid4.SelectedValue =（字符串）会议[PID4];
            ddlpid4_SelectedIndexChanged（这一点，EventArgs.Empty）;            ddlpid5.SelectedValue =（字符串）会议[PID5];
            ddlpid5_SelectedIndexChanged（这一点，EventArgs.Empty）;
        }
    }    保护无效ddlpid4_SelectedIndexChanged（对象发件人，EventArgs的发送）
    {
        如果（ddlpid4.SelectedIndex大于0）
        {
            会话[PID4] = ddlpid4.SelectedValue;            列表项removeItem1 = ddlpid1.Items.FindByValue（ddlpid4.SelectedValue）;
            ddlpid1.Items.Remove（removeItem1）;
            列表项removeItem2 = ddlpid2.Items.FindByValue（ddlpid4.SelectedValue）;
            ddlpid2.Items.Remove（removeItem2）;
            列表项removeItem3 = ddlpid3.Items.FindByValue（ddlpid4.SelectedValue）;
            ddlpid3.Items.Remove（removeItem3）;
            列表项removeItem5 = ddlpid5.Items.FindByValue（ddlpid4.SelectedValue）;
            ddlpid5.Items.Remove（removeItem5）;
        }        否则，如果（ddlpid4.SelectedItem.Text.Equals（警察ID））
        {
            FillDropdown（ddlpid1）;
            FillDropdown（ddlpid2）;
            FillDropdown（ddlpid3）;
            FillDropdown（ddlpid4）;
            FillDropdown（ddlpid5）;            ddlpid1.SelectedValue =（字符串）会议[PID1];
            ddlpid1_SelectedIndexChanged（这一点，EventArgs.Empty）;            ddlpid2.SelectedValue =（字符串）会议[PID2];
            ddlpid2_SelectedIndexChanged（这一点，EventArgs.Empty）;            ddlpid3.SelectedValue =（字符串）会议[PID3];
            ddlpid3_SelectedIndexChanged（这一点，EventArgs.Empty）;            ddlpid5.SelectedValue =（字符串）会议[PID5];
            ddlpid5_SelectedIndexChanged（这一点，EventArgs.Empty）;
        }
    }    保护无效ddlpid5_SelectedIndexChanged（对象发件人，EventArgs的发送）
    {        如果（ddlpid5.SelectedIndex大于0）
        {            会话[PID5] = ddlpid5.SelectedValue;
            列表项removeItem1 = ddlpid1.Items.FindByValue（ddlpid5.SelectedValue）;
            ddlpid1.Items.Remove（removeItem1）;
            列表项removeItem2 = ddlpid2.Items.FindByValue（ddlpid5.SelectedValue）;
            ddlpid2.Items.Remove（removeItem2）;
            列表项removeItem3 = ddlpid3.Items.FindByValue（ddlpid5.SelectedValue）;
            ddlpid3.Items.Remove（removeItem3）;
            列表项removeItem4 = ddlpid4.Items.FindByValue（ddlpid5.SelectedValue）;
            ddlpid4.Items.Remove（removeItem4）;        }    否则，如果（ddlpid5.SelectedItem.Text.Equals（警察ID））
        {
            FillDropdown（ddlpid1）;
            FillDropdown（ddlpid2）;
            FillDropdown（ddlpid3）;
            FillDropdown（ddlpid4）;
            FillDropdown（ddlpid5）;            ddlpid1.SelectedValue =（字符串）会议[PID1];
            ddlpid1_SelectedIndexChanged（这一点，EventArgs.Empty）;            ddlpid2.SelectedValue =（字符串）会议[PID2];
            ddlpid2_SelectedIndexChanged（这一点，EventArgs.Empty）;            ddlpid3.SelectedValue =（字符串）会议[PID3];
            ddlpid3_SelectedIndexChanged（这一点，EventArgs.Empty）;            ddlpid4.SelectedValue =（字符串）会议[PID4];
            ddlpid4_SelectedIndexChanged（这一点，EventArgs.Empty）;
        }    }

解决方案

首先，我会成立了的AutoPostBack 属性的下拉列表中为true在我的标记：

 ＆LT; ASP：DropDownList的ID =memberID1的AutoPostBack =真=服务器可见=假OnSelectedIndexChanged =ddlpid1_SelectedIndexChanged＆GT;
    ＆LT; / ASP：DropDownList的＆GT;
    ＆LT; ASP：DropDownList的ID =memberID2的AutoPostBack =真=服务器可见=假OnSelectedIndexChanged =ddlpid2_SelectedIndexChanged＆GT;
    ＆LT; / ASP：DropDownList的＆GT;
    ＆LT; ASP：DropDownList的ID =memberID3的AutoPostBack =真=服务器可见=假OnSelectedIndexChanged =ddlpid3_SelectedIndexChanged＆GT;
    ＆LT; / ASP：DropDownList的＆GT;

更新：我们可以选择的值存储在视图状态和重新填充dropdownlists像下面后检索：

 公共部分类WebForm2：System.Web.UI.Page
{
    布尔bFlag = TRUE;    保护无效的Page_Load（对象发件人，EventArgs的发送）
    {
        如果（！的IsPostBack）
        {
            FillddlLocations（）;
        }
    }    //属性存储在ViewState中选定值    保护字符串MemberID1Selection
    {
        得到
        {
            如果（的ViewState [MemberID1Selection]！= NULL）
                返回的ViewState [MemberID1Selection]的ToString（）。
            返回;
        }
        集合{的ViewState [MemberID1Selection] =值; }
    }    保护字符串MemberID2Selection
    {
        得到
        {
            如果（的ViewState [MemberID2Selection]！= NULL）
                返回的ViewState [MemberID2Selection]的ToString（）。
            返回;
        }
        集合{的ViewState [MemberID2Selection] =值; }
    }    保护字符串MemberID3Selection
    {
        得到
        {
            如果（的ViewState [MemberID3Selection]！= NULL）
                返回的ViewState [MemberID3Selection]的ToString（）。
            返回;
        }
        集合{的ViewState [MemberID3Selection] =值; }
    }
    保护无效FillddlLocations（）
    {
        FillDropdown（memberID1）;
        FillDropdown（memberID2）;
        FillDropdown（memberID3）;
        memberID1.Visible = TRUE;
        memberID2.Visible = TRUE;
        memberID3.Visible = TRUE;
    }    保护无效FillDropdown（DropDownList的DDL）
    {        使用（VAR connAdd =新的SqlConnection（数据源=本地主机;初始目录= MajorProject;集成安全性= SSPI））
        {
            connAdd.Open（）;            VAR SQL =从PoliceAccount选择policeid在那里的地位='可用'和处理='offcase和postedto ='+ ddllocation.SelectedValue +';
            使用（VAR cmdAdd =新SqlDataAdapter的（SQL，connAdd））
            {
                数据集DS2 =新的DataSet（）;
                cmdAdd.Fill（DS2）;
                ddl.Items.Clear（）;
                ddl.DataSource = DS2;
                ddl.DataTextField =MEMBERID;
                ddl.DataValueField =MEMBERID;
                ddl.DataBind（）;
                ddl.Items.Insert（0，新的ListItem（请选择一个会员ID，））;
                ddl.SelectedIndex = 0;            }        }
    }    保护无效IndexChanged（DropDownList的ddlChanged，DropDownList的ddlToFilter1，DropDownList的ddlToFilter2）
    {
        字符串removeValue1 = ddlChanged == memberID1？ MemberID1Selection：（ddlChanged == memberID2 MemberID2Selection：MemberID3Selection）;
        字符串selValue2 = ddlChanged == memberID1？ MemberID2Selection：（ddlChanged == memberID2 MemberID1Selection：MemberID1Selection）;
        字符串selValue3 = ddlChanged == memberID1？ MemberID3Selection：（ddlChanged == memberID2 MemberID3Selection：MemberID2Selection）;        bFlag = FALSE; // prevent下再fireing的$ C $，而更改索引
        如果（removeValue1！=）
        {
            列表项ITEM1 = ddlToFilter1.Items.FindByValue（removeValue1）;
            ddlToFilter1.Items.Remove（ITEM1）;
            列表项ITEM2 = ddlToFilter2.Items.FindByValue（removeValue1）;
            ddlToFilter2.Items.Remove（ITEM2）;
        }        如果（selValue3！=）
        {
            列表项项目3 = ddlToFilter1.Items.FindByValue（selValue3）;
            ddlToFilter1.Items.Remove（项目3）;
        }
        如果（selValue2！=）
        {
            列表项ITEM4 = ddlToFilter2.Items.FindByValue（selValue2）;
            ddlToFilter2.Items.Remove（ITEM4）;
        }        bFlag = FALSE;
        ddlToFilter1.SelectedIndex = ddlToFilter1.Items.IndexOf（ddlToFilter1.Items.FindByValue（selValue2））;
        ddlToFilter2.SelectedIndex = ddlToFilter2.Items.IndexOf（ddlToFilter2.Items.FindByValue（selValue3））;
    }    保护无效ddlpid1_SelectedIndexChanged（对象发件人，EventArgs的发送）
    {
        MemberID1Selection = memberID1.SelectedValue;
        如果（bFlag）
        {
            FillDropdown（memberID2）;
            FillDropdown（memberID3）;
            IndexChanged（memberID1，memberID2，memberID3）;
        }
    }    保护无效ddlpid2_SelectedIndexChanged（对象发件人，EventArgs的发送）
    {
        MemberID2Selection = memberID2.SelectedValue;
        如果（bFlag）
        {
            FillDropdown（memberID1）;
            FillDropdown（memberID3）;
            IndexChanged（memberID2，memberID1，memberID3）;
        }
    }
    保护无效ddlpid3_SelectedIndexChanged（对象发件人，EventArgs的发送）
    {
        MemberID3Selection = memberID3.SelectedValue;
        如果（bFlag）
        {
            FillDropdown（memberID1）;
            FillDropdown（memberID2）;
            IndexChanged（memberID3，memberID1，memberID2）;
        }
    }
}

我已经测试code，它是为我工作。希望它能帮助！

I have multiple dropdownlist box all querying the same column, same table and from the same database. For example under memberID column i have the following IDs.

12345
23456
34567

And i have 3 different dropdownlist box as shown below

    <asp:DropDownList ID="memberID3" runat="server" Visible="false" OnSelectedIndexChanged="ddlpid3_SelectedIndexChanged" >
    </asp:DropDownList>
    <asp:DropDownList ID="memberID1" runat="server" Visible="false" OnSelectedIndexChanged="ddlpid1_SelectedIndexChanged">
    </asp:DropDownList>
    <asp:DropDownList ID="memberID2" runat="server" Visible="false" OnSelectedIndexChanged="ddlpid2_SelectedIndexChanged">
    </asp:DropDownList>

I added update panel between the dropdownlist so as to allow my dropdownlist to refresh upon any updates/selections.

  <asp:UpdatePanel ID="UpdatePanel1" runat="server">
  <ContentTemplate>
  </ContentTemplate>
  </asp:UpdatePanel>

For instance, when memberID1 selected 12345, the other 2 dropdownlist (memberID2 and 3) will not display the ID 12345. Vice versa, when memberID1 select the default value of the dropdownlist, the ID reappears in the other 2 dropdownlistbox. I have added a default value for all of the DDL.

 memeberID(number).Items.Insert(0, new ListItem(" Please select a Member ID", ""));
 memeberID(number).SelectedIndex = 0;

If i have not mistaken the property of update panel, isn't that able to make this function work?

here is the binding code as requested.

protected void ddllocation_SelectedIndexChanged(object sender, EventArgs e)
    {

        using (var connAdd = new SqlConnection("Data Source = localhost; Initial Catalog = MajorProject; Integrated Security= SSPI"))
        {
            connAdd.Open();

            var sql = "Select policeid from PoliceAccount where status ='available' and handle ='offcase' and postedto='" + ddllocation.SelectedValue + "'";
            using (var cmdAdd = new SqlDataAdapter(sql, connAdd))
            {
                DataSet ds2 = new DataSet();
                cmdAdd.Fill(ds2);

                memberID1.Items.Clear();
                memberID1.DataSource = ds2;
                memberID1.DataTextField = "memberID";
                memberID1.DataValueField = "memberID";
                memberID1.DataBind();
                memberID1.Items.Insert(0, new ListItem("Please select a Member ID", ""));
                memberID1.SelectedIndex = 0;

                memberID2.Items.Clear();
                memberID2.DataSource = ds2;
                memberID2.DataTextField = "memberID";
                memberID2.DataValueField = "memberID";
                memberID2.DataBind();
                memberID2.Items.Insert(0, new ListItem("Please select a Member ID", ""));
                memberID2.SelectedIndex = 0;

                memberID3.Items.Clear();
                memberID3.DataSource = ds2;
                memberID3.DataTextField = "memberID";
                memberID3.DataValueField = "memberID";
                memberID3.DataBind();
                memberID3.Items.Insert(0, new ListItem("Please select a Member ID", ""));
                memberID3.SelectedIndex = 0;



            }

UPDATE

For now i'm able to allow my other ddl to re-bind and cache the selected value in the other dropdownlist when the default value is selected. However, when i select other ID, the ID are being removed and it wont re-bind the other ddl.

protected void FillddlLocations()
    {
        FillDropdown(ddlpid1);
        FillDropdown(ddlpid2);
        FillDropdown(ddlpid3);
        FillDropdown(ddlpid4);
        FillDropdown(ddlpid5);
        ddlpid1.Visible = false;
        ddlpid2.Visible = false;
        ddlpid3.Visible = false;
        ddlpid4.Visible = false;
        ddlpid5.Visible = false;
    }

    protected void FillDropdown(DropDownList ddl)
    {

        using (var connAdd = new SqlConnection("Data Source = localhost; Initial Catalog = MajorProject; Integrated Security= SSPI"))
        {
            connAdd.Open();

            var sql = "Select policeid from PoliceAccount where status ='available' and handle ='offcase' and postedto='" + ddllocation.SelectedValue + "'";
            using (var cmdAdd = new SqlDataAdapter(sql, connAdd))
            {
                DataSet ds2 = new DataSet();
                cmdAdd.Fill(ds2);

                ddl.Items.Clear();
                ddl.DataSource = ds2;
                ddl.DataBind();
                ddl.Items.Insert(0, new ListItem("Police ID", ""));
                ddl.SelectedIndex = 0;

            }

        }
    }

    protected void ddlpid1_SelectedIndexChanged(object sender, EventArgs e)
    {

        if (ddlpid1.SelectedIndex > 0)
        {

            Session["pid1"] = ddlpid1.SelectedValue;

            ListItem removeItem2 = ddlpid2.Items.FindByValue(ddlpid1.SelectedValue);
            ddlpid2.Items.Remove(removeItem2);
            ListItem removeItem3 = ddlpid3.Items.FindByValue(ddlpid1.SelectedValue);
            ddlpid3.Items.Remove(removeItem3);
            ListItem removeItem4 = ddlpid4.Items.FindByValue(ddlpid1.SelectedValue);
            ddlpid4.Items.Remove(removeItem4);
            ListItem removeItem5 = ddlpid5.Items.FindByValue(ddlpid1.SelectedValue);
            ddlpid5.Items.Remove(removeItem5);


        }

        else

        if (ddlpid1.SelectedItem.Text.Equals("Police ID"))
        {
            FillDropdown(ddlpid1);
            FillDropdown(ddlpid2);
            FillDropdown(ddlpid3);
            FillDropdown(ddlpid4);
            FillDropdown(ddlpid5);


            ddlpid2.SelectedValue = (String)Session["pid2"];
            ddlpid2_SelectedIndexChanged(this, EventArgs.Empty);

            ddlpid3.SelectedValue = (String)Session["pid3"];
            ddlpid3_SelectedIndexChanged(this, EventArgs.Empty);

            ddlpid4.SelectedValue = (String)Session["pid4"];
            ddlpid4_SelectedIndexChanged(this, EventArgs.Empty);

            ddlpid5.SelectedValue = (String)Session["pid5"];
            ddlpid5_SelectedIndexChanged(this, EventArgs.Empty);
        }





    }

    protected void ddlpid2_SelectedIndexChanged(object sender, EventArgs e)
    {

        if (ddlpid2.SelectedIndex > 0)
        {

            Session["pid2"] = ddlpid2.SelectedValue;
            ListItem removeItem1 = ddlpid1.Items.FindByValue(ddlpid2.SelectedValue);
            ddlpid1.Items.Remove(removeItem1);
            ListItem removeItem3 = ddlpid3.Items.FindByValue(ddlpid2.SelectedValue);
            ddlpid3.Items.Remove(removeItem3);
            ListItem removeItem4 = ddlpid4.Items.FindByValue(ddlpid2.SelectedValue);
            ddlpid4.Items.Remove(removeItem4);
            ListItem removeItem5 = ddlpid5.Items.FindByValue(ddlpid2.SelectedValue);
            ddlpid5.Items.Remove(removeItem5);


        }
        else if (ddlpid2.SelectedItem.Text.Equals("Police ID"))
        {
            FillDropdown(ddlpid1);
            FillDropdown(ddlpid2);
            FillDropdown(ddlpid3);
            FillDropdown(ddlpid4);
            FillDropdown(ddlpid5);

            ddlpid1.SelectedValue = (String)Session["pid1"];
            ddlpid1_SelectedIndexChanged(this, EventArgs.Empty);

            ddlpid3.SelectedValue = (String)Session["pid3"];
            ddlpid3_SelectedIndexChanged(this, EventArgs.Empty);

            ddlpid4.SelectedValue = (String)Session["pid4"];
            ddlpid4_SelectedIndexChanged(this, EventArgs.Empty);

            ddlpid5.SelectedValue = (String)Session["pid5"];
            ddlpid5_SelectedIndexChanged(this, EventArgs.Empty);
        }


    }   

    protected void ddlpid3_SelectedIndexChanged(object sender, EventArgs e)
    {          
        if (ddlpid3.SelectedIndex > 0)
        {

            Session["pid3"] = ddlpid3.SelectedValue;
            ListItem removeItem1 = ddlpid1.Items.FindByValue(ddlpid3.SelectedValue);
            ddlpid1.Items.Remove(removeItem1);
            ListItem removeItem2 = ddlpid2.Items.FindByValue(ddlpid3.SelectedValue);
            ddlpid2.Items.Remove(removeItem2);
            ListItem removeItem4 = ddlpid4.Items.FindByValue(ddlpid3.SelectedValue);
            ddlpid4.Items.Remove(removeItem4);
            ListItem removeItem5 = ddlpid5.Items.FindByValue(ddlpid3.SelectedValue);
            ddlpid5.Items.Remove(removeItem5);


        }   
    else if (ddlpid3.SelectedItem.Text.Equals("Police ID"))
        {
            FillDropdown(ddlpid1);
            FillDropdown(ddlpid2);
            FillDropdown(ddlpid3);
            FillDropdown(ddlpid4);
            FillDropdown(ddlpid5);

            ddlpid1.SelectedValue = (String)Session["pid1"];
            ddlpid1_SelectedIndexChanged(this, EventArgs.Empty);

            ddlpid2.SelectedValue = (String)Session["pid2"];
            ddlpid2_SelectedIndexChanged(this, EventArgs.Empty);

            ddlpid4.SelectedValue = (String)Session["pid4"];
            ddlpid4_SelectedIndexChanged(this, EventArgs.Empty);

            ddlpid5.SelectedValue = (String)Session["pid5"];
            ddlpid5_SelectedIndexChanged(this, EventArgs.Empty);
        }


    }

    protected void ddlpid4_SelectedIndexChanged(object sender, EventArgs e)
    {            
        if (ddlpid4.SelectedIndex > 0)
        {
            Session["pid4"] = ddlpid4.SelectedValue;

            ListItem removeItem1 = ddlpid1.Items.FindByValue(ddlpid4.SelectedValue);
            ddlpid1.Items.Remove(removeItem1);
            ListItem removeItem2 = ddlpid2.Items.FindByValue(ddlpid4.SelectedValue);
            ddlpid2.Items.Remove(removeItem2);
            ListItem removeItem3 = ddlpid3.Items.FindByValue(ddlpid4.SelectedValue);
            ddlpid3.Items.Remove(removeItem3);
            ListItem removeItem5 = ddlpid5.Items.FindByValue(ddlpid4.SelectedValue);
            ddlpid5.Items.Remove(removeItem5);


        }

        else if (ddlpid4.SelectedItem.Text.Equals("Police ID"))
        {


            FillDropdown(ddlpid1);
            FillDropdown(ddlpid2);
            FillDropdown(ddlpid3);
            FillDropdown(ddlpid4);
            FillDropdown(ddlpid5);

            ddlpid1.SelectedValue = (String)Session["pid1"];
            ddlpid1_SelectedIndexChanged(this, EventArgs.Empty);

            ddlpid2.SelectedValue = (String)Session["pid2"];
            ddlpid2_SelectedIndexChanged(this, EventArgs.Empty);

            ddlpid3.SelectedValue = (String)Session["pid3"];
            ddlpid3_SelectedIndexChanged(this, EventArgs.Empty);

            ddlpid5.SelectedValue = (String)Session["pid5"];
            ddlpid5_SelectedIndexChanged(this, EventArgs.Empty);
        }


    }       

    protected void ddlpid5_SelectedIndexChanged(object sender, EventArgs e)
    {           

        if (ddlpid5.SelectedIndex > 0)
        {

            Session["pid5"] = ddlpid5.SelectedValue;
            ListItem removeItem1 = ddlpid1.Items.FindByValue(ddlpid5.SelectedValue);
            ddlpid1.Items.Remove(removeItem1);
            ListItem removeItem2 = ddlpid2.Items.FindByValue(ddlpid5.SelectedValue);
            ddlpid2.Items.Remove(removeItem2);
            ListItem removeItem3 = ddlpid3.Items.FindByValue(ddlpid5.SelectedValue);
            ddlpid3.Items.Remove(removeItem3);
            ListItem removeItem4 = ddlpid4.Items.FindByValue(ddlpid5.SelectedValue);
            ddlpid4.Items.Remove(removeItem4);

        }

    else if (ddlpid5.SelectedItem.Text.Equals("Police ID"))
        {
            FillDropdown(ddlpid1);
            FillDropdown(ddlpid2);
            FillDropdown(ddlpid3);
            FillDropdown(ddlpid4);
            FillDropdown(ddlpid5);

            ddlpid1.SelectedValue = (String)Session["pid1"];
            ddlpid1_SelectedIndexChanged(this, EventArgs.Empty);

            ddlpid2.SelectedValue = (String)Session["pid2"];
            ddlpid2_SelectedIndexChanged(this, EventArgs.Empty);

            ddlpid3.SelectedValue = (String)Session["pid3"];
            ddlpid3_SelectedIndexChanged(this, EventArgs.Empty);

            ddlpid4.SelectedValue = (String)Session["pid4"];
            ddlpid4_SelectedIndexChanged(this, EventArgs.Empty);
        }

    }

解决方案

First of all, I would set the AutoPostBack property for dropdowns to true in my markup:

<asp:DropDownList ID="memberID1" AutoPostBack="true" runat="server" Visible="false" OnSelectedIndexChanged="ddlpid1_SelectedIndexChanged">
    </asp:DropDownList>
    <asp:DropDownList ID="memberID2" AutoPostBack="true" runat="server" Visible="false" OnSelectedIndexChanged="ddlpid2_SelectedIndexChanged">
    </asp:DropDownList>
    <asp:DropDownList ID="memberID3" AutoPostBack="true" runat="server" Visible="false" OnSelectedIndexChanged="ddlpid3_SelectedIndexChanged" >
    </asp:DropDownList>

Update: We can store selected values in view state and retrieve after repopulating the dropdownlists like below:

public partial class WebForm2 : System.Web.UI.Page
{
    bool bFlag = true;

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

    //Properties to store selected value in ViewState

    protected string MemberID1Selection
    {
        get
        {
            if (ViewState["MemberID1Selection"] != null)
                return ViewState["MemberID1Selection"].ToString();
            return "";
        }
        set { ViewState["MemberID1Selection"] = value; }
    }

    protected string MemberID2Selection
    {
        get
        {
            if (ViewState["MemberID2Selection"] != null)
                return ViewState["MemberID2Selection"].ToString();
            return "";
        }
        set { ViewState["MemberID2Selection"] = value; }
    }

    protected string MemberID3Selection
    {
        get
        {
            if (ViewState["MemberID3Selection"] != null)
                return ViewState["MemberID3Selection"].ToString();
            return "";
        }
        set { ViewState["MemberID3Selection"] = value; }
    }


    protected void FillddlLocations()
    {
        FillDropdown(memberID1);
        FillDropdown(memberID2);
        FillDropdown(memberID3);
        memberID1.Visible = true;
        memberID2.Visible = true;
        memberID3.Visible = true;
    }

    protected void FillDropdown(DropDownList ddl)
    {

        using (var connAdd = new SqlConnection("Data Source = localhost; Initial Catalog = MajorProject; Integrated Security= SSPI"))
        {
            connAdd.Open();

            var sql = "Select policeid from PoliceAccount where status ='available' and handle ='offcase' and postedto='" + ddllocation.SelectedValue + "'";
            using (var cmdAdd = new SqlDataAdapter(sql, connAdd))
            {
                DataSet ds2 = new DataSet();
                cmdAdd.Fill(ds2);


                ddl.Items.Clear();
                ddl.DataSource = ds2;
                ddl.DataTextField = "memberID";
                ddl.DataValueField = "memberID";
                ddl.DataBind();
                ddl.Items.Insert(0, new ListItem("Please select a Member ID", ""));
                ddl.SelectedIndex = 0;

            }

        }
    }

    protected void IndexChanged(DropDownList ddlChanged, DropDownList ddlToFilter1, DropDownList ddlToFilter2)
    {
        string removeValue1 = ddlChanged == memberID1 ? MemberID1Selection : (ddlChanged == memberID2 ? MemberID2Selection : MemberID3Selection);
        string selValue2 = ddlChanged == memberID1 ? MemberID2Selection : (ddlChanged == memberID2 ? MemberID1Selection : MemberID1Selection);
        string selValue3 = ddlChanged == memberID1 ? MemberID3Selection : (ddlChanged == memberID2 ? MemberID3Selection : MemberID2Selection);

        bFlag = false;//Prevent fireing the code again while changing the index
        if (removeValue1 != "")
        {
            ListItem item1 = ddlToFilter1.Items.FindByValue(removeValue1);
            ddlToFilter1.Items.Remove(item1);
            ListItem item2 = ddlToFilter2.Items.FindByValue(removeValue1);
            ddlToFilter2.Items.Remove(item2);            
        }

        if (selValue3 != "")
        {
            ListItem item3 = ddlToFilter1.Items.FindByValue(selValue3);
            ddlToFilter1.Items.Remove(item3);
        }
        if (selValue2 != "")
        {
            ListItem item4 = ddlToFilter2.Items.FindByValue(selValue2);
            ddlToFilter2.Items.Remove(item4);
        }

        bFlag = false;
        ddlToFilter1.SelectedIndex = ddlToFilter1.Items.IndexOf(ddlToFilter1.Items.FindByValue(selValue2));
        ddlToFilter2.SelectedIndex = ddlToFilter2.Items.IndexOf(ddlToFilter2.Items.FindByValue(selValue3));
    }

    protected void ddlpid1_SelectedIndexChanged(object sender, EventArgs e)
    {
        MemberID1Selection = memberID1.SelectedValue;
        if (bFlag)
        {
            FillDropdown(memberID2);
            FillDropdown(memberID3);
            IndexChanged(memberID1, memberID2, memberID3);
        }
    }

    protected void ddlpid2_SelectedIndexChanged(object sender, EventArgs e)
    {
        MemberID2Selection = memberID2.SelectedValue;
        if (bFlag)
        {
            FillDropdown(memberID1);
            FillDropdown(memberID3);
            IndexChanged(memberID2, memberID1, memberID3);
        }
    }
    protected void ddlpid3_SelectedIndexChanged(object sender, EventArgs e)
    {
        MemberID3Selection = memberID3.SelectedValue;
        if (bFlag)
        {
            FillDropdown(memberID1);
            FillDropdown(memberID2);
            IndexChanged(memberID3, memberID1, memberID2);
        }
    }
}

I have tested the code and it is working for me. Hope it helps!

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DROPDOWNLIST将更新面板后不更新 [英] Dropdownlist does not update after adding update panel

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DROPDOWNLIST将更新面板后不更新 [英] Dropdownlist does not update after adding update panel

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