如何保留asp.net中dropdownlistbox的值 [英] How to retain the value of dropdownlistbox in asp.net

问题描述

在这种情况下，我有1个下拉列表用于选择用户，还有2个列表框，用于为该用户设置项目权限.现在，我希望首先选择下拉列表，然后单击移动"按钮，将listbox1的listitem移至listitem2.然后单击提交"，将它们添加到表中.但是当我自动回传下拉列表和使用更新面板时，下拉列表的选定索引消失了.单击按钮移动时，其选择的值消失.那么我该如何保留其价值

In this i have 1 dropdown which selects the user and 2 list box which sets the permission of items for that user . Now i want that firstly dropdown i selected and then on click of move button the listitem of listbox1 move to listitem2 . And then on click of submit they added in table . But the selected index disappear of dropdown list when i autopostback it and when i am using the update panel . Its selected value disappear when the button move clicked . So how can i retain its value

<div>
    <asp:DropDownList ID="ddlAdmin" runat="server" >
    <table width="70%">
    <tr><td colspan="3">
    <asp:ListBox ID="ProductListBox" runat="server" SelectionMode="Multiple" ></td>
    <td><asp:Button ID="BtnMoveLeft" runat="server" Text="Add Permission" OnClick="BtnMoveleft_Click" /></td>
    <td>
    
    <asp:ListBox ID="PermissionListBox" runat="server" SelectionMode="Multiple" ></td>
    </tr>
   </table>
    </div>

public partial class admin_UserPermission : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        FillProductList();
        FillAdminDropDownList();
    }

    protected void FillAdminDropDownList()
    {
        DataManager myData = new DataManager(DbFunctions.GetConnectionString());
        MySqlConnection myPConn = myData.GetPooledConnection(new MySqlConnection());


        MySqlCommand cmd = new MySqlCommand("SELECT adminuserid,adminusername FROM adminusermast", myPConn);
        DataTable dt = new DataTable();
        myPConn.Open();
        MySqlDataAdapter adptr = new MySqlDataAdapter(cmd);
        adptr.Fill(dt);
        myPConn.Close();
        if (dt.Rows.Count > 0)
        {
            ddlAdmin.Items.Clear();
            ddlAdmin.Items.Add("SELECT");
            foreach (DataRow drow in dt.Rows)
            {
                ListItem lst = new ListItem();
                lst.Value = drow[1].ToString();
                lst.Text = drow[0].ToString();
                ddlAdmin.Items.Add(lst);
            }
        }
    }
    protected void FillProductList()
    {
            DataManager myData = new DataManager(DbFunctions.GetConnectionString());
            MySqlConnection myPConn = myData.GetPooledConnection(new MySqlConnection());
            MySqlCommand com = new MySqlCommand("Select productid,productname from productmast", myPConn);
            MySqlDataReader Reader = null;
            myPConn.Open();
           Reader = com.ExecuteReader();
           while (Reader.Read())
           {

               ListItem newItem = new ListItem();
               newItem.Text = Reader["productname"].ToString();
               newItem.Value = Reader["productid"].ToString();
               ProductListBox.Items.Add(newItem);
           }
           Reader.Close();
       myPConn.Close();
    }

    protected void BtnMoveleft_Click(object sender, EventArgs e)
    {
        for (int i = ProductListBox.Items.Count - 1; i >= 0; i--)
        {
            if (ProductListBox.Items[i].Selected == true)
            {
                PermissionListBox.Items.Add(ProductListBox.Items[i]);
                ListItem li = ProductListBox.Items[i];
                ProductListBox.Items.Remove(li);
            }
        }
    }
}

推荐答案

ViewState属性是否已启用?如果未启用.

如果启用了此功能，则可以将所选索引保存在会话中，以后再重新分配.

OnSelectedindexchanged事件分配类似

Is the ViewState property is Enabled? If not enable it.

If it is enabled you can save the selected index in a Session and reassign it later.

OnSelectedindexchanged event assign something like

Session["ddlAdminValue"] = ddlAdmin.SelectedIndex;

在PageLoad()上，您可以执行类似的操作；

On PageLoad() you can do something like;

if(Page.IsPostBack)
{
  if(Session["ddlAdminValue"] != null)
  {
    ddlAdmin.SelectedIndex = Convert.ToInt32(Session["ddlAdminValue"]);
   } 
}

不确定，但是在大多数情况下，如果页面加载中的！postback可以避免重置它的值，则填充下拉列表.

not sure, but in most cases, filling drop down on if !postback in pageload will save from reseting the values of it.

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