.NET dropdownlist控件绑定数据后，添加“全部”项，实现功能

DropDownList在从数据库中得到数据源绑定后,计划为其添加一个"全部"或"不限"之类的项，添加方法现知的有两种：

1：在脚本中直接添加：<asp:ListItem Value="0">全部</asp:ListItem>，然后在DropDownList中添加一个属性：  AppendDataBoundItems="True" ，如下面的代码所示：

<asp:DropDownList  ID="ddlDepartment" runat="server" AutoPostBack="true"

onselectedindexchanged="ddlDepartment_SelectedIndexChanged" DataTextField="DeptName"

AppendDataBoundItems="True"  DataValueField="DeptID">

<asp:ListItem Value="0">全部</asp:ListItem>

</asp:DropDownList>

2：在后台代码中通过CS文件添加：

ddlDepartment.Items.Insert(0, new ListItem("--所有--", "0"));

******************************************

添加以后，在使用的时候，可以这样写：

If(ddlDepartment.SelectedValue!="0")

{

deptId=ddlDepartment.SelectedValue;

}

--SQL语句的写法：WHERE  @deptId IS NULL OR @deptId="" OR deptID=@deptId

3、我的实践

SQLHelper sqlh = new SQLHelper();
  protected void Page_Load(object sender, EventArgs e)
  {
   //大棚下拉列表数据填充绑定
   if (!IsPostBack)
   {
    string dpsql = "SELECT * FROM [GHInfo]";
    DataTable dpdt = new DataTable();
    dpdt = sqlh.GetDataTable(dpsql);
    dapeng.DataSource = dpdt;
    dapeng.DataValueField = dpdt.Columns[0].ToString();
    dapeng.DataTextField = dpdt.Columns[2].ToString();
    dapeng.DataBind();
    ListItem li = new ListItem("---查看全部---","00");
    dapeng.Items.Insert(0, li );
    string sql = "SELECT   t1.ID, t2.UserName, t1.Address, t3.Name, t1.Tem, t1.Hum, t1.Co2 FROM GHInfo AS t1 LEFT OUTER JOIN  UserInfo AS t2 ON t1.OwnerID = t2.ID LEFT OUTER JOIN Plants AS t3 ON t1.PlantID = t3.ID ";
    DataTable dt = sqlh.GetDataTable(sql);
    DataList1.DataSource = dt;
    DataList1.DataBind();

   }
  }

  protected void dapeng_SelectedIndexChanged(object sender, EventArgs e)
  {

   string id = dapeng.SelectedValue.ToString();
   string sql;
   Label1.Text = id;
   if (id != "00")
   {
    sql = "SELECT   t1.ID, t2.UserName, t1.Address, t3.Name, t1.Tem, t1.Hum, t1.Co2 FROM GHInfo AS t1 LEFT OUTER JOIN  UserInfo AS t2 ON t1.OwnerID = t2.ID LEFT OUTER JOIN Plants AS t3 ON t1.PlantID = t3.ID WHERE(t1.ID = '" + id + "')";
   }
   else
   {
    sql = "SELECT   t1.ID, t2.UserName, t1.Address, t3.Name, t1.Tem, t1.Hum, t1.Co2 FROM GHInfo AS t1 LEFT OUTER JOIN  UserInfo AS t2 ON t1.OwnerID = t2.ID LEFT OUTER JOIN Plants AS t3 ON t1.PlantID = t3.ID";
   }
   DataTable dt = sqlh.GetDataTable(sql);
   
   DataList1.DataSource = dt;

   DataList1.DataBind();
  }