GridView里面的Dropdownlist的问题！！！！！！！急。。。。。。

Question

代码很简单，实现的功能是，如果点击Edit （自带的），出现的Dropdownlist的初始选择值等于点击Edit以前的值public partial class Test2 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {    }    protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e)
    {
        Label mytext = (Label)(GridView1.Rows[e.NewEditIndex].FindControl("Label1"));
   
        this.Label2.Text = mytext.Text;        DropDownList mylist = (DropDownList)(GridView1.Rows[e.NewEditIndex].FindControl("DropDownList1"));        mylist.ClearSelection(); （运行的时候报错为：Object reference not set to an instance of an object.）        mylist.Items.FindByValue(mytext.Text).Selected = true;    }
}请问应该怎么修改啊！！！！！！急，想了几天了

Answer 1

查了一下msdn:http://msdn.microsoft.com/zh-cn/library/bxdf3ekh(VS.80).aspx每一列和每一行的 Selected 属性都设置为 false。这时候你那个dropdownlist的选择的值是null!会报错！

Answer 2

点编辑的时候值没有初始化 选中的是null 可以先将取也来的值添加dropDownlist中并设置默认选择项

Answer 3

我是这样绑定的
<EditItemTemplate>
                        <asp:DropDownList ID="DropDownList1" runat="server" SelectedIndex='<%# GetSelectedTitle(Eval("Cat")) %>' （绑定）
DataSource='<%# Cat %>' >
                            <asp:ListItem>Mr.</asp:ListItem>
                            <asp:ListItem>Mrs.</asp:ListItem>
                            <asp:ListItem>Dr.</asp:ListItem>
                            <asp:ListItem>Ms.</asp:ListItem>
                        </asp:DropDownList>
                    </EditItemTemplate>
 protected string[] Cat
    {
        get { return new string[] { "Mr.", "Dr.", "Ms.", "Mrs." }; }
    }    protected int GetSelectedTitle(object title)
    {
        return Array.IndexOf(Cat, title.ToString());
    }

Answer 4

  protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e)
        {
            GridView1.EditIndex = e.NewEditIndex;
            DropDownList mylist= ((DropDownList)GridView1.Rows[e.NewEditIndex].FindControl("DropDownList1")).SelectedValue.Trim();
if(mylist!=null)
{}
}
在protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
        {
            if (e.Row.RowIndex != -1)
            {
          if ((DropDownList)e.Row.FindControl("DropDownList1") != null)
                {
               ((DropDownList)e.Row.FindControl("DropDownList1")).SelectedValue = "";                }
             }
         }

Answer 5

 楼上：DropDownList mylist= ((DropDownList)GridView1.Rows[e.NewEditIndex].FindControl("DropDownList1")).SelectedValue.Trim(); 报错：错误 2 无法将类型“string”隐式转换为“System.Web.UI.WebControls.DropDownList” G:\My Project\CDPCS\Test2.aspx.cs 28 31 G:\My Project\CDPCS\

Answer 6

目前代码修改成这样了
protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e)
    {
        GridView1.EditIndex = e.NewEditIndex;        DropDownList mylist = ((DropDownList)GridView1.Rows[e.NewEditIndex].FindControl("DropDownList1")).SelectedValue.Trim();        if (mylist != null) （这里虽然不报错，但是因为mylist==null，所以会跳过这里的内容，无法得到想要的结果）
        {
            Label mytext = (Label)(GridView1.Rows[e.NewEditIndex].FindControl("Label1"));            this.Label2.Text = mytext.Text;            mylist.ClearSelection();            mylist.Items.FindByValue(mytext.Text).Selected = true;
        } 
          }
    protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
    {
        if (e.Row.RowIndex != -1)
        {
            if ((DropDownList)e.Row.FindControl("DropDownList1") != null)
            {
                ((DropDownList)e.Row.FindControl("DropDownList1")).SelectedValue = "";
            }
        }
    }

Answer 7

rowediting时似乎无法取得edititemtemplate里的控件，你把这个模板列改成只有itemtemplate的形式，把dropdownlist放到ItemTemplate里

Answer 8

DropDownList mylist= ((DropDownList)GridView1.Rows[e.NewEditIndex].FindControl("DropDownList1"));

Answer 9

空引用了，看看哪个dropdownlist有值没

Answer 10

如果放入ItemTemplate，那么就没法在Edit的时候实现我想要的功能了

Answer 11

貌似DataList是可以实现我想要的功能的，是吗？

Answer 12

哥们你事件写错了.我也碰见过,呵呵,参考下我的 代码吧,呵呵 //行绑定的时候从数据库表中取出对应的名称放在dropdownlist下拉列表中
        protected void GvQuestion_RowDataBound(object sender, GridViewRowEventArgs e)
        {
            if (e.Row.RowIndex == GvQuestion.EditIndex)
            {
                DropDownList ddl = e.Row.FindControl("ddl_name") as DropDownList;
                if (ddl != null)
                {
                    String name = (e.Row.DataItem as DataRowView).Row.ItemArray[1].ToString();
                    for (int i = 0; i < ddl.Items.Count; i++)
                    {
                        if (ddl.Items[i].Text.Trim() == name.Trim())
                        {
                            ddl.SelectedIndex = i;
                            break;
                        }
                    }
                }
            }
        }

Answer 13

//行绑定的时候从数据库表中取出对应的名称放在dropdownlist下拉列表中
        protected void GvQuestion_RowDataBound(object sender, GridViewRowEventArgs e)
        {
            if (e.Row.RowIndex == GvQuestion.EditIndex)
            {
                DropDownList ddl = e.Row.FindControl("ddl_name") as DropDownList;
                if (ddl != null)
                {
                    String name = (e.Row.DataItem as DataRowView).Row.ItemArray[1].ToString();
                    for (int i = 0; i < ddl.Items.Count; i++)
                    {
                        if (ddl.Items[i].Text.Trim() == name.Trim())
                        {
                            ddl.SelectedIndex = i;
                            break;
                        }
                    }
                }
            }
        }ding首先判断是否为空！

Answer 14

1 using System;   
 2 using System.Data;   
 3 using System.Data.SqlClient;   
 4 using System.Configuration;   
 5 using System.Collections;   
 6 using System.Web;   
 7 using System.Web.Security;   
 8 using System.Web.UI;   
 9 using System.Web.UI.WebControls;   
10 using System.Web.UI.WebControls.WebParts;   
11 using System.Web.UI.HtmlControls;   
12    
13 public partial class Demo13 : System.Web.UI.Page   
14 {   
15     protected void Page_Load(object sender, EventArgs e)   
16     {   
17         if (Page.IsPostBack == false)   
18         {   
19             BindData();   
20         }   
21     }   
22    
23     public void BindData()   
24     {   
25         string strSql = "select UserID,C_Name,E_Name,QQ,Blood_Type from Demo_User ";   
26         DataTable dt = SqlHelper.ExecuteDataset(SqlHelper.CONN_STRING, CommandType.Text, strSql, null).Tables[0];   
27    
28         GridView.DataSource = dt;   
29         GridView.DataKeyNames = new string[] { "UserID" };//主键   
30         GridView.DataBind();   
31     }   
32    
33     protected void GridView_PageIndexChanging(object sender, GridViewPageEventArgs e)   
34     {   
35         GridView.PageIndex = e.NewPageIndex;   
36         BindData();   
37     }   
38    
39     protected void GridView_RowDataBound(object sender, GridViewRowEventArgs e)   
40     {   
41         if (((DropDownList)e.Row.FindControl("DropDownList")) != null)   
42         {   
43             DropDownList DropDownList = (DropDownList)e.Row.FindControl("DropDownList");   
44             DropDownList.SelectedValue = ((HiddenField)e.Row.FindControl("HiddenField")).Value;   
45         }   
46     }   
47    
48     protected void DropDownList_SelectedIndexChanged(object sender, EventArgs e)   
49     {   
50         DropDownList DropDownList = sender as DropDownList;   
51         int index = (DropDownList.NamingContainer as GridViewRow).RowIndex;   
52         string UserID = GridView.DataKeys[index].Value.ToString();   
53    
54         string strSql = "Update Demo_User set Blood_Type=@Blood_Type where UserID=@UserID ";   
55         SqlParameter[] para = {   
56                                 new SqlParameter("@Blood_Type", DropDownList.SelectedValue.ToString()),   
57                                 new SqlParameter("@UserID", UserID),   
58                                };   
59         SqlHelper.ExecuteNonQuery(SqlHelper.CONN_STRING, CommandType.Text, strSql, para);   
60         BindData();   
61     }   
62 }    
  
 1 <table align="center" bgcolor="#c0de98" border="0" cellpadding="0" cellspacing="1" width="99%" >    
 2         <tr>   
 3             <th colspan="2">   
 4                 GridView演示</th>   
 5         </tr>        
 6        <tr>   
 7            <td colspan="2" style="width: 100%;" >   
 8               <asp:GridView ID="GridView" runat="server" Width="100%" AutoGenerateColumns="False" AllowPaging="True" OnPageIndexChanging="GridView_PageIndexChanging" PageSize="12" OnRowDataBound="GridView_RowDataBound" >   
 9                 <Columns>   
10                       <asp:BoundField DataField="UserID" HeaderText="UserID" ReadOnly="True" />   
11                       <asp:BoundField DataField="C_Name" HeaderText="中文名字" ReadOnly="True" />   
12                       <asp:BoundField DataField="E_Name" HeaderText="英文名字" ReadOnly="True" />   
13                       <asp:BoundField DataField="QQ" HeaderText="QQ" />   
14                     <asp:TemplateField HeaderText="学生血型">   
15                         <ItemTemplate>   
16                             <asp:DropDownList ID="DropDownList" runat="server" OnSelectedIndexChanged="DropDownList_SelectedIndexChanged" AutoPostBack="True">   
17                               <asp:ListItem Value="1">A</asp:ListItem>   
18                               <asp:ListItem Value="2">B</asp:ListItem>   
19                               <asp:ListItem Value="3">AB</asp:ListItem>   
20                               <asp:ListItem Value="4">O</asp:ListItem>        
21                             </asp:DropDownList>   
22                             <asp:HiddenField ID="HiddenField" runat="server" Value='<%# Eval("Blood_Type") %>'/>   
23                         </ItemTemplate>   
24                     </asp:TemplateField>   
25                   </Columns>   
26                   <RowStyle HorizontalAlign="Center" />     
27                   <PagerStyle HorizontalAlign="Right" />   
28               </asp:GridView>   
29            </td>   
30        </tr>          
31 </table>   
   

Answer 15

在模板列中放入两个控件，一个是DropDownList，另一个是HiddenField,让HiddenField绑定选择的值，然后在事件DataBound时用，先判断GridView1.CurrentMode==DetailsViewMode.Edit时，查找出DropDownList，让它的值等于你隐藏控件HiddenField中的值就可以了。