回发后Dropdownlist为空 [英] Dropdownlist is Empty after Postback
问题描述
嗨朋友们，
我将数据从sql加载到dropdownlist中，如下所示：
if （！IsPostBack）
{
string connStr = ConfigurationManager.ConnectionStrings [ myConnectionString ]的ConnectionString。
da = new SqlDataAdapter（ sp_LabelNames ，connStr）;
DataSet ds = new DataSet（）;
da.Fill（ds）;
lblAdmitto.Text = ds.Tables [ 0 ]。行[ 0 ] [ 1 ]。ToString（）;
lblVitalSigns.Text = ds.Tables [ 0 ]。行[ 1 ] [ 1 ]。ToString（）;
lblActivity.Text = ds.Tables [ 0 ]。行[ 2 ] [ 1 ]。ToString（）;
lblDiet.Text = ds.Tables [ 0 ]。行[ 3 ] [ 1 ]。ToString（）;
lblFluids.Text = ds.Tables [ 0 ]。行[ 4 ] [ 1 ]。ToString（）;
lblNursingOrders.Text = ds.Tables [ 0 ]。行[ 5 ] [ 1 ]。ToString（）;
lblMedications.Text = ds.Tables [ 0 ]。行[ 6 ] [ 1 ]。ToString（）;
lblBetaBlockers.Text = ds.Tables [ 0 ]。行[ 7 ] [ 1 ]。ToString（）;
lblAnalgesics.Text = ds.Tables [ 0 ]。行[ 8 ] [ 1 ]。ToString（）;
da = new SqlDataAdapter（ sp_SelectAdminto，connStr）;
ds = new DataSet（）;
da.Fill（ds）;
ddlGeneral.DataSource = ds.Tables [ 0 ];
ddlGeneral.DataTextField = Text;
ddlGeneral.DataBind（）;
ListItem item = new ListItem（ - - 选择 - ， 0）;
ddlGeneral.Items.Insert（ 0 ，item）;
但是当我做回发时，通过执行一些操作，下拉列表是空的。
我用Google搜索并发现我们需要确保EnableViewState =Truein页面目录以及页面的每个控件（即）启用View State = true。但仍存在问题：
步骤：
1）pageload>数据存在{因为它不是回发）
2）所选索引>回发，但数据存在并转到某些说pageB并再次来到pageA
3）再次选择索引>回发，但数据在下拉列表中为空。 />
这是问题。
下拉列表选择索引更改事件：
protected void ddlVitalSigns_SelectedIndexChanged（object sender，EventArgs e）
{
if （ddlVitalSigns.SelectedIndex < 0 ）
{
lblItemcommentsmsg.Text = ;
}
else
{
lblItemcommentsmsg .Text = ddlVitalSigns.SelectedItem.Value.ToString（）;
foreach （ListItem li in ddlVitalSigns.Items）
{
if （li.Selected == true ）
li.Attributes.Add（ style， background：red;）;
}
DropDownList ddlClicked = sender as DropDownList;
foreach （控制控件 in pnlMain.Controls）
{
如果（control 是 DropDownList）
{
DropDownList ddl = control as DropDownList;
if （ddl.ID！= ddlClicked.ID）
{
ddl.SelectedIndex = 0 ;
}
}
}
会话[ X] = lblItemcommentsmsg.Text;
}
}
< u> 下面是.aspx页面ddl控制代码：
< td class = style25 >
< asp：Label ID = lblVitalSigns runat = server 文本 = 标签 > < / asp：标签 >
< < span class =code-leadattribute> / td >
< ; td class < span class =code-keyword> = style26 >
< asp：DropDownList ID = ddlVitalSigns < span class =code-attribute> runat = server 高度 = 16px
style = margin-left：0px 宽度 = 356px < span class =code-attribute> AutoPostBack = True
onselectedindexchanged = ddlVitalSigns_SelectedIndexChanged >
< / asp：DropDownList >
< / td >
请尽快帮助我。
< blockquote> Plz参考此链接。它可能对你有帮助。
http：/ /stackoverflow.com/questions/17463937/restore-a-drop-down-selected-item-after-postback [ ^ ]
Add
ddlGeneral.DataValueField =你的桌子ID;
代码中的
..
Hi Friends,
I am loading data into dropdownlist from sql as shown below:
if (!IsPostBack)
{
string connStr = ConfigurationManager.ConnectionStrings["myConnectionString"].ConnectionString;
da =new SqlDataAdapter("sp_LabelNames", connStr);
DataSet ds = new DataSet();
da.Fill(ds);
lblAdmitto.Text = ds.Tables[0].Rows[0][1].ToString();
lblVitalSigns.Text = ds.Tables[0].Rows[1][1].ToString();
lblActivity.Text = ds.Tables[0].Rows[2][1].ToString();
lblDiet.Text = ds.Tables[0].Rows[3][1].ToString();
lblFluids.Text = ds.Tables[0].Rows[4][1].ToString();
lblNursingOrders.Text = ds.Tables[0].Rows[5][1].ToString();
lblMedications.Text = ds.Tables[0].Rows[6][1].ToString();
lblBetaBlockers.Text = ds.Tables[0].Rows[7][1].ToString();
lblAnalgesics.Text = ds.Tables[0].Rows[8][1].ToString();
da=new SqlDataAdapter("sp_SelectAdminto",connStr);
ds =new DataSet();
da.Fill(ds);
ddlGeneral.DataSource = ds.Tables[0];
ddlGeneral.DataTextField ="Text";
ddlGeneral.DataBind();
ListItem item = new ListItem("--Select--", "0");
ddlGeneral.Items.Insert(0, item);
but when I do postback,by performing some operations,drop downlist is empty.
I googled and found we need to make sure that EnableViewState="True" in page directory and also in each controls of page (ie) enabled View State=true. but still issue exists:
steps:
1)pageload> data exists {as it is not postback)
2)selected index> postback,but data exists and going to some say pageB and again coming to pageA
3)again selected index>postback,but data is empty in drop down.
this is the issue.
Drop downlist selected index changed event:
protected void ddlVitalSigns_SelectedIndexChanged(object sender, EventArgs e)
{
if (ddlVitalSigns.SelectedIndex < 0)
{
lblItemcommentsmsg.Text ="";
}
else
{
lblItemcommentsmsg.Text = ddlVitalSigns.SelectedItem.Value.ToString();
foreach (ListItem li in ddlVitalSigns.Items)
{
if (li.Selected == true)
li.Attributes.Add("style", "background:red;");
}
DropDownList ddlClicked = sender as DropDownList;
foreach (Control control in pnlMain.Controls)
{
if (control is DropDownList)
{
DropDownList ddl = control as DropDownList;
if (ddl.ID != ddlClicked.ID)
{
ddl.SelectedIndex = 0;
}
}
}
Session["X"] = lblItemcommentsmsg.Text;
}
}
Below is .aspx page ddl control code:
<td class="style25">
<asp:Label ID="lblVitalSigns" runat="server" Text="Label"></asp:Label>
</td>
<td class="style26">
<asp:DropDownList ID="ddlVitalSigns" runat="server" Height="16px"
style="margin-left: 0px" Width="356px" AutoPostBack="True"
onselectedindexchanged="ddlVitalSigns_SelectedIndexChanged">
</asp:DropDownList>
</td>
Please help me ASAP.
Plz refer this link. It may help you.
http://stackoverflow.com/questions/17463937/restore-a-drop-down-selected-item-after-postback[^]
Add
ddlGeneral.DataValueField ="Your Table ID";
in your code..
这篇关于回发后Dropdownlist为空的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
