CODEWITHSUNDEEP
c#asp.net
Antonio Mailtraq
Antonio Mailtraq

Reputation: 1407

Can't getting the Data Value Field setting on Drop Down List in c#

I can't getting the DataValueField setting on Drop Down List on Edit Item Template in c# .

I need update the row of GridView opening new aspx page in window popup where get the ID selected from DB MySQL.

I have this error :

Object reference not set to an instance of an object

in this code-behind line : 

string taskID = ddlID.DataValueField;

Can you help me ?

My code below, thank you in advance for any help, really appreciated.

.cs

protected void ddlID_SelectedIndexChanged(object sender, EventArgs e)
{
    DropDownList ddlID = new DropDownList();
    ddlID = (DropDownList)FindControl("ddlID");         
    string taskID = ddlID.DataValueField;

    string queryString = "newPage.aspx?membershipId=" + taskID.ToString().ToUpper();
    string newWin = "var Mleft = (screen.width/2)-(1200/2);
                     var Mtop = (screen.height/2)-(700/2);
                     window.open('" + queryString + "','_blank','height=600,width=900,
                     status=yes,
                     toolbar=no,scrollbars=yes,menubar=no,
                     location=no,top=\'+Mtop+\', left=\'+Mleft+\';');";

    ClientScript.RegisterStartupScript(this.GetType(), "pop", newWin, true);
}

.aspx

<asp:TemplateField>
    <EditItemTemplate>
        <asp:DropDownList ID="ddlID" runat="server" 
            AutoPostBack="true" OnSelectedIndexChanged="ddlID_SelectedIndexChanged"
            BackColor="Yellow" DataValueField='<%# Eval("ID")%>'>
            <asp:ListItem Text="--------------" Value=""></asp:ListItem>
            <asp:ListItem Text="Update Name" Value="1"></asp:ListItem>
        </asp:DropDownList>
    </EditItemTemplate>
</asp:TemplateField>

#Edit01

<asp:TemplateField>
    <EditItemTemplate>
        <asp:DropDownList ID="ddlID" runat="server" 
            AutoPostBack="true" OnSelectedIndexChanged="ddlID_SelectedIndexChanged"
            BackColor="Yellow" DataValueField="ID">
            <asp:ListItem Text="--------------" Value=""></asp:ListItem>
            <asp:ListItem Text="Update Name" Value="1"></asp:ListItem>
        </asp:DropDownList>
    </EditItemTemplate>
</asp:TemplateField>

protected void ddlID_SelectedIndexChanged(object sender, EventArgs e)
{
    DropDownList ddlID = new DropDownList();      
    string taskID = ddlID.SelectedValue;

    string queryString = "newPage.aspx?membershipId=" + taskID.ToString().ToUpper();
    string newWin = "var Mleft = (screen.width/2)-(1200/2);
                     var Mtop = (screen.height/2)-(700/2);
                     window.open('" + queryString + "','_blank','height=600,width=900,
                     status=yes,
                     toolbar=no,scrollbars=yes,menubar=no,
                     location=no,top=\'+Mtop+\', left=\'+Mleft+\';');";

    ClientScript.RegisterStartupScript(this.GetType(), "pop", newWin, true);
}

Upvotes: 0

Views: 270

Answers (1)

user1773603
user1773603

Reputation:

Your DropDownList is in EditTemplate of GridView so you have to get it from sender:

DropDownList ddlID = sender as DropDownList;
string taskID = ddlID.DataValueField;

Upvotes: 1

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