CODEWITHSUNDEEP
c#javascriptasp.net
Victor
Victor

Reputation: 1108

Getting Error On Javascript document.getElementById('name'). RETURNS NULL

I need to execute a javascript function on ASP.NET, but I've encountered an error that I can't seem to fix...

I have alreay tried a small example that works... here it is...

Aspx file

<title>Untitled Page</title>
<script type="text/javascript" language="javascript">
    function ExecuteConfirm() {
    debugger
        var returnValue = confirm('Do you want to proceed further?');
        if (returnValue) {
            document.getElementById('hdnExecuteAfterConfirm').value = "1";
            document.getElementById('btnClickMe').click();
        }


    }
</script>


<body>
<form id="form1" runat="server">
<asp:Label runat="server" ID="lblMessage">
</asp:Label>

<div>
    <asp:Button ID="btnClickMe" runat="server" Text="Click me" 
        onclick="btnClickMe_Click" />
</div>
<asp:HiddenField runat="server" ID="hdnExecuteAfterConfirm" />
</form>
</body>

CS file

protected void btnClickMe_Click(object sender, EventArgs e)
    {
        //Do server side processing before confirmation
        if (hdnExecuteAfterConfirm.Value != "1")
        {
            lblMessage.Text = "You clicked the button";
            ClientScript.RegisterStartupScript(this.Page.GetType(), btnClickMe.ID, "ExecuteConfirm()", true);

        }
        //Do server side processing after confirmation
        else
        {
            //Proceed further with server side processing

            //Reset the value of hidden field
            hdnExecuteAfterConfirm.Value = "";
            //Notify the user that processing is complete.
            ClientScript.RegisterStartupScript(this.Page.GetType(), btnClickMe.ID, "alert('Processing is complete.')", true);
        }
    }

The goal here is to display a confirm message the first time you click the button (if), and once you click YES on the confirm message it will repeat the button function, however, it'll do something different (else)...

I'm trying to recreate this function on my project, but I am encountering an error...

Here's what I have...

Note, I'm not copying my entire project, those are just the parts that I had to change...

Site.Master

<script type="text/javascript" language="javascript">
        function ConfirmarRegistroFecha(strAdvertencia) {
            debugger
            var returnValue = strAdvertencia;

            if (returnValue) {
                try{
                document.getElementById('hdnExecuteAfterConfirm').value = "1";  
                document.getElementById('btnGuardarEvento').click();
                }

                catch(error){
                    alert(error);
                }
            }
        }
    </script>

Agenda.aspx (I know that is to much, however, I'm copying it all, since maybe the error is around here somewhere. The point is that at least, inside is a HiddenField, and a button) 

<asp:View ID="ViewOperacionesAgenda2" runat="server">
            <asp:HiddenField runat="server" ID="hdnExecuteAfterConfirm" />
            <br />

            <asp:Panel ID="pnlRegistrarEvento" runat="server" DefaultButton="btnGuardarEvento">
                <table>
                    <tr>
                        <td align="left">
                            Seleccione Vendedor:
                            <br />

                            <asp:DropDownList ID="dpdLstVendedoresAgenda" runat="server" Width="150px">
                            </asp:DropDownList>
                        </td>

                        <td align="left" rowspan="3">
                            Descripcion:
                            <br />

                            <asp:TextBox ID="tbxAlAgendaDescripcion" runat="server" Height="150px" TextMode="MultiLine" ValidationGroup="gpAgendaAlta" Width="150px">
                            </asp:TextBox>
                        </td>

                        <td align="left" rowspan="3">
                            Fecha:
                            <br />

                            <asp:Calendar ID="Calendar1" runat="server" BackColor="White" 
                                BorderColor="#3366CC" BorderWidth="1px" CellPadding="1" 
                                DayNameFormat="Shortest" Font-Names="Verdana" Font-Size="7pt" 
                                ForeColor="#003399" Height="150px" Width="150px">
                                <DayHeaderStyle BackColor="#99CCCC" ForeColor="#336666" Height="1px" />
                                <NextPrevStyle Font-Size="8pt" ForeColor="#CCCCFF" />
                                <OtherMonthDayStyle ForeColor="#999999" />
                                <SelectedDayStyle BackColor="#009999" Font-Bold="True" ForeColor="#CCFF99" />
                                <SelectorStyle BackColor="#99CCCC" ForeColor="#336666" />
                                <TitleStyle BackColor="#003399" BorderColor="#3366CC" BorderWidth="1px" Font-Bold="True" Font-Size="10pt" ForeColor="#CCCCFF" Height="25px" />
                                <TodayDayStyle BackColor="#99CCCC" ForeColor="White" />
                                <WeekendDayStyle BackColor="#CCCCFF" />
                            </asp:Calendar>
                        </td>

                        <td rowspan="3">
                            <table>
                                <tr>
                                    <td align="left">
                                        Hora Inicio:
                                        <br />

                                        <asp:TextBox ID="tbxAlAgendaHoraInicio" runat="server" ValidationGroup="gpAgendaAlta" Width="130px">0:00 am</asp:TextBox>

                                        <br />

                                        <asp:RegularExpressionValidator ID="RegularExpressionValidator3" runat="server" 
                                            ControlToValidate="tbxAlAgendaHoraInicio" 
                                            ErrorMessage="Hora Invalida: use 00:00 pm" 
                                            ValidationExpression="^((0?[1-9]|1[012])(:[0-5]\d)((\ )?[ap](.)?m(.)?))" 
                                            ValidationGroup="vgpRegistrarEvento" Font-Bold="True" ForeColor="Red">
                                        </asp:RegularExpressionValidator>

                                        <br />

                                        <asp:RequiredFieldValidator ID="RequiredFieldValidator8" runat="server" 
                                            ControlToValidate="tbxAlAgendaHoraInicio" ErrorMessage="Campo Requerido" 
                                            ValidationGroup="vgpRegistrarEvento" Font-Bold="True" ForeColor="Red">
                                        </asp:RequiredFieldValidator>
                                    </td>
                                </tr>

                                <tr>
                                    <td align="left">
                                        Hora Final:
                                        <br/>

                                        <asp:TextBox ID="tbxAlAgendaHoraFinal" runat="server" ValidationGroup="gpAgendaAlta" Width="130px">0:00 am</asp:TextBox>

                                        <br />

                                        <asp:RegularExpressionValidator ID="RegularExpressionValidator4" runat="server" 
                                            ControlToValidate="tbxAlAgendaHoraFinal" 
                                            ErrorMessage="Hora Invalida: use 00:00 pm" 
                                            ValidationExpression="^((0?[1-9]|1[012])(:[0-5]\d)((\ )?[ap](.)?m(.)?))" 
                                            ValidationGroup="vgpRegistrarEvento" Font-Bold="True" ForeColor="Red">
                                        </asp:RegularExpressionValidator>

                                        <br />

                                        <asp:RequiredFieldValidator ID="RequiredFieldValidator9" runat="server" 
                                            ControlToValidate="tbxAlAgendaHoraFinal" ErrorMessage="Campo Requerido" 
                                            ValidationGroup="vgpRegistrarEvento" Font-Bold="True" ForeColor="Red">
                                        </asp:RequiredFieldValidator>
                                    </td>
                                </tr>
                            </table>
                        </td>
                    </tr>

                    <tr>
                        <td align="left">
                            Seleccione Cliente:
                            <br />

                            <asp:DropDownList ID="dpdLstClientesAgenda" runat="server" AutoPostBack="True" onselectedindexchanged="dpdLstClientesAgenda_SelectedIndexChanged" Width="150px">
                            </asp:DropDownList>
                        </td>
                    </tr>

                    <tr>
                        <td align="left">
                            Tipo:
                            <br />

                            <asp:DropDownList ID="dpdLstAlAgendaTipo" runat="server" Width="150px">
                                <asp:ListItem>Reunion</asp:ListItem>
                                <asp:ListItem>Entrevista</asp:ListItem>
                                <asp:ListItem>Venta</asp:ListItem>
                                <asp:ListItem>Soporte</asp:ListItem>
                                <asp:ListItem>Instalacion</asp:ListItem>
                            </asp:DropDownList>
                        </td>
                    </tr>
                </table>

                <br />
                <asp:Button ID="btnCancelarEvento" runat="server" CausesValidation="False" onclick="btnCancelarEvento_Click" Text="Cancelar" Width="90px" />
                &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
                <asp:Button ID="btnGuardarEvento" runat="server" onclick="btnGuardarEvento_Click" Text="Guardar" ValidationGroup="vgpRegistrarEvento" Width="90px" />
            </asp:Panel>

Agenda.aspx.cs

protected void btnGuardarEvento_Click(object sender, EventArgs e)
    {

            if (hdnExecuteAfterConfirm.Value != "1")
            {
                strAdvertencia = "MESSAGE I WANT TO DISPLAY";
                ClientScript.RegisterStartupScript(this.Page.GetType(), btnGuardarEvento.ID, "ConfirmarRegistroFecha(" + strAdvertencia + ")", true);

            }

            else
            {
                hdnExecuteAfterConfirm.Value = "";
                //Rest of process
            }
    }

Using a debugger with Firebug, I can clearly see that on Site.Master, when it reaches..

document.getElementById('hdnExecuteAfterConfirm').value = "1";

It displays the following exception:

TypeError: document.getElementById("hdnExecuteAfterConfirm") is null

I have already tried to copy the javascript on Agenda.aspx instead of Site.Master... and it still doesn't work...

Does anyone know what the mistake here is... I'm new to javascript, so I'm still believing that is a syntax error...

Thanks in advance and I hope you can help me

Upvotes: 0

Views: 3132

Answers (2)

IUnknown
IUnknown

Reputation: 22448

Use this script:

document.getElementById('<%= hdnExecuteAfterConfirm.ClientID %>').value = "1";  
document.getElementById('<%= btnGuardarEvento.ClientID %>').click();

As you use master page, client id of hdnExecuteAfterConfirm not the same as server id.

Upvotes: 1

competent_tech
competent_tech

Reputation: 44931

The problem is that because the control is embedded in a container control, its ID is modified in the client.

I am not sure what the equivalent is in Firefox, but in internet explorer (v9, at least), you can press F12 to open the developer tools and navigate through the DOM structure to find out what the actual name is.

There are various ways to address this, including hard-coding the full ID, which is a fragile solution, or updating web.config to use the IDs as they are provided, which could lead to conflicting ids.

The way that we solve this problem is to create a javascript variable in code behind using the client id. That way, if the control moves to a different container control or is renamed you will not have to adjust your code to account for this.

To do this, we use Page.ClientScript.PageClient.RegisterStartupScript. For example:

this.ClientScript.RegisterStartupScript(this.GetType(), "LocalVars", "var m_hdnExecuteAfterConfirmId = '" + hdnExecuteAfterConfirm.ClientID + "';" + Environment.NewLine, true);

Then change the javascript to be:

document.getElementById('m_hdnExecuteAfterConfirmId').value = "1";

Upvotes: 1

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