ASP/C#, adding text to textbox problem

For some reason, I cannot get text into any textbox or label!

I'm using Master pages and the code is going in the code behind view. I have created the textbox:

<asp:Textbox ID="whatever" runat="Server">

When I want to add some text I simply add the code in the code behind view like:

whatever.Text = "myText";

I get an error that says:

"System.NullReferenceException:Object reference not set to an instance of an object"

hightlighting this line in red: whatever.Text = "myText";

I guess its because it saying it not there but how can it let me reference the textbox?

Apologies if the answer is on the site, I have searched but found nothing. :)

This is my code in Basket.asp - I've changed the textbox to a label, it's called bskItems

<asp:Content ID="Content3" ContentPlaceHolderID="ContentPlaceHolder3" runat="server"> <asp:Label ID="bskItems" runat="server"></asp:Label> <div id="cart"> <asp:Button ID="btnCheckout" CssClass="BasketBtnAdd" runat="server" CommandName="checkout" Text="Checkout" /> </div> </asp:Content>

This is my masterpage, where I'm using a loginView. ContentPlaceHolder3 is where the textbox should be. I only want it to display a count of items.

<asp:LoginView ID="loginView" runat="server">
    <LoggedInTemplate>
    <asp:LoginName ID="loginName" runat="server" FormatString="Hi, {0}!"/>
    (<asp:LoginStatus ID="loginStatus" runat="server" />)
    <% 
    if (HttpContext.Current.User.IsInRole("Admin"))
    { 
    %>
    <asp:SiteMapDataSource ID="admin" SiteMapProvider="admin" runat="server" ShowStartingNode="false" />
    <asp:Menu ID="Menu" runat="server" DataSourceID="admin">
        <StaticItemTemplate>
            <%# Eval("Text") %>
        </StaticItemTemplate>        
    </asp:Menu>
    <%
    }
    if (HttpContext.Current.User.IsInRole("Users"))
    { 
    %>
    <asp:SiteMapDataSource ID="user" runat="server" SiteMapProvider="user" ShowStartingNode="false" />
    <asp:Menu开发者_如何转开发 ID="Menu1" runat="server" DataSourceID="user">
        <StaticItemTemplate>
            <%# Eval("Text") %>
        </StaticItemTemplate>        
    </asp:Menu>

    <%
    }
    %>
    <asp:ContentPlaceHolder ID="ContentPlaceHolder2" runat="server"></asp:ContentPlaceHolder>
    <asp:ContentPlaceHolder ID="ContentPlaceHolder3" runat="server"></asp:ContentPlaceHolder>
    </LoggedInTemplate>
    <AnonymousTemplate>
        <asp:LoginStatus ID="loginStatus" runat="server" />
        <asp:SiteMapDataSource ID="anon" runat="server" SiteMapProvider="anon" ShowStartingNode="false" />
        <asp:Menu ID="Menu2" runat="server" DataSourceID="anon">
        <StaticItemTemplate>
            <%# Eval("Text") %>
        </StaticItemTemplate>        
    </asp:Menu>
    </AnonymousTemplate>

</asp:LoginView>

In addition to the other answers, if you're setting the value in Page.OnLoad, remember that the Master page controls haven't been created yet.

Here's a complete layout of the order in which things happen: Complete Lifecycle of an ASP Page

What I usualy do is to make the control visible as a property of my MasterPage.

On the master page (AMasterPage.master):

public TextBox MyTextBox { get { return this.theTextBoxControl; } }

So then, on a child using this masterPage (APage.aspx) :

((AMasterPage)this.Master).MyTextBox.Text = "myText";

When accessing Master Page members from Code-Behind in a Content Place Holder file, I believe you need to do:

this.Master.whatever.Text = "new Text";

Check this link on ASP.NET Master Pages, from MSDN.

You need to do get a reference to the textbox on the master page, then set the text

TextBox tb = Master.Page.FindControl("whatever") as TextBox;

if(tb != null)
{
    tb.Text = "myText";

}

Set the ClientIDMode on the textbox to "Static". When the page is rendered it assigns the TextBox's ID to something random. By changing the ClientIDMode to "Static", you should be able to reference the ID because the ID will stay the same and not change.

Or try adding an OnDataBinding event handler and casting the "sender" as a (TextBox). For example:

protected void TextBox_OnDataBinding(object sender, EventArgs e)
{
     var txt = (TextBox)sender;
     txt.Text = "Something";
}

This should talk to the control directly.