ASP.NET TextBox - is it possible to initialize text attribute with in line code <% %>

Question

I need to initialize the text attribute of the text box element with a property from some where else when actually I can simply do this from code but it will be much m

Answer 1

OK so the basic problem here is that if you use an inline expression you can NOT use it to set a property of a server-side control outside of a binding context (using a binding expression). I have inferred that this is probably because of the timing of the evaluation of these inline expressions. You can, however, render client-side markup in this way. If you want to keep the functionality purely in your aspx file, this is the way to do it.

Edit: Based on input from Justin Keyes, it appears it IS possible to use a binding expression to set the property. You need to manually invoke Page.DataBind() to trigger the textbox to evaluate the expression (see answer below).

For instance this:

<asp:Label ID="lbl" runat="server" Text="<%= Now.ToShortDateString() %>"  />

Will produce this output:

<%= Now.ToShortDateString() %>

On the other hand this:

<%= "<span>" & Now.ToShortDateString() & "</span>"%>

Will produce this output:

7/27/2011

The "normal" way to solve this problem is just to set the Label.Text properties in a Page.Load event handler or another appropriate event handler depending on your needs, as below. This is the way I believe most people would prefer to do it, and is most easily understandable in my opinion.

Markup:

<asp:Label ID="lbl" runat="server" />

Code:

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    lbl.Text = Now.ToShortDateString()
End Sub

Answer 2

You can set the text on a page in a similar way.

<asp:TextBox id="TextBox1" runat="server" Text='<%#GetValue('Title)%>' />

But in order for this to work, you will need to DataBind the control on Page_Load. For multiple TextBox controls you could just loop through each and databind them so that you do not have to hard code the databinding of each.

I am not sure what your ContextItem is though, so you would have to modify my code.

Answer 3

Option 1: don't use server controls

If you aren't accessing the value on the server, just use plain HTML instead of an ASP.NET server control:

<input ID="Textbox1" Type="Text"  
    Value='<%= new ContextItem("title").Value %>' />

Option 2: use Page.DataBind()

If you change your code to use <%# instead of <%= (as below) and call Page.DataBind(), it will work (I've tested it). Change your markup to this:

<asp:TextBox runat="server" Text="<%# new ContextItem("title").Value %>" />

And in your logic, call Page.DataBind() in the Load event like this:

protected void Page_Load(object sender, EventArgs e) {
    Page.DataBind(); 
}

Even though the TextBox is not contained in a typical "data bound" control such as a Repeater or GridView, calling DataBind() on a control will force it to evaluate <%# ... %> statements.

The Moof's comment (below) is correct. This post also mentions Page.DataBind().

Answer 4

90% of the time when I try this I have to use single quotes ('') instead of double quotes ("") around the <%%>. Give that a try before you spend too much time on anything else.

Answer 5

The short answer is NO, you can only use this kind of code with databindings, that means inside a GridView for example. But you can use this in the head section.

I use it to prefix my urls sometimes with something predefined. Example

  <script src="<%=Utils.GetGeneralPrefix()%>/Scripts/jquery-1.4.1.min.js" type="text/javascript"></script>

In that case it works.

Hope it helps.