Alrighty to make this quick:
I want to set start and end dates for a calendar extender dynamically on-change or on page load
the values are put into hidden fields on the .ascx and populated during page load in an if not postback
one set of calendar extenders is in the item template field of a grid view call this set A
the others are in a normal html table - set b
set a and set b have flags StartDate="<%# hfStart.value%>" EndDate="<%# hfEnd.value%>"
set a in the item template of a grid view column works like a charm
set b in the HTML table doesn't appear to work at all
What gives?
So far I have tried other server tags with the same code inside but I am obviously missing the salient detail. Why does one work and not the other?
UPDATE: Tried
CDate(hfstart.value).ToString with <%: and <%= tags
<%= hfstart.value %>
Unless I misunderstand, <%= will fire at the very END of the asp.net life cycle stopping it from being useful in this context.
As it turns out you DO need to use <%# %> within asp tags as others like <% %> and <%= %> execute at the end of the ASP.NET life cycle and get spit out the buffer to god knows where. When using <%# %> however, the asp control needs to be DataBound(); at the appropriate time.
This happens automatically for controls modeled in the <item template> tags in the gridview because everything within the gridview is bound on its gridview.DataBound() command.
Could it be because you're using the <%# %> tags which are for data binding? This would explain why they work in the GridView, because it supports data binding.
However in a basic HTML table you should use <% %> tags instead, or <%= %> to call a method.
For full details of the tag types, try this reference.
Related
<%= Session.Item("user_fullname")%>
this supposed to display session value right?
but mine is displaying code itself....
Note: I have included aspx page in another aspx, like:
<% Response.WriteFile("../etc/header1.aspx") %>
the displaing session code is inside header1.aspx
anyone knows how to display session value?
Session items would be stored as an Object. You need to cast to the correct type:
<%= (string)Session.Item("user_fullname") %>
When using Response.WriteFile("../etc/header1.aspx"), the usual Page Life cycle will NOT be executed for the mentioned header1.aspx page.
Since there will be no asp.net page life cycle processing , the inline code
<% %> won't be executed at all and therefore all such statements will be displayed as it is.
Response.WriteFile() is used to write just the Contents of a file, which can contain HTML , Controls, directly to the output stream.
I have a master page and I want to add a placeholder twice - so that I have the same placeholder in two places of the master page so that actual page just specifies content of the placeholder once and that content is rendered twice on the resulting page. The goal is to avoid duplication of content.
If I try to add a placeholder with the same id twice it won't compile - ASP.NET doesn't like that.
How do I achieve that? What are other options?
Place your placeholder in an Action, and call it where necessary.
<%
Action myPlaceholder = () =>
{%>
<asp:ContentPlaceHolder ID="X" runat="server" />
<%}
%>
...then call wherever necessary in code.
<% if (conditionMet)
myPlaceholder(); >%
The error occurs at compile time: a complaint will be made if placeholders with the same ID exist. This approach clears that hurdle, and gives a lot of flexibility.
I think you are probably looking for a user control:
http://msdn.microsoft.com/en-us/library/y6wb1a0e.aspx
With User Controls you can add your markup and code behind into an .ascx and then call this in your Master Page/Web Form multiple times, therefore avoiding duplicate code.
I haven't tried this, but you could lookup the contents of the placeholder you are interested in duplicating, and copying it in your code behind. This post: http://programcsharp.com/blog/archive/2009/01/22/test-if-masterpage-contentplaceholder-has-content-or-is-empty.aspx
has some good insight into manipulating master pages.
What are the differences in these tags?
<%
<%#
<%=
<%$
More importantly, how do I display a page property using declarative syntax in an ASP.NET control? I'm trying to do this in an ASP.NET control. The task is to set the text of a label but I do not want to do this pro grammatically in the event I want to change the output control. I get an error about server side controls can't contain this syntax. I'm not sure that I need a databound control for what I want to do but that is another option.
Partial answer coming up.
Update
There is a new tag I've seen in ASP.NET 4.5? site
<%:
Partial answer
quoted from Mike Banavige
<% %> An embedded code block is
server code that executes during the
page's render phase. The code in the
block can execute programming
statements and call functions in the
current page class.
http://msdn2.microsoft.com/en-gb/library/ms178135(vs.80).aspx
<%= %> most useful for displaying
single pieces of information.
http://msdn2.microsoft.com/en-us/library/6dwsdcf5(VS.71).aspx
<%# %> Data Binding Expression Syntax.
http://msdn2.microsoft.com/en-us/library/bda9bbfx.aspx
<%$ %> ASP.NET Expression.
http://msdn2.microsoft.com/en-us/library/d5bd1tad.aspx
<%# %> Directive Syntax.
http://msdn2.microsoft.com/en-us/library/xz702w3e(VS.80).aspx
<%-- --%> Server-Side Comments.
http://msdn2.microsoft.com/en-US/library/4acf8afk.aspx
Update:
Okay this appears to work
<asp:Label ID="MyLabel" runat="server" Text='<%# MyProperty%>'></asp:Label>
If I use the eval syntax then I get an error about databound control or I use the <% then I get a server side controls error. Any more color appreciated.. not sure I really understand what is going on.
Perhaps it has something to do with the render phase.
Few more observations:
I can use <%= without databinding and get the property value but can not use it in a server side control without getting error.
If I use <%# in server side control but I'm required to do a Page.Databind.
Interestingly, I can use either <%= or <%# when I want to render text that is not inside a control. Although the latter requires databinding.
The new <%: syntax is explained, also called code expression syntax
With ASP.NET 4 we are introducing a new code expression syntax (<%:
%>) that renders output like <%= %> blocks do – but which also
automatically HTML encodes it before doing so.
http://weblogs.asp.net/scottgu/new-lt-gt-syntax-for-html-encoding-output-in-asp-net-4-and-asp-net-mvc-2
No, server-side controls can't. For example, I have a string property named SkinPath that give me the full App_Themes path to the current theme. I use it in the following way:
<img src='<%= SkinPath %>/Images/myImage.png' />
However, the following doesn't work:
<asp:Image ID='image' runat='server' ImageUrl='<%= SkinPath %>/Images/myImage.png' />
Instead, it renders the src literally in the result <img>.
Can someone explain to me the rules around what can and cannot be evaluated/inserted into markup using the <%# %> and <%= %> tags in asp.net?
When I first discovered I could inject code-behind variables into mark-up using <%= I thought 'great'. Then I discovered that if such tags are present you can then not add to the controls collection of the page (that's a whole different question!). But <%# tags are ok.
Is there a way I can inject a code-behind variable or function evaluation into the page using <%# ? Thanks.
<%%> are code blocks. You can put any server side code in them. This is a shortcut for <script runat="server"></script>.
<%=%> is for outputting strings. This is a shortcut for <script runat="server">Response.Write()</script>.
See here for more detail about <%%> and <%=%>.
<%#%> are used for data binding expressions.
See the index page for asp.net Page syntax.
The <%# inline tag is used for data binding, so if you want to use a code-behind variable inside it, you will have to bind the page or control the variable resides in:
Page.DataBind();
You can include this statement in the Page_Load or Page_PreRender event.
See this article for more information about the use of inline tags in ASP.Net, and this article for more about server-side databinding.
I want to learn advanced and basic things about ASP.NET inline scripting like
<img src="<%= Page.ResolveUrl("~")%>Images/Logo.gif"/>
or
<asp:Label ID="lblDesc" runat="server" Text='<%#DataBinder.Eval(Container.DataItem,"Description")%>'></asp:Label>
And so on...
And, what's the difference between <% %> and <%# %> and such stuff?
Where can I find from basic to advanced implementation of those usages?
Check out this article for the specifics of the different inline tag options.
From the article:
<% ... %> -- The most basic inline tag,
basically runs normal code:
<%= ... %> -- Used for small chunks of
information, usually from objects and
single pieces of information
like a single string or int variable:
<%# ... %> -- Used for Binding Expressions;
such as Eval and Bind, most often
found in data controls like GridView,
Repeater, etc.:
<%$ ... %> -- Used for expressions, not code;
often seen with DataSources:
<%# ... %> -- This is for directive syntax;
basically the stuff you see at the top
your your aspx pages like control
registration and page declaration:
<%-- ... %> -- This is a server side comment,
stuff you don't want anyone without
code access to see:
In general, <%#..%> is used for preprocessing a template, such as when databinding, whereby the names of properties of the objects are not known at compile-time. If, for example, you have an ASP.NET Repeater object, and you databind a list of objects to it, this notation is used to pre-populate values that could not be set at any point except during the databind lifecycle.
The other notations, <%..%> and <%=..%> are more standard and you'll see these far more often than the other syntax previously discussed, especially if you use something like ASP.NET MVC instead of ASP.NET Web Forms. The syntax <%..%> executes arbitrary script inline, and nothing more, but allows you to write entire blocks of .NET code such as if statements, while loops, for loops, etc. The syntax <%=..%> is an evaluate-and-write syntax, and is rough equivalent of <% Response.Write([..].ToString()) %>. I.e., <%= myVal %> is the same as <% Response.Write(myVal.ToString()) %>
These syntaxes are basic ASP.NET knowledge.