asp.net+css+jQuery - how does it all work together?

Question

Hi,

I would like to understand how can I use jQuery to work with asp.net and css. When I'm writing asp.net code and for example I'm adding to a page DropDownList, I can't see it in the source when I'm opening source of a page in web browser. Instead of dropdownlist I can see select tag. When does the "magic" is done to change asp.net tag to select? What is more I can't see my CSS classes names added to asp.net tags. There are some kind of differen CSS class names. But when I'm opening developer tools in IE, I can see CSS class names, which are same as in my definition. And the last thing. What names of a tags sould I use in jQuery to traverse page which was developed in asp.net. Shoud I use a tags which I see in the source code of a page in a browser or can I ask jQuery about asp.net tags? What about CSS classes? Why I can't see them in a source of a page in a browser? Can use my names of a CCS classes under jQuery queries? Please, can anybody explain me how does this three technologies work together?

Answer 1

ASP.NET: High-level web development framework. When you create a web form in .NET, the framework will work together with the IIS handlers and create (hopefully) valid HTML that will work with your server-side code during postbacks.

JQUERY: This will allow you to perform client-side scripting such as calculation, validation, and most notably AJAX, etc. This is basically just a wrapper for a simpler and easier-to-read version of javascript.

CSS: Takes the HTML and makes it pretty.

All three technologies work very well together if you know what you're doing.

I'm not sure if that's what you're looking for, but it sounds like you might want to invest in some beginner's literature.

Answer 2

The "magic" happens in the render event of the asp.net page lifecycle. Asp.net server controls all render as standard html element(s). The most important difference is that you can access them and their values on the server side. WebControls also have a CssClass property that when rendered becomes the class attribute of the HTML element.

The id can be a bit tricky when working with jQuery and CSS. This is because depending on the controls hierarchy they may have a clientID such as ctl100_containerID_myControl instead of myControl. To overcome this in jQuery when you reference a control you can refrence it by its ClientID like so:

$('#<%=myControlID.ClientID%>')

This is serverside that will write the client side ID of the control after it is rendered.

Answer 3

When does the "magic" is done to change asp.net tag to select?

Most of "magic" you're wondering about is done by ASP.NET controls, which are designed to generate the markup that is sent to the browser.

When a request is received, the application iterates over each control, calling its Render method (inherited from the Control class), which allows each control to generate the markup they represent.

Following your example, the DropDownList control generates a <select> tag. As a ListControl, it uses the ListItem controls to create the <option> tags within.

Another would be the GridView, which generates a <table> using GridViewRow controls for <tr> and various HTML Controls, such as TableCell for <td> and <th>, to create the rest of the markup.

Shoud I use a tags which I see in the source code of a page in a browser or can I ask jQuery about asp.net tags?

No, jQuery/JavaScript have no knowledge of server-side control names, only the markup they generate. So, rather than searching for $('DropDownList'), you'd search for $('select').

What is more I can't see my CSS classes names added to asp.net tags. There are some kind of differen CSS class names.

By "CSS Names," do you mean IDs? I'm sorry to ask, but CssClass attributes shouldn't change in value from server-side to client-side, just in name -- CssClass to just class.

IDs, on the other hand, are prefixed to ensure their uniqueness throughout the page, including a prefix of the MasterPage and ContentPlaceHolder names, if they're used. For this reason, I'd steer away from trying to use IDs to apply CSS to server-side controls, using classes instead.

Now, the end of the ID should remain as the ID you gave in server-side, so you should still be able to find the element in jQuery using the Attribute Ends With Selector [name$='value']:

# ASP
<asp:DropDownList ID="AnyGivenDropDown" runat="server" />

# HTML (generated)
<select id="ctl00_PageContents_AnyGivenDropDown"></select>

# JavaScript
$('select[id$="_AnyGivenDropDown"]');

Otherwise, I'd stick to classes to find the controls you're looking for:

# ASP
<asp:DropDownList ID="AnyGivenDropDown" CssClass="anygiven" runat="server" />

# HTML (generated)
<select id="ctl00_PageContents_AnyGivenDropDown" class="anygiven"></select>

# JavaScript
$('select.anygiven');

# CSS
.anygiven { }