|By Michael Earls||
|May 20, 2005 11:00 AM EDT||
One of the most basic ways to navigate within an application is by use of a tab control. Tabs are easy to use and users are very familiar with them. There have been many implementations of tab controls for Web applications, but they had often required advanced client-side script that was only supported in a few browsers, or they required extensive and confusing server-side include files. ASP.NET 2.0 provides a few things that make this easier to do with no dependency on functional code. In this article I'll show you how you can use the new features of ASP.NET 2.0 to easily create a tab control for your Web application.
To get started, create a new Web site (use your favorite language) on your computer and call it TabDemo. ASP.NET 2.0 introduces a new set of data providers and controls based on the notion of a site map. The site map is the central data store for site navigation data. Let's start by defining a simple site map that we can use for our site. Add a new sitemap to the site (use the default name of Web.sitemap). Listing 1 shows a simple sitemap that will demonstrate the tabs nicely.
Now that we have our sitemap, we can continue with the actual user interface. To get the most benefit from the tab control, we'll use a master page to keep everything together. Add a new master page to your Web site and call it MasterPage.master (see Figure 1).
In order to make our tabs seem as though they're physically connected to our content, we'll need to create a master HTML table to contain the tabs. Delete the code between the <form> and </form> tags in the MasterPage.master file and replace it with the HTML in Listing 2.
That will give us the main table that will hold all of our content (including our tab control). Now we need to define the table that actually holds our tabs and the tab "panels." Let's take a look at Listing 3. It shows the HTML that we should put into the TD with the ID of ContentContainer.
Notice the use of the TD with the CSS class TabMenuSpacer. This cell forces the empty area behind the tabs to take up all of the excess space to the right of the menu. We need to add the SiteMapDataSource to our page so that the menu will be bound to our site map. This is easy to do. Simply add the following code just below the main table:
<asp:SiteMapDataSource ID="TabMenuSitemap" runat="server" ShowStartingNode="false" />
This adds a new SiteMapData-Source to the page. Since we used the default name of Web.sitemap for our site map, ASP.NET will automatically use it as the main site map for the site, so we don't have to do anything else. If you add another site map to the site, you'll need to define a new site map provider to the web.config file that points to your new site map, and then set the SiteMapProvider property of the SiteMapDataSource to your new site map provider. It's also important to point out that we set the ShowStartingNode property to false. We did this because we have a flat site map and we don't want to show the top-most parent node for our menu (since the site map is defined in XML, we had to have a root node, even though we'll never use it).
Let's go ahead and take a look at what we have so far. Delete the Default.aspx page that Visual Studio added to your site and replace it with a new Default.aspx page. This time, when you add the page, check the box labeled "Select master page." Then select MasterPage.master as the master page. Build and run the Web application. At this point, you'll see a very simple page that doesn't look like a whole lot (see Figure 2).
The reason our page looks so odd is because we haven't yet defined the Cascading Style Sheet for the page. We need to add the CSS that will actually render what we have as a Tab menu. Add a new style sheet to your project and name it Stylesheet.css. Then, add the following to the <head> of MasterPage.master:
<link href="StyleSheet.css" rel="stylesheet" type="text/css" />
This will link in the new style sheet. Let's take a look at the individual styles that make up our tab control. We'll start with the CSS class named TabMenuContainer. This style is applied to the entire tab menu. We just need to make sure that we have a top border so that our menu has a lid on it.
border-top: solid 1px black;
The next style that we're concerned with is the TabMenuItem. This is the style that is applied to all of our tabs in their unselected state.
border: solid 1px black;
padding: 3px 3px 3px 3px;
Notice that we've defined a border with a single pixel black line. We then set the left border to be nothing. This is actually an intentional move that prevents the tabs from looking bad against the border of the main container.
The secret to this whole method is in the next style. This is the style that is applied to the selected menu item:
border-right: solid 1px black;
padding: 5px 3px 5px 3px;
We set the bottom border to "none" and the background color to white. This will allow the tab to look as if it is attached to the content cell. We also set the top border to "none" to give the selected tab just a little more height than the other tabs.
Since we want our tab panels (the cell that contains the Content-PlaceHolder control) to be the same height from page to page, we should set them to be a specific height. Once again, we use CSS to define a style to do this. In the HTML for the master page we added a table cell to the right of the content container and set its CSS class to SiteContentSpacer. Let's set the style for that to be a specific height.
Not only did we set the height of the content to 200 pixels (a very small number just for demonstration purposes), but we also made the cell invisible. Listing 4 shows the entire style sheet that contains all of the styles used to make our tab control demo.
Once we've added the remaining styles to the style sheet, we can take a look at the final product. Figure 3 shows a screenshot of the resulting page with our tab control and all of the styles defined.
The tab control is a very useful user interface element that is common to many applications. With the introduction of master pages, SiteMapDataSource, and the menu control in ASP.NET 2.0, creating tabs in Web applications is easy. Best of all, once you have the master page set up for tabs, all you have to do to use them is to set the master page on your new Web forms and edit the page as you normally would. Also, since the solution relies on CSS, these tabs work in the latest Web browsers without any client-side coding.
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