Part III: Enhancing the Interface and User Experience in Visual Studio .NET

Create QR Code in Visual Studio .NET Part III: Enhancing the Interface and User Experience

You can use the ASPNET Panel control to generate <div> tags for layout Use class-based style rules the ones that start with a dot () and set the Panel control s CssClass property to the style s name

As Web pages become busier, performance starts to drag If a page seems slow on your workstation, expect it to get worse when posted to the Web server While you can t always control the speed of the Internet connection or the Web server s horsepower, you can certainly do your part to cut page load times and improve the overall throughput This section looks at two techniques: reducing ViewState and employing caching

ASPNET server controls make programming easier, but they make Web pages fatter If you re not careful, ASPNET can bloat a relatively small page by overdoing a hidden feature called ViewState Look at the output of any ASPNET page and you find ViewState It resembles the following (much abbreviated) markup when you look at the HTML in the browser (View Source): <input type= hidden name= __VIEWSTATE id= __VIEWSTATE value= /wEPDwUL80sXAJunhsp3aKX6m/d /> ViewState is how ASPNET tracks the current settings for all its controls You see an ordinary, hidden <input> tag with a string of nonsense characters as the value attribute That value is the Web server s personal aide-memoire as to what the page was like when it sent the HTML to the browser That blob of overhead travels back and forth (it roundtrips in geekspeak) for no good reason If there s nothing in the server-side code that can change the text in a Label control or GridView, why track the ViewState You can turn off ViewState for an individual control (for instance, a TextBox) by setting its EnableViewState property to False If you re confident that none of the controls on a page will change, you can turn off ViewState for the entire page In Source view, at the top of the page, add the part that you see shown in bold: <%@ Page Language= VB EnableViewState= false %>

Going to extremes, if you re positive that you don t need ViewState anywhere in the whole ASPNET site, you can switch it off in the webconfig file Look for the <page> element (somewhere within the <systemweb> element) and add the following part shown in bold: <pages enableViewState= false > Even when you turn off ViewState for an entire site, ASPNET doesn t give up completely Some remnants remain in the page as if it s using ViewState to track the fact that ViewState is off

Imagine poor old Internet Information Services grinding away to produce an ASPNET page full of elaborate three-dimensional charts The data for the charts comes from a SQL Server database that executes some mindnumbingly complicated queries Eventually, the HTML, images, and associated JavaScript are assembled and shipped across the Internet to the browser Congratulations on a job well done In the next fraction of a second, someone else requests exactly the same page The Web server starts all over again, building the shading and gradients on the charts and re-requesting the data It s a waste of time and, in geekspeak, expensive To reduce the load on the server, you can store a copy of a complicated diagram, image, report, or page in the server s memory On the next identical request, the Web server looks for that content in the cache If it finds something usable, it sends the cached copy

When you identify a page that would benefit from caching, open the page in Source view and, at the top of the page, add the following directive: <%@ OutputCache Duration= 300 VaryByParam= none %> The preceding line of code gives these instructions to the Web server: Create this page as usual on the occasion that someone requests it Hold the page in memory for 300 seconds (five minutes) and send your cached copy if anyone else asks for it Yes, send the cached version even if the data in the database has changed After five minutes, dump the cached version and start over with a new page if asked