"); ','// Write a line break tag','\n }\n }\n}','Code notes.',' The above code sample starts the Timer from the DateList property accessor, and then writes all the contents of the List to the page output.','Reload:','With this Default.aspx page, you can use the Reload button in your web browser. The timer adds to the List every three seconds.','Note:','This tutorial does not show an AJAX timer. For live page updates, you will need a different client-side mechanism.','Error.',' We can hit an "Object reference not set to an instance of an object" error when using HttpContext.Current in the Timer. This is because the Timer is invoked on a separate thread.','Tip:','You can work around the problem by storing important variables in static, global fields or properties.','Property','property','Websites.',' You can use a Timer instance to monitor your ASP.NET site. You can check the file system for changes to the App_Data folder.','And:','When new files are detected, they are parsed and checked for errors. This does affect need to affect site performance.','Tip:','This way, the Timer enables the website to almost always use the most recent valid file.','For important sites,',' you should have logic that tries to detect all errors and then handle them. This can mean visitors don\'t encounter the errors and you detect them on the Timer.','Tip:','Your ASP.NET application should have an App_Code folder. And you can add a C# file that stores a static timer object.','Globals:','For reference, we present material on global variables in ASP.NET, which apply to this subject.','Global Variables','global-variables-aspnet','A summary.',' We looked at the Timer class from the System.Timers namespace. This interval-based validation approach is recommended by Microsoft for mission-critical applications.','