.NET/ASP.NET/C#/VB.NET PDF Document SDK

Myth: People learn more when I wow them with special effects and spice up my presentations with razzle-dazzle. Truth: Research shows that people learn better when extraneous information is removed from a presentation.

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This section has covered only the basics of using controllers and views, but these are the most essential parts to learn. Other features provided by views and controllers rely on the concepts covered in this section. URLs are parsed into the desired controller and action, any other supplied data is passed through the action via the params hash, and once the action code has completed, a view is rendered. In the next section you ll take a look at how you can customize the URL parsing system so that URLs of your own formatting can be converted into any controller and method patterns that you wish. This technique is known as routing.

If you want access to the exception itself in an except clause, you can use two arguments instead of one. (Note that even when you are catching multiple exceptions, you are only supplying except with one argument a tuple.) This can be useful (for example) if you want your program to keep running, but you want to log the error somehow (perhaps just printing it out to the user). The following is an example program that prints out the exception (if it occurs), but keeps running: try: x = input('Enter the first number: ') y = input('Enter the second number: ') print x/y except (ZeroDivisionError, TypeError), e: print e The except clause in this little program again catches two types of exceptions, but because you also explicitly catch the object itself, you can print it out so the user can see what happened. (You see a more useful application of this later in this chapter, in the section When All Is Well. )

When you request a page from a Rails application that isn t present within the public folder, the Rails application tries to work out which controller and action you are trying to use. In the previous sections, you ve seen how a URL such as http://localhost/ entries/view_all means that the request is put through to the entries controller s view_all action. You can use routing to override this default assumption that all URLs are of the form controller_name/action_name/id. Routing configurations for a Rails application are located in config/routes.rb. Let s look at what ours contains by default:

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ActionController::Routing::Routes.draw do |map| # The priority is based upon order of creation: first created -> highest priority # Sample of regular route: # map.connect 'products/:id', :controller => 'catalog', :action => 'view' # Keep in mind you can assign values other than :controller and :action

Whenever a program is run on a computer, it s contained with a certain environment, whether that s the command line or a GUI. The operating system sets a number of special variables called environment variables that contain information about the environment. They vary by operating system, but can be a good way of detecting things that could be useful in your programs. You can quickly and easily inspect the environment variables (as supplied by your operating system) on your current machine with irb by using the special ENV hash:

Audiences might not know about the research that indicates that you need to guide their attention, but they do know what they are talking about when they frequently say conventional presentations are incoherent lists with no direction and a jumble. Instead of guiding working memory through the experience, this example slide creates unnecessary work by not quickly getting to the clear point, by not tapping into the visual channel, and by creating split attention and redundancy with the narration of a live presenter.