"Hello World" perhaps is the simplest interactive PRADO application that you can build. It displays to end-users a page with a submit button whose caption is Click Me. When the user clicks on the button, the button changes the caption to Hello World.
There are many approaches that can achieve the above goal. One can submit the page to the server, examine the POST variable, and generate a new page with the button caption updated. Or one can simply use JavaScript to update the button caption upon its onclick event.
PRADO promotes component-based and event-driven Web programming. The button is represented by a TButton object. It encapsulates the button caption as the Text property and associates the user button click action with a server-side Click event. Therefore, the "Hello World" task can be handled intuitively and easily. One simply needs to attach a function to the button's Click event. Within the function, the button's Text property is modified as "Hello World". The following diagram shows the above sequence,
The code that a developer needs to write is merely the following event handler function, where $sender refers to the button object.
public function buttonClicked($sender,$param)
{
$sender->Text="Hello World";
}