<com:TContent ID="body" > <h1>Sample: Hello World</h1> <p> "Hello World" perhaps is the simplest <i>interactive</i> PRADO application that you can build. It displays to end-users a page with a submit button whose caption is <i>Click Me</i>. When the user clicks on the button, the button changes the caption to <i>Hello World</i>. </p> <p> 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 <i>onclick</i> event. </p> <p> PRADO promotes component-based and event-driven Web programming. The button is represented by a <i>TButton</i> object. It encapsulates the button caption as the <i>Text</i> property and associates the user button click action with a server-side <i>Click</i> event. Therefore, the "Hello World" task can be handled intuitively and easily. One simply needs to attach a function to the button's <i>Click</i> event. Within the function, the button's <i>Text</i> property is modified as "Hello World". The following diagram shows the above sequence, </p> <img src="<%~HelloWorld/sequence.gif%>" /> <p> The code that a developer needs to write is merely the following event handler function, where <tt>$sender</tt> refers to the button object. </p> <pre class="source"> public function buttonClicked($sender,$param) { $sender->Text="Hello World"; } </pre> <com:RunBar PagePath="Samples.HelloWorld.Home" /> </com:TContent>