Switching Cases
With Tapestry's If
component you can only test one condition at a time. In order to distinguish multiple cases, you'd have to write complex nested if/else constructs in your page template and have a checker method for each test inside your page class.
Delegate
component comes in. It delegates rendering to some other component, for example a Block
. For each case you have, you basically wrap the content inside a Block
that doesn't get rendered by default. You then place a Delegate component on your page and point it to a method inside your page class that will decide which of your Blocks should be rendered.Imagine for example a use case, where you want to distinguish between 4 cases and you have an int property called whichCase
that should be tested against. Your page template would look as follows:
<html xmlns:t="http://tapestry.apache.org/schema/tapestry_5_1_0.xsd"> <body> <h1>Switch</h1> <t:delegate to="case"/> <t:block t:id="case1"> Here is the content for case1. </t:block> <t:block t:id="case2"> Here is the content for case2. </t:block> <t:block t:id="case3"> Here is the content for case3. </t:block> <t:block t:id="case4"> Here is the content for case4. </t:block> </body> </html>
You can see, that the Delegate
component's to
parameter is bound to the case property of your page class. In your page class you therefore have a getCase()
method that is responsible for telling the Delegate
component which component should be rendered. For that we are injecting references to the Block}}s defined in your page template into the page class and return the according {{Block
in the getCase()
method.
public class SwitchMe { @Persist private int whichCase; @Inject private Block case1, case2, case3, case4; public Object getCase() { switch (whichCase) { case 1: return case1; case 2: return case2; case 3: return case3; case 4: return case4; default: return null; } } }
Happy switching!