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| Performing the equivalent of a "switch" statement in your component template using blocks and a delegate |
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.
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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:
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<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>
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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.
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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;
}
}
}
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Switching Cases 