Conditional Rendering

If you want to render a component in Wicket conditionally, it is not as straightforward. Wicket generates component hierarchy based on java and markup files. Therefore you can’t have a conditional if-else in java because markup(html) doesn’t support if-else. A workaround is to hide the component.We can create a component adaptor that will wrap our component that needs to be conditionally rendered. Adaptor will extend Border class.

import org.apache.wicket.Component;
import org.apache.wicket.markup.html.border.Border;

public abstract class ConditionalRenderAdaptor extends Border {
/**
* Component that provides conditional rendering to the child component
*
* @param id
* @param child
*/
public ConditionalRenderAdaptor(String id, Component child) {
super(id);
add(child);
setVisible(renderCondition());
}

public abstract boolean renderCondition ();
}

And the markup looks like this

<wicket:border>
<table width=”0%” border=”0″>
<tr>
<td width=”0%” valign=”top”>
<wicket:body/>
</td>
</tr>
</table>
</wicket:border>

Example

You want to hide an instance of class Record, if the user hasn’t registered yet and show it if the user has registered.Extend ConditionalRenderAdaptor and provide an implementation for renderCondition().

class Record extends ConditionalRenderAdaptor {

private static final long serialVersionUID = 1L;

public Record() {
super(“record”, new Label(“User Name”, new Model (user.getUserName() )) );
}

@Override
public boolean renderCondition() {
return user != null;
}

}

You can use it like this:

class HomePage extends WebPage {

….

Record userRecord= new Record ();

add(userRecord);

…

}

and in the markup:

<span wicket:id=”record” >

<tr>

<td>

<span wicket:id=”userName”>some value</span>

</td>

</tr>

</span>

“userName” will only show if the user record exists.This is not a perfect solution and if anyone knows how to do actual conditional rendering please let me know!

Tags: Wicket