Software Technology Tips

This tip demonstrates how to add a Wicket component to your web page conditionally. To keep it simple I will add a Wicket Label component to a panel if a List is null otherwise not. Here, in my sample code, I am creating a panel named "ExamplePanel" in which I am loading a list of  "Strings" dynamically.

"ExamplePanel.java"

public class ExamplePanel extends Panel {

   //declared a boolean variable and setted it to false

   boolean isListEmpty = false;

  /*
   * constructor here
   */

  public ExamplePanel(String id) {

    super(id);

    /*
     * getting the list of Strings by executing a sql query under getList() method of "ExamplePanelDAO.java".
     * Just suppose that in getList() method a sql query executes and it returns a list of some String object.
    */

    final List<String> list = new ExamplePanelDAO().getList();

    /*
     * Check whether list is empty or not. If it is empty then set "isListEmpty to true"
     */

    if(list.size() == 0)

       isListEmpty = true;

    /*
     * Added a Label here with wicket:id="dataNotFoundLabel". Now the most important thing is that we need to override the "isVisible()" method of Wicket component class.
     * Since we setted "isListEmpty" to true if list is empty, so this label will be visible only if "isListEmpty" will be true. Otherwise Label will not  be visible.
     */

    add(new Label("dataNotFoundLabel","Sorry!! Data Not Available.") {

        public boolean isVisible() {

           return isListEmpty;

        }

     });

  }

}

Another important thing to remember is that when you write markup for the Label in "ExamplePanel.html" you have to write the markup within "<wicket:enclosure>" tag.

"ExamplePanel.html"

<wicket:panel>
<wicket:enclosure>
<label wicket:id="dataNotFoundLabel"></label>
</wicket:enclosure>
</wicket:panel>