Question

I want to create an ajaxcheckbox without wiring it to a class attribute using propertymodel. Why does the code in the example not work? The boolean value doesnt change when the user checks or unchecks the checkbox.

boolean show = false;
AjaxCheckBox showBox = new AjaxCheckBox("showBox", new Model<Boolean>(show)){
    //onUpdate stuff
};

Answer 1

The boolean value will not change because the showBox does not have a reference to the original variable show. You just initialized the showBox model with false. The code you have there is equivalent to:

AjaxCheckBox showBox = new AjaxCheckBox("showBox", new Model<Boolean>(false)){
    //onUpdate stuff
};

If you want to access the model value of the showBox you can use getModelObject(), which will return the boolean value stored in the AjaxCheckBox‘s model.

Models are complex in wicket – but very powerful.

To illustrate further, Model keeps its own reference to a value. PropertyModel keeps a reference to a different object, and then stores the value in the property of that object. Look at the source code of Model and you’ll see it is very simple.