Conditional Validation

Flagging a form field as "required" is the most common kind of validation. In most cases, this can be specified statically as follows:

add(new TextField("foo").setRequired(true));

In some cases, however, whether or not the field is required cannot be determined when the form is created. Like many properties in Wicket, we can override the property setter (isRequired, in this case) to defer the evaluation of the property until the last possible moment:

add(new TextField("foo") {
    public boolean isRequired() {
        // return true if the field is required
    }
}

That's the simple part. Unfortunately, implementing isRequired can be tricky, since it's called very early in the form processing cycle, before values are converted and models are updated. Below we provide a few recipes that cover some common scenarios.

Submit Button

In this recipe, the field is in a form with multiple submit buttons. We only want to require the field when one of the buttons is clicked:

Button submit = new Button("submit") {
    public void onSubmit() {
        // handle form submission
    }
}
form.add(submit);

TextField foo = new TextField("foo") {
    public boolean isRequired() {
        Form form = (Form) findParent(Form.class);
        return form.getRootForm().findSubmittingButton() == submitButton;
    }
}
form.add(foo);

Note the call to getRootForm. Technically, this is only required in nested forms.

If you would like to bypass validation altogether you can do so by:

new Button("submit").setDefaultFormProcessing(false);

CheckBox

In this recipe, the field is only required when a checkbox on the form is checked:

final CheckBox checkBox = new CheckBox("cb");
form.add(checkBox);

TextField foo = new TextField("foo") {
    public boolean isRequired() {
        return Strings.isTrue(checkBox.getValue());
    }
}
form.add(foo);

Radio Button

Here the field is only required when a particular radio button on the form is selected:

final RadioGroup radioGroup = new RadioGroup("radioGroup");
form.add(radioGroup);

final Radio radio1 = new Radio("radio1");
radioGroup.add(radio1);

TextField foo = new TextField("foo") {
    public boolean isRequired() {
        return Strings.isEqual(radioGroup.getInput(), radio1.getValue());
    }
}
form.add(foo);