Show, hide or disable a component

Use this when part of a page should only appear, or only be usable, under some condition: a link for administrators, a warning when a list is empty, a field that cannot be changed after an order is placed.

Hide a component

Call setVisible(false). An invisible component renders nothing, not even its tag, and neither do its children.

Label warning = new Label("warning", "Your trial ends tomorrow.");
warning.setVisible(account.isTrialEndingSoon());
add(warning);

This decides the visibility once, when the page is built. If the page stays on screen and the condition changes, the component keeps its old state.

Decide visibility on every request with onConfigure

Override onConfigure and set the visibility there. Wicket calls onConfigure once per request, before it renders the component, so the condition is always current.

add(new Label("warning", "Your trial ends tomorrow.") {
    @Override
    protected void onConfigure() {
        super.onConfigure();
        setVisible(account.isTrialEndingSoon());
    }
});

Always call super.onConfigure(); Wicket checks that you do.

Prefer this to overriding isVisible(). Wicket calls isVisible() many times while it processes a request, so any work in it, such as a database query, runs many times. An overridden isVisible() can also return different answers within one request, which makes isVisibleInHierarchy() unreliable.

Hide a group of components at once

Hiding a container hides all of its children. Put the components in a WebMarkupContainer and set the visibility on the container. See Group components with WebMarkupContainer.

To hide the text around a single component together with it, without a container in Java, use wicket:enclosure.

Disable a component

Call setEnabled(false), in onConfigure when the condition can change:

add(new TextField<>("customerNumber", customerNumberModel) {
    @Override
    protected void onConfigure() {
        super.onConfigure();
        setEnabled(!order.isPlaced());
    }
});

A disabled component is still rendered, but:

• form components get the disabled attribute, and Wicket ignores their input;
• links lose their href, and buttons get the disabled attribute;
• Wicket refuses requests to the component’s listeners, so its Ajax behaviors do nothing, even when someone calls their URL by hand.

Disabling a container disables everything inside it. isEnabledInHierarchy() tells you whether a component and all its parents are enabled.

Show a hidden component with Ajax

An invisible component leaves no tag in the page, so an Ajax response has nowhere to put it when it becomes visible. Call setOutputMarkupPlaceholderTag(true) on it: Wicket then renders an empty, hidden placeholder tag with the component’s markup id in its place.

Label details = new Label("details", detailsModel);
details.setVisible(false);
details.setOutputMarkupPlaceholderTag(true);
add(details);

add(new AjaxLink<Void>("toggle") {
    @Override
    public void onClick(AjaxRequestTarget target) {
        details.setVisible(!details.isVisible());
        target.add(details);
    }
});

See Update components with Ajax for more on repainting components.