The JavaFX User Interface Controls (UI Controls or just Controls) are specialized Nodes in the JavaFX Scenegraph especially suited for reuse in many different application contexts. They are designed to be highly customizable visually by designers and developers. They are designed to work well with layout systems. Examples of prominent controls include {@link javafx.scene.control.Button Button}, {@link javafx.scene.control.Label Label}, {@link javafx.scene.control.ListView ListView}, and {@link javafx.scene.control.TextField TextField}.

Since Controls are {@link javafx.scene.Node Nodes} in the scenegraph, they can be freely mixed with {@link javafx.scene.Group Groups}, {@link javafx.scene.image.ImageView Images}, {@link javafx.scene.media.MediaView Media}, {@link javafx.scene.text.Text Text}, and {@link javafx.scene.shape.Shape basic geometric shapes}. While writing new UI Controls is not trivial, using and styling them is very easy, especially to existing web developers.

The remainder of this document will describe the basic architecture of the JavaFX UI Control library, how to style existing controls, write custom skins, and how to use controls to build up more complicated user interfaces.

## Architecture

Controls follow the classic MVC design pattern. The {@link javafx.scene.control.Control Control} is the "model". It contains both the state and the functions which manipulate that state. The Control class itself does not know how it is rendered or what the user interaction is. These tasks are delegated to the {@link javafx.scene.control.Skin Skin} ("view"), which may internally separate out the view and controller functionality into separate classes, although at present there is no public API for the "controller" aspect.

All Controls extend from the Control class, which is in turn a {@link javafx.scene.Parent Parent} node, and which is a {@link javafx.scene.Node Node}. Every Control has a reference to a single Skin, which is the view implementation for the Control. The Control delegates to the Skin the responsibility of computing the min, max, and pref sizes of the Control, the baseline offset, and hit testing (containment and intersection). It is also the responsibility of the Skin, or a delegate of the Skin, to implement and repond to all relevant key events which occur on the Control when it contains the focus.

## Control

Control extends from {@link javafx.scene.Parent Parent}, and as such, is not a leaf node. From the perspective of a developer or designer the Control can be thought of as if it were a leaf node in many cases. For example, the developer or designer can consider a Button as if it were a Rectangle or other simple leaf node.

Since a Control is resizable, a Control will be auto-sized to its preferred size on each scenegraph pulse. Setting the width and height of the Control does not affect its preferred size. When used in a layout container, the layout constraints imposed upon the Control (or manually specified on the Control) will determine how it is positioned and sized.

The Skin of a Control can be changed at any time. Doing so will mark the Control as needing to be laid out since changing the Skin likely has changed the preferred size of the Control. If no Skin is specified at the time that the Control is created, then a default CSS-based skin will be provided for all of the built-in Controls.

Each Control may have an optional tooltip specified. The Tooltip is a Control which displays some (usually textual) information about the control to the user when the mouse hovers over the Control from some period of time. It can be styled from CSS the same as with other Controls.

{@code focusTraversable} is overridden in Control to be true by default, whereas with Node it is false by default. Controls which should not be focusable by default (such as Label) override this to be false.

The getMinWidth, getMinHeight, getPrefWidth, getPrefHeight, getMaxWidth, and getMaxHeight functions are delegated directly to the Skin. The baselineOffset method is delegated to the node of the skin. It is not recommended that subclasses alter these delegations.

## Styling Controls

There are two methods for customizing the look of a Control. The most difficult and yet most flexible approach is to write a new Skin for the Control which precisely implements the visuals which you desire for the Control. Consult the Skin documentation for more details.

The easiest and yet very powerful method for styling the built in Controls is by using CSS. Please note that in this release the following CSS description applies only to the default Skins provided for the built in Controls. Subsequent releases will make this generally available for any custom third party Controls which desire to take advantage of these CSS capabilities.

Each of the default Skins for the built in Controls is comprised of multiple individually styleable areas or regions. This is much like an HTML page which is made up of {@literal

's} and then styled from CSS. Each individual region may be drawn with backgrounds, borders, images, padding, margins, and so on. The JavaFX CSS support includes the ability to have multiple backgrounds and borders, and to derive colors. These capabilities make it extremely easy to alter the look of Controls in JavaFX from CSS.

The colors used for drawing the default Skins of the built in Controls are all derived from a base color, an accent color and a background color. Simply by modifying the base color for a Control you can alter the derived gradients and create Buttons or other Controls which visually fit in with the default Skins but visually stand out.

As with all other Nodes in the scenegraph, Controls can be styled by using an external stylesheet, or by specifying the style directly on the Control. Although for examples it is easier to express and understand by specifying the style directly on the Node, it is recommended to use an external stylesheet and use either the styleClass or id of the Control, just as you would use the "class" or id of an HTML element with HTML CSS.

Each UI Control specifies a styleClass which may be used to style controls from an external stylesheet. For example, the Button control is given the "button" CSS style class. The CSS style class names are hyphen-separated lower case as opposed to camel case, otherwise, they are exactly the same. For example, Button is "button", RadioButton is "radio-button", Tooltip is "tooltip" and so on.

The class documentation for each Control defines the default Skin regions which can be styled. For further information regarding the CSS capabilities provided with JavaFX, see the CSS Reference Guide.