UI Builder

The UI Builder lets you visually create and edit UI assets (UXML and USS) for use with the UI Toolkit (formally UIElements). Once the package is installed, the UI Builder window can be opened via the Window > UI > UI Builder menu, or double-clicking on a .uxml asset in the Project Browser.

Overview

UI Builder Main Window

The UI Builder window has the following sections:

Section: Function:
Explorer Access components of open documents.
Library Find available elements.
Viewport Preview and edit the UI.
Code Previews See the USS and UXML files that UI Builder generates.
Inspector Edit properties of elements and USS selectors.

Explorer

The Explorer is similar to the Hierarchy window in the Unity Editor. It gives you access to all components of any open documents.

The Explorer has two sections: the StyleSheet and the Hierarchy.

StyleSheet

The StyleSheet section lists all of the USS selectors in the main USS document. Use it to create and edit selectors.

Note

UI Builder supports one USS style sheet per UXML document.

Creating new selectors

To create a new selector from the StyleSheet section, do one of the following:

  1. In the Explorer, click the StyleSheet header.
  2. In the Inspector, enter the selector name in the StyleSheet > Selector field.
  3. Click the Create new USS Selector button.

You can also create simple or complex selectors directly in the Explorer.

To create a simple selector:

  1. In the Explorer, beside the Add new selector... text field, select the pseudo State (for example, Hover or Active).
  2. Enter the class name in the Add new selector... field.
  3. Press Enter.

To create a complex selector:

  1. In the Explorer, beside the Add new selector... text field, change Type to Complex.
  2. Enter the full selector name in the Add new selector... field.
  3. Press Enter.

UI Builder converts any class names in selectors into "pills" that you can drag onto elements in the Viewport or Hierarchy to apply the classes.

Editing selectors

Select a selector from the list to open it in the Inspector, where you can edit its properties. Any elements that the selector affects are highlighted in the Viewport.

Hierarchy

The Hierarchy section displays a live tree view of a UXML document's hierarchy.

You can select elements to edit their properties in the Inspector. You can drag elements in the Hierarchy to re-parent them.

Elements appear in the tree according to their name attributes. If an element's name attribute is not set, it appears according to its C# type. You can double-click an element to quickly rename it.

Click the ⋮ icon in the top right corner of the Explorer toolbar to access a menu of display options for elements in the Hierarchy.

  • Select Type to force the Hierarchy to display each element's C# type, regardless of whether it has a name.
  • Select Class List to display each element's style class list next to its Hierarchy entry.

Library

The Library pane is similar to the Project window in the Unity Editor. It lists available UI elements.

  • The Unity section lists the standard elements that Unity provides. These elements include standard styling that works for all supported Unity Editor and run time themes.
  • The Project section lists custom .uxml assets in the Project. It also lists any custom C# elements that inherit from VisualElement and have their UxmlFactory set up to be instantiable via UXML).

To instantiate an element, do one of the following:

  • Drag it into the Hierarchy section of the Explorer pane.
  • Drag it onto the Canvas in the Viewport.
  • Double-click it. This adds the element as a sibling of the currently selected element. If nothing is selected, the element is added at the root.

To preview any element in the Library, hover over it. The preview appears to the right of the Library pane.

Viewport

The Viewport displays the output of a UXML document on a resizable edit-time Canvas provided by UI Builder.

  • The title bar displays the name of the currently loaded document. An asterisk * next to the name indicates unsaved changes.
  • The toolbar contains menus of UI Builder commands, Viewport settings, and the Preview button.
  • The Canvas is where you edit, preview, and interact with UI.
Note

The Canvas size, and all other Canvas attributes, only apply to the UI Builder authoring environment. They are not saved in the document itself.

Viewport toolbar menus

The Viewport toolbar contains the following menus:

Menu: Function:
File Create a New document, Save/Save As the current document, or Open another document.
Theme Switch between the Dark and Light Editor themes, or the Runtime theme, to see how your UI looks in each theme.

Resizing the Canvas

To resize the Canvas from the Viewport drag the handles on left, right, or bottom.

To resize the Canvas from the Inspector:

  1. In the Explorer pane, select the Hierarchy element.
  2. In the Inspector, set the Canvas Size > Width/Height values.

Interacting with UI in the Canvas

To select an element, click it. UI Builder highlights it in the Canvas.

To resize the selected element, use its drag handles:

  • If the element's Position > Position setting is Relative, you can only adjust its height and width.

  • If the element's Position > Position setting is Absolute, you have full control over how you resize and position the element.

    Note

    Absolute positioning is not recommended because it bypasses UI Toolkit's automatic layouting functionality.

Setting a background

To set an edit-time background for the Canvas:

  1. In the Explorer pane, select the Hierarchy element.
  2. In the Inspector choose the Canvas Background mode.
    • None: No background
    • Color: A color that you choose using a Unity color picker.
    • Image: An image that you choose using a Unity object picker.
    • Camera: A live feed from a Camera. This is useful for seeing run time UI in context without launching a full game.
  3. You can also adjust the background's Opacity.

Previewing UI

Use the Preview button in the Viewport toolbar to preview your UI as though it were running on a device.

Activating Preview mode removes the selection layer that allows you to select elements on the Canvas by clicking them.

While in Preview mode, you can interact with the UI the way a user might. For example, you can click buttons, type in text fields, and expand and collapse foldout controls.

Code Previews

As you build your UI, UI Builder automatically generates the underlying UXML and USS, and displays them in the UXML Preview and USS Preview panes.

Inspector

The UI Builder Inspector is similar to the Unity Inspector window. Use it to change the properties and styles of the selected element or USS selector.

Editing an element's attributes

When you select a visual element in the Canvas or the Hierarchy, you can change its UXML attributes (for example, Name, Tooltip, and Text) in the Attributes section of the Inspector. Attributes are per-element, and cannot be shared.

The Attributes section header displays the selected element's type. The section only appears when you select a visual element. It does not appear when you select a USS selector.

Editing an element's StyleSheet styles

USS selectors allow you to share styles between multiple elements. When you change a shared style, you automatically update every element that uses it.

USS selectors can match elements by name, style class, C# type, a combination of all three, and/or a parent/child relationship.

However, the easiest way to share styles is to assign a style class to one or more elements and create a simple selector. For example, you might assign a class called my-red-button, and create a corresponding selector called .my-red-button.

Use the StyleSheet section of the Inspector to apply styles from the StyleSheet on the selected element.

A selected element's styles from matching selectors appear in the StyleSheet > Matching Selectors list.

Adding style classes to elements

To add a style class to an element:

  1. Select the element.
  2. In the Inspector, enter the style class name in the Style Class List field.
  3. Press the Add Style Class to List button.

If a matching selector already exists, you should see the effect of the styles immediately.

Creating selectors for style classes

The bottom of the StyleSheet > Style Class List section displays a pill for each style class assigned to the selected element.

To create a selector:

  • Double-click a pill. If a selector already exists, double-clicking the pill selects it.

You can also create selectors and style classes, from inlined styles that you created for the selected element.

To create a selector and style class from inlined styles:

  1. In the StyleSheet > Style Class List section of the Inspector, type the new selector's name.
  2. Use the Extract Inlined Styles to New Class button to create a new USS selector and also add the matching style class to the current element.

The new selector appears in the StyleSheet section of the Explorer.

Removing styles from elements

The bottom of the StyleSheet > Style Class List section displays a pill for each style class assigned to the selected element. Click the X on any pill to remove the style from the element. For example, you might remove the default styling on a Unity-provided button.

Editing inlined styles for elements and USS selectors

When you select a visual element or a USS selector, you can add and edit its inlined styles from the Inlined Styles section of the Inspector.

  • For elements, inlined styles override styles coming from the StyleSheet. They are stored in the UXML document as inline styles.
  • For USS selectors, inlined styles are added as properties to the USS rules in the StyleSheet.

When you change an inlined style for an element or a USS selector, a solid border appears next to the property in the Inlined Styles section of the Inspector, and the property name appears in bold.