UXML element DropdownField

A DropdownField lets users choose a value from a list. When clicking on the control, it opens a drawer that presents multiple options, allowing users to select one. If you want to always display all the choices, use RadioButtonGroup.

Note: To align an element with other fields in an Inspector window, simply apply the .unity-base-field__aligned USS class to it. For more information, refer to BaseField.

Create a DropdownField

You can create a DropdownField with UI Builder, UXML, or C#.

UI Builder

To add options for a DropdownField in UI Builder, in the Inspector panel of the DropdownField, enter the options separated by commas in Choices.

To set the default value, in the Inspector of the DropdownField, enter the numbering sequence of the option in Index, starting at 0.

C#

The following C# example create a DropdownField with three options. The DropdownField selects the first option by default:

var dropdown = new DropdownField("Options", new List<string> { "Option 1", "Option 2", "Option 3" }, 0);

//Add another option
dropdown.choices.Add("Option 4");

// To return int value instead of string
dropdown.index = 1; // Option 2
dropdown.value = "Option3";
Assert.IsTrue(myDropdown.index == 2);

// Register to the value changed callback
dropdown.RegisterValueChangedCallback(evt => Debug.Log(evt.newValue));

Change styles for a DropdownField

You can override the default Panel Settings fields in a USS file to change the styles of a DropdownField:

1. In the Hierarchy window, select your UI Document (.uxml).
2. Set Panel Settings as your Panel Settings asset. If you don’t have an existing Panel Settings asset, follow the instructions in the dialog to create one.
3. In your Panel Settings asset, assign a Theme Style Sheet.
4. In the Project window, select your TSS file.
5. Go to Style Sheets and select the Add (+) button.
6. Set your Style Sheet as your USS file.

示例

The following UXML example creates a DropdownField:

[!code-xml[(External/Resources/editor_resources/Assets/Editor Default Resources/UIPackageResources/Snippets/UXML/DropdownFieldSnippet.uxml)]

The following C# example illustrates some of the customizable functionalities of the DropdownField:

[!code-cs[(Modules/UIElementsSamplesEditor/Snippets/DropdownFieldSnippet.cs#sample)]

To try this example live in Unity, go to Window > UI Toolkit > Samples.

C# base class and namespace

C# class: DropdownField
Namespace: UnityEngine.UIElements
Base class: PopupField_1

Inherited UXML attributes

This element inherits the following attributes from its base class:

名称	类型	描述
binding-path	string	Path of the target property to be bound.
choices	IList	The list of choices to display in the popup menu.
focusable	boolean	True if the element can be focused.
index	int	The currently selected index in the popup menu. Setting the index will update the ::ref::value field and send a property change notification.
label	string	The string representing the label that will appear beside the field.
tabindex	int	An integer used to sort focusables in the focus ring. Must be greater than or equal to zero.
value	int	The currently selected value in the popup menu.

This element also inherits the following attributes from VisualElement:

名称	类型	描述
content-container	string	Child elements are added to it, usually this is the same as the element itself.
data-source	Object	Assigns a data source to this VisualElement which overrides any inherited data source. This data source is inherited by all children.
data-source-path	string	Path from the data source to the value.
name	string	The name of this VisualElement. Use this property to write USS selectors that target a specific element. The standard practice is to give an element a unique name.
picking-mode	UIElements.PickingMode	Determines if this element can be pick during mouseEvents or IPanel.Pick queries.
style	string	Reference to the style object of this element. Contains data computed from USS files or inline styles written to this object in C#.
tooltip	string	Text to display inside an information box after the user hovers the element for a small amount of time. This is only supported in the Editor UI.
usage-hints	UIElements.UsageHints	A combination of hint values that specify high-level intended usage patterns for the VisualElement. This property can only be set when the VisualElement is not yet part of a Panel. Once part of a Panel, this property becomes effectively read-only, and attempts to change it will throw an exception. The specification of proper UsageHints drives the system to make better decisions on how to process or accelerate certain operations based on the anticipated usage pattern. Note that those hints do not affect behavioral or visual results, but only affect the overall performance of the panel and the elements within. It’s advised to always consider specifying the proper UsageHints, but keep in mind that some UsageHints might be internally ignored under certain conditions (e.g. due to hardware limitations on the target platform).
view-data-key	string	Used for view data persistence, such as tree expanded states, scroll position, or zoom level. This key is used to save and load the view data from the view data store. If you don’t set this key, the persistence is disabled for the associated VisualElement. For more information, refer to View data persistence.

USS classes

The following table lists all the C# public property names and their related USS selector.

C# property	USS selector	描述
ussClassName	.unity-popup-field	USS class name of elements of this type.
labelUssClassName	.unity-popup-field__label	USS class name of labels in elements of this type.
inputUssClassName	.unity-popup-field__input	USS class name of input elements in elements of this type.
ussClassName	.unity-base-popup-field	USS class name of elements of this type.
textUssClassName	.unity-base-popup-field__text	USS class name of text elements in elements of this type.
arrowUssClassName	.unity-base-popup-field__arrow	USS class name of arrow indicators in elements of this type.
labelUssClassName	.unity-base-popup-field__label	USS class name of labels in elements of this type.
inputUssClassName	.unity-base-popup-field__input	USS class name of input elements in elements of this type.
ussClassName	.unity-base-field	USS class name of elements of this type.
labelUssClassName	.unity-base-field__label	USS class name of labels in elements of this type.
inputUssClassName	.unity-base-field__input	USS class name of input elements in elements of this type.
noLabelVariantUssClassName	.unity-base-field--no-label	USS class name of elements of this type, when there is no label.
labelDraggerVariantUssClassName	.unity-base-field__label--with-dragger	USS class name of labels in elements of this type, when there is a dragger attached on them.
mixedValueLabelUssClassName	.unity-base-field__label--mixed-value	USS class name of elements that show mixed values
alignedFieldUssClassName	.unity-base-field__aligned	USS class name of elements that are aligned in a inspector element
disabledUssClassName	.unity-disabled	USS class name of local disabled elements.

You can also use the Matching Selectors section in the Inspector or the UI Toolkit Debugger to see which USS selectors affect the components of the VisualElement at every level of its hierarchy.

其他资源

• RadioButtonGroup