Version: 2020.3
Supporting IMGUI
Controls reference
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Controls

A control is an element of a graphical user interface, such as a button, label or checkbox. It includes the visuals of the control, and the scripted logic needed to operate and interact with the control.

In UI(User Interface) Allows a user to interact with your application. More info
See in Glossary
Toolkit, a control is similar to a PrefabAn asset type that allows you to store a GameObject complete with components and properties. The prefab acts as a template from which you can create new object instances in the scene. More info
See in Glossary
, combining visual elements and scripted logic into a template that’s ready to use inside a UI panel.

Controls can consist of a single visual element, for example a label or an image. Or they can consist of a combination of multiple visual elements.

For example, the Toggle control consists of three elements:

Toggle control
Toggle control
  • a text label
  • the image of a box
  • image of a checkmark

The implementation of the Toggle control defines the behavior of the control. It has an internal value of whether the toggle state is true or false. This logic alternates the visibility of the checkmark image when the value changes.

Adding controls to a UI

To use a control in a UI, you need add it to a UI hierarchy called the Visual Tree. You can add the control through a script, UXML or in the UI Builder.

The code snippet below demonstrates how to add a Button control to an existing visual tree.

var newButton = new Button("Click me!");
rootVisualElement.Add(newButton);

When adding controls to a UI hierarchy, the layout engine will handle the sizing and positioning automatically. You can also influence or override the size and position manually.

To learn more about the automatic layout, see the Layout Engine. To learn more about controlling the position manually, see the Visual Tree page.

The visual appearance of an element in UI Toolkit is defined through styles, either by directly modifying the style property of the element via code, by creating a USS style sheets, or by applying the appropriate properties in UI Builder.

Interaction with controls

Many controls are interactive and represent a value that the user can change. For example, a FloatField represents a float value. You can use code in multiple ways to react when the user changes the value of a control, such as:

  • Reading the control value directly
  • Registering a callback
  • Data Binding

Control value property

If a control represents a value that the user can modify, it contains a value property. ScriptsA piece of code that allows you to create your own Components, trigger game events, modify Component properties over time and respond to user input in any way you like. More info
See in Glossary
can use the value property to directly access the value of the control. The code snippet below creates a Toggle control and a Button control. When you click the button, the value of the toggle flips.

// Create a toggle and register callback
m_MyToggle = new Toggle("Test Toggle") { name = "My Toggle" };
rootVisualElement.Add(m_MyToggle);

// Create button to flip the toggle's value
Button button01 = new Button() { text = "Toggle" };
button01.clicked += () =>
{
    m_MyToggle.value = !m_MyToggle.value;
};
rootVisualElement.Add(button01);

To learn more about the properties of a specific control, see the UI Toolkit controls reference.

Registering a callback

All built-in controls that have value properties send an event if the value changes. The code can register a callback to receive this event. The following code snippet shows how to create a Toggle control and register a callback:

// Create a toggle and register callback
m_MyToggle = new Toggle("Test Toggle") { name = "My Toggle" };
m_MyToggle.RegisterValueChangedCallback((evt) => { Debug.Log("Change Event received"); });
rootVisualElement.Add(m_MyToggle);

To learn more about callbacks and events, see Events Handling.

Data Binding

Controls can bind directly to an object or serialized property. For example, a FloatField control can bind to a public float variable that belongs to a MonoBehaviour. Once the control and the property are bound, the control automatically displays the value of the property. When the user modifies the control, the value of the property updates. Similarly, when the property value changes via code, the UI displays the updated value. This two-way connection is useful when creating custom inspectorsA Unity window that displays information about the currently selected GameObject, asset or project settings, allowing you to inspect and edit the values. More info
See in Glossary
using UI Toolkit.

To learn more about data binding, see the Binding page.

Not all controls are bindable. To see a list of all built-in controls and whether they support binding, see the UI Toolkit controls reference.

Creating custom controls

UI Toolkit allows you to create custom controls, in addition to the ones included in Unity. This makes it possible to create complex controls, or implement custom logic for user interface elements. Controls are derived directly from VisualElement, or a subclass of VisualElement, such as TextElement. They might also add manipulators to implement the behavior of the control. For example, the Button control adds a Clickable manipulator.

Built-in controls

Unity includes a large range of standard controls, such as labels, text fields, and toggles. Some controls are only available in the Editor. For a complete list of built-in controls for UI Toolkit, see the UI Toolkit controls reference.

Supporting IMGUI
Controls reference