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Showing content from https://docs.unity3d.com/Manual/sprite/../UIE-uxml-element-ListView.html below:

Unity - Manual: ListView

A ListView is a vertically scrollable area that links to and displays a list of items.

Note: The horizontal and vertical Scroller elements are standard UI Toolkit Scrollers.

You can create a ListView with UI Builder, UXML, and C#. The following C# example creates a ListView:

var listView = new ListView();

You can use a ScrollViewA UI Control which displays a large set of Controls in a viewable area that you can see by using a scrollbar. More info
See in Glossary control to create the same functionalities as using a ListView. However, a ListView is more efficient than a ScrollView when you do the following:

• Populate list items
• Manage item height
• Bind and unbind to objects
• Instantiate the number of visual elementsA node of a visual tree that instantiates or derives from the C# VisualElement class. You can style the look, define the behaviour, and display it on screen as part of the UI. More info
  See in Glossary required to fill a page
• Recycle visual elements to optimize memory handling

To refresh the collection view, in general, call the RefreshItems or RefreshItem method. However, in the following cases, call Rebuild instead to refresh the collection view:

• You change the type of the data source, such as changing from a List<float> to a List<Vector3>.
• You make changes to makeItem or destroyItem.

Note: If you call Rebuild, the collection view is completely rebuilt, which can be expensive. If you call RefreshItems or RefreshItem, the collection view is only refreshed, which is less expensive.

To change how item height is used to drive content, use the VirtualizationMethod:

• VirtualizationMethod.FixedHeight sets all items to the same height.
• VirtualizationMethod.DynamicHeight allows items to have varying heights.

The ListView has a built-in child ScrollView element that lets users scroll through the list. You can control the speed of the scroll by overriding the mouseWheelScrollSize, horizontalPageSize, and verticalPageSize properties of the ScrollView with C#.

By default, the ListView control is not reorderable. To make it reorderable, set the reorderable property to true in UI Builder, UXML, or C#.

listView.reorderable = true;

Drag-and-drop is a common feature in UI design. To implement the drag-and-drop operations, override the following methods:

• To enable dragging items, override canStartDrag.
• To set which items are dragged, override setupDragAndDrop.
• To get item status changes, override dragAndDropUpdate. You can perform certain actions based on the drag position or other conditions.
• To control the drag-and-drop behavior, override handleDrop.

During the drag-and-drop operation, you can enable the reordering of items by dragging. To enable, set the reorderable attribute to true in UI Builder, UXML, and C#.

Refer to Create a drag-and-drop list and tree views between windows for an example.

The following are some frequently asked questions about the ListView control.

Can I get the indices of the rows that are visible on the screen?

There are no dedicated APIs for this. You can use the bindItem and unbindItem callbacks to track these indices.

Can I get the list of rows that are visible in the view?

There are no dedicated APIs for this. You can use UQuery to retrieve the elements of interest.

Is it mandatory for any of the overridden functions of a view controller to call base.Method?

Call this method only if you want to extend its default behavior.

I’ve added a Toggle to my row. Why doesn’t the selection jump to that row when the user selects it?

By default, the row is selected only if the mouse down event is not consumed by the row’s contents. In this case, your Toggle stops the event propagation. To fix this, register a PointerDownEvent callback with TrickleDown on the Toggle to call SetSelection.

How do I receive a callback when a user changes their selection in the view?

It is recommended to use the selectedIndicesChanged callback to retrieve data by index when needed. While you can also use selectionChanged, be aware that it returns a list of objects, which can cause boxing allocations when used with value types.

Can I have a horizontal ListView?

The ListView control doesn’t support horizontal layout and virtualization. It’s recommended to use a ScrollView with flex-direction: row to layout elements horizontally. However, applying this to a ListView breaks virtualization.

The following UXML example creates a ListView:

<UXML xmlns="UnityEngine.UIElements">
    <ListView class="the-uxml-listview" fixed-item-height="20" />
</UXML>

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

/// <sample>
// Create some list of data, here simply numbers in interval [1, 1000]
const int itemCount = 1000;
var items = new List<string>(itemCount);
for (var i = 0; i < itemCount; i++)
    items.Add(i.ToString());

// The "makeItem" function will be called as needed
// when the ListView needs more items to render
Func<VisualElement> makeItem = () => new Label();

// As the user scrolls through the list, the ListView object
// will recycle elements created by the "makeItem"
// and invoke the "bindItem" callback to associate
// the element with the matching data item (specified as an index in the list)
Action<VisualElement, int> bindItem = (e, i) => ((Label)e).text = items[i];

var listView = container.Q<ListView>();
listView.makeItem = makeItem;
listView.bindItem = bindItem;
listView.itemsSource = items;
listView.selectionType = SelectionType.Multiple;

// Callback invoked when the user double clicks an item
listView.itemsChosen += (selectedItems) =>
{
    Debug.Log("Items chosen: " + string.Join(", ", selectedItems));
};

// Callback invoked when the user changes the selection inside the ListView
listView.selectedIndicesChanged += (selectedIndices) =>
{
    Debug.Log("Index selected: " + string.Join(", ", selectedIndices));

    // Note: selectedIndices can also be used to get the selected items from the itemsSource directly or
    // by using listView.viewController.GetItemForIndex(index).
};
/// </sample>

To try this example live in Unity, go to Window > UI Toolkit > Samples. ​ For more examples, refer to the following:

• Create list and tree views: Use ListView, TreeView, MultiColumnListView, and MultiColumnTreeView to create list and tree views.
• Create a complex list view: Use ListView to create a custom Editor window with a list of characters.
• Bind to a list with ListView: Create a list of toggles and bind the list to an underlying list of GameSwitch objects.
• Create a drag-and-drop list and tree views between windows: Use ListView, TreeView, and MultiColumnListView to create a drag-and-drop UI between windows.

C# class: ListView
Namespace: UnityEngine.UIElements
Base class: BaseListView

This element has the following member attributes:

You can use it along with BaseListView.bindingSourceSelectionMode and bindings to have a completely codeless workflow.

This element inherits the following attributes from its base class:

If the callback is not set to false, any Add operation will be allowed.

If the property is not set to false, any Remove operation will be allowed.

When set to AutoAssign, the bind callbacks don’t need to be specified, since bindings can be used to fill the elements.

This property must be set when using the virtualizationMethod is set to FixedHeight, for the collection view to function. If set when virtualizationMethod is DynamicHeight, it serves as the default height to help calculate the number of items necessary and the scrollable area, before items are laid out. It should be set to the minimum expected height of an item.

If the makeHeader callback is set, this property gets overridden and the title is not shown.

The default value is Simple. When this property is set to Animated, Unity adds drag handles in front of every item and the drag and drop manipulation pushes items with an animation when the reordering happens. Multiple item reordering is only supported with the Simple drag mode.

The default value is false which allows the user to drag items to and from other views when you implement canStartDrag, setupDragAndDrop, dragAndDropUpdate, and handleDrop. Set this value to true to allow the user to reorder items in the list.

The default value is SelectionType.Single. When you set the collection view to disable selections, any current selection is cleared.

The default value is false. When this property is set to true, Unity adds a footer under the scroll view. This footer contains two buttons: A “+” button. When clicked, it adds a single item at the end of the list view. A “-” button. When clicked, it removes all selected items, or the last item if none are selected. If the makeFooter callback is set, it will override this property.

If set to true, a border appears around the ScrollView that the collection view uses internally.

The default value is true. When this property is set to to true, the ListView includes a TextField to control the array size.

SA: UnityEditor.UIElements.BindingExtensions.Bind

The default value is false. When this property is set to true, Unity adds a foldout in the hierarchy of the list view and moves the scroll view inside that newly created foldout. You can change the text of this foldout with headerTitle property on the ListView. If showBoundCollectionSize is set to true, the ListView includes a TextField to control the array size. If the makeHeader callback is set, no Foldout is shown.

The default value is FixedHeight. When using fixed height, specify the fixedItemHeight property. Fixed height is more performant but offers less flexibility on content. When using DynamicHeight, the collection will wait for the actual height to be computed. Dynamic height is more flexible but less performant.

This element also inherits the following attributes from VisualElement:

This information is only used by the UI Builder as a hint to provide some completion to the data source path field when the effective data source cannot be specified at design time.

Setting the languageDirection to RTL adds basic support for right-to-left (RTL) by reversing the text and handling linebreaking and word wrapping appropriately. However, it does not provide comprehensive RTL support, as this would require text shaping, which includes the reordering of characters, and OpenType font feature support. Comprehensive RTL support is planned for future updates, which will involve additional APIs to handle language, script, and font feature specifications.

To enhance the RTL functionality of this property, users can explore available third-party plugins in the Unity Asset Store and make use of ITextElementExperimentalFeatures.renderedText

Use this property to write USS selectors that target a specific element. The standard practice is to give an element a unique name.

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.

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

Unity adds this USS class to every instance of the ListView element. Any styling applied to this class affects every ListView located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to every item element the ListView contains. Any styling applied to this class affects every item element located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to the label displayed if the ListView is empty. Any styling applied to this class affects every empty label located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to every instance of the ListView element when reorderMode is set to Animated. Any styling applied to this class affects every ListView located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to every element in the ListView when reorderMode is set to Animated. Any styling applied to this class affects every element located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to every item container in the ListView when reorderMode is set to Animated. Any styling applied to this class affects every item container located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to drag handles in the ListView when reorderMode is set to Animated. Any styling applied to this class affects every drag handle located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to every drag handle bar in the ListView when reorderMode is set to Animated. Any styling applied to this class affects every drag handle bar located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to the footer element in the ListView. Any styling applied to this class affects every ListView located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to the foldout element in the ListView. Any styling applied to this class affects every foldout located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to the size field element in the ListView when showBoundCollectionSize is set to true. Any styling applied to this class affects every size field located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to the size field element in the ListView when showBoundCollectionSize is set to true. Any styling applied to this class affects every size field located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to the size field element in the ListView when showBoundCollectionSize is set to true. Any styling applied to this class affects every size field located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to ListView when showFoldoutHeader is set to true. Any styling applied to this class affects every list located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to ListView when showAddRemoveFooter is set to true. Any styling applied to this class affects every list located beside, or below the stylesheet in the visual tree.

Unity adds this USS class scroll view of BaseListViewwhen showAddRemoveFooter is set to true. Any styling applied to this class affects every list located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to every instance of the BaseVerticalCollectionView element. Any styling applied to this class affects every BaseVerticalCollectionView located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to an instance of the BaseVerticalCollectionView element if the instance’s BaseVerticalCollectionView.showBorder property is set to true. Any styling applied to this class affects every such BaseVerticalCollectionView located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to every item element the BaseVerticalCollectionView contains. Any styling applied to this class affects every item element located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to the bar that appears when the user drags an item in the list. Any styling applied to this class affects every BaseVerticalCollectionView located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to the bar that appears when the user drags an item in the list. Any styling applied to this class affects every BaseVerticalCollectionView located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to the item element when it’s being dragged. Any styling applied to this class affects every BaseVerticalCollectionView item located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to every selected element in the BaseVerticalCollectionView. The BaseVerticalCollectionView.selectionType property decides if zero, one, or more elements can be selected. Any styling applied to this class affects every BaseVerticalCollectionView item located beside, or below the stylesheet in the visual tree.

Unity adds this USS class to every odd-numbered item in the BaseVerticalCollectionView when the BaseVerticalCollectionView.showAlternatingRowBackgrounds property is set to ContentOnly or All. When the showAlternatingRowBackgrounds property is set to either of those values, odd-numbered items are displayed with a different background color than even-numbered items. This USS class is used to differentiate odd-numbered items from even-numbered items. When the showAlternatingRowBackgrounds property is set to None, the USS class is not added, and any styling or behavior that relies on it’s invalidated.

Unity adds this USS class to the BaseVerticalCollectionView’s scroll view. Any styling applied to this class affects every BaseVerticalCollectionView scroll view located beside, or below the stylesheet in the visual tree.

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.

• MultiColumnListView
• MultiColumnTreeView
• ScrollView
• TreeView

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