Class TreeView

Namespace: Alternet.UI

Assembly: Alternet.UI.Common.dll

Displays a hierarchical collection of labeled items with optional images, each represented by a TreeViewItem.

[ControlCategory("Common")]
public class TreeView : Control, IBaseObject, IDisposableObject, ISupportInitialize, IFocusable, ITextProperty, IComponent, IControl, IDisposable, IWin32Window, INotifyDataErrorInfo

Inheritance: object

BaseObject

DisposableObject

DispatcherObject

DependencyObject

UIElement

FrameworkElement

Control

TreeView

Implements: IBaseObject

IDisposableObject

ISupportInitialize

IFocusable

ITextProperty

IComponent

IControl

IDisposable

IWin32Window

INotifyDataErrorInfo

Examples

Here is how to declare a TreeView in UIXML:

<TreeView Width="300" Height="240" Name="treeView"
          SelectionChanged="TreeView_SelectionChanged"
          ExpandedChanged="TreeView_ExpandedChanged" />

And the corresponding event handler in the code-behind:

private void TreeView_SelectionChanged(object? sender, EventArgs e)
{
    Application.Log($"TreeView: SelectionChanged. SelectedItem: {treeView.SelectedItem?.Text}");
}

private void TreeView_ExpandedChanged(object? sender, TreeViewEventArgs e)
{
    Application.Log($"TreeView: ExpandedChanged. Item: {e.Item.Text} {e.Item.IsExpanded}");
}

Also, a TreeView can be created from code:

void AddItems(Alternet.UI.TreeView treeView, int count)
{
    var r = new Random();

    int start = treeView.Items.Count + 1;

    treeView.BeginUpdate();
    try
    {
        for (int i = start; i < start + count; i++)
        {
            int imageIndex = r.Next(4);
            var item = new TreeViewItem("Item " + i)
            {
                ImageIndex = imageIndex,
            };
            for (int j = 0; j < 3; j++)
                item.Items.Add(new TreeViewItem(item.Text + "." + j, r.Next(4)));
            treeView.Items.Add(item);
        }
    }
    finally
    {
        treeView.EndUpdate();
    }
}

public Alternet.UI.TreeView CreateTreeView()
{
    var result = new Alternet.UI.TreeView();
    AddItems(result, 10);
    return result;
}

Remarks

The Items collection holds all the TreeViewItem objects that are assigned to the TreeView control. The items in this collection are referred to as root items. Any item that is subsequently added to a root item is referred to as a child node. Each TreeViewItem can contain a collection of other TreeViewItem objects.

You can display images next to the tree nodes by assigning an ImageList to the ImageList property and referencing the index value of an Image in the ImageList to assign that Image. Set the ImageIndex property to the index value of the Image that you want to display for all items by default. Individual items can override the default images by setting the ImageIndex property.

TreeView items can be expanded to display the next level of child items. The user can expand the TreeViewItem by clicking the expand button if one is displayed next to the TreeViewItem, or you can expand the TreeViewItem by calling the Expand() method. To expand all the child item levels in the Items collection, call the ExpandAll() method. You can collapse the child TreeViewItem level by calling the Collapse() method, or the user can press the expand button, if one is displayed next to the TreeViewItem. You can also call the Toggle() method to alternate between the expanded and collapsed states.

Examples of how a TreeView can look on different platforms:

TreeView on Windows

Constructors

TreeView(): Initializes a new instance of the TreeView class.

Fields

DefaultCreateStyleLinux: The set of flags that are closest to the defaults for the native control under Linux.

DefaultCreateStyleMacOs: The set of flags that are closest to the defaults for the native control under MacOs.

DefaultCreateStyleWin: The set of flags that are closest to the defaults for the native control under Windows.

Properties

AllowLabelEdit: Gets or sets a value indicating whether the label text of the tree items can be edited.

ControlKind: Returns control identifier.

FirstItem: Gets first root item in the control or null if there are no items.

FullRowSelect: Gets or sets a value indicating whether the selection highlight spans the width of the tree view control.

HasBorder: Gets or sets a value indicating whether the control has a border.

HideRoot: Gets or sets a value indicating whether the display of the root node is supressed. This effectively causing the first-level nodes to appear as a series of root nodes.

ImageIndex: Gets or sets the index of the image that is displayed for the items in this TreeView by default.

ImageList: Gets or sets the ImageList to use when displaying item images in the control.

Indentation: Gets or sets the current control indentation.

Items: Gets a collection containing all the root items in the control.

LastItem: Gets last item in the control or null if there are no items.

LastRootItem: Gets last root item in the control or null if there are no items.

RowLines: Gets or sets a value indicating whether to draw a contrasting border between displayed rows.

SelectedItem: Gets or sets the currently selected item in the TreeView.

SelectedItems: Gets a collection containing the currently selected items in the TreeView.

SelectionMode: Gets or sets the method in which items are selected in the TreeView.

ShowExpandButtons: Gets or sets a value indicating whether expand buttons are displayed next to tree items that contain child tree items.

ShowLines: Gets or sets a value indicating whether lines are drawn between tree items in the tree view control.

ShowRootLines: Gets or sets a value indicating whether lines are drawn between the tree items that are at the root of the tree view.

StateImageSpacing: Gets or sets the number of horizontal pixels between the buttons and the state images.

TopItem: Gets or sets the first fully-visible tree item in the tree view control.

TwistButtons: Gets or sets a value indicating whether to select alternative style of +/- buttons and to show rotating ("twisting") arrows instead.

VariableRowHeight: Gets or sets a value indicating whether row heights become big enough to fit the content.

Methods

Add(TreeViewItem): Adds an object to the end of the Items collection.

Add(string): Adds string to the end of the Items collection.

ClearSelected(): Unselects all items in the TreeView.

CollapseAll(): Collapses all child tree items.

CreateHandler(): Creates a handler for the control.

EnsureVisible(TreeViewItem?): Ensures that the tree item is visible, expanding tree items and scrolling the tree view control as necessary.

ExpandAll(): Expands all child tree items.

HitTest(PointD): Provides tree view item information, at a given client point, in device-independent units.

MakeAsListBox(): Changes visual style of the control to look like ListBox.

OnAfterCollapse(TreeViewEventArgs): Called after a tree item is collapsed.

OnAfterExpand(TreeViewEventArgs): Called after a tree item is expanded.

OnAfterLabelEdit(TreeViewEditEventArgs): Called after a tree item label is edited.

OnBeforeCollapse(TreeViewCancelEventArgs): Called before a tree item is collapsed.

OnBeforeExpand(TreeViewCancelEventArgs): Called before a tree item is expanded.

OnBeforeLabelEdit(TreeViewEditEventArgs): Called before a tree item label is edited.

OnExpandedChanged(TreeViewEventArgs): Called after IsExpanded property value of a tree item belonging to this TreeView changes.

OnItemAdded(TreeViewEventArgs): Called when an item is added to this TreeView control, at any nesting level.

OnItemRemoved(TreeViewEventArgs): Called when an item is removed from this TreeView control, at any nesting level.

OnSelectionChanged(EventArgs): Called when the SelectedItem property or the SelectedItems collection has changed.

RaiseAfterCollapse(TreeViewEventArgs): Raises the AfterCollapse event and calls OnAfterCollapse(TreeViewEventArgs).

RaiseAfterExpand(TreeViewEventArgs): Raises the AfterExpand event and calls OnAfterExpand(TreeViewEventArgs).

RaiseAfterLabelEdit(TreeViewEditEventArgs): Raises the AfterLabelEdit event and calls OnAfterLabelEdit(TreeViewEditEventArgs).

RaiseBeforeCollapse(TreeViewCancelEventArgs): Raises the BeforeCollapse event and calls OnBeforeCollapse(TreeViewCancelEventArgs).

RaiseBeforeExpand(TreeViewCancelEventArgs): Raises the BeforeExpand event and calls OnBeforeExpand(TreeViewCancelEventArgs).

RaiseBeforeLabelEdit(TreeViewEditEventArgs): Raises the BeforeLabelEdit event and calls OnBeforeLabelEdit(TreeViewEditEventArgs).

RaiseExpandedChanged(TreeViewEventArgs): Raises the ExpandedChanged event and calls OnExpandedChanged(TreeViewEventArgs).

RaiseSelectionChanged(EventArgs): Raises the SelectionChanged event and calls OnSelectionChanged(EventArgs).

RemoveAll(): Removed all items from the control.

RemoveItemAndSelectSibling(TreeViewItem?): Removes item and selects its sibling (next or previous on the same level).

RemoveSelected(): Removes selected items from the control.

ScrollIntoView(TreeViewItem?): Scrolls the specified item into view.

SelectAndShowItem(TreeViewItem?): Selects and shows specified item in the control.

SelectFirstItem(): Selects first item in the control.

SetSelected(TreeViewItem, bool): Selects or clears the selection for the specified item in a TreeView.

SetSelectedIndex(int?): Sets SelectedItem to the item on the root level with the specified index.

Events

AfterCollapse: Occurs after the tree item is collapsed.

AfterExpand: Occurs after the tree item is expanded.

AfterLabelEdit: Occurs after the tree item label text is edited. This event can be canceled.

BeforeCollapse: Occurs before the tree item is collapsed. This event can be canceled.

BeforeExpand: Occurs before the tree item is expanded. This event can be canceled.

BeforeLabelEdit: Occurs before the tree item label text is edited. This event can be canceled.

ExpandedChanged: Occurs after IsExpanded property value of a tree item belonging to this TreeView changes.

ImageListChanged: Occurs when the ImageList property value changes.

ItemAdded: Occurs when an item is added to this TreeView control, at any nesting level.

ItemRemoved: Occurs when an item is removed from this TreeView control, at any nesting level.

SelectionChanged: Occurs when the SelectedItem property or the SelectedItems collection has changed.

SelectionModeChanged: Occurs when the value of the SelectionMode property changes.

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