Selection in Xamarin TreeView (SfTreeView)

2 Oct 20236 minutes to read

This section explains how to perform selection and its related operations in the TreeView.

UI Selection

The TreeView allows selecting the items either programmatically or touch interactions by setting the SelectionMode property value to other than None. The control has different selection modes to perform selection operations as listed as follows.

None: Allows disabling the selection.
Single: Allows selecting the single item only. When clicking on the selected item, selection not will not be cleared. This is the default value for SelectionMode.
SingleDeselect: Allows selecting the single item only. When clicking on the selected item, selection gets cleared.
Multiple: Allows selecting more than one item. Selection is not cleared when selecting more than one items. When clicking on the selected item, selection gets cleared.
Extended: Allows to select the multiple items using the common key modifiers in UWP platform and for other platforms, it works as Single selection.

XAML
C#
<syncfusion:SfTreeView x:Name="TreeView" SelectionMode="Multiple"/>
TreeView.SelectionMode = SelectionMode.Multiple;

Xamarin Forms TreeView with Selection

Programmatic Selection

When the SelectionMode is other than None, the item or items in the TreeView can be selected from the code by setting the SelectedItem, or adding items to the SelectedItems property based on the SelectionMode.

When the selection mode is Single or SingleDeselect, programmatically select an item by setting the underlying object to the SelectedItem property.

C#
treeView.SelectedItem = viewModel.CountriesInfo[2];

When the selection mode is Multiple, programmatically select more than one item by adding the underlying object to the SelectedItems property.

C#
treeView.SelectedItems.Add(viewModel.CountriesInfo[2]);
treeView.SelectedItems.Add(viewModel.CountriesInfo[3]);

WARNING

If an item is selected programmatically when SelectionMode is None and if multiple items are programmatically selected when SelectionMode is Single or SingleDeselect, then exception will be thrown internally.

Selected items

Gets selected Items

The TreeView gets all the selected items through the SelectedItems property and gets the single item by using the SelectedItem property.

Clear selected items

The selected items can be cleared by calling the SelectedItems.Clear() method.

C#
treeView.SelectedItems.Clear();

CurrentItem vs SelectedItem

The TreeView gets the selected item by using the SelectedItem and CurrentItem properties. Both SelectedItem and CurrentItem returns the same data object when selecting single item. When selecting more than one item, the SelectedItem property returns the first selected item, and the CurrentItem property returns the last selected item.

Select an entire row

By default, the selection starts from the indent level only. You can select the full row by enabling the FullRowSelect property. By setting the FullRowSelect to true the selection spans the width of tree view control.

XAML
C#
<syncfusion:SfTreeView x:Name="TreeView" FullRowSelect="True" />
TreeView.FullRowSelect = true;

Xamarin Forms TreeView with FullRowSelect

Selected item style

Selection background

The TreeView allows changing the selection background color for the selected items by using the SelectionBackgroundColor property. You can also change the selection background color at runtime.

Selection foreground

The TreeView allows changing the selection foreground color for the selected items by using the SelectionForegroundColor property. You can also change the selection foreground color at runtime.

NOTE

SelectionForegroundColor is applicable only for unbound mode.

Events

SelectionChanging Event

The SelectionChanging event is raised while selecting an item at the execution time. The ItemSelectionChangingEventArgs has the following members which provides the information for SelectionChanging event:

AddedItems: Gets collection of the underlying data objects where the selection is going to process.
RemovedItems: Gets collection of the underlying data objects where the selection is going to remove.

You can cancel the selection process within this event by setting the ItemSelectionChangingEventArgs.Cancel property to true.

C#
treeView.SelectionChanging += TreeView_SelectionChanging;  

private void TreeView_SelectionChanging(object sender, ItemSelectionChangingEventArgs e)
{
   if (e.AddedItems.Count > 0 && e.AddedItems[0] == ViewModel.Items[0])
       e.Cancel = true;
}

SelectionChanged event

The SelectionChanged event will occur once selection process has been completed for the selected item in the TreeView. The ItemSelectionChangedEventArgs has the following members which provides information for SelectionChanged event:

AddedItems: Gets collection of the underlying data objects where the selection has been processed.
RemovedItems: Gets collection of the underlying data objects where the selection has been removed.

C#
treeView.SelectionChanged += TreeView_SelectionChanged;  

private void TreeView_SelectionChanged(object sender, ItemSelectionChangedEventArgs e)
{
   treeView.SelectedItems.Clear();
}

NOTE

SelectionChanging and SelectionChanged events will be triggered only on UI interactions.

The TreeView allows to select the items through keyboard interactions. Behavior of key navigation in UWP platform is explained as follows:

When the SelectionMode is Single or SingleDeselect, the selected item is highlighted with FocusBorderColor around the item while key navigation.
When the SelectionMode is Multiple or Extended, the FocusBorderColor will set to the CurrentItem.

FocusBorderColor

The FocusBorderColor property is used to set the border color for the current focused item. For Android and iOS platform, the default color is Color.Transparent and for UWP platform, the default color is Color.FromRgb(213, 213, 213).

FocusBorderThickness

The FocusBorderThickness property is used to set the border thickness for the current focused item. For Android and iOS platform, the default thickness is 0 and for UWP platform, the default thickness is 1.

Limitation

When a grid is loaded inside the ItemTemplate with background color, the SelectionBackgroundColor will not display. Because, it overlaps the SelectionBackgroundColor. In this case, set the background color for the TreeView instead of grid in the ItemTemplate.
When the TreeView contains duplicated items in the collection, only the first item whose instance was created initially will be selected or deselected.