How to filter Xamarin.Forms TreeView (SfTreeView)?

You can filter the TreeView nodes based on the search text in Xamarin.Forms SfTreeView by changing the collection.

XAML

Use SearchBar to search the TreeViewNodes.

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:TreeViewXamarin"
             xmlns:syncfusion="clr-namespace:Syncfusion.XForms.TreeView;assembly=Syncfusion.SfTreeView.XForms"
             x:Class="TreeViewXamarin.MainPage">
 
    <ContentPage.BindingContext>
        <local:FileManagerViewModel x:Name="viewModel"/>
    </ContentPage.BindingContext>
    <ContentPage.Behaviors>
        <local:Behavior/>
    </ContentPage.Behaviors>
    <StackLayout>
        <SearchBar Placeholder="Search TreeView" x:Name="searchBar"/>
        <syncfusion:SfTreeView x:Name="treeView" ChildPropertyName="SubFiles" ItemTemplateContextType="Node" AutoExpandMode="AllNodesExpanded" ItemsSource="{Binding ImageNodeInfo}">
            <syncfusion:SfTreeView.ItemTemplate>
                <DataTemplate>
                    <Grid x:Name="grid" RowSpacing="0" >
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="40" />
                            <ColumnDefinition Width="*" />
                        </Grid.ColumnDefinitions>
                        <Image Source="{Binding Content.ImageIcon}" VerticalOptions="Center" HorizontalOptions="Center" HeightRequest="35" WidthRequest="35"/>
                        <Grid Grid.Column="1" RowSpacing="1" Padding="1,0,0,0" VerticalOptions="Center">
                            <Label LineBreakMode="NoWrap" Text="{Binding Content.ItemName}" VerticalTextAlignment="Center"/>
                        </Grid>
                    </Grid>
                </DataTemplate>
            </syncfusion:SfTreeView.ItemTemplate>
        </syncfusion:SfTreeView>
    </StackLayout>
</ContentPage>

C#

TextChanged event of the SerachBar to filter the TreeView collection.

namespace TreeViewXamarin
{
    public class Behavior : Behavior<ContentPage>
    {
        SearchBar SearchBar;
        protected override void OnAttachedTo(ContentPage bindable)
        {
            SearchBar = bindable.FindByName<SearchBar>("searchBar");
            SearchBar.TextChanged += SearchBar_TextChanged;
            base.OnAttachedTo(bindable);
        }
    }
}

Compare the search text to the model class property to filter the item. The filtered objects are set to TreeView.ItemsSource.

private void SearchBar_TextChanged(object sender, TextChangedEventArgs e)
{
    if (string.IsNullOrEmpty(e.NewTextValue))
    {
        TreeView.ItemsSource = ViewModel.ImageNodeInfo;
    }
    else
    {
        List<FileManager> items = ViewModel.ImageNodeInfo.Where(x => (x.ItemName.ToLower()).StartsWith(e.NewTextValue.ToLower())).ToList<FileManager>();
        TreeView.ItemsSource = items;
 
        if (items.Count == 0)
        {
            foreach (var node in ViewModel.ImageNodeInfo)
                this.GetChildNode(node, e.NewTextValue);
        }
    }
}
 
private void GetChildNode(FileManager node, string searchText)
{
    if (node.SubFiles.Count < 0) return;
 
    foreach (var child in node.SubFiles)
    {
        if (child.ItemName.ToLower().StartsWith(searchText.ToLower()))
        {
            List<FileManager> items = new List<FileManager>();
            items.Add(child);
            TreeView.ItemsSource = items;
        }
        if (child.SubFiles != null)
        {
            this.GetChildNode(child, searchText);
        }
    }
}