How to Search in a Nested TreeView with ItemsSource?

Question

i have a treeView which i loaded data with ItemsSource like this:

[ObservableProperty]
private ObservableCollection<FileSystemItem> items = new ObservableCollection<FileSystemItem>();

private async Task LoadFolder(string folderPath, ObservableCollection<FileSystemItem> parentCollection)
{
    foreach (string directoryPath in Directory.EnumerateDirectories(folderPath))
    {
        var directoryInfo = new DirectoryInfo(directoryPath);
        
        var directoryNode = new FileSystemItem(directoryInfo);
        await LoadFolder(directoryPath, directoryNode.Children);
        parentCollection.Add(directoryNode);
    }

    foreach (string filePath in Directory.EnumerateFiles(folderPath))
    {
        var fileInfo = new FileInfo(filePath);
        var fileNode = new FileSystemItem(fileInfo);
            parentCollection.Add(fileNode);
    }
}

now, i want to search in my treeview, i am using following code:

Items = new(Search(query, _backupItems));

public IEnumerable<FileSystemItem> Search(string query, ObservableCollection<FileSystemItem> nodes)
{
    foreach (var node in nodes)
    {
        if (node.DisplayName.Contains(query, StringComparison.OrdinalIgnoreCase))
        {
            yield return node;
        }

        foreach (var result in Search(query, node.Children))
        {
            yield return result;
        }
    }
}

but there is 2 issues: 1.after searching and removing text from textbox ItemTemplaceSelector uses a wrong template! 2.i want to show every searched item in its parent folder, currently all searched items added into treeview root level.

---

UPDATE 1:

This is a sample repo App5.zip

First of all change folder path (please create a folder with some sub folders which contains some ttf,otf or woff files. )

await LoadFilesAndFolders(@"D:\Applications\Font");

---

UPDATE 2:

i used following codes and it seems that everything is working fine.

public void OnAutoSuggestBoxTextChanged(AutoSuggestBox sender, AutoSuggestBoxTextChangedEventArgs args)
{
    var query = sender.Text.ToLower();

    // Apply filter to the main collection
    advancedCollectionView.Filter = item =>
    {
        var fileSystemItem = item as FileSystemItem;
        if (fileSystemItem == null) return false;
        return FilterItems(fileSystemItem, query);
    };

    // Apply filter to children of each item in the main collection
    foreach (var item in Items)
    {
        ApplyFilterToItem(item, query);
    }
}

private void ApplyFilterToItem(FileSystemItem item, string query)
{
    item.MyChildren.Filter = childItem =>
    {
        var childFileSystemItem = childItem as FileSystemItem;
        if (childFileSystemItem == null) return false;
        return FilterItems(childFileSystemItem, query);
    };

    // Recursively apply the filter to each child
    foreach (var child in item.Children)
    {
        ApplyFilterToItem(child, query);
    }
}
bool FilterItems(FileSystemItem item, string query)
{
    // Check if the item matches the query
    if (item.DisplayName.ToLower().Contains(query))
    {
        return true;
    }

    // Recursively check if any child item matches the query
    foreach (var child in item.Children)
    {
        if (FilterItems(child, query))
        {
            return true;
        }
    }

    return false;
}

Answer 1

Did you mean this?

I make a little change on your code but note OnAutoSuggestBoxTextChanged need rewriting for the general condition.

I use one more AdvancedCollectionView for children based on your application design.

public class FileSystemItem
{
    ...
    public ObservableCollection<FileSystemItem> Children { get; } = new ObservableCollection<FileSystemItem>();
    public AdvancedCollectionView MyChildren { get; } = new AdvancedCollectionView();
  
    public FileSystemItem(FileSystemInfo fileSystemInfo)
    {
        ...
        MyChildren = new AdvancedCollectionView(Children, true);
    }
}

XAML

<TreeView x:Name="treeView"
          ItemsSource="{x:Bind ViewModel.advancedCollectionView, Mode=OneWay}"
          SelectionMode="Multiple">
    <TreeView.ItemTemplate>
        <DataTemplate x:DataType="local:FileSystemItem">
            <TreeViewItem ItemsSource="{x:Bind MyChildren}">
                <TextBlock Text="{x:Bind DisplayName}" />
            </TreeViewItem>
        </DataTemplate>
    </TreeView.ItemTemplate>
</TreeView>

The Code behind

    public void OnAutoSuggestBoxTextChanged(AutoSuggestBox sender, AutoSuggestBoxTextChangedEventArgs args)
{
    advancedCollectionView.Filter = _ => true;
    advancedCollectionView.Filter = item =>
    {
        var node = (FileSystemItem)item;
        var name = node.DisplayName ?? "";

        // Check if the current node matches the search text
        if (name.Contains(sender.Text, StringComparison.OrdinalIgnoreCase))
            return true;

        if (node.HasChildren)
        {
            node.MyChildren.Filter = _ => true;
            node.MyChildren.Filter = item =>
            {
                var node = (FileSystemItem)item;
                var name = node.DisplayName ?? "";

                // Check if the current node matches the search text
                if (name.Contains(sender.Text, StringComparison.OrdinalIgnoreCase))
                    return true;
                else
                    return false;

                //TODO rewrite the code. This is Just for example.
            };
            if (node.MyChildren.Count > 0)
            {
                return true;
            }
        }

        // Check if any child node matches the search text
        //foreach (var child in node.Children)
        //{
        //    if (FilterRecursive(child, sender.Text))
        //        return true;
        //}

        // If none of the current node or its children match, return false
        return false;

    };
}

Update with the more general code example.

private string _theFilterString;
public void OnAutoSuggestBoxTextChanged(AutoSuggestBox sender, AutoSuggestBoxTextChangedEventArgs args)
{
    _theFilterString = sender.Text;
    advancedCollectionView.Filter = _ => true;
    advancedCollectionView.Filter = MyFilter;
}

bool MyFilter(object item)
{
    var node = (FileSystemItem)item;
    var name = node.DisplayName ?? "";

    if (name.Contains(_theFilterString, StringComparison.OrdinalIgnoreCase))
        return true;

    if (node.HasChildren)
    {
        node.MyChildren.Filter = _ => true;
        node.MyChildren.Filter = MyFilter;
        if (node.MyChildren.Count > 0)
        {
            return true;
        }
    }
    return false;
}