Bind a TextBox to filter a listbox...

TextSearchFilter.cs

public class TextSearchFilter {
     public TextSearchFilter(ICollectionView filteredView, TextBox textBox) {
          string filterText = "";

          filteredView.Filter = delegate(object obj) {
               if (String.IsNullOrEmpty(filterText)) return true;

               string str = obj as string;
               if (String.IsNullOrEmpty(str)) return false;

               int index = str.IndexOf(
               filterText,
               0,
               StringComparison.InvariantCultureIgnoreCase);

               return index > -1;
          };

          textBox.TextChanged += delegate {
               filterText = textBox.Text;
               filteredView.Refresh();
          };
     }
}

//The ViewModel unfortunately will need to know about the textbox...

string[] wordList = this.FindResource("WordList") as string[];
ICollectionView view = CollectionViewSource.GetDefaultView(wordList);
new TextSearchFilter(view, this.txtSearch);