Making a WPF TextBox binding fire on each new character?

Question

How can I make a data binding update as soon as a new character is typed in a TextBox?

I'm learning about bindings in WPF and now I've become stuck on a (hopefully) simple matter.

I have a simple FileLister class where you can set a Path property, and then it will give you a listing of files when you access the FileNames property. Here is that class:

class FileLister:INotifyPropertyChanged {     private string _path = "";      public string Path {         get {             return _path;         }         set {             if (_path.Equals(value)) return;             _path = value;             OnPropertyChanged("Path");             OnPropertyChanged("FileNames");         }     }      public List<String> FileNames {         get {             return getListing(Path);         }     }      private List<string> getListing(string path) {         DirectoryInfo dir = new DirectoryInfo(path);         List<string> result = new List<string>();         if (!dir.Exists) return result;         foreach (FileInfo fi in dir.GetFiles()) {             result.Add(fi.Name);         }         return result;     }      public event PropertyChangedEventHandler PropertyChanged;     protected void OnPropertyChanged(string property) {         PropertyChangedEventHandler handler = PropertyChanged;         if (handler != null) {             handler(this, new PropertyChangedEventArgs(property));         }     } } 

I'm using the the FileLister as a StaticResource in this very simple app:

<Window x:Class="WpfTest4.MainWindow"     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"     xmlns:local="clr-namespace:WpfTest4"     Title="MainWindow" Height="350" Width="525">     <Window.Resources>         <local:FileLister x:Key="fileLister" Path="d:\temp" />     </Window.Resources>     <Grid>         <TextBox Text="{Binding Source={StaticResource fileLister}, Path=Path, Mode=TwoWay}"         Height="25" Margin="12,12,12,0" VerticalAlignment="Top" />         <ListBox Margin="12,43,12,12" Name="listBox1" ItemsSource="{Binding Source={StaticResource ResourceKey=fileLister}, Path=FileNames}"/>     </Grid> </Window> 

The binding is working. If I change the value in the textbox and then click outside of it, the listbox contents will update (as long as the path exists).

The problem is that I would like to update as soon as a new character is typed, and not wait until the textbox lose focus.

How can I do that? Is there a way to do this directly in the xaml, or do I have to handle TextChanged or TextInput events on the box?

Answer 1

In your textbox binding, all you have to do is set UpdateSourceTrigger=PropertyChanged.