This is a property on a binding that controls the data flow from a target to a source and used for two-way data binding. The default mode is when the focus changes but there are many other options available. Properties available with UpdateSourceTrigger:

. Default: This is the default value and it means a lost focus for most of the controls.
. LostFocus: Value update will be on hold until the focus moves out of the control.
. PropertyChanged: Value update will happen whenever a target property changes. It usually happens on every keystoke.
. Explicit: Used to defer source updates until the user does it forcibly by the click of a button or so.

Default vs LostFocus: Default and LostFocus means the same thing for most of the controls with the exception of DataGrid. For DataGrid:

. Lost Focus: Cell lost focus
. Default: Row lost focus

Code:

1. <grid>
2. <Grid.ColumnDefinitions>
3. <ColumnDefinition Width="50*" />
4. <ColumnDefinition Width="50*" />
5. </Grid.ColumnDefinitions>
6. <TextBlock Text="Source:" Width="auto" />
7. <TextBox Name="SourceText" Width="160" Height="30" Margin="48,0,44,82" />
8. <TextBlock Text="Target:" Grid.Column="1" Width="auto" />
9. <TextBox Name="TargetText" Width="160" Height="30" Text="{Binding ElementName=SourceText, Path=Text,UpdateSourceTrigger=Default}" Grid.Column="1" Margin="44,0,47,82" />
10. </grid>

Output:

When the user types into the source TextBox:

<br><br><img src='./qimages/F652-7-32.jpg'> <br><br>   _{Your Comment}