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 happen 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 :
<grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="50*" />
<ColumnDefinition Width="50*" />
</Grid.ColumnDefinitions>
<TextBlock Text="Source:" Width="auto" />
<TextBox Name="SourceText" Width="160" Height="30" Margin="48,0,44,82" />
<TextBlock Text="Target:" Grid.Column="1" Width="auto" />
<TextBox Name="TargetText" Width="160" Height="30" Text="{Binding ElementName=SourceText, Path=Text,UpdateSourceTrigger=Default}" Grid.Column="1" Margin="44,0,47,82" />
</grid>
Output :
When the user types into the source TextBox :
