Question

How does “UpdateSourceTrigger” affect bindings?

Answer 1

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

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: