Question: I have two textboxes in my wpf application `tb1` and `tb2`.  

I want `tb1.text` to be updated with `tb2.Text` **only** when `tb2` loses focus.  

I tried:  

xaml

```
<TextBox Name="tb1" Text="{Binding Text, ElementName=tb2 }" "/>
<TextBox Name="tb2" /> 

```

But `tb1.Text` is updated instantly.   

Can it be done using Bindings?

Answer: 
The default value for `UpdateSourceTrigger` property of the `Binding` is `LostFocus`, so if you choose `tb2` as the **binding target** you can update `tb1` or the **binding source** on lose focus.

Now you want the binding to work in a one-way mode **from target to source** (tb2->tb1), so you need to change `Mode` of `Binding` to `OneWayToSource`. 

```
<TextBox Name="tb1" /> <!--tb1.Text is source of binding-->
<TextBox Name="tb2" Text="{Binding Text, ElementName=tb1, Mode=OneWayToSource}"/> 

```

in case of one-way **source to target** use `OneWay`, otherwise use default which is `TwoWay`.
```
private void tb2_LostFocus(object sender, RoutedEventArgs e)
{
    tb1.Text = tb2.Text;
}

```