WPF TextBox lostFocus event trigger - wpf

Question

I am new to WPF,
In my mainWindow I have multiple TextBox, so whenever a user enters different inputs in these textbox I want to implement those changes in the code behind, as soon as user leaves the focus of the textbox.
For example, my textBox looks like this:
<TextBox Name="SpiralAngleTextBox"
Grid.Column="1" Grid.Row="4"
Margin="5,5,5,5" SelectedText="0"/>
I am not looking to do any kind of input validation. What I want is to trigger some calculations or call a function whenever the TextBox leaves focus after contents of TextBox is updated.

Answer 1

You can write an EventHandler
<TextBox Name="SpiralAngleTextBox"
Grid.Column="1" Grid.Row="4"
Margin="5,5,5,5" SelectedText="0" LostFocus="SpiralAngleTextBox_LostFocus"/>
and in the xaml.cs
private void SpiralAngleTextBox_LostFocus(object sender, RoutedEventArgs e)
{
foo();
}
If you just want it to do stuff when the textbox content changes you can try something like this:
<TextBox Name="SpiralAngleTextBox"
Grid.Column="1" Grid.Row="4"
Margin="5,5,5,5" SelectedText="0" LostFocus="SpiralAngleTextBox_LostFocus"
TextChanged="SpiralAngleTextBox_TextChanged"/>
and in the xaml.cs
bool hasChanged;
private void SpiralAngleTextBox_LostFocus(object sender, RoutedEventArgs e)
{
if(hasChanged)
foo();
hasChanged = false;
}
private void SpiralAngleTextBox_TextChanged(object sender, TextChangedEventArgs e)
{
hasChanged = true;
}

Answer 2

All you need to do is to bind to TextBox.Text
<TextBox Text="{Binding MyProperty}" />
Where MyProperty is some property in your code-behind. This is because TextBox.Text updates on lost focus (UpdateSourceTrigger=LostFocus by default.) You can learn more here: https://learn.microsoft.com/en-us/dotnet/framework/wpf/data/how-to-control-when-the-textbox-text-updates-the-source