# How to: Detect When Text in a TextBox Has Changed

This example shows one way to use the TextChanged event to execute a method whenever the text in a TextBox control has changed.

In the code-behind class for the XAML that contains the TextBox control that you want to monitor for changes, insert a method to call whenever the TextChanged event fires. This method must have a signature that matches what is expected by the TextChangedEventHandler delegate.

The event handler is called whenever the contents of the TextBox control are changed, either by a user or programmatically.

Note

This event fires when the TextBox control is created and initially populated with text.

## Example

In the Extensible Application Markup Language (XAML) that defines your TextBox control, specify the TextChanged attribute with a value that matches the event handler method name.

<TextBox  TextChanged="textChangedEventHandler">
Here is the initial text in my TextBox.  Each time the contents of this TextBox are changed,
the TextChanged event  fires and textChangedEventHandler is called.
</TextBox>


## Example

In the code-behind class for the XAML that contains the TextBox control that you want to monitor for changes, insert a method to call whenever the TextChanged event fires. This method must have a signature that matches what is expected by the TextChangedEventHandler delegate.

// TextChangedEventHandler delegate method.
private void textChangedEventHandler(object sender, TextChangedEventArgs args)
{
// Omitted Code: Insert code that does something whenever
// the text changes...
} // end textChangedEventHandler

' TextChangedEventHandler delegate method.
Private Sub textChangedEventHandler(ByVal sender As Object, ByVal args As TextChangedEventArgs)
' Omitted Code: Insert code that does something whenever
' the text changes...
End Sub


The event handler is called whenever the contents of the TextBox control are changed, either by a user or programmatically.

Note

This event fires when the TextBox control is created and initially populated with text.