WPF Combobox & Textbox Behavior

I made a simple test to try and isolate out an issue I was having with comboboxes. I want to give the user the opportunity to cancel the edit made to a control before triggering calculations.

In the test, a textbox gave me the result that I was looking for. When canceling, the control reverts back to what it was. When canceling the input in the combobox, the combobox appears as though it was not canceled. In both of these cases, the model and viewmodel are correct.

How can I have the combobox behave the same way the textbox does to allow the control to reflect the viewmodel correctly?

Model and viewmodel:

Option Explicit On
Option Strict On
Imports System.ComponentModel

Public Class ViewModel
	Implements INotifyPropertyChanged
	Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
	Protected Overridable Sub OnPropertyChanged(propertyName As String)
		RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
	End Sub

	Public Sub New()
		Model = New Model
	End Sub

	Public Property Model As Model
	Public Property Text As String
		Get
			Return Model.Text
		End Get
		Set(value As String)
			If cancel() Then
				OnPropertyChanged("Text")
				Exit Property
			End If
			Model.Text = value
			OnPropertyChanged("Text")
		End Set
	End Property

	Private Function cancel() As Boolean
		If MsgBox("Cancel?", MsgBoxStyle.YesNo) = MsgBoxResult.Yes Then
			Return True
		Else Return False
		End If
	End Function
End Class

Public Class Model
	Public Sub New()
		Text = "Hello, World!"
	End Sub
	Public Property Text As String
End Class

View:

<Window x:Class="MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:test"
        mc:Ignorable="d"
        Title="MainWindow" Height="241" Width="416" d:DataContext="{d:DesignInstance Type=local:ViewModel}">
	<Grid>
		<TextBox HorizontalAlignment="Left" Margin="108,95,0,0" TextWrapping="Wrap" Text="{Binding Text, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" VerticalAlignment="Top" Width="120"/>
		<ComboBox HorizontalAlignment="Left" Margin="108,144,0,0" VerticalAlignment="Top" Width="120" IsEditable="True" Text="{Binding Text, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
	</Grid>
</Window>

Window code-behind:

Class MainWindow
	Public Sub New()
		InitializeComponent()
		DataContext = New ViewModel
	End Sub
End Class

Because the ComboBox contains a TextBox, when the user Cancel(), it does not affect the TextBox.Text, which is why this issue occurs.

We can add a Button and in its Click event, obtain the Text property of the Model, ComboBox, and the TextBox inside the ComboBox.

I'm using C# and I believe you should be able to understand.

// in Button click event

// get TextBox inside the ComboBox
var textBox = cb.Template.FindName("PART_EditableTextBox", cb) as TextBox;

MessageBox.Show($"model: {Model.Text}, cb: {cb.Text}, textBox: {textBox.Text}");

I solved the problem using this method. You can give it a try.

<ComboBox x:Name="cb" IsEditable="True" Text="{Binding Path=Text, Delay=5}" />