TextBox not triggering PropertyChanged event - xaml

Question

I am struggling to figure out why a propertychanged event or lostfocus event is not being triggered when I enter text into a textbox and navigate away from the control.
I am building a Universal Windows Platform app.
I know I'm doing something retarded but I just don't see it.
Any suggestions?
XAML:
<Page
x:Class="xxx.Client.FormPage"
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:viewModels="using:xxx.xxx.ViewModels"
Background="LightBlue"
mc:Ignorable="d">
<Page.Resources>
<Style x:Key="TextBoxStyle" TargetType="TextBox">
<Setter Property="HorizontalAlignment" Value="Stretch" />
<Setter Property="TextAlignment" Value="Center" />
</Style>
</Page.Resources>
<Page.DataContext>
<viewModels:FormViewModel />
</Page.DataContext>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="auto" />
<RowDefinition Height="auto" />
<RowDefinition Height="auto" />
<RowDefinition Height="*" />
<RowDefinition Height="auto" />
</Grid.RowDefinitions>
<TextBox Grid.Row="0" Text="{Binding InstructorNameInput}" Style="{StaticResource TextBoxStyle}"
PlaceholderText="Instructor Name" />
<TextBox Grid.Row="1" Text="{Binding InstructorIdInput}" Style="{StaticResource TextBoxStyle}"
PlaceholderText="Instructor Id" />
<TextBox Grid.Row="2" Text="{Binding CourseInput}" Style="{StaticResource TextBoxStyle}"
PlaceholderText="Course" />
<Button Grid.Row="4" Content="Accept" Command="{Binding Submit}"
HorizontalAlignment="Stretch"
Foreground="Black" />
</Grid>
</Page>
ViewModel:
public partial class FormViewModel : ViewModelBase
{
public FormViewModel()
{
InstructorName = new RequiredField("Instructor's Name:");
InstructorId = new RequiredField("Instructor's Employee#:");
Course = new RequiredField("Course:");
var courses = CourseFactory.Produce();
var administration = new Administration(courses, null);
Submit = new DelegateCommand(_=> OnSubmit(), CanSubmit);
}
string _instructorNameInput = null;
public string InstructorNameInput
{
get { return _instructorNameInput; }
set
{
if (_instructorNameInput != value)
{
_instructorNameInput = value;
OnNotifyPropertyChanged();
}
}
}
string instructorIdInput = null;
public string InstructorIdInput
{
get { return instructorIdInput; }
set
{
if (instructorIdInput != value)
{
instructorIdInput = value;
OnNotifyPropertyChanged();
}
}
}
string courseInput = null;
public string CourseInput
{
get { return courseInput; }
set
{
if (courseInput != value)
{
courseInput = value;
OnNotifyPropertyChanged();
}
}
}
public RequiredField InstructorName { get; }
public RequiredField InstructorId { get; }
public RequiredField Course { get; }
public ObservableCollection<RequiredField> RequiredFields { get; } = new ObservableCollection<RequiredField>();
}
ViewModel.internal:
public partial class FormViewModel
{
static void OnSubmit()
{
var adminsistration = new Administration();
}
bool CanSubmit(object obj) => !GetUnsatisfied().Any();
IEnumerable<RequiredField> GetUnsatisfied()
{
if (string.IsNullOrEmpty(InstructorIdInput))
{
RequiredFields.Add(InstructorId);
}
else
{
var result = 0;
var isNumeric = int.TryParse(InstructorIdInput, out result);
if (!isNumeric)
{
RequiredFields.Add(new RequiredField(InstructorId.About, "Instructor ID must be numeric"));
}
}
if (string.IsNullOrEmpty(InstructorNameInput))
{
RequiredFields.Add(InstructorName);
}
if (string.IsNullOrEmpty(CourseInput))
{
RequiredFields.Add(Course);
}
return RequiredFields;
}
}

Answer 1

The default binding mode for UWP as MSDN says:
The default is OneWay.
Set it to TwoWay:
<TextBox Grid.Row="0" Text="{Binding InstructorNameInput, Mode=TwoWay}" .../>