Property change is not propagated to binding target (UWP) - xaml

Question

I have a ViewModel and a Class. They look like this:
//viewmodel
public class MyViewModel : ViewModelBase {
private MyClass myClass;
public MyClass MyClass{
get{
return myClass;
}
set{
this.myClass = value;
base.OnPropertyChanged();
}
}
private string testString;
public string TestString{
get{
return testString;
}
set{
this.testString = value;
base.OnPropertyChanged();
}
}
public MyViewModel(){
this.MyClass = new MyClass();
this.TestString = "blah, blah, blah"
}}
//class
public class MyClass : ViewModelBase{
private string myString;
public string MyString{
get {
return myString
}
set{
this.myString = value;
base.OnPropertyChanged();
}
}
public MyClass (){
this.MyString = "25"; }}
The base class - ViewModelBase implements INotifyChange and contains OnPropertyChanged handler logic.
I have a UserControl where I wish to bind values from MyClass like this:
<TextBlock Text="{x:Bind Path=MyViewModel.MyClass.MyString, Mode=TwoWay}"></TextBlock>
However this does not work. Value is binded in initialisation correctly, but any change in MyViewModel.MyClass.MyString is not reflected in texblock, the text remains the same. The OnPropertyChange is raised, the breakpoint in ViewModelBase is hit with MyString value changed, but it is somehow not propagated to texblock.
Binding on simple value from MyClass works like charm, this textblock is updated, when property is changed:
<TextBlock Text="{x:Bind Path=MyViewModel.TestString, Mode=TwoWay}"></TextBlock>
What am I missing? Why the textblock with binding to "MyViewModel.MyClass.MyString" is not being updated?

Answer 1

I have tested the code you provided and don't think there is any problem with it. Where the problem could be, however, is your Page's code-behind. By any chance, aren't you using this as the property declaration?
public MyViewModel MyViewModel => new MyViewModel();
Because in this case, every access to MyViewModel property evaluates as a new instance of MyViewModel class. In this configuration, you would properly change the property, but the UI would never notice, as you would update the property on a new instance. If you instead use
public MyViewModel MyViewModel { get; } = new MyViewModel();
You will get the correct behavior of creating only one instance when the page is created.
I have the following code:
public sealed partial class MainPage : Page
{
public MainPage()
{
this.InitializeComponent();
}
public MyViewModel MyViewModel { get; } = new MyViewModel();
private void Button_Click(object sender, RoutedEventArgs e)
{
MyViewModel.MyClass.MyString = "test";
}
}
And my simple ViewModelBase:
public class ViewModelBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}