Propagating property change to parent object

[JkPersson]

I would like to utilize 'dot-notation' in my views to avoid dummy properties in the view models. However I have not been able to propagate UI changes of child properties to the view model. Is it even possible? Following is a simplified example of what I am trying to accomplish:

View:
<?xml version="1.0" encoding="utf-8" ?> <ContentPage x:Class="MauiApp1.Views.MyPage" xmlns="http://schemas.microsoft.com/dotnet/2021/maui" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" xmlns:viewmodels="clr-namespace:MauiApp1.ViewModels" Title="MyPage" x:DataType="viewmodels:MyViewModel"> <VerticalStackLayout> <Entry Text="{Binding A.B.Bb}" /> <Button IsEnabled="{Binding IsButtonEnabled}" Text="{Binding ButtonText}"/> <!-- These labels are just for debug purposes --> <Label Text="{Binding A.B.Bbb}" /> <Label Text="{Binding A.Aa}" /> </VerticalStackLayout> </ContentPage>

ViewModel:
`using CommunityToolkit.Mvvm.ComponentModel;
using MauiApp1.Models;

namespace MauiApp1.ViewModels;
internal partial class MyViewModel : ObservableObject
{
internal MyViewModel()
{
a = new A { B = new B() };
}

[ObservableProperty]
private A a;

partial void OnAChanged(A value)
{
    // In the real world implementation, I would have some validation code here.
    IsButtonEnabled = true;
    ButtonText = "Enabled";
}

[ObservableProperty]
private bool isButtonEnabled = false;

[ObservableProperty]
private string buttonText = "Disabled";

}
`

Model classes:
`using CommunityToolkit.Mvvm.ComponentModel;

namespace MauiApp1.Models;
internal partial class A : ObservableObject
{
[ObservableProperty]
private B b;
partial void OnBChanged(B value)
{
Aa = "Aa: " + value.Bbb;
}

[ObservableProperty]
private string aa;

}

using CommunityToolkit.Mvvm.ComponentModel;

namespace MauiApp1.Models;
internal partial class B : ObservableObject
{
[ObservableProperty]
private string bb;
partial void OnBbChanged(string value)
{
Bbb = "Bbb: " + value;
}

[ObservableProperty]
private string bbb;

}
`

Label Bbb is updating just fine, but Aa and the button is not.
Also A.OnBChanged is not called - which is probably the core of my problem. Please help.

[Mzazvor]

Hey did you manage to solve this ?

[stephenquan]

In A's view model, you can subscribe to B's PropertyChanged event handler, e.g.

internal partial class A : ObservableObject
{
    public B B { get; } = new B();
    [ObservableProperty]
    private string aa;
    public A()
    {
        B.PropertyChanged += (s, e) =>
        {
            switch (e.PropertyName)
            {
                case nameof(B.Bbb):
                    Aa = "Aa: " + value.Bbb;
                    break;
            }
        };
    }
}

Because Aa is a derivative of B.Bbb, I would implement Aa with a read-only getter, i.e.

internal partial class A : ObservableObject
{
    public B B { get; } = new B();
    public string Aa => "Aa: " + B.Bbb;
    public A()
    {
        B.PropertyChanged += (s, e) =>
        {
            switch (e.PropertyName)
            {
                case nameof(B.Bbb):
                    OnPropertyChanged(nameof(Aa));
                    break;
            }
        };
    }
}