冒泡NotifyPropertyChanged

根据 this answer 我不需要费心去为层叠结构上冒泡的NotifyPropertyChanges而烦恼,但我仍然无法让它与这样一个(简化的测试)结构一起工作:

数据保持类

public class TestNotifyChanged : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private string _Test = "default";
    public string Test
    {
        get
        {
            return _Test;
        }
        set
        {
            if(_Test!=value)
            {
                _Test = value;
                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("Test"));
            }
        }
    }
}

使用该测试类和测试属性的ViewModel:

public class ViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private TestNotifyChanged tnc = new TestNotifyChanged(); // only to init, otherwise VS screams at me

    public ViewModel(TestNotifyChanged tnc)
    {
        tnc = tnc; // getting an instance of TestNotifyChanged from "Master" passed in, which hopefully will be replaces by a singleton class.
    }

    private string _Test;
    public string Test
    {
        get
        {
            return tnc.Test;  // this might be the crucial part!?
        }
        set
        {
            if (_Test != value) // never hits that, as I would expect, but you never know..
            {
                _Test = value;
                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("Test"));  // of course also never hit, as expected
            }
        }
    }
}

最后是我的主窗口

public partial class MainWindow : Window
{
    TestNotifyChanged tnc;
    public MainWindow()
    {
        InitializeComponent();
        tnc = new TestNotifyChanged();
        DataContext = new ViewModel(tnc); // pass in my Test-Object that has the Values.
    }

    private void ButtonGet_Click(object sender, RoutedEventArgs e)
    {
        tnc.Test = "new Value";
        MessageBox.Show($"{tnc.Test}"); // got "new Value" here!
    }
}

在xaml中,除了这个按钮之外,我还有一个简单的文本块,它绑定到ViewModel的测试属性:

 <TextBlock x:Name="OutputId" Text="{Binding Path=Test, Mode=OneWay}"/>

现在发生了什么:

• 默认值“default”显示在TextBlock中。

• 当我单击按钮时,消息框显示“新值”

• 文本块是 不 更新为“新值”

我想实现的目标:

• 似乎很简单:TextBlock应该更新为“新值”

当我直接设置测试值时,我可以很容易地使这个工作 在视图模型上 -但这似乎不对,而且与我认为我可以构建应用程序/代码的想法相去甚远。未来的目标是要有一个单例(静态的我想不通)的“记录存储”,它拥有大部分的数据(并且从一个API、本地数据库或者仅仅从内存中获取,如果这些都完成了的话)

所以问题是:
为什么NotifyPropertyChange没有冒泡到View/ViewModel?
或者还有什么我看不到的问题?

我读过 INotifyPropertyChanged bubbling in class hierarchy 和 What is a good way to bubble up INotifyPropertyChanged events through ViewModel properties with MVVM? 和 https://docs.microsoft.com/en-us/dotnet/framework/winforms/how-to-implement-the-inotifypropertychanged-interface 和 OnPropertyChange called but not taking any effect on UI

这些问题大多也很古老。。。

编辑:
我试过“矿工”的建议:

// made tnc public in ViewModel
public TestNotifyChanged tnc = new TestNotifyChanged();

// changed Binding directly to that (and it's Property):
<TextBlock x:Name="OutputId" Text="{Binding Path=tnc.Test, Mode=OneWay}"/>

不幸的是,现在我甚至没有得到默认值,所以我一定误解了smth。

编辑2 :
我在第一次编辑中做错了一件事:

// this isn't recognized as bindable parameter:
public TestNotifyChanged tnc = new TestNotifyChanged();
// it instead has to be
public TestNotifyChanged tnc { get; }

我成功了 TNC ,删除了本地 Test 参数,直接绑定到 Path=TNC.Test

所以我明白了,财产的变化 不要 按照我的期望/想法,最好直接绑定到嵌套对象。