Question

根据this answer，我不必为NotifyPropertyChanges烦恼而冒充层次结构，但仍然无法使其与像这样的（简化的test-）结构一起工作：

数据保存类

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Test-Class和Test-Property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MainWindow cs

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，除了那个按钮外，我还有一个简单的TextBlock，它绑定到ViewModel的Test属性：

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

现在发生的事情：

默认值“ default”显示在TextBlock中。
当我单击按钮时，消息框将显示“新值”
TextBlock 不更新为“新值”

我要实现的目标：

似乎很简单：TextBlock应该更新为“新值”

当我直接在ViewModel上设置测试值时，我可以轻松完成这项工作-但这似乎不正确，并且与我认为可以构造应用程序/代码的地方相去甚远。未来的目标是拥有一个拥有大部分数据（并从API，本地数据库或仅从内存中获取数据）的Singleton（我认为静态无法工作）“ RecordStore”

所以问题是：
为什么NotifyPropertyChange不冒泡到View / ViewModel？
还是我没有看到另一个问题？

我已经读过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

其中大多数问题还很老...

编辑：
我以这种方式尝试了@MineR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，现在我什至没有得到默认值，所以我一定误会了。

EDIT2 ：
我在第一次编辑中做错了一件事情：

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

我完成了TNC，删除了本地Test参数，直接绑定到Path=TNC.Test

所以我知道，PropertyChanges 不会冒泡，就像我希望的那样，最好直接绑定到嵌套对象。

Answer 1

“冒泡”是routed events的概念。像PropertyChanged这样的常规事件不会“冒泡”。

除了ViewModel中的明显错误tnc = tnc;（应该为this.tnc = tnc;）之外，这两个类的Test属性也不相关。为了更新其自己的Test属性，ViewModel必须在tnc注册一个PropertyChanged事件处理程序。并且当其自己的Test属性更改时，它必须更新tnc的属性。

public class ViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private TestNotifyChanged tnc;

    public ViewModel(TestNotifyChanged t)
    {
        tnc = t;
        tnc.PropertyChanged += (s, e) =>
        {
            if (e.PropertyName == nameof(Test) || string.IsNullOrEmpty(e.PropertyName))
            {
                Test = tnc.Test; // update ViewModel.Test from TestNotifyChanged.Test
            }
        };
    }

    private string test;
    public string Test
    {
        get
        {
            return test; // always return own value
        }
        set
        {
            if (test != value)
            {
                test = value;
                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Test)));

                tnc.Test = Test; // update TestNotifyChanged.Test from ViewModel.Test
            }
        }
    }
}

或者，删除Test属性的后备字段，仅在tnc.Test上操作：

public class ViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private TestNotifyChanged tnc;

    public ViewModel(TestNotifyChanged t)
    {
        tnc = t;
        tnc.PropertyChanged += (s, e) =>
        {
            if (e.PropertyName == nameof(Test) || string.IsNullOrEmpty(e.PropertyName))
            {
                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Test)));
            }
        };
    }

    public string Test
    {
        get { return tnc.Test; }
        set { tnc.Test = Test; }
    }
}

幸运的是，根本没有必要。

相反，可能只是像这样的公共Tnc属性

public class ViewModel
{
    public TestNotifyChanged Tnc { get; }

    public ViewModel(TestNotifyChanged tnc)
    {
        Tnc = tnc;
    }
}

具有这样的绑定：

<TextBlock Text="{Binding Tnc.Test}"/>

冒泡NotifyPropertyChanged

1 个答案: