MVVM：模型如何使用 inotifypropertychanged 通知 viewmodel 的变化

Question

如果有任何属性发生更改，我需要 Model 通知 ViewModel，因为我需要将更改的模型实例收集到集合中以进行进一步处理，还需要启用和禁用视图模型中的命令按钮。 所以我使用了 ModelBase 抽象类并添加了 HasChanges 属性，我可以在视图模型中对其进行测试并捕获更改的模型。但它不起作用，我不知道我缺少什么。

public abstract class ModelBase : INotifyPropertyChanged
{
    protected ModelBase()
    {
    }

    private bool _hasChanges;
    public bool HasChanges
    {
        get
        { 
            return _hasChanges;
        }

        set
        {
            if (_hasChanges != value)
            {
                _hasChanges = value;
                RaisePropertyChanged("HasChanges");
            }
        }
    }

    protected void RaisePropertyChanged(string propertyName)
    {
        HasChanges = true;
        this.OnPropertyChanged(new PropertyChangedEventArgs(propertyName));
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged(PropertyChangedEventArgs e)
    {
        var handler = this.PropertyChanged;

        if (handler != null)
        {
            handler(this, e);
        }
    }
}

Model 被包裹在 ViewModel 中，并绑定到 DataGrid 的 View：

private Model_selectedModel;

public Mode SelectedModel
{
    get 
    {
        return _selectedModel; 
    }

    set
    {
        if (_selectedModel != value)
        {
            _selectedModel = value;
            NotifyPropertyChanged("SelectedModel");
        }
    }
}

感谢您的宝贵帮助。

Answer 1

我测试了你的课程，没关系。我认为这里的重点是一个错字：

private Model_selectedModel;

public Mode SelectedModel
{
    get 
    {
        return _selectedModel; 
    }

    set
    {
        if (_selectedModel != value)
        {
            _selectedModel = value;
            NotifyPropertyChanged("SelectedModel");
        }
    }
}

应该有 RaisePropertyChanged 而不是 NotifyPropertyChanged。

下面是我的测试：

XAML

<Window x:Class="TestUpdatePropertyChanged.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:this="clr-namespace:TestUpdatePropertyChanged"
        Title="MainWindow" Height="350" Width="525">

    <Window.DataContext>
        <this:TestViewModel />
    </Window.DataContext>

    <Grid>
        <TextBox Width="100" Height="25" Text="{Binding Path=TestString, UpdateSourceTrigger=PropertyChanged}" />

        <Button Width="100" Height="30" VerticalAlignment="Top" Content="Click" Click="Button_Click" />
    </Grid>
</Window>

Code-behind

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        var testData = this.DataContext as TestViewModel;

        testData.TestString = "Yay, it's change!";

        if (testData.HasChanges == true) 
        {
            MessageBox.Show("It's Change!");
        }
    }
}

public class TestViewModel : ModelBase 
{
   private string _testString = "test";

    public string TestString
    {
        get { return _testString; }

        set
        {
            if (_testString != value)
            {
                _testString = value;
                RaisePropertyChanged("TestString");
            }
        }
    }
} 

public abstract class ModelBase : INotifyPropertyChanged
{
    protected ModelBase()
    {
    }

    private bool _hasChanges;
    public bool HasChanges
    {
        get
        { 
            return _hasChanges;
        }

        set
        {
            if (_hasChanges != value)
            {
                _hasChanges = value;
                RaisePropertyChanged("HasChanges");
            }
        }
    }

    protected void RaisePropertyChanged(string propertyName)
    {
        HasChanges = true;
        this.OnPropertyChanged(new PropertyChangedEventArgs(propertyName));
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged(PropertyChangedEventArgs e)
    {
        var handler = this.PropertyChanged;

        if (handler != null)
        {
            handler(this, e);
        }
    }
}