从不同的类更改 ViewModel 属性并更新视图 - MVVM

Question

我需要从class 中的方法调用更改View 上的Button 的Visibility。

我尝试通过在class 中公开VeiwModel 来访问它，然后成功地将Property“ShowRedHat”从真更改为假，但这不会更新Button 的可见性在视图中。这也会双重加载 ViewModel，这在我的解决方案中是不可接受的。

感谢任何帮助。

班级：

   public class HatEngine
   {
      
       public void SetShowRedHat()
       {
          ????.ShowRedHat = false;
       }
   }

ViewModel 中的属性：

public class MyViewModel : ObservableObject
{
    private bool _showRedHat;
    public bool ShowRedHat
    {
        get { return _showRedHat; }
        set
        {
            OnPropertyChanged(ref _showRedHat, value);
        }
    }
}

视图中的按钮：

    <Button Content="Red Hat"                    
            Command="{Binding RedHatCommand}"
            Visibility="{Binding ShowRedHat, Converter={StaticResource BoolToVis}}"/>

Answer 1

如果HatEngine 的目的是成为MyViewModel 使用的服务，那么类似下面的内容就是获得所需内容的开始。

这个例子通过构造函数使用依赖注入；这在 MVVM 中很常见，如果您不熟悉它，我强烈建议您进一步研究。

// define delegate for event to be fired from HatEngine instances
public delegate void HatEngineNotifyEventHandler(object sender, bool shouldShow);

// interface declaration for HatEngine - this is important for injecting mocks for unit testing
public interface IHatEngine
{
    event HatEngineNotifyEventHandler Notify;
    void SetShowRedHat(bool show);
}

// simple IHatEngine implementation
public sealed class HatEngine : IHatEngine
{
    public event HatEngineNotifyEventHandler Notify;

    public void SetShowRedHat(bool show) => OnNotify(show);

    private void OnNotify(bool shouldShow) =>
        Notify?.Invoke(this, shouldShow);
}

public class MyViewModel : ObservableObject
{
    private readonly IHatEngine _hatEngine;
    private bool _showRedHat;

    // MyViewModel consumes an IHatEngine instance and subscribes to its Notify event
    public MyViewModel(IHatEngine hatEngine = null)
    {
        // many MVVM frameworks include a DI container that should be used here
        // to resolve an IHatEngine instance; however, for simplicity for this
        // example just create HatEngine() directly
        _hatEngine = hatEngine ?? new HatEngine();

        // when the event is received, update ShowRedHat accordingly
        _hatEngine.Notify += (_, shouldShow) => ShowRedHat = shouldShow;
    }

    public bool ShowRedHat
    {
        get => _showRedHat;
        set => OnPropertyChanged(ref _showRedHat, value);
    }
}