c# - 子属性更新调用它的父属性 `OnPropertyChanged`

Question

我正在尝试创建一个 XF 组件，其某些属性属于从 BindableObject 继承的类型。为了说明，我有类 Shadow 和 double Radius 和 Color ShadowColor 属性和类 MyBoxText，有一个bool IsLoading 和一个 Shadow Ghost 属性。

我的 View 和它的 Bindings 按预期工作，但我的自定义渲染器有问题:

当我更改 Ghost 属性时，我需要重绘整个 View (MyBoxText 控件)，例如，以视觉方式更新阴影颜色。

这里有一些mcve:

类(class)代码:

public class MyBoxText : Label /* It's bindable by inheritance */
{
    #region Properties
    public static readonly BindableProperty IsLoadingProperty = BindableProperty.Create(nameof(IsLoading), typeof(bool), typeof(MyBoxText), false) ;
    public bool IsLoading
    {
        get { return (bool)GetValue(IsLoadingProperty); }
        set { SetValue(IsLoadingProperty, value); }
    }

    public static readonly BindableProperty GhostProperty = BindableProperty.Create(nameof(Ghost), typeof(Shadow), typeof(MyBoxText), null) ;
    public Shadow Ghost
    {
        get { return (Shadow)GetValue(GhostProperty); }
        set { SetValue(GhostProperty, value); }
    }
    #endregion
}

public class Shadow : BindableObject /* It's explictly bindable */
{
    #region Properties
    public static readonly BindableProperty ShadowColorProperty = BindableProperty.Create(nameof(ShadowColor), typeof(Color), typeof(Shadow), Color.Black) ;
    public Color ShadowColor
    {
        get { return (Color)GetValue(ShadowColorProperty); }
        set { SetValue(ShadowColorProperty, value); }
    }

    public static readonly BindableProperty ShadowRadiusProperty = BindableProperty.Create(nameof(ShadowRadius), typeof(double), typeof(Shadow), 20) ;
    public double ShadowRadius
    {
        get { return (double)GetValue(ShadowRadiusProperty); }
        set { SetValue(ShadowRadiusProperty, value); }
    }
    #endregion

    public Shadow()
    {

    }
}

我的渲染器的代码是这样的:

public class MyBoxText : LabelRenderer
{
    public MyBoxText()
    {
        SetWillNotDraw(false);
    }

    public override void Draw(Canvas canvas)
    {
        MyBoxText myView = (MyBoxText)this.Element;

        // Some drawing logic
    }

    protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        base.OnElementPropertyChanged(sender, e);

        if (e.PropertyName == MyBoxText.IsLoadingProperty.PropertyName  ||
            e.PropertyName == MyBoxText.GhostProperty.PropertyName )
            Invalidate();
    }
}

问题是，当我更改 Ghost.ShadowColor 属性时，我的“OnElementPropertyChanged”覆盖未被调用，并且 View 在屏幕上保持旧颜色。

有没有办法将 child 的“属性更新”事件传播到父 View “属性已更改”或其他方式来实现这一点？

Answer 1

The issue is that when I change the Ghost.ShadowColor property my 'OnElementPropertyChanged' override is not called, and the View stays with the old color on the screen. Is there a way to propagate the child's 'Property Update' event to parent view 'Property Changed' or another way to achieve this?

是的，有办法。由于您的 Shadow 继承自 BindableObject，它实现了 INotifyPropertyChanged 接口(interface)。您可以设置通知 ShadowColor 更改:

1. 在 Shadow.cs 中 ShadowColor 的 Setter 添加 OnPropertyChanged():

   public class Shadow : BindableObject /* It's explictly bindable */
   {
       #region Properties
       public static readonly BindableProperty ShadowColorProperty = BindableProperty.Create(nameof(ShadowColor), typeof(Color), typeof(Shadow), Color.Black);
       public Color ShadowColor
       {
           get { return (Color)GetValue(ShadowColorProperty); }
           set { SetValue(ShadowColorProperty, value);
               //Notify the ShadowColorProperty Changed
               OnPropertyChanged();
           }
       }
      ...
   }
   

2. 像这样修改您的 MyBoxText.cs:

   public class MyBoxText : Label /* It's bindable by inheritance */
   {
    ...
   
       public static readonly BindableProperty GhostProperty = BindableProperty.Create(nameof(Ghost), typeof(Shadow), typeof(MyBoxText), null);
       public Shadow Ghost
       {
           get { return (Shadow)GetValue(GhostProperty); }
           set {
               //register the ShadowColor change event
               value.PropertyChanged += ShadowColor_PropertyChanged;
               SetValue(GhostProperty, value); }
       }
   
       private void ShadowColor_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
       {
           //unregister the event
           this.Ghost.PropertyChanged -= ShadowColor_PropertyChanged;
           //set this.Ghost to a new object with new ShadowColor to trigger the OnPropertyChanged
           this.Ghost = new Shadow
           {
               ShadowColor = (sender as Shadow).ShadowColor,
               ShadowRadius = Ghost.ShadowRadius
           };
       }
   }