c# - 为什么 INotifyPropertyChanged 不起作用？

Question

我使用了Multibinding来绑定(bind)一些属性，并使用INotifyPropertyChanged接口(interface)来通知这些属性的变化。但遗憾的是，INotifyPropertyChanged似乎并没有起作用。 PropertyChangedEventHandler“PropertyChanged”始终为 null。

问题:

一个。你能告诉我为什么事件为null吗？在我看来，事件PropertyChangedEventHandler应该有一个默认方法，我错了吗？(已解决，谢谢!)

B.就像一些 friend 说的，我没有使用INotifyPropertyChanged再次尝试。但是目标的属性值似乎没有改变......

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1. 属性

   public static readonly DependencyProperty LeftOffsetProperty = DependencyProperty.Register("LeftOffset", typeof(double), typeof(NetworkTaskLable), new FrameworkPropertyMetadata(0d, FrameworkPropertyMetadataOptions.AffectsRender));
   public static readonly DependencyProperty TopOffsetProperty = DependencyProperty.Register("TopOffset", typeof(double), typeof(NetworkTaskLable), new FrameworkPropertyMetadata(0d, FrameworkPropertyMetadataOptions.AffectsRender));
   
   public double LeftOffset
   {
       get { return (double)GetValue(LeftOffsetProperty); }
       set { SetValue(LeftOffsetProperty, value); }
   }
   public double TopOffset
   {
       get { return (double)GetValue(TopOffsetProperty); }
       set { SetValue(TopOffsetProperty, value); }
   }
   

2. 多重绑定(bind)(看起来效果不错。通过使用转换器计算受“TopOffset”和“LeftOffset”影响的位置)

   var multibinding = new MultiBinding() { Converter = new BeginAndStartDateToLeftConverter_NetworkTaskLable(), ConverterParameter = NetworkView };
   multibinding.Bindings.Add(new Binding("Start"));
   multibinding.Bindings.Add(new Binding("StartDate") { Source = NetworkView });
   multibinding.Bindings.Add(new Binding("LeftOffset") { Source = this });
   MainCanvas.SetBinding(LeftProperty, multibinding);
   

3. INotifyPropertyChanged

   public event PropertyChangedEventHandler PropertyChanged;
   public void CallPropertyChanged(string PropertyName)
   {
       if (PropertyChanged != null)//It seems to be null all the time!!!And the properties'changes were never notified!!!
           PropertyChanged(this, new PropertyChangedEventArgs(PropertyName));
   }
   

4. 通知变更

   SetValue(LeftOffsetProperty, moveAdorner.LeftOffset);
   CallPropertyChanged("LeftOffset");
   SetValue(TopOffsetProperty, moveAdorner.TopOffset);
   CallPropertyChanged("TopOffset");
   

Answer 1

您不需要为依赖属性实现 INotifyPropertyChanged。绑定(bind)将自动跟踪这些属性的变化。