當可觀察集合中的任何項目發生更改時，更新當前的類屬性

Question

我上課了

public class SomeModel : INotifyPropertyChanged {

  public ObservableCollection<SomeSubModel> SubModels {get; set;}

  public int Sum { get { return SubModels.Sum(x=> x.Count) }}

  private string _url;
  public string Url
  {
    get { return _url; }
    set
    {
        _url = value;
        OnPropertyChanged();
    }
  }

  public event PropertyChangedEventHandler PropertyChanged;

  [NotifyPropertyChangedInvocator]
  protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
  {
    var handler = PropertyChanged;
    if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
  }

}

public class SomeSubModel : INotifyPropertyChanged {

  private string _count;
  public string Count
  {
    get { return _count; }
    set
    {
        _count = value;
        OnPropertyChanged();
    }
  }

  public event PropertyChangedEventHandler PropertyChanged;

  [NotifyPropertyChangedInvocator]
  protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
  {
    var handler = PropertyChanged;
    if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
  }

}

我將在WPF UI中使用綁定到SomeSubModel.Sum 。

SomeSubModel.Count屬性經常更改。

當SomeModel.SubModels可觀察集合中的任何項屬性SomeSubModel.Count被更改為通過綁定反映WPF UI中的實際SomeSubModel.Sum時，如何通知SomeSubModel.Sum被更改？

主要目標是在UI中反映可觀察集合中所有Count對象的實際總和。

謝謝！

Answer 1

在這種情況下，您應該觸發為Sum屬性更改的notify屬性：

private string _count;
public string Count
{
    get { return _count; }
    set
    {
        _count = value;
        OnPropertyChanged();
        var handler = PropertyChanged;
        if (handler != null) 
            handler(this, new PropertyChangedEventArgs("Sum"));
    }
}