PROSAGA码农传奇-模型托管-c＃ObservableCollection：如何实现CollectionChanged事件

<div class =“post-text”itemprop =“text”>
  <P>
     <code>
      e
    </code>
     属于Type
     <code>
      NotifyCollectionChangedEventArgs
    </code>
     它包含
     <code>
      NewItems
    </code>
    ，
     <code>
      OldItems
    </code>
     和
     <code>
      Action
    </code>
    。
  </p>
   <pre>
    <code>
      c.CollectionChanged += (sender, e) => { 
    Console.WriteLine($"{e.Action}");
    // check e.Action and draw your stuff       
};

</code>
  </pre>
  <P>
    <a href="https://msdn.microsoft.com/en-us/library/system.collections.specialized.notifycollectionchangedeventargs(v=vs.110).aspx" rel="nofollow">
      https://msdn.microsoft.com/en-us/library/system.collections.specialized.notifycollectionchangedeventargs(v=vs.110).aspx
    </A>
  </p>
  <P>
    的<strong>
      在评论中草绘精神上的解决方案
    </强>
  </p>
   <pre>
    <code>
      class MyObject : INotifyPropertyChanged
{
    private string _a;
    public event PropertyChangedEventHandler PropertyChanged;

public string A
    {
        get { return _a; }
        set
        {
            _a = value;
            OnPropertyChanged();
        }
    }

protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

class Pagey : ContentPage
{
    private ObservableCollection<MyObject> c = new ObservableCollection<MyObject>();

// somwhere in your code 
    c.CollectionChanged += OnCollectionChanged;

private void OnCollectionChanged(object sender, NotifyCollectionChangedEventArgs args)
    {
        if (args.NewItems != null)
        {
            foreach (var item in args.NewItems.Cast<MyObject>())
            {
                item.PropertyChanged += OnChanged;
            }
        }

if(args.OldItems != null)
        {
            foreach (var item in args.OldItems.Cast<MyObject>())
            {
                item.PropertyChanged -= OnChanged;
            }
        }

Redraw();
    }

private void OnChanged(object sender, PropertyChangedEventArgs e)
    {
        Redraw();
    }

private void Redraw()
    {

}
}

</code>
  </pre>
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