c# - ObservableCollection 如何将 INotifyPropertyChanged 实现为 protected ？

Question

这是 INotifyPropertyChanged 的定义

public interface INotifyPropertyChanged
{
    event PropertyChangedEventHandler PropertyChanged;
}

ObservableCollection<T>实现这个...

public class ObservableCollection<T> : Collection<T>, INotifyCollectionChanged, INotifyPropertyChanged
{
    protected virtual event PropertyChangedEventHandler PropertyChanged;
}

当我测试这个时...

public class Test : INotifyPropertyChanged
{
    protected virtual event PropertyChangedEventHandler PropertyChanged;
}

我收到以下错误:

Test does not implement interface member 'System.ComponentModel.INotifyPropertyChanged.PropertyChanged'. 'Test.PropertyChanged' cannot implement an interface member because it is not public.

这怎么可能？

Answer 1

接口(interface)本身是显式实现的，具有供类覆盖的 protected 事件

public class Test : INotifyPropertyChanged
{
   // explicit interface implementation
    event PropertyChangedEventHandler INotifyPropertyChanged.PropertyChanged
    {
        add
        {
            PropertyChanged += value;
        }
        remove
        {
            PropertyChanged -= value;
        }
    }

    // protected virtual (for derived classes to override)   
    protected virtual event PropertyChangedEventHandler PropertyChanged;
}