如何传播集合中对象的属性更改通知

Question

假设我有这样的课程

public class R
{
    protected string name;
    protected List<S> listOfObjectS;
}

public class S
{
    private string name, ID;
    private A objectA;
}

public class A
{
    private string name;
    private int count;
}

如果用户打开了两个视图，一个显示R 的实例，另一个允许用户修改A 的实例，我需要R 的视图在用户更改@987654325 的任何实例时更改@。

如果用户更改A 实例的属性，传播该更改的最佳方式是什么（通过S 的实例），以便R 的所有实例显示A 的新状态?

Answer 1

编辑：修改此答案以更具体地解决问题，因为标签显示您已经知道INotifyPropertyChanged。

您需要在A 类和S 类中实现INotifyPropertyChanged。使objectA 只能通过一个属性设置，该属性将在A 中更改属性时在S 上引发PropertyChanged 事件。示例：

public class A : INotifyPropertyChanged
{
    private string name;
    public string Name
    {
        get { return name; }
        set { name = value; OnPropertyChanged("Name"); }
    }

    private int count;

    public int Count
    {
        get { return count; } 
        set { count = value; OnPropertyChanged("Count"); }
    }

    public event PropertyChangedEventHandler PropertyChanged;
    protected void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}

...和班级S...

public class S : INotifyPropertyChanged
{
    private string name, ID;
    private A objectA;

    public A ObjectA
    {
        get { return objectA; }
        set
        {
            var old = objectA;
            objectA = value;

            // Remove the event subscription from the old instance.
            if (old != null) old.PropertyChanged -= objectA_PropertyChanged;

            // Add the event subscription to the new instance.
            if (objectA != null) objectA.PropertyChanged += objectA_PropertyChanged;

            OnPropertyChanged("ObjectA");
        }
    }

    void objectA_PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        // Propagate the change to any listeners. Prefix with ObjectA so listeners can tell the difference.
        OnPropertyChanged("ObjectA." + e.PropertyName);
    }

    public event PropertyChangedEventHandler PropertyChanged;
    protected void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}

对于R 类，使用ObservableCollection<S> 代替List<S>，并订阅其CollectionChanged 事件，并监视何时向listOfObjectS 添加或删除对象。添加后，订阅S 的PropertyChanged 事件。然后更新了R 的观点。示例：

public class R
{
    protected string name;
    protected System.Collections.ObjectModel.ObservableCollection<S> ListOfObjectS { get; private set; }

    public R()
    {
        // Use ObservableCollection instead.
        ListOfObjectS = new ObservableCollection<S>();

        // Subscribe to all changes to the collection.
        ListOfObjectS.CollectionChanged += listOfObjectS_CollectionChanged;
    }

    void listOfObjectS_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    {
        if (e.Action == NotifyCollectionChangedAction.Remove)
        {
            // When items are removed, unsubscribe from property change notifications.
            var oldItems = (e.OldItems ?? new INotifyPropertyChanged[0]).OfType<INotifyPropertyChanged>();
            foreach (var item in oldItems)
                item.PropertyChanged -= item_PropertyChanged;
        }

        // When item(s) are added, subscribe to property notifications.
        if (e.Action == NotifyCollectionChangedAction.Add)
        {
            var newItems = (e.NewItems ?? new INotifyPropertyChanged[0]).OfType<INotifyPropertyChanged>();
            foreach (var item in newItems)
                item.PropertyChanged += item_PropertyChanged;
        }

        // NOTE: I'm not handling NotifyCollectionChangedAction.Reset.
        // You'll want to look into when this event is raised and handle it
        // in a special fashion.
    }

    void item_PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        if (e.PropertyName.StartsWith("ObjectA."))
        {
            // Refresh any dependent views, forms, controls, whatever...
        }
    }
}

Answer 2

假设您有一个 form1，您在其中使用类 R 的实例来显示类 A 的实例列表。然后按下编辑，然后将同一类 A 的实例从类 R 实例发送到新表单.

这将是对 R 实例中包含的对象的引用，因此会在 form2 中更新。您唯一需要做的就是刷新 form1 列表中的类 A 的实例。

解释一下：当您使用类的对象实例调用表单或方法时，这将创建一个引用，而不是克隆，因此可以从第二个表单更新。