我看过很多关于这个问题的讨论，但也许我只是太多的新手才能得到它。如果我有一个可观察的集合，它是msdn示例（http: //msdn.microsoft.com/en-us/library/ms748365.aspx）中“PersonNames”的集合，如果添加或删除了PersonName等，我会获得对View的更新。我想要在我更改PersonName中的属性时，我会更新我的视图。就像我改名字一样。我可以为每个属性实现OnPropertyChanged，并让此类派生自INotifyPropertyChanged，并且似乎按预期调用。我的问题是，View如何从ObservableCollection获取更新的数据，因为更改的属性不会导致ObservableCollection的任何事件。这可能是非常简单的事情，但为什么我似乎无法找到一个令我惊讶的例子。任何人都可以为我阐明这一点，或者对示例有任何指示我会非常感激。我们在当前的WPF应用程序的多个位置都有这种情况，并且正在努力搞清楚。
“通常，负责显示数据的代码会为当前显示在屏幕上的每个对象添加PropertyChanged事件处理程序。”
有人可以举个例子说明这意味着什么吗？我的观点与我的ViewModel绑定，ObservableCollection有RowViewModel。此集合由PropertiesChanged组成，其中包含支持{{1}}事件的属性。但我无法弄清楚如何使集合更新，以便更新我的视图。
答案 0 :(得分：63)
以下是如何附加/分离每个项目的PropertyChanged事件。
ObservableCollection<INotifyPropertyChanged> items = new ObservableCollection<INotifyPropertyChanged>();
items.CollectionChanged += items_CollectionChanged;
static void items_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
if (e.OldItems != null)
{
foreach (INotifyPropertyChanged item in e.OldItems)
item.PropertyChanged -= item_PropertyChanged;
}
if (e.NewItems != null)
{
foreach (INotifyPropertyChanged item in e.NewItems)
item.PropertyChanged += item_PropertyChanged;
}
}
static void item_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
throw new NotImplementedException();
}
答案 1 :(得分：19)
我们在WPF聊天中写道：
public class OcPropertyChangedListener<T> : INotifyPropertyChanged where T : INotifyPropertyChanged
{
private readonly ObservableCollection<T> _collection;
private readonly string _propertyName;
private readonly Dictionary<T, int> _items = new Dictionary<T, int>(new ObjectIdentityComparer());
public OcPropertyChangedListener(ObservableCollection<T> collection, string propertyName = "")
{
_collection = collection;
_propertyName = propertyName ?? "";
AddRange(collection);
CollectionChangedEventManager.AddHandler(collection, CollectionChanged);
}
private void CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
switch (e.Action)
{
case NotifyCollectionChangedAction.Add:
AddRange(e.NewItems.Cast<T>());
break;
case NotifyCollectionChangedAction.Remove:
RemoveRange(e.OldItems.Cast<T>());
break;
case NotifyCollectionChangedAction.Replace:
AddRange(e.NewItems.Cast<T>());
RemoveRange(e.OldItems.Cast<T>());
break;
case NotifyCollectionChangedAction.Move:
break;
case NotifyCollectionChangedAction.Reset:
Reset();
break;
default:
throw new ArgumentOutOfRangeException();
}
}
private void AddRange(IEnumerable<T> newItems)
{
foreach (T item in newItems)
{
if (_items.ContainsKey(item))
{
_items[item]++;
}
else
{
_items.Add(item, 1);
PropertyChangedEventManager.AddHandler(item, ChildPropertyChanged, _propertyName);
}
}
}
private void RemoveRange(IEnumerable<T> oldItems)
{
foreach (T item in oldItems)
{
_items[item]--;
if (_items[item] == 0)
{
_items.Remove(item);
PropertyChangedEventManager.RemoveHandler(item, ChildPropertyChanged, _propertyName);
}
}
}
private void Reset()
{
foreach (T item in _items.Keys.ToList())
{
PropertyChangedEventManager.RemoveHandler(item, ChildPropertyChanged, _propertyName);
_items.Remove(item);
}
AddRange(_collection);
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void ChildPropertyChanged(object sender, PropertyChangedEventArgs e)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
handler(sender, e);
}
private class ObjectIdentityComparer : IEqualityComparer<T>
{
public bool Equals(T x, T y)
{
return object.ReferenceEquals(x, y);
}
public int GetHashCode(T obj)
{
return System.Runtime.CompilerServices.RuntimeHelpers.GetHashCode(obj);
}
}
}
public static class OcPropertyChangedListener
{
public static OcPropertyChangedListener<T> Create<T>(ObservableCollection<T> collection, string propertyName = "") where T : INotifyPropertyChanged
{
return new OcPropertyChangedListener<T>(collection, propertyName);
}
}
像这样使用：
var listener = OcPropertyChangedListener.Create(yourCollection);
listener.PropertyChanged += (sender, args) => { //do you stuff}
答案 2 :(得分：13)
比尔，
我确信您现在已经找到了解决问题的方法或解决方案，但我已将此问题发布给有此常见问题的任何人。您可以将此类替换为ObservableCollections，它们是实现INotifyPropertyChanged的对象的集合。它有点严厉，因为它表示列表需要重置而不是找到已更改的一个属性/项，但对于小列表，性能命中应该是不可用的。
Marc
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.ComponentModel;
namespace WCIOPublishing.Helpers
{
public class ObservableCollectionWithItemNotify<T> : ObservableCollection<T> where T: INotifyPropertyChanged
{
public ObservableCollectionWithItemNotify()
{
this.CollectionChanged += items_CollectionChanged;
}
public ObservableCollectionWithItemNotify(IEnumerable<T> collection) :base( collection)
{
this.CollectionChanged += items_CollectionChanged;
foreach (INotifyPropertyChanged item in collection)
item.PropertyChanged += item_PropertyChanged;
}
private void items_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
if(e != null)
{
if(e.OldItems!=null)
foreach (INotifyPropertyChanged item in e.OldItems)
item.PropertyChanged -= item_PropertyChanged;
if(e.NewItems!=null)
foreach (INotifyPropertyChanged item in e.NewItems)
item.PropertyChanged += item_PropertyChanged;
}
}
private void item_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
var reset = new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset);
this.OnCollectionChanged(reset);
}
}
}
答案 3 :(得分：4)
如您所知，没有集合级事件表明集合中项目的属性已更改。通常，负责显示数据的代码会向当前显示在屏幕上的每个对象添加一个PropertyChanged事件处理程序。
答案 4 :(得分：2)
而不是ObservableCollection只需使用BindingList<T> 以下代码显示了绑定到List和项目属性的DataGrid。
<Window x:Class="WpfApplication1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<DataGrid ItemsSource="{Binding}" AutoGenerateColumns="False" >
<DataGrid.Columns>
<DataGridTextColumn Header="Values" Binding="{Binding Value}" />
</DataGrid.Columns>
</DataGrid>
</Window>
using System;
using System.ComponentModel;
using System.Windows;
using System.Windows.Threading;
namespace WpfApplication1 {
public partial class MainWindow : Window {
public MainWindow() {
var c = new BindingList<Data>();
this.DataContext = c;
// add new item to list on each timer tick
var t = new DispatcherTimer() { Interval = TimeSpan.FromSeconds(1) };
t.Tick += (s, e) => {
if (c.Count >= 10) t.Stop();
c.Add(new Data());
};
t.Start();
}
}
public class Data : INotifyPropertyChanged {
public event PropertyChangedEventHandler PropertyChanged = delegate { };
System.Timers.Timer t;
static Random r = new Random();
public Data() {
// update value on each timer tick
t = new System.Timers.Timer() { Interval = r.Next(500, 1000) };
t.Elapsed += (s, e) => {
Value = DateTime.Now.Ticks;
this.PropertyChanged(this, new PropertyChangedEventArgs("Value"));
};
t.Start();
}
public long Value { get; private set; }
}
}
答案 5 :(得分：1)
以下是代码，@Stack给出答案的简单解释，并显示BindingList如果有项目更改后如何观察，并显示ObservableCollection将无法观察项目内的更改
using System;
using System.Collections.ObjectModel;
using System.ComponentModel;
namespace BindingListExample
{
class Program
{
public ObservableCollection<MyStruct> oc = new ObservableCollection<MyStruct>();
public System.ComponentModel.BindingList<MyStruct> bl = new BindingList<MyStruct>();
public Program()
{
oc.Add(new MyStruct());
oc.CollectionChanged += CollectionChanged;
bl.Add(new MyStruct());
bl.ListChanged += ListChanged;
}
void ListChanged(object sender, ListChangedEventArgs e)
{
//Observe when the IsActive value is changed this event is triggered.
Console.WriteLine(e.ListChangedType.ToString());
}
void CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
{
//Observe when the IsActive value is changed this event is not triggered.
Console.WriteLine(e.Action.ToString());
}
static void Main(string[] args)
{
Program pm = new Program();
pm.bl[0].IsActive = false;
}
}
public class MyStruct : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private bool isactive;
public bool IsActive
{
get { return isactive; }
set
{
isactive = value;
NotifyPropertyChanged("IsActive");
}
}
private void NotifyPropertyChanged(String PropertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(PropertyName));
}
}
}
}