我在此链接上找到了
ObservableCollection不会注意到其中的Item更改的时间(即使使用INotifyPropertyChanged)
通知Observablecollection某项已更改的某些技术。该链接中的TrulyObservableCollection似乎是我正在寻找的东西。
public class TrulyObservableCollection<T> : ObservableCollection<T> where T : INotifyPropertyChanged { public TrulyObservableCollection() : base() { CollectionChanged += new NotifyCollectionChangedEventHandler(TrulyObservableCollection_CollectionChanged); } void TrulyObservableCollection_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e) { if (e.NewItems != null) { foreach (Object item in e.NewItems) { (item as INotifyPropertyChanged).PropertyChanged += new PropertyChangedEventHandler(item_PropertyChanged); } } if (e.OldItems != null) { foreach (Object item in e.OldItems) { (item as INotifyPropertyChanged).PropertyChanged -= new PropertyChangedEventHandler(item_PropertyChanged); } } } void item_PropertyChanged(object sender, PropertyChangedEventArgs e) { NotifyCollectionChangedEventArgs a = new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset); OnCollectionChanged(a); } }
但是,当我尝试使用它时,我没有收到关于集合的通知。我不确定如何在我的C#代码中正确实现这一点:
XAML:
<DataGrid AutoGenerateColumns="False" ItemsSource="{Binding MyItemsSource, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"> <DataGrid.Columns> <DataGridCheckBoxColumn Binding="{Binding MyProperty, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/> </DataGrid.Columns> </DataGrid>
ViewModel:
public class MyViewModel : ViewModelBase { private TrulyObservableCollection<MyType> myItemsSource; public TrulyObservableCollection<MyType> MyItemsSource { get { return myItemsSource; } set { myItemsSource = value; // Code to trig on item change... RaisePropertyChangedEvent("MyItemsSource"); } } public MyViewModel() { MyItemsSource = new TrulyObservableCollection<MyType>() { new MyType() { MyProperty = false }, new MyType() { MyProperty = true }, new MyType() { MyProperty = false } }; } } public class MyType : ViewModelBase { private bool myProperty; public bool MyProperty { get { return myProperty; } set { myProperty = value; RaisePropertyChangedEvent("MyProperty"); } } } public class ViewModelBase : INotifyPropertyChanged { public event PropertyChangedEventHandler PropertyChanged; protected void RaisePropertyChangedEvent(string propertyName) { if (PropertyChanged != null) { PropertyChangedEventArgs e = new PropertyChangedEventArgs(propertyName); PropertyChanged(this, e); } } }
当我运行程序时,与属性初始化一样,我有3个复选框为false,true,false。但是,当我更改ckeckbox之一的状态时,该程序将通过item_PropertyChanged,但永远不会在MyItemsSource属性代码中进行。
您注释为的位置// Code to trig on item change...仅在更改集合对象(例如将其设置为新对象或设置为null)时触发。
// Code to trig on item change...
根据您目前的实现TrulyObservableCollection的,处理您的收藏的属性更改事件,注册一些东西到CollectionChanged的事件MyItemsSource
CollectionChanged
MyItemsSource
public MyViewModel() { MyItemsSource = new TrulyObservableCollection<MyType>(); MyItemsSource.CollectionChanged += MyItemsSource_CollectionChanged; MyItemsSource.Add(new MyType() { MyProperty = false }); MyItemsSource.Add(new MyType() { MyProperty = true}); MyItemsSource.Add(new MyType() { MyProperty = false }); } void MyItemsSource_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e) { // Handle here }
我个人真的不喜欢这种实现。您正在引发一个CollectionChanged事件,该事件表明在属性更改时,整个集合已被重置。当然,只要集合中的某个项目发生更改,它就可以使UI随时更新,但是我发现这样做对性能不利,而且似乎没有办法确定更改了哪些属性,这是关键信息之一做某事时我通常需要PropertyChanged。
PropertyChanged
我更喜欢使用常规方法,ObservableCollection而只是将PropertyChanged事件关联到上的项目CollectionChanged。如果您的UI已正确绑定到中的项目,则ObservableCollection当集合中某个项目的属性发生更改时,您无需告诉UI进行更新。
ObservableCollection
public MyViewModel() { MyItemsSource = new ObservableCollection<MyType>(); MyItemsSource.CollectionChanged += MyItemsSource_CollectionChanged; MyItemsSource.Add(new MyType() { MyProperty = false }); MyItemsSource.Add(new MyType() { MyProperty = true}); MyItemsSource.Add(new MyType() { MyProperty = false }); } void MyItemsSource_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e) { if (e.NewItems != null) foreach(MyType item in e.NewItems) item.PropertyChanged += MyType_PropertyChanged; if (e.OldItems != null) foreach(MyType item in e.OldItems) item.PropertyChanged -= MyType_PropertyChanged; } void MyType_PropertyChanged(object sender, PropertyChangedEventArgs e) { if (e.PropertyName == "MyProperty") DoWork(); }