Question

我在此链接上找到了

ObservableCollection not noticing when Item in it changes (even with INotifyPropertyChanged)

通知Observablecollection项目已更改的一些技巧。这个链接中的TrulyObservableCollection似乎正是我正在寻找的。

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，我没有收到关于该集合的通知。我不确定如何在我的C＃代码中正确实现它：

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，我将3复选框设置为false，true，false，如属性初始化。但是当我改变其中一个ckeckbox的状态时，程序会通过item_PropertyChanged但从不在MyItemsSource属性代码中。

Answer 1

您评论为// Code to trig on item change...的地点只会在集合对象发生更改时触发，例如当它被设置为新对象或设置为null时。

使用您当前的TrulyObservableCollection实现，要处理集合中属性更改的事件，请在CollectionChanged事件MyItemsSource

中注册一些内容

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个实现。您正在提出一个CollectionChanged事件，表示在财产发生变化时，整个集合已被重置。当然，它会在集合中的项目发生变化时随时更新UI，但我发现性能不佳，并且它似乎无法识别哪些属性发生了变化，这是关键信息之一我在PropertyChanged做某事时通常需要。

我更喜欢使用常规ObservableCollection，只是将PropertyChanged事件与CollectionChanged上的项目挂钩。如果您的UI正确绑定到ObservableCollection中的项目，则当集合中项目的属性发生更改时，您无需告知UI更新。

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();
}

Answer 2

我通过使用静态操作

解决了这种情况

public class CatalogoModel 
{
    private String _Id;
    private String _Descripcion;
    private Boolean _IsChecked;

    public String Id
    {
        get { return _Id; }
        set { _Id = value; }
    }
    public String Descripcion
    {
        get { return _Descripcion; }
        set { _Descripcion = value; }
    }
    public Boolean IsChecked
    {
        get { return _IsChecked; }
        set
        {
           _IsChecked = value;
            NotifyPropertyChanged("IsChecked");
            OnItemChecked.Invoke();
        }
    }

    public static Action OnItemChecked;
} 

public class ReglaViewModel : ViewModelBase
{
    private ObservableCollection<CatalogoModel> _origenes;

    CatalogoModel.OnItemChecked = () =>
            {
                var x = Origenes.Count;  //Entra cada vez que cambia algo en _origenes
            };
}

Answer 3

ObservableCollection及其派生词在内部引发其属性变化。只有在为TrulyObservableCollection<MyType>属性分配新的MyItemsSource时，才会触发setter中的代码。也就是说，它应该只从构造函数发生一次。

从那时起，您将从集合中获取属性更改通知，而不是从视图模型中的setter获取。

Answer 4

您可以使用扩展方法以通用方式获取有关集合中项目的已更改属性的通知。

public static class ObservableCollectionExtension
{
    public static void NotifyPropertyChanged<T>(this ObservableCollection<T> observableCollection, Action<T, PropertyChangedEventArgs> callBackAction)
        where T : INotifyPropertyChanged
    {
        observableCollection.CollectionChanged += (sender, args) =>
        {
            //Does not prevent garbage collection says: http://stackoverflow.com/questions/298261/do-event-handlers-stop-garbage-collection-from-occuring
            //publisher.SomeEvent += target.SomeHandler;
            //then "publisher" will keep "target" alive, but "target" will not keep "publisher" alive.
            if (args.NewItems == null) return;
            foreach (T item in args.NewItems)
            {
                item.PropertyChanged += (obj, eventArgs) =>
                {
                    callBackAction((T)obj, eventArgs);
                };
            }
        };
    }
}

public void ExampleUsage()
{
    var myObservableCollection = new ObservableCollection<MyTypeWithNotifyPropertyChanged>();
    myObservableCollection.NotifyPropertyChanged((obj, notifyPropertyChangedEventArgs) =>
    {
        //DO here what you want when a property of an item in the collection has changed.
    });
}

Answer 5

我知道现在已经很晚了，但也许这对其他人有帮助。我创建了一个类NotifyObservableCollection，它解决了项目属性发生变化时缺少对项目本身的通知的问题。用法就像ObservableCollection一样简单。

public class NotifyObservableCollection<T> : ObservableCollection<T> where T : INotifyPropertyChanged
{
    private void Handle(object sender, PropertyChangedEventArgs args)
    {
        OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset, null));
    }

    protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
    {
        if (e.NewItems != null) {
            foreach (object t in e.NewItems) {
                ((T) t).PropertyChanged += Handle;
            }
        }
        if (e.OldItems != null) {
            foreach (object t in e.OldItems) {
                ((T) t).PropertyChanged -= Handle;
            }
        }
        base.OnCollectionChanged(e);
    }

在添加或删除项目时，该类会将项目PropertyChanged事件转发给集合PropertyChanged事件。

用法：

public abstract class ParameterBase : INotifyPropertyChanged
{
    protected readonly CultureInfo Ci = new CultureInfo("en-US");
    private string _value;

    public string Value {
        get { return _value; }
        set {
            if (value == _value) return;
            _value = value;
            OnPropertyChanged();
        }
    }
}

public class AItem {
    public NotifyObservableCollection<ParameterBase> Parameters {
        get { return _parameters; }
        set {
            NotifyCollectionChangedEventHandler cceh = (sender, args) => OnPropertyChanged();
            if (_parameters != null) _parameters.CollectionChanged -= cceh;
            _parameters = value;
            //needed for Binding to AItem at xaml directly
            _parameters.CollectionChanged += cceh; 
        }
    }

    public NotifyObservableCollection<ParameterBase> DefaultParameters {
        get { return _defaultParameters; }
        set {
            NotifyCollectionChangedEventHandler cceh = (sender, args) => OnPropertyChanged();
            if (_defaultParameters != null) _defaultParameters.CollectionChanged -= cceh;
            _defaultParameters = value;
            //needed for Binding to AItem at xaml directly
            _defaultParameters.CollectionChanged += cceh;
        }
    }


public class MyViewModel {
    public NotifyObservableCollection<AItem> DataItems { get; set; }
}

如果现在DataItems中某个项的属性发生更改，则以下xaml会收到通知，但它会绑定到Parameters[0]或项目本身，但更改属性Value除外该项目（触发器转换器在每次更改时都称为可靠）。

<DataGrid CanUserAddRows="False" AutoGenerateColumns="False" ItemsSource="{Binding DataItems}">
    <DataGrid.Columns>
        <DataGridTextColumn Binding="{Binding Parameters[0].Value}" Header="P1">
            <DataGridTextColumn.CellStyle>
                <Style TargetType="DataGridCell">
                    <Setter Property="Background" Value="Aqua" />
                    <Style.Triggers>
                        <DataTrigger Value="False">
                            <!-- Bind to Items with changing properties -->
                            <DataTrigger.Binding>
                                <MultiBinding Converter="{StaticResource ParameterCompareConverter}">
                                    <Binding Path="DefaultParameters[0]" />
                                    <Binding Path="Parameters[0]" />
                                </MultiBinding>
                            </DataTrigger.Binding>
                            <Setter Property="Background" Value="DeepPink" />
                        </DataTrigger>
                        <!-- Binds to AItem directly -->
                        <DataTrigger Value="True" Binding="{Binding Converter={StaticResource CheckParametersConverter}}">
                            <Setter Property="FontWeight" Value="ExtraBold" />
                        </DataTrigger>
                    </Style.Triggers>
                </Style>
            </DataGridTextColumn.CellStyle>
        </DataGridTextColumn>

Answer 6

一个简单的解决方案是使用BindingList<T>而不是ObservableCollection<T>。实际上，BindingList中继项更改通知。因此，使用绑定列表，如果该项目实现了接口INotifyPropertyChanged，则您可以简单地使用the ListChanged event来获取通知。

另请参见this答案。

Answer 7

此处的所有解决方案都是正确的，但它们缺少使用方法http://docs.spring.io/spring-data/jpa/docs/current/reference/html/#repositories.query-methods.query-creation的重要方案，该方法未在OldItems对象中提供NotifyCollectionChangedEventArgs。

这是完美的ObservableCollection。

public class ObservableCollectionEX<T> : ObservableCollection<T>
{
    #region Constructors
    public ObservableCollectionEX() : base()
    {
        CollectionChanged += ObservableCollection_CollectionChanged;
    }
    public ObservableCollectionEX(IEnumerable<T> c) : base(c)
    {
        CollectionChanged += ObservableCollection_CollectionChanged;
    }
    public ObservableCollectionEX(List<T> l) : base(l)
    {
        CollectionChanged += ObservableCollection_CollectionChanged;
    }

    #endregion



    public new void Clear()
    {
        foreach (var item in this)
        {
            if (item is INotifyPropertyChanged i)
            {
                if (i != null)
                    i.PropertyChanged -= Element_PropertyChanged;
            }
        }
        base.Clear();
    }
    private void ObservableCollection_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        if (e.OldItems != null)
            foreach (var item in e.OldItems)
            {
                if (item != null && item is INotifyPropertyChanged i)
                {
                    i.PropertyChanged -= Element_PropertyChanged;
                }
            }
        if (e.NewItems != null)
            foreach (var item in e.NewItems)
            {
                if (item != null && item is INotifyPropertyChanged i)
                {
                    i.PropertyChanged -= Element_PropertyChanged;
                    i.PropertyChanged += Element_PropertyChanged;
                }
            }
    }
    private void Element_PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        //raise the event
        ItemPropertyChanged?.Invoke(sender, e);
    }


    /// <summary>
    /// the sender is the Item
    /// </summary>
    public PropertyChangedEventHandler ItemPropertyChanged;

}

您甚至可以加倍努力并更改ItemPropertyChanged以提供此类所有者列表

某些命名空间中的课外：
public delegate void ListedItemPropertyChangedEventHandler(IList SourceList, object Item, PropertyChangedEventArgs e);

在课堂上

改变这些：

private void Element_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
    //raise the event
    ItemPropertyChanged?.Invoke(this,sender, e);
}
public ListedItemPropertyChangedEventHandler ItemPropertyChanged;

Answer 8

一个简单的解决方案是替换ObservableCollection中要更改的项目，该项目通知已更改的项目的集合。在下面的示例代码片段中，Artists是ObservableCollection，而artist是ObservableCollection中类型的项：

    var index = Artists.IndexOf(artist);
    Artists.RemoveAt(index);
    artist.IsFollowed = true; // change something in the item
    Artists.Insert(index, artist);

项目更改时通知ObservableCollection

8 个答案: