当 Item 改变时通知 ObservableCollection [英] Notify ObservableCollection when Item changes
问题描述
我在这个链接上找到了
ObservableCollection 没有注意到当 Item它发生了变化(即使使用 INotifyPropertyChanged)
一些通知 Observablecollection 项目已更改的技术.此链接中的 TrulyObservableCollection 似乎是我正在寻找的.
some techniques to notify a Observablecollection that an item has changed. the TrulyObservableCollection in this link seems to be what i'm looking for.
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，我没有收到有关集合的通知.我不确定如何在我的 C# 代码中正确实现它:
But when I try to use it, I don't get notifications on the collection. I'm not sure how to correctly implement this in my C# Code:
XAML :
<DataGrid AutoGenerateColumns="False" ItemsSource="{Binding MyItemsSource, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}">
<DataGrid.Columns>
<DataGridCheckBoxColumn Binding="{Binding MyProperty, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
</DataGrid.Columns>
</DataGrid>
视图模型:
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，我在属性初始化中将 3 个复选框设置为 false、true、false.但是当我更改其中一个 ckeckbox 的状态时，程序会通过 item_PropertyChanged 但从未在 MyItemsSource 属性代码中.
When i run the program, i have the 3 checkbox to false, true, false as in the property initialisation. but when i change the state of one of the ckeckbox, the program go through item_PropertyChanged but never in MyItemsSource Property code.
推荐答案
您评论为 //触发项目更改的代码... 只会在集合对象发生更改时触发，例如当它被设置为一个新对象，或设置为空.
The spot you have commented as // Code to trig on item change... will only trigger when the collection object gets changed, such as when it gets set to a new object, or set to null.
使用您当前的 TrulyObservableCollection 实现，要处理集合的属性更改事件，请向 MyItemsSource
With your current implementation of TrulyObservableCollection, to handle the property changed events of your collection, register something to the CollectionChanged event of 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个实现.您正在引发一个 CollectionChanged 事件，表明整个集合已被重置，只要属性发生变化.当然，只要集合中的项目发生更改，它就会使 UI 更新，但我认为这对性能很不利，而且它似乎没有办法识别更改的属性，这是关键信息之一我通常需要在 PropertyChanged 上做一些事情.
Personally I really don't like this implementation. You are raising a CollectionChanged event that says the entire collection has been reset, anytime a property changes. Sure it'll make the UI update anytime an item in the collection changes, but I see that being bad on performance, and it doesn't seem to have a way to identify what property changed, which is one of the key pieces of information I usually need when doing something on PropertyChanged.
我更喜欢使用常规的 ObservableCollection 并且只是将 PropertyChanged 事件连接到 CollectionChanged 上的项目.如果您的 UI 正确绑定到 ObservableCollection 中的项目，您就不需要告诉 UI 在集合中项目的属性发生更改时进行更新.
I prefer using a regular ObservableCollection and just hooking up the PropertyChanged events to it's items on CollectionChanged. Providing your UI is bound correctly to the items in the ObservableCollection, you shouldn't need to tell the UI to update when a property on an item in the collection changes.
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();
}
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