不久前，我为 XamDataGrid 和作为 ObservableCollection 的“业务对象”之间的两种方式同步编写了一个“附加行为”。XamDataGrid 是源，ObservableCollection as DataSource 是目标。由于特定原因，我没有使用 ListCollectionView。
问题
当 DataGrid 的 DataContext 更改为另一个 Vehicle 时，当前加载的 DataGrid 不会更新行为的 DependencyProperty。
我不知道为什么。
我能想到的唯一解决方案是挂钩 DataGrid 的 DataContextChanged 并使用 Path 进行新的 BindingOperation ，然后将其设置为相对于 DataContext 以确定 SelectedItems 属性。但在这种情况下，行为的 DependencyProperty 应设置为 SelectedItems 属性的路径，而不是绑定。
有以下课程
示例模型
public class Vehicle
{
public PassengerList Passengers { get; set; }
}
public class PassengerList : ObservableCollection<Passenger>
{
public PassengerList()
{
SelectedPassengers = new ObservableCollection<Passenger>();
}
public ObservableCollection<Passenger> SelectedPassengers { get; private set; }
}
public class Passenger
{
public string Name { get; set; }
}
xml
<igDG:XamDataGrid DataSource="{Binding Passengers}">
<i:Interaction.Behaviors>
<b:XamDataGridSelectedItemsBehavior SelectedItems="{Binding Path=Passengers.SelectedPssengers}" />
</i:Interaction.Behaviors>
</igDG:XamDataGrid>
PS：我也尝试过将元素绑定到 DataGrid 作为元素，但这并不能解决问题。DependencyProperty 仅设置一次。例如模型
双向行为
当模型中的选定项更改时，网格选定项也必须更新。它也不需要使用弱事件分离。
public class XamDataGridSelectedItemsBehavior : Behavior<XamDataGrid>, IWeakEventListener
{
#region Properties
private XamDataGrid Grid
{
get { return AssociatedObject as XamDataGrid; }
}
public static readonly DependencyProperty SelectedItemsProperty = DependencyProperty.Register(
"SelectedItems",
typeof(INotifyCollectionChanged),
typeof(XamDataGridSelectedItemsBehavior),
new UIPropertyMetadata(new PropertyChangedCallback(OnSelectedItemsChanged)));
private static void OnSelectedItemsChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
{
if (obj != null)
{
(obj as XamDataGridSelectedItemsBehavior).SelectedItems = (e.NewValue as INotifyCollectionChanged);
}
}
public INotifyCollectionChanged SelectedItems
{
get { return (INotifyCollectionChanged)GetValue(SelectedItemsProperty); }
set
{
// remove old listener
if (SelectedItems != null)
CollectionChangedEventManager.RemoveListener(SelectedItems, this);
SetValue(SelectedItemsProperty, value);
// add new listener
if (SelectedItems != null)
CollectionChangedEventManager.AddListener(SelectedItems, this);
}
}
#endregion
#region Init
/// <summary>
/// Hook up event listeners to the associated object.
/// </summary>
protected override void OnAttached()
{
base.OnAttached();
SelectedItemsChangedEventManager.AddListener(Grid, this);
XamDataGridRecordActivatedEventManager.AddListener(Grid, this);
XamDataGridLoadedEventManager.AddListener(Grid, this);
}
void Grid_RecordActivated(object sender, RecordActivatedEventArgs e)
{
if (_transferingToTarget)
return;
// if the CellClickAction is EnterEditModeIfAllowed, the grid does not always select the actual record
// In our case we want it to always select the record
if (e.Record.DataPresenter.FieldSettings.CellClickAction == CellClickAction.EnterEditModeIfAllowed)
{
TransferSourceToTarget();
}
}
void Grid_Loaded(object sender, RoutedEventArgs e)
{
TransferTargetToSource(true);
}
#endregion
#region Target to Source
/// <summary>
/// When selected items in the target as model has changed, then transfer selected item to grid as the source.
/// Not when transfering from grid to selected items.
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
void SelectedItems_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
if (_transferingToTarget)
return;
TransferTargetToSource(false);
}
private bool _transferingToSource = false;
/// <summary>
/// Transfer selected item in the target as model to the grid as source.
/// </summary>
private void TransferTargetToSource(bool notifyTargetListeners)
{
if (SelectedItems == null)
return;
List<Record> newSelection = new List<Record>();
foreach (var item in (SelectedItems as IList))
{
var record = Grid.Records.FirstOrDefault(r => (r is DataRecord) && ((r as DataRecord).DataItem == item));
if (record != null)
{
newSelection.Add(record);
}
}
_transferingToSource = true;
try
{
Grid.SelectedItems.Records.Clear();
Grid.SelectedItems.Records.AddRange(newSelection.ToArray());
if ((newSelection.Count > 0) && !newSelection.Contains(Grid.ActiveRecord))
{
Grid.ActiveRecord = newSelection.FirstOrDefault();
Grid.ActiveRecord.IsSelected = true;
}
if (notifyTargetListeners)
{
// Hack to notify the target listeners
(SelectedItems as IList).Clear();
foreach (var record in newSelection)
{
(SelectedItems as IList).Add((record as DataRecord).DataItem);
}
}
}
finally
{
_transferingToSource = false;
}
}
#endregion
#region Source to Target
/// <summary>
/// When selected items in the source as grid has changed, then transfer selected item to model as the target.
/// Not when transfering from selected items to grid.
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
void Grid_SelectedItemsChanged(object sender, SelectedItemsChangedEventArgs e)
{
if (_transferingToSource)
return;
TransferSourceToTarget();
}
private bool _transferingToTarget = false;
/// <summary>
/// Transfer the selected item in the grid as source to the selected item in the target as model.
/// </summary>
private void TransferSourceToTarget()
{
var target = this.SelectedItems as IList;
if (target == null)
return;
_transferingToTarget = true;
try
{
// clear the target first
target.Clear();
// When no item is selected there might still be an active record
if (Grid.SelectedItems.Count() == 0)
{
if (Grid.ActiveDataItem != null)
target.Add(Grid.ActiveDataItem);
else if (Grid.ActiveRecord != null && Grid.ActiveRecord.IsDataRecord)
target.Add((Grid.ActiveRecord as DataRecord).DataItem);
else if (Grid.ActiveCell != null && Grid.ActiveCell.Record != null && Grid.ActiveCell.Record.IsDataRecord)
target.Add((Grid.ActiveCell.Record as DataRecord).DataItem);
}
else
{
// foreach record in the source add it to the target
foreach (var r in Grid.SelectedItems.Records)
{
if (r.IsDataRecord)
{
target.Add((r as DataRecord).DataItem);
}
}
}
}
finally
{
_transferingToTarget = false;
}
}
#endregion
/// <summary>
/// Receive an event and delegate it to the correct eventhandler.
/// </summary>
/// <param name="managerType"></param>
/// <param name="sender"></param>
/// <param name="e"></param>
/// <returns></returns>
bool IWeakEventListener.ReceiveWeakEvent(Type managerType, object sender, EventArgs e)
{
if (managerType == typeof(CollectionChangedEventManager))
{
SelectedItems_CollectionChanged(sender, e as NotifyCollectionChangedEventArgs);
return true;
}
else if (managerType == typeof(SelectedItemsChangedEventManager))
{
Grid_SelectedItemsChanged(sender, e as SelectedItemsChangedEventArgs);
return true;
}
else if (managerType == typeof(XamDataGridRecordActivatedEventManager))
{
Grid_RecordActivated(sender, e as RecordActivatedEventArgs);
return true;
}
else if (managerType == typeof(XamDataGridLoadedEventManager))
{
Grid_Loaded(sender, e as RoutedEventArgs);
return true;
}
return false;
}
}
#region EventManagers
public class CollectionChangedEventManager : WeakEventManagerBase<CollectionChangedEventManager, INotifyCollectionChanged>
{
protected override void StartListeningTo(INotifyCollectionChanged source)
{
source.CollectionChanged += DeliverEvent;
}
protected override void StopListeningTo(INotifyCollectionChanged source)
{
source.CollectionChanged -= DeliverEvent;
}
}
public class XamDataGridRecordActivatedEventManager : WeakEventManagerBase<XamDataGridRecordActivatedEventManager, XamDataGrid>
{
protected override void StartListeningTo(XamDataGrid source)
{
source.RecordActivated += DeliverEvent;
}
protected override void StopListeningTo(XamDataGrid source)
{
source.RecordActivated -= DeliverEvent;
}
}
public class XamDataGridLoadedEventManager : WeakEventManagerBase<XamDataGridLoadedEventManager, XamDataGrid>
{
protected override void StartListeningTo(XamDataGrid source)
{
source.Loaded += DeliverEvent;
}
protected override void StopListeningTo(XamDataGrid source)
{
source.Loaded -= DeliverEvent;
}
}
public class SelectedItemsChangedEventManager : WeakEventManagerBase<SelectedItemsChangedEventManager, XamDataGrid>
{
protected override void StartListeningTo(XamDataGrid source)
{
source.SelectedItemsChanged += DeliverEvent;
}
protected override void StopListeningTo(XamDataGrid source)
{
source.SelectedItemsChanged -= DeliverEvent;
}
}
#endregion
#region EventManager base class
// TODO: 10-10-2011 (rdj): Deze class misschien opnemen in het frontend framework? In ieder geval zolang we nog geen .NET 4.5 gebruiken
// http://10rem.net/blog/2012/02/01/event-handler-memory-leaks-unwiring-events-and-the-weakeventmanager-in-wpf-45
/// <summary>
/// Weak event manager base class to provide easy implementation of weak event managers.
/// </summary>
/// <typeparam name="TManager">Type of the manager.</typeparam>
/// <typeparam name="TEventSource">Type of the event source.</typeparam>
public abstract class WeakEventManagerBase<TManager, TEventSource> : WeakEventManager
where TManager : WeakEventManagerBase<TManager, TEventSource>, new()
where TEventSource : class
{
/// <summary>
/// Adds a listener
/// </summary>
/// <param name="source">The source of the event, should be null if listening to static events</param>
/// <param name="listener">The listener of the event. This is the class that will recieve the ReceiveWeakEvent method call</param>
public static void AddListener(object source, IWeakEventListener listener)
{
CurrentManager.ProtectedAddListener(source, listener);
}
/// <summary>
/// Removes a listener
/// </summary>
/// <param name="source">The source of the event, should be null if listening to static events</param>
/// <param name="listener">The listener of the event. This is the class that will recieve the ReceiveWeakEvent method call</param>
public static void RemoveListener(object source, IWeakEventListener listener)
{
CurrentManager.ProtectedRemoveListener(source, listener);
}
/// <inheritdoc/>
protected sealed override void StartListening(object source)
{
StartListeningTo((TEventSource)source);
}
/// <inheritdoc/>
protected sealed override void StopListening(object source)
{
StopListeningTo((TEventSource)source);
}
/// <summary>
/// Attaches the event handler.
/// </summary>
protected abstract void StartListeningTo(TEventSource source);
/// <summary>
/// Detaches the event handler.
/// </summary>
protected abstract void StopListeningTo(TEventSource source);
/// <summary>
/// Gets the current manager
/// </summary>
protected static TManager CurrentManager
{
get
{
var mType = typeof(TManager);
var mgr = (TManager)GetCurrentManager(mType);
if (mgr == null)
{
mgr = new TManager();
SetCurrentManager(mType, mgr);
}
return mgr;
}
}
}
#endregion