Windows Community Toolkit 5.0 - DataGrid - Part01
概述
在上面一篇 Windows Community Toolkit 5.0 - DataGrid - Overview 中，我们对 DataGrid 控件做了一个概览的介绍，今天开始我们会做进一步的详细分享。
按照概述中分析代码结构的顺序，今天我们先对 CollectionViews 文件夹中的类做详细的分析。
下面是 Windows Community Toolkit Sample App 的示例截图和 code/doc 地址：
Windows Community Toolkit Doc - DataGrid
Windows Community Toolkit Source Code - DataGrid
Namespace: Microsoft.Toolkit.Uwp.UI.Controls; Nuget: Microsoft.Toolkit.Uwp.UI.Controls.DataGrid;
开发过程
首先再来看一下 CollectionViews 文件夹的代码结构：
4 个类中，CollectionView 是 EnumerableCollectionView 和 ListCollectionView 的基类，而 CollectionViewsError 是和 DataGrid 数据源中错误的处理类，接下来我们来分别看一下：
1. CollectionView
CollectionView 类是 DataGrid 数据相关处理的基类，这个类里的处理方法和属性设置很多，同时还针对 FILTER，SORT 和 GROUP 特性做了处理，下面先来看看类中定义的属性：
Count - 表示 DataGrid 控件数据的数量，在 OnCollectionChanged 事件处理中，非 Replace 情况下触发；
IsEmpty - 表示 DataGrid 控件中数据是否为空，同样在 OnCollectionChanged 事件处理中，空和非空状态切换时触发；
Culture - 表示 DataGrid 控件的区域性信息，在 Culture 变化时，包括名称，日历系统，字符排序等会发生变化；
CurrentPosition - 表示 DataGrid 控件的当前位置，在子类的 RaiseCurrencyChanges 和 LoadSnapshot 事件中被使用；
CurrentItem - 表示 DataGrid 控件当前选中的元素，同样在子类的 RaiseCurrencyChanges 和 LoadSnapshot 事件中被使用；
IsCurrentBeforeFirst - 表示 DataGrid 控件中当前选中是否在首个元素之前；
IsCurrentAfterLast - 表示 DataGrid 控件中当前选中是否在最后一个元素之后；
接下来看几个重要的方法：
1). CollectionView()
CollectionView 类的构造方法，可以看到方法中创建了监听器，对时间的 Action 调用和卸载做了定义，对于集合改变事件做了绑定，并对布尔类型的属性做了初始设置；
public CollectionView(IEnumerable collection)
{
_sourceCollection = collection ?? throw new ArgumentNullException("collection"); // forward collection change events from underlying collection to our listeners.
INotifyCollectionChanged incc = collection as INotifyCollectionChanged; if (incc != null)
{
_sourceWeakEventListener = new WeakEventListener<CollectionView, object, NotifyCollectionChangedEventArgs>(this)
{ // Call the actual collection changed event
OnEventAction = (source, changed, arg) => OnCollectionChanged(source, arg), // The source doesn't exist anymore
OnDetachAction = (listener) => incc.CollectionChanged -= _sourceWeakEventListener.OnEvent
};
incc.CollectionChanged += _sourceWeakEventListener.OnEvent;
}
_currentItem = null;
_currentPosition = -1;
SetFlag(CollectionViewFlags.IsCurrentBeforeFirst, _currentPosition < 0);
SetFlag(CollectionViewFlags.IsCurrentAfterLast, _currentPosition < 0);
SetFlag(CollectionViewFlags.CachedIsEmpty, _currentPosition < 0);
}2). OnCollectionChanged()
集合变化的处理，包括对变化动画的判断，当变化不是替换时，触发 count 属性变化；以及对于集合空的判断，空和为空切换时，触发 isEmpty 属性变化，前面在属性说明中我们提提到了；
protected virtual void OnCollectionChanged(NotifyCollectionChangedEventArgs args)
{ if (args == null)
{ throw new ArgumentNullException("args");
} unchecked
{ // invalidate enumerators because of a change
++_timestamp;
}
CollectionChanged?.Invoke(this, args); // Collection changes change the count unless an item is being // replaced or moved within the collection.
if (args.Action != NotifyCollectionChangedAction.Replace)
{
OnPropertyChanged(CountPropertyName);
} bool isEmpty = IsEmpty; if (isEmpty != CheckFlag(CollectionViewFlags.CachedIsEmpty))
{
SetFlag(CollectionViewFlags.CachedIsEmpty, isEmpty);
OnPropertyChanged(IsEmptyPropertyName);
}
}3). SetCurrent()
根据当前选择的元素，当前位置和元素数量设置当前选中；新元素不为空时，设置 IsCurrentBeforeFirst 和 IsCurrentAfterLast 属性为 false；当集合为空时，设置两个属性为 true，设置新的选中位置为 -1；否则，根据 newPosition 的值来设置这两个属性；
protected void SetCurrent(object newItem, int newPosition, int count)
{ if (newItem != null)
{ // non-null item implies position is within range. // We ignore count - it's just a placeholder
SetFlag(CollectionViewFlags.IsCurrentBeforeFirst, false);
SetFlag(CollectionViewFlags.IsCurrentAfterLast, false);
} else if (count == 0)
{ // empty collection - by convention both flags are true and position is -1
SetFlag(CollectionViewFlags.IsCurrentBeforeFirst, true);
SetFlag(CollectionViewFlags.IsCurrentAfterLast, true);
newPosition = -1;
} else
{ // null item, possibly within range.
SetFlag(CollectionViewFlags.IsCurrentBeforeFirst, newPosition < 0);
SetFlag(CollectionViewFlags.IsCurrentAfterLast, newPosition >= count);
}
_currentItem = newItem;
_currentPosition = newPosition;
}
2. EnumerableCollectionView
该类是 CollectionView 类的子类，支持枚举类型的数据集合。下面我们主要分享它基于 CollectionView 的特殊实现部分：
1). EnumerableCollectionView()
先看看构造方法，首先根据数据源设置当前元素和位置等，绑定集合改变，属性改变和当前的改变和改变后事件；重点说一下 OnCurrentChanging 和 OnCurrentChanged 事件，分别可以在改变前做干预处理，改变后做对应处理；
internal EnumerableCollectionView(IEnumerable source)
: base(source)
{
_snapshot = new ObservableCollection<object>();
LoadSnapshotCore(source); if (_snapshot.Count > 0)
{
SetCurrent(_snapshot[0], 0, 1);
} else
{
SetCurrent(null, -1, 0);
} // If the source doesn't raise collection change events, try to detect changes by polling the enumerator.
_pollForChanges = !(source is INotifyCollectionChanged);
_view = new ListCollectionView(_snapshot);
INotifyCollectionChanged incc = _view as INotifyCollectionChanged;
incc.CollectionChanged += new NotifyCollectionChangedEventHandler(EnumerableCollectionView_OnViewChanged);
INotifyPropertyChanged ipc = _view as INotifyPropertyChanged;
ipc.PropertyChanged += new PropertyChangedEventHandler(EnumerableCollectionView_OnPropertyChanged);
_view.CurrentChanging += new CurrentChangingEventHandler(EnumerableCollectionView_OnCurrentChanging);
_view.CurrentChanged += new EventHandler<object>(EnumerableCollectionView_OnCurrentChanged);
}2). ProcessCollectionChanged()
处理集合变化事件的方法，主要对改变做了 Add，Remove，Replace 和 Reset 四种情况的处理；分别看一下处理内容：
Add - Add 操作后，对 snapshot 集合做对应变化，当新增索引 < 0 或小于当前开始索引时，加到集合开始位置，否则插入对应位置；
Remove - Remove 操作后，在 snapshot 集合中删除对应位置的元素；
Replace - Replace 操作后，在 snapshot 集合中替换对应位置的元素；
Reset - Reset 操作后，对应重置 snapshot 集合；
protected override void ProcessCollectionChanged(NotifyCollectionChangedEventArgs args)
{ // Apply the change to the snapshot
switch (args.Action)
{ case NotifyCollectionChangedAction.Add: if (args.NewStartingIndex < 0 || _snapshot.Count <= args.NewStartingIndex)
{ // Append
for (int i = 0; i < args.NewItems.Count; ++i)
{
_snapshot.Add(args.NewItems[i]);
}
} else
{ // Insert
for (int i = args.NewItems.Count - 1; i >= 0; --i)
{
_snapshot.Insert(args.NewStartingIndex, args.NewItems[i]);
}
} break; case NotifyCollectionChangedAction.Remove: if (args.OldStartingIndex < 0)
{ throw CollectionViewsError.EnumerableCollectionView.RemovedItemNotFound();
} for (int i = args.OldItems.Count - 1, index = args.OldStartingIndex + i; i >= 0; --i, --index)
{ if (!object.Equals(args.OldItems[i], _snapshot[index]))
{ throw CollectionViewsError.CollectionView.ItemNotAtIndex("removed");
}
_snapshot.RemoveAt(index);
} break; case NotifyCollectionChangedAction.Replace: for (int i = args.NewItems.Count - 1, index = args.NewStartingIndex + i; i >= 0; --i, --index)
{ if (!object.Equals(args.OldItems[i], _snapshot[index]))
{ throw CollectionViewsError.CollectionView.ItemNotAtIndex("replaced");
}
_snapshot[index] = args.NewItems[i];
} break; case NotifyCollectionChangedAction.Reset:
LoadSnapshot(SourceCollection); break;
}
}3). LoadSnapshot()
加载 snapshot 方法，根据重新加载的元素集合，判断以下属性是否需要响应变化：IsCurrentAfterLast，IsCurrentBeforeFirst，CurrentPosition 和 CurrentItem。
private void LoadSnapshot(IEnumerable source)
{ // Force currency off the collection (gives user a chance to save dirty information). OnCurrentChanging(); // Remember the values of the scalar properties, so that we can restore // them and raise events after reloading the data
object oldCurrentItem = CurrentItem; int oldCurrentPosition = CurrentPosition; bool oldIsCurrentBeforeFirst = IsCurrentBeforeFirst; bool oldIsCurrentAfterLast = IsCurrentAfterLast; // Reload the data LoadSnapshotCore(source); // Tell listeners everything has changed
OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
OnCurrentChanged(); if (IsCurrentAfterLast != oldIsCurrentAfterLast)
{
OnPropertyChanged(new PropertyChangedEventArgs(IsCurrentAfterLastPropertyName));
} if (IsCurrentBeforeFirst != oldIsCurrentBeforeFirst)
{
OnPropertyChanged(new PropertyChangedEventArgs(IsCurrentBeforeFirstPropertyName));
} if (oldCurrentPosition != CurrentPosition)
{
OnPropertyChanged(new PropertyChangedEventArgs(CurrentPositionPropertyName));
} if (oldCurrentItem != CurrentItem)
{
OnPropertyChanged(new PropertyChangedEventArgs(CurrentItemPropertyName));
}
}
3. ListCollectionView
该类是 CollectionView 类的子类，支持列表类型的数据集合。下面我们也会主要分享它基于 CollectionView 的特殊实现部分：
1). ListCollectionView()
ListCollectionView 类的构造方法，当支持编辑行为时，需要刷新可增加，可删除，可取消编辑的判断；然后设置当前位置和元素；当支持分组时，注册分组描述，分组改变和分组依据的变化处理事件；
public ListCollectionView(IList list) : base(list)
{
_internalList = list; #if FEATURE_IEDITABLECOLLECTIONVIEW
RefreshCanAddNew();
RefreshCanRemove();
RefreshCanCancelEdit(); #endif
if (InternalList.Count == 0)
{ // don't call virtual IsEmpty in ctor
SetCurrent(null, -1, 0);
} else
{
SetCurrent(InternalList[0], 0, 1);
} #if FEATURE_ICOLLECTIONVIEW_GROUP
_group = new CollectionViewGroupRoot(this);
_group.GroupDescriptionChanged += new EventHandler(OnGroupDescriptionChanged);
((INotifyCollectionChanged)_group).CollectionChanged += new NotifyCollectionChangedEventHandler(OnGroupChanged);
((INotifyCollectionChanged)_group.GroupDescriptions).CollectionChanged += new NotifyCollectionChangedEventHandler(OnGroupByChanged); #endif}2). ProcessCollectionChangedWithAdjustedIndex()
处于集合变化和索引调整的方法，首先判断当前动作的类型：Add，Remove 或 Replace，并针对每种不同类型的操作，进行分别的处理；再对 afterLastHasChanged，beforeFirstHasChanged，currentPositionHasChanged 和 currentItemHasChanged 属性进行设置；
private void ProcessCollectionChangedWithAdjustedIndex(EffectiveNotifyCollectionChangedAction action, object oldItem, object newItem, int adjustedOldIndex, int adjustedNewIndex)
{
EffectiveNotifyCollectionChangedAction effectiveAction = action; if (adjustedOldIndex == adjustedNewIndex && adjustedOldIndex >= 0)
{
effectiveAction = EffectiveNotifyCollectionChangedAction.Replace;
} else if (adjustedOldIndex == -1)
{ if (adjustedNewIndex < 0)
{ if (action == EffectiveNotifyCollectionChangedAction.Add)
{ return;
}
effectiveAction = EffectiveNotifyCollectionChangedAction.Remove;
}
} else if (adjustedOldIndex < -1)
{ ... } else
{ ... } int originalCurrentPosition = CurrentPosition; int oldCurrentPosition = CurrentPosition; object oldCurrentItem = CurrentItem; bool oldIsCurrentAfterLast = IsCurrentAfterLast; bool oldIsCurrentBeforeFirst = IsCurrentBeforeFirst;
NotifyCollectionChangedEventArgs args = null, args2 = null; switch (effectiveAction)
{ case EffectiveNotifyCollectionChangedAction.Add: // insert into private view#if FEATURE_ICOLLECTIONVIEW_SORT_OR_FILTER#if FEATURE_IEDITABLECOLLECTIONVIEW // (unless it's a special item (i.e. new item))
if (UsesLocalArray && (!IsAddingNew || !object.Equals(_newItem, newItem)))#else
if (UsesLocalArray)#endif
{
InternalList.Insert(adjustedNewIndex, newItem);
}#endif
if (!IsGrouping)
{
AdjustCurrencyForAdd(adjustedNewIndex);
args = new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, newItem, adjustedNewIndex);
}#if FEATURE_ICOLLECTIONVIEW_GROUP else
{
AddItemToGroups(newItem);
}#endif
break; case EffectiveNotifyCollectionChangedAction.Remove:
... case EffectiveNotifyCollectionChangedAction.Replace:
... case EffectiveNotifyCollectionChangedAction.Move:
... default:
Debug.Assert(false, "Unexpected Effective Collection Change Action"); break;
} bool afterLastHasChanged = IsCurrentAfterLast != oldIsCurrentAfterLast; bool beforeFirstHasChanged = IsCurrentBeforeFirst != oldIsCurrentBeforeFirst; bool currentPositionHasChanged = CurrentPosition != oldCurrentPosition; bool currentItemHasChanged = CurrentItem != oldCurrentItem;
oldIsCurrentAfterLast = IsCurrentAfterLast;
oldIsCurrentBeforeFirst = IsCurrentBeforeFirst;
oldCurrentPosition = CurrentPosition;
oldCurrentItem = CurrentItem; // base class will raise an event to our listeners
if (!IsGrouping)
{
Debug.Assert(!CurrentChangedMonitor.Busy, "Expected _currentChangedMonitor.Busy is false.");
CurrentChangedMonitor.Enter(); using (CurrentChangedMonitor)
{
OnCollectionChanged(args); if (args2 != null)
{
OnCollectionChanged(args2);
}
} // Any scalar properties that changed don't need a further notification, // but do need a new snapshot ...
} // currency has to change after firing the deletion event, // so event handlers have the right picture
if (_currentElementWasRemoved)
{ int oldCurPos = originalCurrentPosition;#if FEATURE_ICOLLECTIONVIEW_GROUP if (_newGroupedItem != null)
{
oldCurPos = IndexOf(_newGroupedItem);
}#endif
MoveCurrencyOffDeletedElement(oldCurPos); // changes to the scalar properties need notification
afterLastHasChanged = afterLastHasChanged || (IsCurrentAfterLast != oldIsCurrentAfterLast);
beforeFirstHasChanged = beforeFirstHasChanged || (IsCurrentBeforeFirst != oldIsCurrentBeforeFirst);
currentPositionHasChanged = currentPositionHasChanged || (CurrentPosition != oldCurrentPosition);
currentItemHasChanged = currentItemHasChanged || (CurrentItem != oldCurrentItem);
}
RaiseCurrencyChanges(false, currentItemHasChanged, currentPositionHasChanged, beforeFirstHasChanged, afterLastHasChanged);
}
4. CollectionViewsError
CollectionViewsError 类中主要定义了 DataGrid 控件数据，就是 CollectionView 中的错误，我们来看一下都定义了哪些错误：
EnumeratorVersionChanged - InvalidOperationException，“Collection was modified; enumeration operation cannot execute.”
MemberNotAllowedDuringAddOrEdit - InvalidOperationException，"'{0}' is not allowed during an AddNew or EditItem transaction."
NoAccessWhileChangesAreDeferred - InvalidOperationException，"This value cannot be accessed while changes are deferred."
ItemNotAtIndex - InvalidOperationException，"The {0} item is not in the collection."
RemovedItemNotFound - InvalidOperationException，"The removed item is not found in the source collection."
CollectionChangedOutOfRange - InvalidOperationException，"The collection change is out of bounds of the original collection."
AddedItemNotInCollection - InvalidOperationException，"The added item is not in the collection."
CancelEditNotSupported - InvalidOperationException，"CancelEdit is not supported for the current edit item."
MemberNotAllowedDuringTransaction - InvalidOperationException，"'{0}' is not allowed during a transaction started by '{1}'."
MemberNotAllowedForView - InvalidOperationException，"'{0}' is not allowed for this view."
总结
这里我们把 DataGrid 的 CollectionView 相关类介绍完成了，作为 DataGrid 相关分享的第一篇，后面我们会继续分享 Utilities 和最重要的 DataGrid 的相关重点。
最后，再跟大家安利一下 WindowsCommunityToolkit 的官方微博：https://weibo.com/u/6506046490, 大家可以通过微博关注最新动态。
衷心感谢 WindowsCommunityToolkit 的作者们杰出的工作，感谢每一位贡献者，Thank you so much, ALL WindowsCommunityToolkit AUTHORS !!!
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