// There are several cases handled here with respect to which element gets returned and when DataContext is modified.
//
// 1. If there is no ItemTemplate:
// 1.1 If data is a UIElement . the data is returned
// 1.2 If data is not a UIElement . a default DataTemplate is used to fetch element and DataContext is set to data**
//
// 2. If there is an ItemTemplate:
// 2.1 If data is not a FrameworkElement . Element is fetched from ElementFactory and DataContext is set to the data**
// 2.2 If data is a FrameworkElement:
// 2.2.1 If Element returned by the ElementFactory is the same as the data . Element (a.k.a. data) is returned as is
// 2.2.2 If Element returned by the ElementFactory is not the same as the data
// . Element that is fetched from the ElementFactory is returned and
// DataContext is set to the data's DataContext (if it exists), otherwise it is set to the data itself**
//
// **data context is set only if no x:Bind was used. ie. No data template component on the root.
UIElement GetElementFromElementFactory(int index)
{
// The view generator is the provider of last resort.
var data = m_owner.ItemsSourceView.GetAt(index);
UIElement GetElement()
{
var elementFactory = m_owner.ItemTemplateShim;
if (elementFactory == null)
{
if (data is UIElement dataAsElement)
{
return(dataAsElement);
}
else
{
// If no ItemTemplate was provided, use a default
//var factory = XamlReader.Load("<DataTemplate xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation'><TextBlock Text='{Binding}'/></DataTemplate>") as DataTemplate;
var factory = new DataTemplate(() =>
{
var tb = new TextBlock();
tb.SetBinding(TextBlock.TextProperty, new Binding());
return(tb);
});
m_owner.ItemTemplate = factory;
elementFactory = m_owner.ItemTemplateShim;
}
}
if (m_ElementFactoryGetArgs == null)
{
m_ElementFactoryGetArgs = new ElementFactoryGetArgs();
}
var args = m_ElementFactoryGetArgs;
using var scopeGuard = Disposable.Create(() =>
{
args.Data = null;
args.Parent = null;
});
args.Data = data;
args.Parent = m_owner;
args.Index = index;
return(elementFactory.GetElement(args));
};
var element = GetElement();
var virtInfo = ItemsRepeater.TryGetVirtualizationInfo(element);
if (virtInfo == null)
{
virtInfo = ItemsRepeater.CreateAndInitializeVirtualizationInfo(element);
REPEATER_TRACE_PERF("ElementCreated");
}
else
{
// View obtained from ElementFactory already has a VirtualizationInfo attached to it
// which means that the element has been recycled and not created from scratch.
REPEATER_TRACE_PERF("ElementRecycled");
}
if (data != element)
{
// Prepare the element
// If we are phasing, run phase 0 before setting DataContext. If phase 0 is not
// run before setting DataContext, when setting DataContext all the phases will be
// run in the OnDataContextChanged handler in code generated by the xaml compiler (code-gen).
var extension = CachedVisualTreeHelpers.GetDataTemplateComponent(element);
if (extension != null)
{
// Clear out old data.
extension.Recycle();
int nextPhase = VirtualizationInfo.PhaseReachedEnd;
// Run Phase 0
extension.ProcessBindings(data, index, 0 /* currentPhase */, out nextPhase);
// Setup phasing information, so that Phaser can pick up any pending phases left.
// Update phase on virtInfo. Set data and templateComponent only if x:Phase was used.
virtInfo.UpdatePhasingInfo(nextPhase, nextPhase > 0 ? data : null, nextPhase > 0 ? extension : null);
}
else if (element is FrameworkElement elementAsFE)
{
// Set data context only if no x:Bind was used. ie. No data template component on the root.
// If the passed in data is a UIElement and is different from the element returned by
// the template factory then we need to propagate the DataContext.
// Otherwise just set the DataContext on the element as the data.
var elementDataContext = data;
if (data is FrameworkElement dataAsElement)
{
var dataDataContext = dataAsElement.DataContext;
if (dataDataContext != null)
{
elementDataContext = dataDataContext;
}
}
elementAsFE.DataContext = elementDataContext;
}
else
{
MUX_ASSERT(false, "Element returned by factory is not a FrameworkElement!");
}
}
virtInfo.MoveOwnershipToLayoutFromElementFactory(
index,
/* uniqueId: */
m_owner.ItemsSourceView.HasKeyIndexMapping ? m_owner.ItemsSourceView.KeyFromIndex(index) : null);
// The view generator is the only provider that prepares the element.
var repeater = m_owner;
#if IS_UNO //TODO: Uno specific - remove when #4689 is fixed
repeater.OnUnoBeforeElementPrepared(element, index);
#endif
// Add the element to the children collection here before raising OnElementPrepared so
// that handlers can walk up the tree in case they want to find their IndexPath in the
// nested case.
var children = repeater.Children;
if (CachedVisualTreeHelpers.GetParent(element) != repeater)
{
children.Add(element);
}
repeater.AnimationManager.OnElementPrepared(element);
repeater.OnElementPrepared(element, index);
if (data != element)
{
m_phaser.PhaseElement(element, virtInfo);
}
// Update realized indices
m_firstRealizedElementIndexHeldByLayout = Math.Min(m_firstRealizedElementIndexHeldByLayout, index);
m_lastRealizedElementIndexHeldByLayout = Math.Max(m_lastRealizedElementIndexHeldByLayout, index);
return(element);
}
