// We need to clear the datacontext to prevent crashes from happening,
// however we only do that if we were the ones setting it.
// That is when one of the following is the case (numbering taken from line ~642):
// 1.2 No ItemTemplate, data is not a UIElement
// 2.1 ItemTemplate, data is not FrameworkElement
// 2.2.2 Itemtemplate, data is FrameworkElement, ElementFactory returned Element different to data
//
// In all of those three cases, we the ItemTemplateShim is NOT null.
// Luckily when we create the items, we store whether we were the once setting the DataContext.
public void ClearElementToElementFactory(UIElement element)
{
m_owner.OnElementClearing(element);
var virtInfo = ItemsRepeater.GetVirtualizationInfo(element);
virtInfo.MoveOwnershipToElementFactory();
// During creation of this object, we were the one setting the DataContext, so clear it now.
if (virtInfo.MustClearDataContext)
{
if (element is FrameworkElement elementAsFE)
{
elementAsFE.DataContext = null;
}
}
if (m_owner.ItemTemplateShim != null)
{
if (m_ElementFactoryRecycleArgs == null)
{
// Create one.
m_ElementFactoryRecycleArgs = new ElementFactoryRecycleArgs();
}
var context = m_ElementFactoryRecycleArgs;
context.Element = element;
context.Parent = m_owner;
m_owner.ItemTemplateShim.RecycleElement(context);
context.Element = null;
context.Parent = null;
}
else
{
// No ItemTemplate to recycle to, remove the element from the children collection.
var children = m_owner.Children;
int childIndex = 0;
bool found = children.IndexOf(element, out childIndex);
if (!found)
{
throw new Exception("ItemsRepeater's child not found in its Children collection.");
}
children.RemoveAt(childIndex);
}
if (m_lastFocusedElement == element)
{
// Focused element is going away. Remove the tracked last focused element
// and pick a reasonable next focus if we can find one within the layout
// realized elements.
int clearedIndex = virtInfo.Index;
MoveFocusFromClearedIndex(clearedIndex);
}
}
void UnlinkElementFromParent(ElementFactoryRecycleArgs args)
{
// We want to unlink the containers from the parent repeater
// in case we are required to move it to a different repeater.
if (args.Parent is Panel panel)
{
var children = panel.Children;
int childIndex = 0;
if (children.IndexOf(args.Element, out childIndex))
{
children.RemoveAt(childIndex);
}
}
}
public void RecycleElement(ElementFactoryRecycleArgs args)
{
var element = args.Element;
DataTemplate selectedTemplate = Template ??
element.GetValue(RecyclePool.OriginTemplateProperty) as DataTemplate;
var recyclePool = RecyclePool.GetPoolInstance(selectedTemplate);
if (recyclePool == null)
{
// No Recycle pool in the template, create one.
recyclePool = new RecyclePool();
RecyclePool.SetPoolInstance(selectedTemplate, recyclePool);
}
recyclePool.PutElement(args.Element, string.Empty /* key */, args.Parent);
}
protected override void RecycleElementCore(ElementFactoryRecycleArgs args)
{
if (m_itemTemplateWrapper != null)
{
m_itemTemplateWrapper.RecycleElement(args);
}
else
{
// We want to unlink the containers from the parent repeater
// in case we are required to move it to a different repeater.
if (args.Parent is Panel panel)
{
var children = panel.Children;
int childIndex = 0;
if (children.IndexOf(args.Element, out childIndex))
{
children.RemoveAt(childIndex);
}
}
}
}
protected override void RecycleElementCore(ElementFactoryRecycleArgs args)
{
if (args.Element is { } element)
{
if (element is NavigationViewItem nvi)
{
var nviImpl = nvi;
// Check whether we wrapped the element in a NavigationViewItem ourselves.
// If yes, we are responsible for recycling it.
if (nviImpl.CreatedByNavigationViewItemsFactory)
{
nviImpl.CreatedByNavigationViewItemsFactory = false;
UnlinkElementFromParent(args);
args.Element = null;
// Retain the NVI that we created for future re-use
navigationViewItemPool.Add(nvi);
// Retrieve the proper element that requires recycling for a user defined item template
// and update the args correspondingly
if (m_itemTemplateWrapper != null)
{
// TODO: Retrieve the element and add to the args
}
}
}
// Do not recycle SettingsItem
bool isSettingsItem = m_settingsItem != null && m_settingsItem == args.Element;
if (m_itemTemplateWrapper != null && !isSettingsItem)
{
m_itemTemplateWrapper.RecycleElement(args);
}
else
{
UnlinkElementFromParent(args);
}
}
}
protected virtual void RecycleElementCore(ElementFactoryRecycleArgs args)
{
throw new NotImplementedException();
}
public void RecycleElement(ElementFactoryRecycleArgs args)
{
RecycleElementCore(args);
}
// Retrieve the element that will be displayed for a specific data item.
// If the resolved element is not derived from NavigationViewItemBase, wrap in a NavigationViewItem before returning.
protected override UIElement GetElementCore(ElementFactoryGetArgs args)
{
object newContent;
{
object init()
{
if (m_itemTemplateWrapper != null)
{
return(m_itemTemplateWrapper.GetElement(args));
}
return(args.Data);
}
newContent = init();
}
// Element is already of expected type, just return it
if (newContent is NavigationViewItemBase newItem)
{
return(newItem);
}
// Get or create a wrapping container for the data
NavigationViewItem nvi;
{
nvi = init();
NavigationViewItem init()
{
if (navigationViewItemPool.Count > 0)
{
var nvi = navigationViewItemPool.Last();
navigationViewItemPool.RemoveLast();
return(nvi);
}
return(new NavigationViewItem());
}
}
var nviImpl = nvi;
nviImpl.CreatedByNavigationViewItemsFactory = true;
// If a user provided item template exists, just pass the template and data down to the ContentPresenter of the NavigationViewItem
if (m_itemTemplateWrapper != null)
{
if (m_itemTemplateWrapper is ItemTemplateWrapper itemTemplateWrapper)
{
// Recycle newContent
var tempArgs = new ElementFactoryRecycleArgs();
tempArgs.Element = newContent as UIElement;
m_itemTemplateWrapper.RecycleElement(tempArgs);
nviImpl.Content = args.Data;
nviImpl.ContentTemplate = itemTemplateWrapper.Template;
nviImpl.ContentTemplateSelector = itemTemplateWrapper.TemplateSelector;
return(nviImpl);
}
}
nviImpl.Content = newContent;
return(nviImpl);
}
protected override void RecycleElementCore(ElementFactoryRecycleArgs args)
{
}
protected abstract void RecycleElementCore(ElementFactoryRecycleArgs args);