protected void BuildHeader()
{
// the new HeaderContent will inherit its BindingContext from this.BindingContext [recursive down]
if (HeaderCreationFactory != null)
{
HeaderContent = HeaderCreationFactory.Invoke();
}
}
// [recursive down] create item template instances, attach and layout, and set descendents until finding overrides
protected void BuildVisualChildren()
{
var bindingContextNode = (ITreeNode)BindingContext;
if (bindingContextNode == null)
{
return;
}
// STEP 1: remove child visual tree nodes (TreeNodeViews) that don't correspond to an item in our data source
var nodeViewsToRemove = new List <TreeNodeView>();
var bindingChildList = new List <ITreeNode>(bindingContextNode != null ? bindingContextNode.ChildNodes : null);
// which ChildTreeNodeViews are in the visual tree... ?
foreach (TreeNodeView nodeView in ChildTreeNodeViews)
{
// but missing from the bound data source?
if (!bindingChildList.Contains(nodeView.BindingContext))
{
// tag them for removal from the visual tree
nodeViewsToRemove.Add(nodeView);
}
}
BatchBegin();
try
{
// perform removal in a batch
foreach (TreeNodeView nodeView in nodeViewsToRemove)
{
MainLayoutGrid.Children.Remove(nodeView);
}
}
finally
{
// ensure we commit
BatchCommit();
}
// STEP 2: add visual tree nodes (TreeNodeViews) for children of the binding context not already associated with a TreeNodeView
if (NodeCreationFactory != null)
{
var nodeViewsToAdd = new Dictionary <TreeNodeView, ITreeNode>();
foreach (ITreeNode node in bindingContextNode.ChildNodes)
{
if (!ChildTreeNodeViews.Any(nodeView => nodeView.BindingContext == node))
{
var nodeView = NodeCreationFactory.Invoke();
nodeView.ParentTreeNodeView = this;
if (HeaderCreationFactory != null)
{
nodeView.HeaderContent = HeaderCreationFactory.Invoke();
}
// the order of these may be critical
nodeViewsToAdd.Add(nodeView, node);
}
}
BatchBegin();
try
{
// perform the additions in a batch
foreach (KeyValuePair <TreeNodeView, ITreeNode> nodeView in nodeViewsToAdd)
{
// only set BindingContext after the node has Parent != null
nodeView.Key.BindingContext = nodeView.Value;
nodeView.Value.ExpandAction = () => nodeView.Key.BuildVisualChildren();
nodeView.Key.ChildrenStackLayout.IsVisible = nodeView.Key.IsExpanded;
ChildrenStackLayout.Children.Add(nodeView.Key);
ChildrenStackLayout.SetBinding(StackLayout.IsVisibleProperty, new Binding("IsExpanded", BindingMode.TwoWay));
// TODO: make sure to unsubscribe elsewhere
nodeView.Value.PropertyChanged += HandleListCountChanged;
}
}
finally
{
// ensure we commit
BatchCommit();
}
}
}