private TreeViewItemEx GetPageUpDownContainer(TreeViewItemEx container, bool down)
{
if (container == null)
{
return(down ? GetLastContainer(this, true) : GetFirstContainer(this, true));
}
double yThreshold = container.TransformToAncestor(this).Transform(new Point()).Y;
double itemHeight = container.HeaderHeight;
double viewportHeight = _scrollViewer?.ViewportHeight ?? ActualHeight;
double offset = viewportHeight - 2 * itemHeight;
if (down)
{
yThreshold += offset;
var nextContainer = GetNextContainer(container, true);
while (nextContainer != null)
{
container = nextContainer;
double y = container.TransformToAncestor(this).Transform(new Point()).Y;
if (y > yThreshold)
{
break;
}
nextContainer = GetNextContainer(nextContainer, true);
}
}
else
{
yThreshold -= offset;
var previousContainer = GetPreviousContainer(container, true);
while (previousContainer != null)
{
container = previousContainer;
double y = container.TransformToAncestor(this).Transform(new Point()).Y;
if (y < yThreshold)
{
break;
}
previousContainer = GetPreviousContainer(previousContainer, true);
}
}
return(container);
}
private TreeViewItemEx GetPageUpDownContainer(TreeViewItemEx container, bool down)
{
if (container == null)
return down ? GetLastContainer(this, true) : GetFirstContainer(this, true);
double yThreshold = container.TransformToAncestor(this).Transform(new Point()).Y;
double itemHeight = container.HeaderHeight;
double viewportHeight = _scrollViewer?.ViewportHeight ?? ActualHeight;
double offset = viewportHeight - 2 * itemHeight;
if (down)
{
yThreshold += offset;
var nextContainer = GetNextContainer(container, true);
while (nextContainer != null)
{
container = nextContainer;
double y = container.TransformToAncestor(this).Transform(new Point()).Y;
if (y > yThreshold)
break;
nextContainer = GetNextContainer(nextContainer, true);
}
}
else
{
yThreshold -= offset;
var previousContainer = GetPreviousContainer(container, true);
while (previousContainer != null)
{
container = previousContainer;
double y = container.TransformToAncestor(this).Transform(new Point()).Y;
if (y < yThreshold)
break;
previousContainer = GetPreviousContainer(previousContainer, true);
}
}
return container;
}
