protected override void OnLayout(bool changed, int l, int t, int r, int b)
{
AToolbar bar = _toolbar;
// make sure bar stays on top of everything
bar.BringToFront();
int barHeight = ActionBarHeight();
if (Element.IsSet(BarHeightProperty))
{
barHeight = Element.OnThisPlatform().GetBarHeight();
}
if (barHeight != _lastActionBarHeight && _lastActionBarHeight > 0)
{
ResetToolbar();
bar = _toolbar;
}
_lastActionBarHeight = barHeight;
bar.Measure(MeasureSpecFactory.MakeMeasureSpec(r - l, MeasureSpecMode.Exactly), MeasureSpecFactory.MakeMeasureSpec(barHeight, MeasureSpecMode.Exactly));
var barOffset = ToolbarVisible ? barHeight : 0;
int containerHeight = b - t - ContainerTopPadding - barOffset - ContainerBottomPadding;
PageController.ContainerArea = new Rectangle(0, 0, Context.FromPixels(r - l), Context.FromPixels(containerHeight));
// Potential for optimization here, the exact conditions by which you don't need to do this are complex
// and the cost of doing when it's not needed is moderate to low since the layout will short circuit pretty fast
Element.ForceLayout();
base.OnLayout(changed, l, t, r, b);
bool toolbarLayoutCompleted = false;
for (var i = 0; i < ChildCount; i++)
{
AView child = GetChildAt(i);
Page childPage = (child as PageContainer)?.Child?.Element as Page;
if (childPage == null)
{
return;
}
// We need to base the layout of both the child and the bar on the presence of the NavBar on the child Page itself.
// If we layout the bar based on ToolbarVisible, we get a white bar flashing at the top of the screen.
// If we layout the child based on ToolbarVisible, we get a white bar flashing at the bottom of the screen.
bool childHasNavBar = NavigationPage.GetHasNavigationBar(childPage);
if (childHasNavBar)
{
bar.Layout(0, 0, r - l, barHeight);
child.Layout(0, barHeight + ContainerTopPadding, r, b - ContainerBottomPadding);
}
else
{
bar.Layout(0, -1000, r, barHeight - 1000);
child.Layout(0, ContainerTopPadding, r, b - ContainerBottomPadding);
}
toolbarLayoutCompleted = true;
}
// Making the layout of the toolbar dependant on having a child Page could potentially mean that the toolbar is not laid out.
// We'll do one more check to make sure it isn't missed.
if (!toolbarLayoutCompleted)
{
if (ToolbarVisible)
{
bar.Layout(0, 0, r - l, barHeight);
}
else
{
bar.Layout(0, -1000, r, barHeight - 1000);
}
}
}