/// <summary>
/// Call this method to perform the specified action in a Dispatcher.Invoke call, but only
/// if another action is not already pending execution. This is useful for example to redraw
/// the screen when a collection of item changes, doing so only once if the collection changes
/// multiple times. Another example is redrawing an element when any of its properties change,
/// while ensuring that if many properties are changed, the element is redrawn only once.
/// </summary>
/// <param name="action">The action to queue</param>
public void QueueActionIfQueueIsEmpty(Action action)
{
if (_queueIsEmpty) // This ensures that the "QueueAction" method below is only called once, and it is not called again until its delegate has been executed.
{
_queueIsEmpty = false;
INTERNAL_DispatcherHelpers.QueueAction(() =>
{
_queueIsEmpty = true;
action();
});
}
}
static void AttachVisualChild_Private(UIElement child, UIElement parent, int index)
{
//
// THIS IS WHAT THE FINAL STRUCTURE IN THE DOM TREE WILL LOOK LIKE:
//
// domElementWhereToPlaceChildStuff
// --- [wrapperForChild]
// --- --- [innerDivOfWrapperForChild]
// --- --- --- [additionalOutsideDivForMargins, aka BoxSizing]
// --- --- --- --- outerDomElement
//
//--------------------------------------------------------
// PREPARE THE PARENT:
//--------------------------------------------------------
#if PERFSTAT
var t0 = Performance.now();
#endif
// Prepare the parent DOM structure so that it is ready to contain the child (for example, in case of a grid, we need to (re)create the rows and columns where to place the elements).
//parent.INTERNAL_UpdateDomStructureIfNecessary();
object domElementWhereToPlaceChildStuff = (parent.GetDomElementWhereToPlaceChild(child) ?? parent.INTERNAL_InnerDomElement);
// A "wrapper for child" is sometimes needed between the child and the parent (for example in case of a grid). It is usually one or more DIVs that fit in-between the child and the parent, and that are used to position the child within the parent.
object innerDivOfWrapperForChild;
object wrapperForChild = parent.CreateDomChildWrapper(domElementWhereToPlaceChildStuff, out innerDivOfWrapperForChild, index);
bool comparison1 = (wrapperForChild == null); // Note: we need due to a bug of JSIL where translation fails if we do not use this temp variable.
bool comparison2 = (innerDivOfWrapperForChild == null); // Note: we need due to a bug of JSIL where translation fails if we do not use this temp variable.
bool doesParentRequireToCreateAWrapperForEachChild = (!comparison1 && !comparison2); // Note: The result is "True" for complex structures such as tables, false otherwise (cf. documentation in "INTERNAL_VisualChildInformation" class).
#if PERFSTAT
Performance.Counter("VisualTreeManager: Prepare the parent", t0);
#endif
//--------------------------------------------------------
// CONTINUE WITH THE OTHER STEPS (AND DEFER SOME OF THEM WHEN THE ELEMENT IS COLLAPSED):
//--------------------------------------------------------
// Defer loading to when the control becomes visible if the option to not load collapsed controls is enabled:
if (EnableOptimizationWhereCollapsedControlsAreNotLoaded && child.Visibility == Visibility.Collapsed)
{
child.INTERNAL_DeferredLoadingWhenControlBecomesVisible = () =>
{
AttachVisualChild_Private_MainSteps(
child,
parent,
doesParentRequireToCreateAWrapperForEachChild,
innerDivOfWrapperForChild,
domElementWhereToPlaceChildStuff,
wrapperForChild);
};
}
else if (EnableOptimizationWhereCollapsedControlsAreLoadedLast && child.Visibility == Visibility.Collapsed)
{
child.INTERNAL_DeferredLoadingWhenControlBecomesVisible = () =>
{
AttachVisualChild_Private_MainSteps(
child,
parent,
doesParentRequireToCreateAWrapperForEachChild,
innerDivOfWrapperForChild,
domElementWhereToPlaceChildStuff,
wrapperForChild);
};
INTERNAL_DispatcherHelpers.QueueAction(() =>
{
Action deferredLoadingWhenControlBecomesVisible = child.INTERNAL_DeferredLoadingWhenControlBecomesVisible;
if (deferredLoadingWhenControlBecomesVisible != null) // Note: it may have become "null" if the visibility was changed to "Visible" before the dispatched was called, in which case the element is loaded earlier (cf. "Visibility_Changed" handler)
{
child.INTERNAL_DeferredLoadingWhenControlBecomesVisible = null;
deferredLoadingWhenControlBecomesVisible();
}
});
}
else
{
AttachVisualChild_Private_MainSteps(
child,
parent,
doesParentRequireToCreateAWrapperForEachChild,
innerDivOfWrapperForChild,
domElementWhereToPlaceChildStuff,
wrapperForChild);
}
}