WPF “Expand All” Control Load Time

Question

I have integrated a feature in my tool that allows me to expand all recursively. I realise this would generally be a slow process anyway but currently. I have maybe 100 nested controls which are all expanded at once, so calling Expand All means that each control/datatemplate etc is processed at once.

This causes the tool to lock up for a good 10 seconds before responding. Of course, once the view hierarchy has been constructed, its then fast (I can collapse and expand instantly from then on). But it seems a little odd that there isn't a faster way to generate large forms, I wouldn't consider 100-500~ controls very many.

I have looked into virtualisation, but it doesn't appear to be useful to me in this case because all controls are expanded at once. Its fine if I expand them on a singular basis.

Edit:

Updates we're needed to the question to describe what the layout of my window is:

I have a number of TextBoxes, ComboBoxes, Sliders which are all nested inside of a number of Expanders. Each expander can contain N number of expanders, this is recursive to an extent. Depending on how the data is laid out. Some of these data types (which are represented by datatemplates) may contain StackPanels if needed and numerous grids for layouts.

To expand all it simply means to iterate each expander (which IsExpanded is bound to an IsExpanded property). I set this property on each data type (and its children) to true. And let the binding do the work of expanding everything. This causes every single control to be added at once.

Thanks

Answer 1

So after reading the edited question, I have a guess what's going on:

The UI is busy on rendering controls. And I assume there's not much data kept behind in viewmodels bound, so the data is not the point in your issue.

When the Expander control gets IsExpanded = true the first time, Xaml is parsed (object / resource parsing, not compiling) and visual tree children are created. 100-500 visual tree elements is a high number for rendering, because each of them (if it's belonging to the System.Windows.Controls namespace) consists of many sub-controls ( Border , Grids , TextBox ,..).

What you can achieve is NOT shortening the expanding time, but to unblock the UI: advise the dispatcher to handle IsExpanded asynchronously and see how it behaves. This requires that you don't use the expanders default action: In the arrow button click handler, skip default handling and insert this ( IsExpanded is your bound viewmodel property here):

Dispatcher.BeginInvoke(DispatcherPriority.Normal, new Action(
                () => { this.IsExpanded = true; } ));