I am currently using PanelBarBinding.ContentTemplate in conjonction with RenderTreeBuilder and I am able to have different content per panel.
My problem is when I close one of the panes, it removes itself from the DOM. Please provide a way to keep the panes in the DOM (at least when open once) like the PersistTabContent feature of TelerikTabStrip.
Currently, the PanelBar does not have a concept for selection. When I click on an item, it looks like "selected" due to the background but there is no way I can save that selection or set it programmatically if I need to retrieve the selected state at some point.
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ADMIN EDIT
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For the time being, you can use the OnItemRender event and some custom CSS to visually mark the desired item as selected: https://blazorrepl.telerik.com/GobwQhly107nUDoZ51.
If you need to get the item that the user last "selected", you can use the OnItemClick event as we mark the item as selected when the user clicks on it.
Currently, it is possible to expand or collapse PanelBar items programmatically.
There should be a way to prevent a specific PanelBar item from collapsing or expanding.
Please expose cancellable OnExpand and OnCollapse events similar to other components. This will give developers the ability to apply custom interaction based on their scenario.