❔ WPF draw over other arbitrary controls
I want to draw over items contained in an
ItemsControl, without wrapping the ItemsControl into any sort of other object. Can anyone suggest a starting point / best practice? With my knowledge of WPF I don't know where to start solving this one.22 Replies
Depending on what you want to draw, adorners might work: https://learn.microsoft.com/en-us/dotnet/desktop/wpf/controls/adorners-overview?view=netframeworkdesktop-4.8&viewFallbackFrom=netdesktop-7.0
Adorners Overview - WPF .NET Framework
Learn about Windows Presentation Foundation Adorners, a special type of FrameworkElement that provides cues to a user, such as functional handles for elements.
I thought these had to wrap the element, but they seem to be more general. thanks
Yeah actually it's not what I need. I actually realize I explained it wrong. I actually need to put actual controls over other controls
What I need is to make checkboxes over other elements
Specifically, the elements inside an ItemsControl
But I can't modify the data template
The other idea is if there's an event that triggers when an item is added to the ItemsControl, to inject the checkbox with that
If I just bind to the underlying collection, then the event handler priority kicks in (I won't be able to modify the item before it's been created in the ui)
I had to do a hack that:
1. defines a ui event service that binds itself to the same collection as the
ItemsControl, but after it's been created, so the events are triggered after the individual items get created in the ItemsControl;
2. some INotifyCollectionChanged event handler logic that injects a checkbox into the newly created items, and then updates them when the underlying collection changes, but after the items are changed (supposedly). This kinda couples itself to the internals of ItemsControl, ig I could do something more generic by going through all of the items every time looking for a checkbox, perhaps a tagged one, adding one if none is found, and binding the sources correctly, but it seems as tho my event idea did not work out. https://github.com/AntonC9018/uni_csharp/blob/aa20cb73ac5ffe98636e0fbfbe91177a9c82f2db/sem2_lab1/SortingUI.cs#L139-L217
If you've got a better idea of how to do this, please enlighten me
Keep in mind that I can't modify the templates in the ItemsContol
That is, I can like wrap them in a panel like I did, but no checkboxes should be enabled there by default, and in general, the template shouldn't be bothered by that
Nevermind, the problem is that ItemsContol does not parent the items directly, it may be wrapped in a border or something
How do I get to the items?What do you mean?
I don't think INotifyCollectionChanged is what you are after here. The binding might not be (usually isn't) to a collection of controls, it's usually to a view model
I need more info on the exact situation here to recommend something, i.e. how robust does this need to be for all possible ItemsControl configurations?
Can you subclass ItemsControl and use that?
Do you need to be able to support a variety of items panels? What if it's a virtualizing stack panel which recycles the item controls?
I have an observable collection of ints/strings which the ItemsControl is bound to
Etc
the checkboxes are added by a totally different component
so the templates in the item control should bot know about it
Right, so why is binding to that going to be helpful for getting at the controls?
I looked for an event that triggers when some created control changed, or like the hierarchy changes, but couldn't find anything
and had to try the aforementioned hack to try and imitate such event
Ok...let's start again. Why can the template not know about the checkboxes?
Because the reason for that will dictate suitable approaches
i.e. Why do you need to do it this way
because the checkboxes are managed by a different component
Idk what that means
Why
like a different module
think of that module as imported from a dll
also it is conditionally applied
Conditionally applying is easy, you just show or hide it
I still dont understand this architecture or why the template cant have the checkboxes
It all sounds very strange
Without an actual understanding of what you can or can't do it's hard to suggest something here
Does it need to be an ItemsControl or can you subclass ItemsControl and use that?
yeah I could
Ok, then why can't you wrap whatever you have inside the item template with something that overlays the checkboxes?
the templates should not know about the checkboxes by design
I think this is what you want: https://learn.microsoft.com/en-us/dotnet/api/system.windows.controls.itemscontrol.itemcontainergenerator?view=windowsdesktop-7.0#system-windows-controls-itemscontrol-itemcontainergenerator
ItemsControl.ItemContainerGenerator Property (System.Windows.Controls)
Gets the ItemContainerGenerator that is associated with the control.
ig I kinda could
You can modify the container it generates for each item
So it puts the item into a container and overlays the checkbox on top
I'm gonna do it a bit more generically to allow introducing custom logic there
but it should work
thanks for an idea
There's some good info here that you can use: http://drwpf.com/blog/2008/07/20/itemscontrol-g-is-for-generator/
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/close - otherwise I will mark this as stale and this post will be archived until there is new activity.