I want to create an expandable empty treenode in C#, i.e. a treenode which is empty and has the [+] sign beside it. The reason is because initially it is empty, but once a node is clicked, I want to populate it with many child nodes.
The only problem I am facing is that empty treenodes aren't expandable, so I don't know what to do. Is there a way to solve this problem, or are there any workarounds?
You have to redraw the tree itself, or create an empty node and simply remove it when the parent node is expanded.
Personally, I'd go for option b). I've done this before, a while ago and thanks to the events raised by the TreeView it pretty easy to accomplish.
You can give the empty node a value like 'Loading...' so it gives some feedback to the user as well. :)
Add a dummy child node, and remove it when you expand.
Have a look at Josh Smiths excellent tutorial on treeviews. It allows lazy loading of child tree nodes by having a dummy node that is removed upon expansion.
Related
When handling the DataGrid, in code-behind I can walk downwards the visual tree, to cells and their descendants.
In XAML, FindAncestor lets us walk up the visual tree to access a target element that has no Name.
As there is no FindDescendant, I wanted to figure out how to walk downwards, not in code-behind or by MVVM.
No, at least at the moment, such FindDescendant feature is not here. And the main problem you may face trying to implement it by XAML-only is the fact there could be zero or more results matching your criteria, unlike walking the tree up where you see only one parent (or no parent at all for the root element). So the result is a collection, not a single element.
Another aspect of the problem is an ability to alter children representation by template selectors: that way, a parent node should be aware of all alterations down the tree, all the way down (maybe, zillions of levels). However, from system design point, it's better to hide such knowledge and delegate it to children nodes themselves.
Not last and not least: if you alter a parent depending on a child behavior, it may cause a circular dependency/lock if in turn the child is instructed to track the parent behavior via FindAncestor. XAML deadlocks? Thank you but no, thank you!
So, all after all, it could be very arguable ability.
I want to show the expand option against a tree node even if the node has no children. Is this possible?
(The expand option being the little plus sign in a box to the left of the node.)
If your purpose is to dynamically load children nodes when expanding the best solution is to add a fake child nodes to all the leaf nodes. Then replace the fake node with real ones when needed.
Try it with property TreeNode.PopulateOnDemand = true; - this is ideal for dynamically created trees and it adds plus sign icon also to node with no children.
Sorry this is not a direct answer to your question, but I do feel it is relevant.
Why would you want to do this? It is confusing for the user.
(I have just been through exactly the same process in another environment and user feedback was "This item is broken and won't let me see what's underneath like the other ones do").
In short, I would recommend evaluating the requirement carefully before you proceed.
I have a Treeview that the user cannot edit. The way I'm trying to refresh is clearing the entire tree and re-adding all the nodes (and children). I'm accomplishing this by the following lines of code:
treeView.BeginUpdate(); //Freeze drawing
treeView.Nodes.Clear(); //Empty Tree
addAllNodes(); //This adds the nodes for the tree and sets their name/text property
treeView.EndUpdate(); //Unfreeze drawing
I've tried adding the Update and Refresh method before I call addAllNodes but hasn't made a difference. Doing the above gets me an error:
System.ArgumentException: Cannot add or insert the item 'NodeNameHere' in more than one place. You must first remove it from its current location or clone it
My first question is, what am I doing to cause this error and how can I properly refresh my tree?
My second question is, after the refresh is there any way I can restore the user's expanded nodes? (so that everything does not end up collapsed)
each node has a path (called something like .Path or .FullPath; dont have VS open right now). So you can walk your nodes before you clear them and record all the expanded nodes, then walk them again after refresh and see if the node's path matches a stored one.. if it does, expand it.
I have a .net 2.0 C# Project.
I have a Treeview with 2 Nodes, each of them has many child nodes.
When you click on a child node, a PDF is displayed in a webbrowser control depending on the properties of the node.
Fine, but the problem is that when both Nodes are expanded, and I click on a child node, the other node gets collapsed! I don't have any code that collapses any node of the treeview, but somehow it happens! I also had a look at the BeforeCollapse Event, but somehow it doesn't fire, alltough the other node collapses!
Can anyone imagine why this happens?
I would be very grateful if anyone can teach me how to prevent this happening!
Thank you very much!
I stopped using the WinForms TreeView some time ago because of it's limits and quirks.
My favorite replacement is the open-source TreeViewAdv:
TreeViewAdv on Source Forge
TreeViewAdv on CodeProject
This happens if the TVS_SINGLEEXPAND style is ON for the treeview. Try setting the HotTracking property to false.
I have a Silverlight project where the main objects are just a bunch of nodes that are joined to each other. A parent node can have many children.
I want to be able to bind the nodes to an itemscontrol or similar and so was wondering how to best structure the parent child relationship.
Is it OK to create a flat top level list of all nodes (List allNodes) and add each node to that, binding the list to the itemscontrol, then on top of that add each node to it's parent's 'childnodes' list to establish the structure - or am I doing some kind of ugly doubling up?
Just hoping there is some kind of best practice or pattern I can latch on to
Thanks
You should use the treeview found in the official silverlight toolkit. Here is an online demo.