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RadTreeView suggestion

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answered on 25 Jun 2008, 05:51 AM

Yes - this is a major and very important concept of the Silverlight/WPF ItemsControl. It is not related to the implementation of the RadTreeView, but you will see it in any control that derives from ItemsControl (another example is the ListBox).

The Items collection of the ItemsControl is a collection of data objects , NOT from RadTreeViewItems. There is a very important concept in Silverlight/WPF about the items and item containers. When you bind an ItemsControl you have your data items populating the Items collection of the control. The containers are the visual presentations of those data items (in our case the containers are the RadTreeViewItems). Containers are not created automatically when the ItemsControl is bound, but are created asyncronously and only when needed. For example in our case with the TreeView, the containers are not being created until there parent is expanded.

So how you can get the container from the data item? Or in our case - how to get the RadTreeViewItem from your data object that you receive when traversing the Items collection?

There are several helper methods that can be used. Each ItemsControl have a Property named ItemContainerGenerator. It is of type ItemContainerGenerator . This class has the following methods that can helps us in our case:

- DependencyObject ContainerFromIndex(int index) - returns the Container for the given index from the Items collection.

- DependencyObject ContainerFromItem(object item) - returns the Container for the given data item from the Items collection.

So here is an example about how to get access to all the Containers in the RadTreeView:

    
              void getContainers()  
        
                    {  
        
                        // gets all nodes from the TreeView  
        
                        Collection<RadTreeViewItem> allTreeContainers = GetAllItemContainers(tree1);  
        
                        // gets all nodes (recursively) for the first node  
        
                        RadTreeViewItem firstNode = tree1.ItemContainerGenerator.ContainerFromIndex(0) as RadTreeViewItem;  
        
                        if (firstNode != null)  
        
                        {  
        
                            Collection<RadTreeViewItem> firstNodeContainers = GetAllItemContainers(firstNode);  
        
                        }  
        
                    }  
        
                    Collection<RadTreeViewItem> GetAllItemContainers(Telerik.Windows.Controls.ItemsControl itemsControl)  
        
                    {  
        
                        Collection<RadTreeViewItem> allItems = new Collection<RadTreeViewItem>();  
        
                        for (int i = 0; i < itemsControl.Items.Count; i++)  
        
                        {  
        
                            // try to get the item Container  
        
                            RadTreeViewItem childItemContainer = itemsControl.ItemContainerGenerator.ContainerFromIndex(i) as RadTreeViewItem;  
        
                            // the item container maybe null if it is still not generated from the runtime  
        
                            if (childItemContainer != null)  
        
                            {  
        
                                allItems.Add(childItemContainer);  
        
                                Collection<RadTreeViewItem> childItems = GetAllItemContainers(childItemContainer);  
        
                                foreach (RadTreeViewItem childItem in childItems)  
        
                                {  
        
                                    allItems.Add(childItem);  
        
                                }  
        
                            }  
        
                        }  
        
                        return allItems;  
        
                    }

I hope this makes the picture a little more clear. These concepts are all borowed from WPF and it is hard to understand without to play with the ItemsControl for some time. I can recommend the following great blogs posts which are written for WPF, but they explain the concept very well and will be of help for the Silverlight learning:
http://blog.quantumbitdesigns.com/2008/05/22/programmatically-selecting-an-item-in-a-treeview/
http://www.drwpf.com/blog/Home/tabid/36/EntryID/32/Default.aspx - all posts regarding the ItemsControl.

Please let us know if you still have any questions regarding those concepts!

All the best,
Valentin.Stoychev
the Telerik team

Instantly find answers to your questions at the new Telerik Support Center

answered on 25 Jun 2008, 12:52 PM

I'm afraid I cannot get the example code working. ItemContainerGenerator doesn't seem to be available in the CTP. Perhaps this is something that will be available in the July beta? I cannot find it in System.Windows.Controls.ItemsControl either.

I did get something similar working though after some studying (thanks for the links), and I have to say I still think there's a need for the AutoSelectChildren and AutoCheckChildren properties. In my application I need to switch between these two modes, and the current checkbox selection implementation is much too limited for my purposes. For example, it is not possible to check a single node in the middle of a branch. As soon as all children of a node are unchecked the node itself will be unchecked too, and that doesn't work for me.

answered on 25 Jun 2008, 02:43 PM

Sorry, what I meant was "checkbox behaviour". I've posted a screen shot here to illustrate my point:

http://cid-cc43a90a79374ebd.skydrive.live.com/self.aspx/Public/TreeViewExample.png

When IsTriState is True, it doesn't matter whether I check "Salmon", "FloralWhite" or "CornflowerBlue", all three are checked automatically. The behaviour I would like is as follows:
When FloralWhite is checked, that node and only that node should be checked, but all its parent nodes should display the indeterminate state.
I would also like to have an AutoCheckChildren property. When this is True, and FloralWhite is checked, CornflowerBlue should also be checked, but not Salmon. Still, if IsTriState is True, all parent nodes should display the indeterminate checkbox state.
At the moment, if I check FloralWhite with IsTriState set to False and then change IsTriState to True, the node will automatically be unchecked. Which is not what I want. The indeterminate state is a great way of indicating to the user that something is selected at a deeper level in the tree, but I do not want that visual cue to affect the way the checkboxes behave when checked.