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Example of how to both obtain an item handle (hItem) from any given Node, and a Node object reference from a given item handle.

Unlike the listview control that uses sequential indices to uniquely identify each item it contains, the treeview uses a different scheme to identify treeview items, refereed to the item "handle" or "hItem". The trick with doing anything really interesting API-wise with the TreeView" control in Comctl32.ocx is obtaining an item handle for a respective node, since "hItem" is obviously not a Node property.

So that's simply what this demo is all about, how to get a Node's hItem, and visa versa. It's easier said than done though. The only accurate method of matching the hItem to a particular Node, is by retrieving the handle of the item whose relative position in the treeview equals that of the desired Node. The same approach is taken when retrieving a Node reference from the corresponding hItem. It all takes a bit of doing. Do note though, the code in this demo is the foundation for all subsequent demos, whose elements and concept should be understood before proceeding.

Download tvnode-hitem.zip (6kb)
Last update: 08/03/98

TVCheckBoxesEx: Example of how to add and use custom checkboxes in VB's TreeView control

The easy way to do checkboxes in the TreeView is by simply applying the TVS_CHECKBOXES treeview window style, or to just use the VB6 TreeView that does its own checkboxes (though not very well, see the MS kb). But we don't do things like that around here, at all. This demo is about treeview (the real one) item state images.

This demo does it all. It includes 12 custom checkbox icons, compiled into a resource file, that are loaded into both a VB ImageList control, and a real imagelist common control window created in code, either of which can be assigned to the TreeView as its state imagelist. From there we show how to set any checkbox icon to any Node, how to toggle the checkbox's state (we have to do that), and how to retrieve which icon any given Node is currently using. A couple of other treeview item state image related topic are covered as well.

Note, this is a major update to the previous checkbox demo found here.

Download tvcheckboxesex.zip (17kb)
Last update: 04/2/99

TVEventCancel: Demonstrates how to prevent a Node selection change, expand, and collapse in the Comctl32.ocx TreeView control. 

The TreeView's specific events AfterLabelEdit, BeforeLabelEdit, Collapse, Expand and NodeClick are a raised as a result of the treeview's window procedure responding to certain treeview specific notification messages: TVN_ENDLABELEDIT, TVN_BEGINLABELEDIT, TVN_ITEMEXPANDED (for both Collapse and Expand), and TVN_SELCHANGED respectively. The only one of these the *can* be canceled is AfterLabelEdit, which in turn tells the treeview to return C TRUE (or 1) in response to the TVN_BEGINLABELEDIT notification message.

Now, to cancel either a NodeClick, Expand or Collapse, a value of 1 must be returned in response to the TVN_SELCHANGING and TVN_ITEMEXPANDING notifications respectively (both happen right before TVN_SELCHANGED and TVN_ITEMEXPANDED respectively). The hitch is that the only way to tell the treeview this is by subclassing it's parent window, where the notification messages are sent, and return 1 yourself. So this example gets a bit more involved because it does the subclassing itself.

To help assist in the understanding of treeview notification messages, and what specific treeview events cause them to occur, a code module is included that not only returns the corresponding constant string of any specified treeview notification message value (TVN_*), but also the corresponding constant string of any window message (WM_*) and any general common control notification message (NM_*).

Note that because of the inherent instabilities incurred as a result of subclassing, care must be taken not only when stepping through code, but most of all, to allow the subclassing to be removed on it is applied (i. e. never using VB's End command to end the project's execution). Consider either going to the VB Owner's area on the MS site, picking up the "Debug Object for AddressOf Subclassing", or grabbing the subclassing control at http://www.softcircuits.com/, and plugging either into the demo's code. Doing so will allow things to go much smoother.

Download tveventcancel.zip (11kb)
Last update: 08/20/98

TVItemData: Treeview item data (or how undocumented can you get?)

After the many hours spent with both the real common control treeview and VB's TreeView control, something finally occurred to me: How do both controls store internal data for their respective items (Nodes)? And, is this item data accessible? Well, as it just so turns out, it is...

For instance it was discovered that a treeview item handle (HTREEITEM) is nothing more that a pointer to a treeview internal data structure that describes the item:

Public Type TREEITEM   ' ti
  hitemParent As Long       ' handle of the item's parent, can be 0 (root's
                            ' parent is a dummy item, whose only valid member
                            ' is the hitemChild, the root itself)
  hitemNextSibling As Long  ' handle of the item's next sibling, can be 0
  hitemChild As Long        ' handle of the item's first child, can be 0
  lpszText As Long          ' pointer to the item's text, allocated in DWORD
                            ' chunks, can be LPSTR_TEXTCALLBACK, is Unicode
                            ' on NT4 Comctl32.dll v4.xx, and all v5.xx
  wState As Integer         ' item's state flags, 1st byte is state, low
                            ' nibble of 2nd byte is overlay image index,
                            ' high nibble of 2nd byte is state image index
  wImage As Integer         ' normal icon index, can be I_IMAGECALLBACK
  wSelectedImage As Integer ' selected icon index, can be I_IMAGECALLBACK
  cxItem As Integer         ' item's label width (TVM_GETITEMRECT/TRUE)
  wIndex As Integer         ' visible item's 0-based physical tree position,
                            ' is -1 if in collapsed parent, can change
  bLevel As Byte            ' item's 0-based hierarchical level in the tree
  bChildren As Byte         ' TVITEM.cChildren (can't be I_CHILDRENCALLBACK?)
  lParam As Long            ' TVITEM.lParam, can point to allocated data
#If (WIN32_IE >= &H400) Then
  dwID As Long              ' always &HABCD0001 ?
#End If
End Type   ' / 36 bytes (WIN32_IE < &H400 = 32 bytes)

that is obtained simply with:  MoveMemory ti, ByVal hItem, Len(ti)

The demo also shows how to obtain a Node reference from the TVITEM struct's lParam member (the same lParam as above), as well as a few other interesting tricks. Take note that most of the information presented in this demo is completely undocumented, and as a result is obviously not recommended for use in production applications (see below).

09-27-99 update (v1.20)
- The new cchTextMax member again wasn't correct, and is actually the item label width, cxItem.
- Finally tested Win2K rc1 and Comctl32.dll v5.xx (IE5), where it appears that the lpszText member is always Unicode. This was confirmed in IE5 installs on Win95 and WinNT4 SP5 as well.
- Even more minor demo code updates were performed.

09-23-99 update (v1.10)
- Microsoft, in its complete freedom to break the undocumented, has done just that. Beginning with Win2K b3 (Comctl32.dll v5.xx), the TREEITEM structure above has been changed, not by much, but just enough to break the apps of folks who decided to use it. The lParam member has been moved up, from below the bChildren member, to below the lpszText member. The dwID (was dwIDBit) member's value has also been changed. A new TREEITEM5 structure was introduced in the demo for Comctl32.dll v5.xx installs.
- The description of the cchTextMax member (was wID) was updated.
- Various other minor demo code updates were also performed.

0711-99 initial release (v1.00)

Download tvitemdata.zip (10kb)
Last update: 09/27/99

VBDirectoryTV: Make the TreeView into a DirListBox

Here's one a lot of folks have been asking about: How do I assign the system imagelist to the VB TreeView? Well, it's not so hard actually...

It's simply a matter of telling the TreeView that it should get its icon images not from a VB ImageList, but from the actual system imagelist with the TVM_SETIMAGELIST treeview window message, and explicitly setting the Node Image and SelectedImage properties with TVM_SETITEM. There are a couple of hitches though: if the VB TreeView doesn't see a VB ImageList associated with it, it will remove the system imagelist assignment; and the Node Image and SelectedImage properties are uninitialized. This example demonstrates how to circumvent the first problem by subclassing the treeview (the second is left as an exercise for the developer) with code that gives the TreeView quite useful DirListBox type functionality.

Download vbdirectorytv.zip (24kb)
Last update: 07/11/99

TVFastLoad: How to load the VB TreeView quickly

First, load Nodes on demand: only load child Nodes under any given parent Node when the parent Node is expanding. No need to load all data under parent Nodes if the user doesn't end up expanding them.

Load child Nodes under any given parent Node *while* the parent Node is collapsed: each time a Node is added under an expanded parent Node, the TreeView must update the tree to show the new child Node. No updating happens when the parent is collapsed.

Make sure the parent Node's Sorted property is set to False: If Sorted = True, the TreeView must sort every Node as it is added under the parent Node. Make Sorted = True after all child Nodes are added.

Eat extraneous TreeView drawing messages (TVN_GETDISPINFO): the TreeView's internal code mistakenly calls WM_SETREDRAW/0 before Nodes are added. Once Nodes are done being added, or TreeView code is allowed to process (by the DoEvents call), and the TreeView calls WM_SETREDRAW/1 to turn drawing back on, every Node in the TreeView is redrawn, whether visible or not. This unnecessary redrawing can cause quite a perceptible lag after many Nodes are added.

The demo below utilizes all of the above techniques (and uses subclassing).

Download tvfastload.zip (9kb)
Last update: 09/17/99 (posted 05/19/99)

TVCustomButtons: How to use state images in place of TreeView buttons ("+", "-")

This demo employs user-specified state images to expand and collapse parent Nodes, instead of using the TreeView's familiar "+", "-" buttons. Common use of treeview state images are checkboxes.

The demo sets the TreeView's Style property to tvwTreelinesPictureText, specifying no "PlusMinus" images (buttons) for Nodes. The demo's working code simply sets each parent Node's TVITEM.state member value (TVIF_STATE) to the specified index in a VB ImageList of the new custom buttons to be used. Each Node's state image button is toggled as the Node is collapsed and expanded, and visa versa.

Download tvcustombuttons.zip (6kb)
Last update: 09/24/99

TVDragDrop: How to create a real drag image when dragging TreeView Nodes

If it's not already obvious, the TreeView Node's CreateDragImage method that creates a drag image of the selected Node and is used by various Knowledge Base articles, specifically Q177743, is just this side of being completely inept. Why on earth CreateDragImage creates a 32x32 size image is well beyond me... Anyway, this demo shows how things are supposed to be done...

The drag image is created in the demo with the real deal, the treeview's TVM_CREATEDRAGIMAGE message, and looks just like the drag image Explorer displays when dragging its treeview items. Imagelist APIs are used to display and move the drag image around the specified owner window, hiding it when necessary. Also like Explorer, the demo not only does auto scrolling when dragging and the cursor is near the edge of the TreeView's client window, but automatically expands collapsed parent Nodes when the when the cursor is held over them for a user-specified period of time as well. But all this functionality is not without its intricacies, and quantity of code (almost 40K worth), but it's well worth the effort...

Download tvdragdrop.zip (13kb)
Last update: 10/14/99

TVButtonState: How to control the appearance of TreeView buttons ("+", "-")

This demo shows both how to add and remove buttons to and from TreeView Nodes, and how to set and return the state of any Node's button, whether a Node has child Nodes or not.

All that the demo's working code essentially does is simply read and set the specified Node's TVITEM.cChildren (TVIF_CHILDREN) value, while performing various operations on the Node. The key is that if the Node's cChildren value is 0, no button will be shown, otherwise a button will be shown if cChildren is non-zero (and not the TreeView default I_CHILDRENCALLBACK value).

Download tvbuttonstate.zip (8kb)
Last update: 10/16/99

TVOverlayIcons: How to add overlay icons to Nodes

This demo shows both how to add and remove overlay icons to and from TreeView Nodes, and how determine which overlay icon a Node is using, if any.

The demo uses a single VB ImageList associated with the TreeView to hold both Node icons and overlay icons. The ImageList_SetOverlayImage API is used to tell the ImageList which icons are designated as overlay icons. The TVM_SETITEM treeview message is then used to specify the index of the overlay icon a Node is to display. A Node's overlay icon index is retrieved with the TVM_GETITEM message.

Download tvoverlayicons.zip (6kb)
Last update: 11/30/99

Over time a few demos have been added to this web folder, but as of yet have no descriptions written up about them. Click here for the file listing.