Tutorial 19: Tree View Control
In this tutorial, we will learn how to use tree view control.
Moreover, we will also learn how to do drag and drop under tree view control and
how to use an image list with it.
Download the example here.
Theory:
A tree view control is a special kind of window that represents objects in hierarchical
order. An example of it is the left pane of Windows Explorer. You can use this
control to show relationships between objects.
You can create a tree view control by calling CreateWindowEx, passing "SysTreeView32"
as the class name or you can incorporate it into a dialog box. Don't forget to
put InitCommonControls call in your code.
There are several styles specific to the tree view control. These three are the
ones mostly used.
TVS_HASBUTTONS == Displays plus (+) and minus (-) buttons next to parent
items. The user clicks the buttons to expand or collapse a parent item's list
of child items. To include buttons with items at the root of the tree view,
TVS_LINESATROOT must also be specified.
TVS_HASLINES == Uses lines to show the hierarchy of items.
TVS_LINESATROOT == Uses lines to link items at the root of the tree-view
control. This value is ignored if TVS_HASLINES is not also specified.
The tree view control, like other common controls, communicates with the parent
window via messages. The parent window can send various messages to it and the
tree view control can send "notification" messages to its parent window. In this
regard, the tree view control is not different that any window.
When something interesting occurs to it, it sends a WM_NOTIFY message to
the parent window with accompanying information.
WM_NOTIFY
wParam == Control ID, this value is not guaranteed to be unique so we don't
use it.
Instead, we use hwndFrom or IDFrom member of the NMHDR structure
pointed to by lParam
lParam == Pointer to NMHDR structure. Some controls may pass a pointer to
larger
structure but it must have a NMHDR structure as its first member.
That is, when you have lParam, you can be sure that it points to a
NMHDR structure at least.
Next we will examine NMHDR structure.
NMHDR struct DWORD
hwndFrom DWORD ?
idFrom
DWORD ?
code
DWORD ?
NMHDR ends
hwndFrom is the window handle of the control that sends this WM_NOTIFY
message.
idFrom is the control ID of the control that sends this WM_NOTIFY message.
code is the actual message the control wants to send to the parent window.
Tree view notifications are those with TVN_ at the beginning of the name. Tree
view messages are those with TVM_, like TVM_CREATEDRAGIMAGE. The tree view
control sends TVN_xxxx in the code member of NMHDR. The parent window can send
TVM_xxxx to control it.
Adding items to a tree view control
After you create a tree view control, you can add items to it. You can do this
by sending TVM_INSERTITEM to it.
TVM_INSERTITEM
wParam = 0;
lParam = pointer to a TV_INSERTSTRUCT;
You should know some terminology at this point about the relationship between
items in the tree view control.
An item can be parent, child, or both at the same time. A parent item is the item
that has some other subitem(s) associated with it. At the same time, the parent
item may be a child of some other item. An item without a parent is called a root
item. There can be many root items in a tree view control. Now we examine TV_INSERTSTRUCT
structure
TV_INSERTSTRUCT STRUCT DWORD
hParent DWORD
?
hInsertAfter DWORD ?
ITEMTYPE <>
TV_INSERTSTRUCT ENDS
hParent = Handle to the parent item. If this member is the TVI_ROOT
value or NULL, the item is inserted at the root of the tree-view control.
hInsertAfter = Handle to the item after which the new item is to be inserted
or one of the following values:
- TVI_FIRST ==> Inserts the item at the beginning of the list.
- TVI_LAST ==> Inserts the item at the end of the list.
- TVI_SORT ==> Inserts the item into the list in alphabetical order.
ITEMTYPE UNION
itemex TVITEMEX <>
item TVITEM <>
ITEMTYPE ENDS
We will use only TVITEM here.
TV_ITEM STRUCT DWORD
imask
DWORD ?
hItem
DWORD ?
state
DWORD ?
stateMask DWORD
?
pszText
DWORD ?
cchTextMax DWORD
?
iImage
DWORD ?
iSelectedImage DWORD
?
cChildren DWORD
?
lParam
DWORD ?
TV_ITEM ENDS
This structure is used to send and receive info about a tree view item, depending
on messages. For example, with TVM_INSERTITEM, it is used to specify the
attribute of the item to be inserted into the tree view control. With TVM_GETITEM,
it'll be filled with information about the selected tree view item.
imask is used to specify which member(s) of the TV_ITEM structure
is (are) valid. For example, if the value in imask is TVIF_TEXT, it means
only the pszText member is valid. You can combine several flags together.
hItem is the handle to the tree view item. Each item has its own handle,
like a window handle. If you want to do something with an item, you must select
it by its handle.
pszText is the pointer to a null-terminated string that is the label of
the tree view item.
cchTextMax is used only when you want to retrieve the label of the tree
view item. Because you will supply the pointer to the buffer in pszText, Windows
has to know the size of the provided buffer. You have to give the size of the
buffer in this member.
iImage and iSelectedImage refers to the index into an image list
that contains the images to be shown when the item is not selected and when it's
selected. If you recall Windows Explorer left pane, the folder images are specified
by these two members.
In order to insert an item into the tree view control, you must at least fill
in the hParent, hInsertAfter and you should fill imask and pszText members as
well.
Adding images to the tree view control
If you want to put an image to the left of the tree view item's label, you have
to create an image list and associate it with the tree view control. You can create
an image list by calling ImageList_Create.
ImageList_Create PROTO cx:DWORD, cy:DWORD, flags:DWORD, \
cInitial:DWORD, cGrow:DWORD
This function returns the handle to an empty image list if successful.
cx == width of each image in this image list, in pixels.
cy == height of each image in this image list, in pixels. Every image in
an image list must be equal to each other in size. If you specify a large bitmap,
Windows will use cx and cy to *cut* it into several pieces. So you should prepare
your own image as a strip of pictures with identical dimensions.
flags == specify the type of images in this image list whether they are
color or monochrome and their color depth. Consult your win32 api reference for
more detail
cInitial == The number of images that this image list will initially contain.
Windows will use this info to allocate memory for the images.
cGrow == Amount of images by which the image list can grow when the system
needs to resize the list to make room for new images. This parameter represents
the number of new images that the resized image list can contain.
An image list is not a window! It's only an image deposit for use by other windows.
After an image list is created, you can add images to it by calling ImageList_Add
ImageList_Add PROTO himl:DWORD, hbmImage:DWORD, hbmMask:DWORD
This function returns -1 if unsuccessful.
himl == the handle of the image list you want to add images to. It is the
value returned by a successful call to ImageList_Create
hbmImage == the handle to the bitmap to be added to the image list. You
usually store the bitmap in the resource and load it with LoadBitmap call.
Note that you don't have to specify the number of images contained in this bitmap
because this information is inferred from cx and cy parameters passed to ImageList_Create
call.
hbmMask == Handle to the bitmap that contains the mask. If no mask is used
with the image list, this parameter is ignored.
Normally, we will add only two images to the image list for use with the tree
view control: one that is used when the tree view item is not selected, and the
other when the item is selected.
When the image list is ready, you associate it with the tree view control by sending
TVM_SETIMAGELIST to the tree view control.
TVM_SETIMAGELIST
wParam = type of image list to set. There are two choices:
- TVSIL_NORMAL Set the normal image list, which contains the selected
and unselected images for the tree-view item.
- TVSIL_STATE Set the state image list, which contains the images for
tree-view items that are in a user-defined state.
lParam = Handle to the image list
Retrieve the info about tree view item
You can retrieve the information about a tree view item by sending TVM_GETITEM
message.
TVM_GETITEM
wParam = 0
lParam = pointer to the TV_ITEM structure to be filled with the information
Before you send this message, you must fill imask member with the flag(s) that
specifies which member(s) of TV_ITEM you want Windows to fill. And most
importantly, you must fill hItem with the handle to the item you want to get information
from. And this poses a problem: How can you know the handle of the item you want
to retrieve info from? Will you have to store all tree view handles?
The answer is quite simple: you don't have to. You can send TVM_GETNEXTITEM
message to the tree view control to retrieve the handle to the tree view item
that has the attribute(s) you specified. For example, you can query the handle
of the first child item, the root item, the selected item, and so on.
TVM_GETNEXTITEM
wParam = flag
lParam = handle to a tree view item (only necessary for some flag values)
The value in wParam is very important so I present all the flags below:
- TVGN_CARET Retrieves the currently selected item.
- TVGN_CHILD Retrieves the first child item of the item specified
by the hitem parameter
- TVGN_DROPHILITE Retrieves the item that is the target of a drag-and-drop
operation.
- TVGN_FIRSTVISIBLE Retrieves the first visible item.
- TVGN_NEXT Retrieves the next sibling item.
- TVGN_NEXTVISIBLE Retrieves the next visible item that follows
the specified item. The specified item must be visible. Use the TVM_GETITEMRECT
message to determine whether an item is visible.
- TVGN_PARENT Retrieves the parent of the specified item.
- TVGN_PREVIOUS Retrieves the previous sibling item.
- TVGN_PREVIOUSVISIBLE Retrieves the first visible item that precedes
the specified item. The specified item must be visible. Use the TVM_GETITEMRECT
message to determine whether an item is visible.
- TVGN_ROOT Retrieves the topmost or very first item of the tree-view
control.
You can see that, you can retrieve the handle to the tree view item you are interested
in from this message. SendMessage returns the handle to the tree view item
if successful. You can then fill the returned handle into hItem member of TV_ITEM
to be used with TVM_GETITEM message.
Drag and Drop Operation in tree view control
This part is the reason I decided to write this tutorial. When I tried to follow
the example in win32 api reference (the win32.hlp from InPrise), I was very frustrated
because the vital information is lacking. From trial and error, I finally figured
out how to implement drag & drop in a tree view control and I don't want anyone
to walk the same path as myself.
Below is the steps in implementing drag & drop operation in a tree view control.
- When the user tries to drag an item, the tree view control sends TVN_BEGINDRAG
notification to the parent window. You can use this opportunity to create
a drag image which is the image that will be used to represent the item while
it's being dragged. You can send TVM_CREATEDRAGIMAGE to the tree view
control to tell it to create a default drag image from the image that is currently
used by the item that will be dragged. The tree view control will create an
image list with just one drag image and return the handle to that image list
to you.
- After the drag image is created, you specify the hotspot of the drag image
by calling ImageList_BeginDrag.
ImageList_BeginDrag PROTO himlTrack:DWORD, \
iTrack:DWORD , \
dxHotspot:DWORD, \
dyHotspot:DWORD
himlTrack is the handle to the image list that contains the drag image.
iTrack is the index into the image list that specifies the drag image
dxHotspot specifies the relative distance of the hotspot in horizontal
plance in the drag image since this image will be used in place of the mouse
cursor, so we need to specify which part of the image is the hotspot.
dyHotspot specifies the relative distance of the hotspot in the vertical
plane.
Normally, iTrack would be 0 if you tell the tree view control to create the
drag image for you. and dxHotspot and dyHotspot can be 0 if you want the left
upper corner of the drag image to be the hotspot.
- When the drag image is ready to be displayed, we call ImageList_DragEnter
to display the drag image in the window.
ImageList_DragEnter PROTO hwndLock:DWORD, x:DWORD, y:DWORD
hwndLock is the handle of the window that owns the drag image. The
drag image will not be able to move outside that window.
x and y are the x-and y-coordinate of the place where the drag image
should be initially displayed. Note that these values are relative to the
left upper corner of the window, not the client area.
- Now that the drag image is displayed on the window, you will have to support
the drag operation in the tree view control. However, there is a little problem
here. We have to monitor the drag path with WM_MOUSEMOVE and the drop
location with WM_LBUTTONUP messages. However, if the drag image is
over some other child windows, the parent window will never receive any mouse
message. The solution is to capture the mouse input with SetCapture.
Using the call, the mouse messages will be directed to the specified window
regardless of where the mouse cursor is.
- Within WM_MOUSEMOVE handler, you will update the drag path with
ImageList_DragMove call. This function moves the image that is being dragged
during a drag-and-drop operation. Furthermore, if you so desire, you can hilite
the item that the drag image is over by sending TVM_HITTEST to check
if the drag image is over some item. If it is, you can send TVM_SELECTITEM
with TVGN_DROPHILITE flag to hilite that item. Note that before sending
TVM_SELECTITEM message, you must hide the drag image first else your
drag image will leave ugly traces. You can hide the drag image by calling
ImageList_DragShowNolock and, after the hilite operation is finished, call
ImageList_DragShowNolock again to show the drag image.
- When the user releases the left mouse button, you must do several things.
If you hilite an item, you must un-hilite it by sending TVM_SELECTITEM
with TVGN_DROPHILITE flag again, but this time, lParam MUST be zero.
If you don't un-hilite the item, you will get a strange effect: when you select
some other item, that item will be enclosed by a rectangle but the hilite
will still be on the last hilited item. Next, you must call ImageList_DragLeave
followed by ImageList_EndDrag. You must release the mouse by calling
ReleaseCapture. If you create an image list, you must destroy it by
calling ImageList_Destroy. After that, you can go on with what your
program wants to do when the drag & drop operation is completed.
Code sample:
.386
.model flat,stdcall
option casemap:none
include \masm32\include\windows.inc
include \masm32\include\user32.inc
include \masm32\include\kernel32.inc
include \masm32\include\comctl32.inc
include \masm32\include\gdi32.inc
includelib \masm32\lib\gdi32.lib
includelib \masm32\lib\comctl32.lib
includelib \masm32\lib\user32.lib
includelib \masm32\lib\kernel32.lib
WinMain PROTO :DWORD,:DWORD,:DWORD,:DWORD
.const
IDB_TREE equ 4006
; ID of the bitmap resource
.data
ClassName db "TreeViewWinClass",0
AppName db "Tree View Demo",0
TreeViewClass db "SysTreeView32",0
Parent db "Parent Item",0
Child1 db "child1",0
Child2 db "child2",0
DragMode dd FALSE
; a flag to determine if we are in drag mode
.data?
hInstance HINSTANCE ?
hwndTreeView dd ?
; handle of the tree view control
hParent dd ?
; handle of the root tree view item
hImageList dd ?
; handle of the image list used in the tree view control
hDragImageList dd ? ; handle
of the image list used to store the drag image
.code
start:
invoke GetModuleHandle, NULL
mov hInstance,eax
invoke WinMain, hInstance,NULL,NULL, SW_SHOWDEFAULT
invoke ExitProcess,eax
invoke InitCommonControls
WinMain proc hInst:HINSTANCE,hPrevInst:HINSTANCE,CmdLine:LPSTR,CmdShow:DWORD
LOCAL wc:WNDCLASSEX
LOCAL msg:MSG
LOCAL hwnd:HWND
mov wc.cbSize,SIZEOF WNDCLASSEX
mov wc.style, CS_HREDRAW or CS_VREDRAW
mov wc.lpfnWndProc, OFFSET WndProc
mov wc.cbClsExtra,NULL
mov wc.cbWndExtra,NULL
push hInst
pop wc.hInstance
mov wc.hbrBackground,COLOR_APPWORKSPACE
mov wc.lpszMenuName,NULL
mov wc.lpszClassName,OFFSET ClassName
invoke LoadIcon,NULL,IDI_APPLICATION
mov wc.hIcon,eax
mov wc.hIconSm,eax
invoke LoadCursor,NULL,IDC_ARROW
mov wc.hCursor,eax
invoke RegisterClassEx, addr wc
invoke CreateWindowEx,WS_EX_CLIENTEDGE,ADDR ClassName,ADDR
AppName,\ WS_OVERLAPPED+WS_CAPTION+WS_SYSMENU+WS_MINIMIZEBOX+WS_MAXIMIZEBOX+WS_VISIBLE,CW_USEDEFAULT,\
CW_USEDEFAULT,200,400,NULL,NULL,\
hInst,NULL
mov hwnd,eax
.while TRUE
invoke GetMessage, ADDR msg,NULL,0,0
.BREAK .IF (!eax)
invoke TranslateMessage, ADDR
msg
invoke DispatchMessage, ADDR msg
.endw
mov eax,msg.wParam
ret
WinMain endp
WndProc proc uses edi hWnd:HWND, uMsg:UINT, wParam:WPARAM, lParam:LPARAM
LOCAL tvinsert:TV_INSERTSTRUCT
LOCAL hBitmap:DWORD
LOCAL tvhit:TV_HITTESTINFO
.if uMsg==WM_CREATE
invoke CreateWindowEx,NULL,ADDR
TreeViewClass,NULL,\
WS_CHILD+WS_VISIBLE+TVS_HASLINES+TVS_HASBUTTONS+TVS_LINESATROOT,0,\
0,200,400,hWnd,NULL,\
hInstance,NULL
; Create the tree view control
mov hwndTreeView,eax
invoke ImageList_Create,16,16,ILC_COLOR16,2,10
; create the associated image list
mov hImageList,eax
invoke LoadBitmap,hInstance,IDB_TREE
; load the bitmap from the resource
mov hBitmap,eax
invoke ImageList_Add,hImageList,hBitmap,NULL
; Add the bitmap into the image list
invoke DeleteObject,hBitmap
; always delete the bitmap resource
invoke SendMessage,hwndTreeView,TVM_SETIMAGELIST,0,hImageList
mov tvinsert.hParent,NULL
mov tvinsert.hInsertAfter,TVI_ROOT
mov tvinsert.item.imask,TVIF_TEXT+TVIF_IMAGE+TVIF_SELECTEDIMAGE
mov tvinsert.item.pszText,offset
Parent
mov tvinsert.item.iImage,0
mov tvinsert.item.iSelectedImage,1
invoke SendMessage,hwndTreeView,TVM_INSERTITEM,0,addr
tvinsert
mov hParent,eax
mov tvinsert.hParent,eax
mov tvinsert.hInsertAfter,TVI_LAST
mov tvinsert.item.pszText,offset
Child1
invoke SendMessage,hwndTreeView,TVM_INSERTITEM,0,addr
tvinsert
mov tvinsert.item.pszText,offset
Child2
invoke SendMessage,hwndTreeView,TVM_INSERTITEM,0,addr
tvinsert
.elseif uMsg==WM_MOUSEMOVE
.if DragMode==TRUE
mov eax,lParam
and eax,0ffffh
mov ecx,lParam
shr ecx,16
mov tvhit.pt.x,eax
mov tvhit.pt.y,ecx
invoke
ImageList_DragMove,eax,ecx
invoke
ImageList_DragShowNolock,FALSE
invoke
SendMessage,hwndTreeView,TVM_HITTEST,NULL,addr tvhit
.if eax!=NULL
invoke SendMessage,hwndTreeView,TVM_SELECTITEM,TVGN_DROPHILITE,eax
.endif
invoke
ImageList_DragShowNolock,TRUE
.endif
.elseif uMsg==WM_LBUTTONUP
.if DragMode==TRUE
invoke
ImageList_DragLeave,hwndTreeView
invoke
ImageList_EndDrag
invoke
ImageList_Destroy,hDragImageList
invoke
SendMessage,hwndTreeView,TVM_GETNEXTITEM,TVGN_DROPHILITE,0
invoke
SendMessage,hwndTreeView,TVM_SELECTITEM,TVGN_CARET,eax
invoke
SendMessage,hwndTreeView,TVM_SELECTITEM,TVGN_DROPHILITE,0
invoke
ReleaseCapture
mov DragMode,FALSE
.endif
.elseif uMsg==WM_NOTIFY
mov edi,lParam
assume edi:ptr NM_TREEVIEW
.if [edi].hdr.code==TVN_BEGINDRAG
invoke
SendMessage,hwndTreeView,TVM_CREATEDRAGIMAGE,0,[edi].itemNew.hItem
mov hDragImageList,eax
invoke
ImageList_BeginDrag,hDragImageList,0,0,0
invoke
ImageList_DragEnter,hwndTreeView,[edi].ptDrag.x,[edi].ptDrag.y
invoke
SetCapture,hWnd
mov DragMode,TRUE
.endif
assume edi:nothing
.elseif uMsg==WM_DESTROY
invoke PostQuitMessage,NULL
.else
invoke DefWindowProc,hWnd,uMsg,wParam,lParam
ret
.endif
xor eax,eax
ret
WndProc endp
end start
Analysis:
Within WM_CREATE handler, you create the tree view control
invoke CreateWindowEx,NULL,ADDR
TreeViewClass,NULL,\
WS_CHILD+WS_VISIBLE+TVS_HASLINES+TVS_HASBUTTONS+TVS_LINESATROOT,0,\
0,200,400,hWnd,NULL,\
hInstance,NULL
Note the styles. TVS_xxxx are the tree view specific styles.
invoke ImageList_Create,16,16,ILC_COLOR16,2,10
mov hImageList,eax
invoke LoadBitmap,hInstance,IDB_TREE
mov hBitmap,eax
invoke ImageList_Add,hImageList,hBitmap,NULL
invoke DeleteObject,hBitmap
invoke SendMessage,hwndTreeView,TVM_SETIMAGELIST,0,hImageList
Next, you create an empty image list with will accept images of 16x16 pixels in
size, 16-bit color and initially, it will contain 2 images but can be expanded
to 10 if need arises. We then load the bitmap from the resource and add it to
the image list just created. After that, we delete the handle to the bitmap since
it will not be used anymore. When the image list is all set, we associate it with
the tree view control by sending TVM_SETIMAGELIST to the tree view control.
mov tvinsert.hParent,NULL
mov tvinsert.hInsertAfter,TVI_ROOT
mov tvinsert.u.item.imask,TVIF_TEXT+TVIF_IMAGE+TVIF_SELECTEDIMAGE
mov tvinsert.u.item.pszText,offset
Parent
mov tvinsert.u.item.iImage,0
mov tvinsert.u.item.iSelectedImage,1
invoke SendMessage,hwndTreeView,TVM_INSERTITEM,0,addr
tvinsert
We insert items into the tree view control, beginning from the root item. Since
it will be root item, hParent member is NULL and hInsertAfter is TVI_ROOT. imask
member specifies that pszText, iImage and iSelectedImage members of the TV_ITEM
structure is valid. We fill those three members with appropriate value. pszText
contains the label of the root item, iImage is the index into the image in the
image list that will be displayed to the left of the unselected item, and iSelectedImage
is the index into the image in the image list that will be displayed when the
item is selected. When all appropriate members are filled in, we send TVM_INSERTITEM
message to the tree view control to add the root item to it.
mov hParent,eax
mov tvinsert.hParent,eax
mov tvinsert.hInsertAfter,TVI_LAST
mov tvinsert.u.item.pszText,offset
Child1
invoke SendMessage,hwndTreeView,TVM_INSERTITEM,0,addr
tvinsert
mov tvinsert.u.item.pszText,offset
Child2
invoke SendMessage,hwndTreeView,TVM_INSERTITEM,0,addr
tvinsert
After the root item is added, we can attach the child items to it. hParent member
is now filled with the handle of the parent item. And we will use identical images
in the image list so we don't change iImage and iSelectedImage member.
.elseif uMsg==WM_NOTIFY
mov edi,lParam
assume edi:ptr NM_TREEVIEW
.if [edi].hdr.code==TVN_BEGINDRAG
invoke
SendMessage,hwndTreeView,TVM_CREATEDRAGIMAGE,0,[edi].itemNew.hItem
mov hDragImageList,eax
invoke
ImageList_BeginDrag,hDragImageList,0,0,0
invoke
ImageList_DragEnter,hwndTreeView,[edi].ptDrag.x,[edi].ptDrag.y
invoke
SetCapture,hWnd
mov DragMode,TRUE
.endif
assume edi:nothing
Now when the user tries to drag an item, the tree view control sends WM_NOTIFY
message with TVN_BEGINDRAG as the code. lParam is the pointer to an NM_TREEVIEW
structure which contains several pieces of information we need so we put its value
into edi and use edi as the pointer to NM_TREEVIEW structure. assume edi:ptr NM_TREEVIEW
is a way to tell MASM to treat edi as the pointer to NM_TREEVIEW structure. We
then create a drag image by sending TVM_CREATEDRAGIMAGE to the tree view control.
It returns the handle to the newly created image list with a drag image inside.
We call ImageList_BeginDrag to set the hotspot in the drag image. Then we enter
the drag operation by calling ImageList_DragEnter. This function displays the
drag image at the specified location in the specified window. We use ptDrag structure
that is a member of NM_TREEVIEW structure as the point where the drag image should
be initially displayed.After that, we capture the mouse input and set the flag
to indicate that we now enter drag mode.
.elseif uMsg==WM_MOUSEMOVE
.if DragMode==TRUE
mov eax,lParam
and eax,0ffffh
mov ecx,lParam
shr ecx,16
mov tvhit.pt.x,eax
mov tvhit.pt.y,ecx
invoke
ImageList_DragMove,eax,ecx
invoke
ImageList_DragShowNolock,FALSE
invoke
SendMessage,hwndTreeView,TVM_HITTEST,NULL,addr tvhit
.if eax!=NULL
invoke SendMessage,hwndTreeView,TVM_SELECTITEM,TVGN_DROPHILITE,eax
.endif
invoke
ImageList_DragShowNolock,TRUE
.endif
Now we concentrate on WM_MOUSEMOVE. When the user drags the drag image along,
our parent window receives WM_MOUSEMOVE messages. In response to these messages,
we update the drag image position with ImageList_DragMove. After that, we check
if the drag image is over some item. We do that by sending TVM_HITTEST message
to the tree view control with a point for it to check. If the drag image is over
some item, we hilite that item by sending TVM_SELECTITEM message with TVGN_DROPHILITE
flag to the tree view control. During the hilite operation, we hide the drag image
so that it will not leave unsightly blots on the tree view control.
.elseif uMsg==WM_LBUTTONUP
.if DragMode==TRUE
invoke
ImageList_DragLeave,hwndTreeView
invoke
ImageList_EndDrag
invoke
ImageList_Destroy,hDragImageList
invoke
SendMessage,hwndTreeView,TVM_GETNEXTITEM,TVGN_DROPHILITE,0
invoke
SendMessage,hwndTreeView,TVM_SELECTITEM,TVGN_CARET,eax
invoke
SendMessage,hwndTreeView,TVM_SELECTITEM,TVGN_DROPHILITE,0
invoke
ReleaseCapture
mov DragMode,FALSE
.endif
When the user releases the left mouse button, the drag operation is at the end.
We leave the drag mode by calling ImageList_DragLeave, followed by ImageList_EndDrag
and ImageList_Destroy. To make the tree view items look good, we also check the
last hilited item, and select it. We must also un-hilite it else the other items
will not get hilited when they are selected. And lastly, we release the mouse
capture.