Tutorial 18: Common Controls Tutorial 19: Tree View Control Tutorial 20: Window Subclassing

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.

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.

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.

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.

ImageList_Add PROTO himl:DWORD, hbmImage:DWORD, hbmMask:DWORD

This function returns -1 if unsuccessful.

TVM_GETIMAGELIST

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.

  1. 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.
  2. 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.
  3. 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
    1. hwndLock is the handle of the window that owns the drag image. The drag image will not be able to move outside that window.
    2. 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.
  4. 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.
  5. 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.
  6. 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 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 ; 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 mov hwndTreeView,eax ; create the associated image list invoke ImageList_Create,16,16,ILC_COLOR16,2,10 mov hImageList,eax invoke LoadBitmap,hInstance,IDB_TREE ; load the bitmap from ; the resource mov hBitmap,eax ; add the bitmap into the image list invoke ImageList_Add,hImageList,hBitmap,NULL 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 th e 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.

Tutorial 18: Common Controls Overview Tutorial 20: Window Subclassing
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