Advanced MFC Programming

Chapter 14. Views
how the default styles of the tree control are customized in the sample (within function CDirView::
OnInitialUpdate()):
……
……
lStyleOld=::GetWindowLong(GetTreeCtrl().GetSafeHwnd(), GWL_STYLE);
lStyleOld|=TVS_HASLINES | TVS_LINESATROOT | TVS_HASBUTTONS;
::SetWindowLong(GetTreeCtrl().GetSafeHwnd(), GWL_STYLE, lStyleOld);
Style TVS_HASLINES will let the nodes be connected by dotted lines, TVS_LINESATROOT will add a line
at the root node, and TVS_HASBUTTONS will add a rectangle button (displays either “+” or “-”) for each
expandable node. If we do not specify these styles, the tree control will look slightly different.
These styles can also be customized in function CView::PreCreateWindw(…). In order to do so, we
need to set the corresponding style flags for member dwExStyle of structure CREATESTRUCT. The difference
between two methods is that using ::SetWindowLong(…) can let us change the styles of a window
dynamically.
Adding Root Node
The next step is to add nodes to the tree. We need to call function CTreeCtrl::InsertItem(…) to add a
node to the tree. To call this function, we need to prepare a TV_INSERTSTRUCT type object, and specify the
properties of node. For example, we can specify the node’s parent, associated image, label and states. This
procedure has been discussed in chapter 5. One thing we need to pay attention to is that since
InsertItem(…) is not a member function of CTreeView, we must first call function
CTreeView::GetTreeCtrl() to obtain the tree control before adding any node. The following portion of
function CDirView::OnInitialUpdate() shows how the root node is added:
……
memset(&tvInsertStruct, 0, sizeof(TV_INSERTSTRUCT));
tvInsertStruct.hParent=NULL;
tvInsertStruct.hInsertAfter=TVI_LAST;
tvInsertStruct.item.iImage=0;
tvInsertStruct.item.iSelectedImage=0;
tvInsertStruct.item.pszText="Desktop";
tvInsertStruct.item.mask=TVIF_IMAGE | TVIF_SELECTEDIMAGE | TVIF_TEXT | TVIF_STATE;
tvInsertStruct.item.stateMask|=TVIS_EXPANDED;
tvInsertStruct.item.state|=TVIS_EXPANDED;
……
hTreeItem=GetTreeCtrl().InsertItem(&tvInsertStruct);
ASSERT(hTreeItem);
Finding out Available Drives in the System
By stuffing TV_INSERTSTRUCT type object and calling function CTreeCtrl::InsertItem(…) repeatedly,
the tree can be created. However, before proceeding to create other nodes, we need to find out all the
available drives in the system.
Currently there can be at most 26 drives contained in one system, which are labeled from “A:” to “Z:”.
We can call runtime function _chdrive(…) to change the current working drive (Calling this function has
the same effect with typing command “a:” in a DOS prompt window). Function _chdrive(…) has one
parameter:
int _chdrive(int drive);
Parameter drive specifies target drive. It can be any number from 1 to 26, which represents drive A:,
B:, C:… and so on. The function will return 0 if the working drive is changed successfully, otherwise it
returns -1.
So we can call this function repeatedly by passing 1, 2, 3…26 to it and examining the returned value. If
the function returns 0, this means the drive is available, and we need to add it to the tree control. If the
function returns -1, we can just go on to check the next drive.
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