In the preceding section, you learned how to use the list view control to organize the display of many items in a window. The list view control enables you to display items both as objects in a window and objects in a report organized into columns. Often, however, the data you’d like to organize for your application’s user is best placed in a hierarchical view. That is, elements of the data are shown as they relate to one other. A good example of a hierarchical display is the directory tree used by Windows to display directories and the files that they contain.

MFC provides this functionality in the CTreeCtrl class. This versatile control displays data in various ways, all the while retaining the hierarchical relationship between the data objects in the view.

Tree views are a little simpler than list views. You will write the rest of CreateTreeView(), which performs the following tasks:

Creating the image list, creating the tree control, and associating the control with the image list are very similar to the steps completed for the image list. You’ve already written the code to create the image list, so add these lines to CreateTreeView():

(Remember to add a resource ID for IDC_TREEVIEW.) The CTreeCtrl class, of which m_treeView is an object, defines special styles to be used with tree view controls. Table 8.3 lists these special styles.

Creating items for a tree view control is much like creating items for a list view control. As with the list view, Visual C++ defines a structure that you must initialize and pass to the function that creates the items. This structure is called TVITEM and is defined in Listing 8.6.

In the TVITEM structure, the mask member specifies the other structure members that are valid. The flags you can use are as follows:

The hItem member is the handle of the item, whereas the state and stateMask members hold the item’s current state and its valid states, which can be one or more of TVIS_BOLD, TVIS_CUT, TVIS_DROPHILITED, TVIS_EXPANDED, TVIS_EXPANDEDONCE, TVIS_FOCUSED, TVIS_OVERLAYMASK, TVIS_SELECTED, TVIS_STATEIMAGEMASK, and TVIS_USERMASK.

The pszText member is the address of a string buffer. When using the TVITEM structure to create an item, the string buffer contains the item’s text. When obtaining information about the item, pszText is the buffer where the information will be stored, and cchTextMax is the size of the buffer. If pszText is set to LPSTR_TEXTCALLBACK, the item uses the callback mechanism. Finally, the iImage member is the index of the item’s icon in the image list. If set to I_IMAGECALLBACK, the iImage member indicates that the item uses the callback mechanism.

The iSelectedImage member is the index of the icon in the image list that represents the item when the item is selected. As with iImage, if this member is set to I_IMAGECALLBACK, the iSelectedImage member indicates that the item uses the callback mechanism. Finally, cChildren specifies whether there are child items associated with the item.

In addition to the TVITEM structure, you must initialize a TVINSERTSTRUCT structure that holds information about how to insert the new structure into the tree view control. That structure is declared in Listing 8.7.

In this structure, hParent is the handle to the parent tree-view item. A value of NULL or TVI_ROOT specifies that the item should be placed at the root of the tree. The hInsertAfter member specifies the handle of the item after which this new item should be inserted. It can also be one of the flags TVI_FIRST (beginning of the list), TVI_LAST (end of the list), or TVI_SORT (alphabetical order). Finally, the item member is the TVITEM structure containing information about the item to be inserted into the tree.

Common first initializes the TVITEM structure for the root item (the first item in the tree). Add these lines:

The CTreeCtrl member function InsertItem() inserts the item into the tree view control. Its single argument is the address of the TVINSERTSTRUCT structure.

CreateTreeView() then inserts the remaining items into the tree view control. Add these lines to insert some hard-coded sample items into the tree view: