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VC++ Example: Tree Control With Expand node, SetImageList, InsertItem, NM_CLICK, TVN_ITEMEXPANDING

Tree Control Messages

Most messages of the tree controls are notification messages that are sent to its parent window. For example, the NM_CLICK message is sent to the dialog box or the form, that acts as the parent, that the tree control has been clicked. If the click was done with the right mouse button, the NM_RCLICK message is sent instead. In the same way, if the user double-clicks the control an NM_DBLCLK message is sent. If the user double-clicked with the right mouse button, the NM_CDBLCLK message is sent.

As mentioned already, the user has the ability to expand a node that has at least one child. When the user initiates an action that would expand a node, the tree control sends a TVN_ITEMEXPANDING. After the item has expanded, the control sends the TVN_ITEMEXPANDED message.

Tree Control With Bitmaps or Icons

Bitmaps can be used to enhanced the display of items on a tree control. Each tree item can be configured to display or not to display a small picture on its left. To do this, you can declare a CImageList variable and add pictures to it. Once the image list is ready, you can call the CTreeCtrl::SetImageList() method. Its syntax is:

CImageList* SetImageList(CImageList * pImageList, int nImageListType);

The first argument, pImageList, is a pointer to a CImageList variable. The nImageListType argument specifies the type of image list that will be used. The possible values are:

 
To specify the pictures used for a tree item, call one of the following versions of the CTreeCtrl:: InsertItem() methods:

HTREEITEM InsertItem(UINT nMask,
                                    LPCTSTR lpszItem,
                                    int nImage,
                                     int nSelectedImage,
                                     UINT nState,
                                     UINT nStateMask,
                                     LPARAM lParam,
                                     HTREEITEM hParent,
                                     HTREEITEM hInsertAfter );
HTREEITEM InsertItem(LPCTSTR lpszItem,
                                    int nImage,
                                    int nSelectedImage, 
                                    HTREEITEM hParent = TVI_ROOT,
                                    HTREEITEM hInsertAfter = TVI_LAST);

The nMask argument specifies the type of value used to set on the list item. As seen already, the lpszItem is the text that will be displayed for the current item.

The value of nImage is the index of the image used for the item being inserted from the image list. The nSelectedImage value is the index of the image that will display when the inserted item is selected or has focus.