Simple Tree Control

• Download demo and source - 18 Kb

Why a new tree control

First of all, there are lots of custom tree controls available so what's the need for this? In one of my projects I happened to use several tree controls to show data objects at different levels and I had to deal with user actions. Each time, my tree control has to respond in different way depending on the selected item. Here I present what I have (I re-wrote some of my code to use this custom control and I believe that it is more readeble and easy to understand now)

How it works

CSimpleTreeCtrl "simply" overrides the MFC CTreeCtrl class and provides some access functions to deal with it. CSimpleTreeCtrl::TreeCtrlItem is used to add new items in the tree control. You should write your own class (to use it in a better way) and override virtual functions to be notified by windows messages such as item selection, right click etc.

CSimpleTreeCtrl provides the following virtual functions:

     virtual void          selChanged ( TreeCtrlItem *item ) {} ;
     virtual void          lClick ( TreeCtrlItem *item ) {} ;
     virtual void          lDblClick ( TreeCtrlItem *item ) {} ;
     virtual void          rClick ( TreeCtrlItem *item ) {} ;
     // will be called after three control is created
     virtual void          postCreate ( void ) {} ;

As you noticed base class has nothing to do with these functions. It simply handles windows messages and calls the virtual function (I just got bored having to register my message handling functions). The base class also will let CTreeCtrl do its own stuff, so whenever you receive a lClick() you will also get a selChanged() if this click causes the current selection to change. The only difference is with rClick(): since in most cases I want right click to change the selected item, I handled this case in my message handler, so it will also send a selChanged() as well (if a selection exists). You may change this behaviour if you want.

For me the most useful part is CSimpleTreeCtrl::TreeCtrlItem. This class provides the following virtual functions:

     // will be called on selection
     virtual void          onSelected   ( void ) {} ;
     // will be called for old selected item when there is a new selection (before 
     // onSelected() for new item)
     virtual void          onUnSelected ( void ) {} ;
     // will be called with position in screen coordinates if user right clicks on item
     virtual void          onRClick    ( CPoint pos ) {} ;
     // will be called if user left double clicks on item
     virtual void          onLDblClick ( void ) {} ;
     // will be called after item inserted in tree
     virtual void          postInsert  ( void ) {} ;

It also provides two additional functions which you may find necessary. Thanks to Michael Dunn and his article "Neat Stuff to do in List Controls Using Custom Draw"

     void          setTextColor   ( COLORREF color ) ;
     void          setBkColor     ( COLORREF color ) ;

The default color for item text is black ( RGB(0, 0, 0) ) and item background is white ( RGB(255, 255, 255) ).

You can write your own class handling only required virtual functions as shown below.

     class BaseCtrlItem : public CSimpleTreeCtrl::TreeCtrlItem
     {
     public:
          BaseCtrlItem ( CString name, CMyDataClass *myData ) 
               : CSimpleTreeCtrl::TreeCtrlItem ( name ) 
          {
               m_myData = myData ;
          } ;

          virtual ~BaseCtrlItem () {} ;

          virtual void     postInsert ( void ) 
          {
               //You can insert sub items to the tree control if necessary
          } ;

          virtual void     onRClick ( CPoint pos ) 
          {
               //Show popup menu according to your data pointer
          } ;

     protected:
          CMyDataClass *m_myData ;          
     };

If an item is removed from the tree (using CSimpleTreeCtrl or CTreeCtrl functions) related the CSimpleTreeCtrl::TreeCtrlItem pointer will be removed as well, so you do not need to worry about deleting the item pointers.

There is some more to add to this class but I prefer to keep it as simple as possible. Also, it handles most of the requirements in my project. I would, however, like to hear if there is any usefull features to add while keeping it simple.

The demo application creates a new tree control and adds some items in different colors. It also handles the onRClick() function in items. You can just add SimpleTreeCtrl.h and SimpleTreeCtrl.cpp to your project and enjoy it. The header file should be clear enough for documentation, if it is not, just let me know :-)

Known Problems:

1. CSimpleTreeCtrl does not hide the base implementation of CTreeCtrl so users may use the base class functionality as well. However this may cause some problems. Whenever a CSimpleTreeCtrl::TreeCtrlItem item is added to the tree, it's pointer is added as item data in CTreeCtrl. If you use HTREEITEM to add new items and set item data by yourself, CSimpleTreeCtrl will assume that user data is a CSimpleTreeCtrl::TreeCtrlItem or derived pointer. If there is no user data, there should not be any problem

2. CSimpleTreeCtrl::postCreate() will be called when tree control receives an OnCreate() message. I noticed that in some cases (according to how you use the tree) that control does not get this message. But I did not check it in detail. If you've got any problem send me the details.