Treeview Recursive Program

It is a simple way to implement a Treeview in Foxpro.


Create a catalog database

Create Table Catalog (ID N(10), Parent N(10), Name C(50))
The ID field must be an unique number with start from 1 to 9999999999. Parent is the number pointing to the parent node (Previous level). In this program, 0 (zero) is the root node (first node) of the tree.

Create a form

Add a TreeView control into a form. Name it as tvwCatalog. This is what I usually do. I use txtSomething to indicate the object is a text box. tvw is stand for TreeView. Although it is not quite necessary, but with a good practice is always a good idea. In the Form1.Init, add Do Load_Catalog with this, 0

Create a recursive program (Load_Catalog)

Here is the code of the Load_Catalog.Prg

LPARAMETERS pTree, pNode

Private xQ, xParent, xID, xName, xCheck

***** Add the root node when the tree is empty

IF pTree.Nodes.Count = 0

pTree.Nodes.Add (,, 'C0', 'Root')

pTree.Nodes.Item('C0').Expanded = .T.

pTree.Nodes.Item('C0').Checked  = .T.

ENDIF

***** SYS(2015) returns a temporary file name

xQ = SYS(2015)

***** Read the nodes with specified parent node number

Select * from Catalog ;

 WHERE Parent = pNode ;

 ORDER BY Name        ;

 INTO CURSOR &xQ

***** If this parent has child node

IF RECCOUNT() > 0

  SCAN

    xParent = 'C' + ALLTRIM(STR(&xQ..Parent))

    xID     = 'C' + ALLTRIM(STR(&xQ..ID))

    xName   =       ALLTRIM(&xQ..Name)

    pTree.Nodes.Add (xParent, 4, xID, xName)

    DO Load_Catalog WITH pTree, &xQ..ID

  ENDSCAN

ENDIF

Select &xQ

USE

Test the code

Since the Catalog database has no record. You should only see the "Root" in the tree. Later I added an "ADD" button. Here is the code:


PRIVATE xName, xID, xParent, xName


xName = ALLTRIM(INPUTBOX('Please enter a name', ;
                         'Add New Catalog', ''))


IF NOT EMPTY(xName)
  SELECT MAX(ID + 1) as NewID FROM Catalog INTO CURSOR Q1
  IF RECCOUNT() = 0
    xID  = 1
  ELSE
    xID  = IIF(RECCOUNT() = 0, 1, Q1.NewID)
  ENDIF
  xParent = VAL(SUBSTR(thisform.tvwCatalog.SelectedItem.Key, 2))

  INSERT INTO Catalog (ID,  Parent,  Name) ;
               VALUES (xID, xParent, xName)
thisform.tvwCatalog.Init
ENDIF