ID Number: Q79029
1.00
WINDOWS
Summary:
To create an array of picture controls or frames with an array of
child controls (such as command buttons) within each element of the
parent array is not possible in Visual Basic without making use of the
Windows API functions SetParent and GetFocus.
Because Visual Basic does not support overlapping controls, creating
controls and then simply moving them into position within previously
created controls will not function correctly. Using the Windows API
functions in conjunction with the Load and Unload methods can
circumvent this problem and allow dynamic, flexible structures to be
created during execution.
This information applies to Microsoft Visual Basic programming system
version 1.0 for Windows.
More Information:
This article explains how to get the following control structure
Parent Control Child Controls on Parent
-------------- ------------------------
Picture1(1) Command1(1), Command1(2), Command1(3), Command1(4)
Picture1(2) Command1(5), Command1(6), Command1(7), Command1(8)
Picture1(3) Command1(9), Command1(10), Command1(11), Command1(12)
Picture1(4) Command1(13), Command1(14), Command1(15), Command1(16)
(where Picture1 and Command1 are control arrays).
The following example uses the two API functions GetFocus and
SetParent to establish the proper parent/child relationships between
an array of parents (such as picture controls) and an array of
children (such as command buttons), where each child array is within
one element of the parent control.
The function GetFocus requires no parameters. The function SetParent
requires two as follows:
Parameter Type and Description
--------- --------------------
hWndChild HWND Identifies the child window
hWndNewParent HWND Identifies the new parent window
The return value identifies the previous parent window.
This example also demonstrates how Windows handles a drag and drop if
parentage was set at run time. If the control is dragged to another
control of the same type as the previous parent, when released the
control assumes the same relative position it had in the previous
parent. The program demonstrates that before unloading controls nested
using SetParent and moved during the run, parentage should be returned
to the original hierarchy. This is to avoid the possibility of
"Unrecoverable Application Error" (UAE) messages that could occur due
to conflicting messages to Windows.
Create the following controls:
Control Ctlname Property Setting
------- ------- ----------------
Form Form1
Picture Picture1() Index=1
Command button Command1() Index=1
Command button Loadall Taborder=0, Caption="Load All"
Command button Loadsome Taborder=1, Caption="Load Four"
Command button Changemode Taborder=2, Caption="DragMode=0"
Command button Unloadall Taborder=3, Caption="Unload All"
Note: The placement of the original picture box and command button is
important. The picture should be created first and the command button
drawn WITHIN the picture box. The placement of the other controls at
design time is not critical. They are resized and moved at run time.
Code Purpose
---- -------
Loadall_Click Loads all parent controls and all child controls
Loadsome_Click Loads all parent controls and four child controls
Unloadall _Click Unloads all controls. Must reset parentage to the
original first!
Changemode_Click Changes DragMode between auto and manual modes
Resetparent General procedure to reset parentage for Unload and
Close
Cplace General procedure to place the four command buttons
Form_Resize Code to maintain original size
Form_Load Sets initial size and properties of controls
Form_Unload Calls Unloadall_Click to avoid conflicting Windows
messages
Picture1_DragDrop Handles setting of parentage to user actions
Command1_Click Sets captions to reflect change in position and
state
Run the example and try all the buttons. Toggle the DragMode on and
off and drag the command buttons from one picture to another. Add the
following code to your program:
Global Module
-------------
Declare Function setparent% Lib "user" (ByVal h%, ByVal h%)
Declare Function getfocus% Lib "user" ()
Global Handle2Child As Integer
Global Handle2Parent As Integer
Global dragstate, loadstate, toggle, innernum As Integer
Global I, N, K As Integer
Global xoffset, yoffset, cmdnum, childsize, parentsize As Integer
Global Const maxouter = 4
Global Const maxinner = 4
Option Base 1
Global storecaption(16) As String 'array=maxinner*maxouter
Form1
-----
Sub Picture1_DragDrop (index As Integer, source As Control, X As
Single, Y As Single)
picture1(index).SetFocus 'Procedure for control array of parent Picture Boxes
Handle2Parent = getfocus()
source.SetFocus
Handle2Child = getfocus()
ret% = setparent(Handle2Child, Handle2Parent)
source.caption = Mid$(source.caption, 1, 1) + "/" +
LTrim$(RTrim$(Str$(index)))
End Sub
Sub Form_Load ()
form1.width = screen.width - screen.width \ 8
form1.height = screen.height \ 2
form1.backcolor = &HFFFF00
form1.caption = "Nested Control Arrays"
picture1(1).visible = 0
command1(1).visible = 0
parentsize = CInt((form1.width \ maxouter) * .8)
childsize = CInt((2 * parentsize \ maxinner) * .6)
picture1(1).height = parentsize
picture1(1).width = parentsize
command1(1).height = childsize
command1(1).width = childsize
cplace loadall, 1
cplace loadsome, 2
cplace changemode, 3
cplace unloadall, 4
End Sub
Sub resetparent () 'Function to clean up parentage before unload
picture1(1).SetFocus
Handle2Parent = getfocus()
For I = innernum To 1 Step -1
command1(I).SetFocus
Handle2Child = getfocus()
ret% = setparent(Handle2Child, Handle2Parent)
Next I
End Sub
Sub Command1_Click (index As Integer) 'Procedure for control array
'of Buttons
If toggle Then
command1(index).caption = storecaption(index)
toggle = 0
Else
storecaption(index) = command1(index).caption ' change caption to
' reflect state
command1(index).caption = "ON"
toggle = -1
End If
End Sub
Sub Form_Unload (Cancel As Integer) 'Cleans up before program exit
unloadall_click
End Sub
Sub changemode_Click () 'Toggles between automatic & manual dragmodes
If loadstate Then
If Not dragstate Then
For I = 1 To innernum
command1(I).dragmode = 1 'automatic
dragstate = -1 'reset flag
Next I
changemode.caption = "DragMode=1"
Else
For I = 1 To innernum
command1(I).dragmode = 0 'manual
dragstate = 0 'reset flag
Next I
changemode.caption = "DragMode=0"
End If
End If
End Sub
Sub unloadall_click () 'Unloads all dynamically created controls ONLY
Select Case loadstate
Case 1
resetparent 'Must call prior to unload to avoid UAEs
For I = maxouter To 1 Step -1
For N = maxinner To 1 Step -1
cmdnum = ((I - 1) * 4) + N
If cmdnum <> 1 Then Unload command1(cmdnum)
Next N
If I <> 1 Then Unload picture1(I)
Next I
command1(1).visible = 0 'Can't unload controls
picture1(1).visible = 0 'created at design time so hide!
loadstate = 0 'reset flag for load routines
changemode.enabled = 0
Case 2
resetparent 'Must call prior to unload to avoid UAEs
For I = maxouter To 1 Step -1
If I = 1 Then
For N = maxinner To 2 Step -1
Unload command1(N)
Next N
End If
If I <> 1 Then Unload picture1(I)
Next I
command1(1).visible = 0 'Can't unload controls
picture1(1).visible = 0 'created at design time so hide!
loadstate = 0 'reset flag for load routines
changemode.enabled = 0
End Select
End Sub
Sub loadsome_click () 'Loads all parents and one set of children
If loadstate = 0 Then ' to demonstrate drag and drop
changemode.enabled = -1
command1(1).Move 0, 0
For I = 1 To maxouter
If I <> 1 Then
Load picture1(I) ' can't load control created at design time
End If
picture1(I).Move -picture1(1).width, -picture1(1).height,
parentsize, parentsize ' **
picture1(I).visible = -1 'load off-screen /\
picture1(I).SetFocus
Handle2Parent = getfocus() 'get handle by API call
If I = 1 Then
For N = 1 To 4
If N <> 1 Then
Load command1(N) 'can't load control created at design time
End If
xoffset = picture1(I).scalewidth \ 4 -
command1(N).width \ 2 +
((N - 1) Mod 2) * (picture1(I).scalewidth \ 2) ' **
If N > 2 Then
yoffset = picture1(I).scaleheight \ 2 +
(picture1(I).scaleheight \ 4 -
command1(N).height \ 2) ' **
'Note: All code statements (in all procedures) MUST be on one line!
Else yoffset=(picture1(I).scaleheight\4-command1(N).height\2)
End If
command1(N).Move xoffset, yoffset
command1(N).visible = -1
command1(N).SetFocus
Handle2Child = getfocus() 'get handle by API call
ret% = setparent(Handle2Child, Handle2Parent) 'Call API function
command1(N).caption = LTrim$(RTrim$(Str$(N))) + "/" +
LTrim$(RTrim$(Str$(I))) ' **
Next N
End If
Next I
xoffset = ((form1.scalewidth \ maxouter) - picture1(1).width) \ 2
picture1(1).Move xoffset, 0
For I = 2 To maxouter
picture1(I).Move (I - 1) * (form1.scalewidth \ maxouter) +
xoffset, picture1(I - 1).top ' **
Next I
innernum = 4 'set global loop maximum
loadstate = 2
End If
End Sub
Sub loadall_click () 'Loads all parents and children in nested structure
If loadstate = 0 Then
changemode.enabled = -1
command1(1).Move 0, 0
For I = 1 To maxouter '/\ size command button proportionally
If I <> 1 Then Load picture1(I) 'can't load control created at
'design time
'load off-screen:
picture1(I).Move -picture1(1).width, -picture1(1).height
picture1(I).visible = -1
picture1(I).SetFocus
Handle2Parent = getfocus() 'get handle by API call
For N = 1 To maxinner
cmdnum = ((I - 1) * 4) + N
If cmdnum <> 1 Then
Load command1(cmdnum) 'can't load control created at
'design time
End If
xoffset=((N-1) Mod 2)*(picture1(I).scalewidth\(maxinner\2))
If N > 2 Then
yoffset = picture1(I).scaleheight \ 2
Else yoffset = picture1(I).scaletop
End If
command1(cmdnum).Move picture1(I).scalewidth \ 8 +
xoffset, picture1(I).scaleheight \ 8 + yoffset ' **
command1(cmdnum).visible = -1
command1(cmdnum).SetFocus
Handle2Child = getfocus() 'get handle by API call
ret% = setparent(Handle2Child, Handle2Parent) 'Call API function
Next N
Next I 'Caption the control array buttons
For K = 1 To (maxinner * maxouter)
command1(K).caption = LTrim$(RTrim$(Str$(K)))
Next K
xoffset = ((form1.scalewidth \ maxouter) - picture1(1).width) \ 2
picture1(1).Move xoffset, 0
For I = 2 To maxouter
picture1(I).Move (I - 1) * (form1.scalewidth \ maxouter) +
xoffset, picture1(I - 1).top ' **
Next I
innernum = 16 'set global loop maximum
loadstate = 1
End If
End Sub
Sub Form_Resize ()
form1.width = screen.width - screen.width \ 8
form1.height = screen.height \ 2
End Sub
Sub cplace (dummy As Control, num As Integer) 'size static controls
theheight% = parentsize + childsize * 2
dummy.Move (form1.width \ 4) * (num - 1) + parentsize \ 10,
theheight%, parentsize, childsize ' **
End Sub
** Note: These statements are shown on multiple lines, but must be on
a single line in Visual Basic's Code window.
Reference(s):
"Microsoft Windows Programmer's Reference Book and Online Resource,"
version 3.0, Visual Basic add-on #1-55615-413-5
Additional reference words: 1.00