Microsoft KB Archive/79029

= How To Create Nested Control Arrays in Visual Basic =

Article ID: 79029

Article Last Modified on 11/18/2003

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APPLIES TO


 * Microsoft Visual Basic 1.0 Standard Edition
 * Microsoft Visual Basic 2.0 Standard Edition
 * Microsoft Visual Basic 3.0 Professional Edition

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This article was previously published under Q79029



SUMMARY
This article explains how 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 by using the Windows API functions SetParent and GetFocus. This is not possible in Visual Basic for Windows without using the Windows API functions because Visual Basic does not support overlapping controls. In other words, in Visual Basic alone, you cannot create controls and then simply move them into position within previously created controls.

By using the Windows API functions in conjunction with the Load and Unload methods, you can circumvent this problem and allow dynamic, flexible structures to be created during execution.



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 correct parent/child relationships between an array of parents (such as picture controls) and an array of children (such as command buttons). Each child array is placed within one element of the parent control.

The GetFocus function requires no parameters. The SetParent function requires two parameters 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 when parentage was set at run time. If you drag a control to another control of the same type as the previous parent and drop it, the released control assumes the same relative position it had in the previous parent.

The example program demonstrates that before unloading controls nested using SetParent and moved during the run, parentage should be returned to the original hierarchy. This avoids the possibility of general protection (GP) faults or Unrecoverable Application Errors (UAEs) that could occur due to conflicting messages to Windows.

Step-by-Step Example
 Start a new project in Visual Basic. Form1 is created by default.  Add a picture box and five command buttons to Form1, giving them the property settings shown here:   Control           Control Name  Property Setting ---  Form              Form1 Picture          Picture1    Index=1 Command button   Command1    Index=1 Command button   Loadall       TabIndex=0, Caption=&quot;Load All&quot; Command button   Loadsome      TabIndex=1, Caption=&quot;Load Four&quot; Command button   Changemode    TabIndex=2, Caption=&quot;DragMode=0&quot; Command button   Unloadall     TabIndex=3, Caption=&quot;Unload All&quot;

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.   Add code to the examaple application. Here is a summary of each of the Sub procedures you will create:   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

  Add the following code to general declarations section of Form1: Declare Function setparent% Lib &quot;user&quot; (ByVal h%, ByVal h%) Declare Function getfocus% Lib &quot;user&quot; 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

  Add the following Sub procedures to the application in apprpriate events in Form1. Each code statement must be entered as one, single line. ' Enter the following two lines as one, single line:

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$(source.caption, 1, 1) + &quot;/&quot; + LTrim$(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 = &quot;Nested Control Arrays&quot; 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 = &quot;ON&quot; toggle = -1 End If  End Sub

Sub Form_Unload (Cancel As Integer) ' Cleans up before program exits. 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 = &quot;DragMode=1&quot; Else For I = 1 To innernum command1(I).dragmode = 0 ' Manual dragstate = 0            ' Reset flag. Next I           changemode.caption = &quot;DragMode=0&quot; 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 GP fault or UAE

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 GP fault or UAE. 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   ' Can't load control created at design time. Load picture1(I) End If           ' Enter the following two lines as one, single line: 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                  End If               ' design time. ' Enter the following two lines as one, single line: xoffset = picture1(I).scalewidth \ 4 - command1(N).width \ 2 + ((N - 1) Mod 2) * (picture1(I).scalewidth \ 2) If N > 2 Then ' Enter the following three lines as one, single line: yoffset = picture1(I).scaleheight \ 2 + (picture1(I).scaleheight \ 4 -                       command1(N).height \ 2) Else ' Enter the following two lines as one, single line: 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. ' Call API function. ret% = setparent(Handle2Child, Handle2Parent) ' Enter the following two lines as one, single line: command1(N).caption = LTrim$(RTrim$(Str$(N))) + &quot;/&quot; + LTrim$(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 ' Enter the following line as one, single line: 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      If loadstate = 0 Then     ' nested structure. 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              ' Enter the following command as one, single line: 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. ' Call API function. ret% = setparent(Handle2Child, Handle2Parent) 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 ' Enter the following two lines as one, single line: dummy.Move (form1.width \ 4) * (num - 1) + parentsize \ 10, theheight%, parentsize, childsize ' ** End Sub </li> Run the example and try all the buttons. Toggle the DragMode on and off and drag the command buttons from one picture to another.</li></ol>

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Keywords: kbcode KB79029

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