PRB: Accelerator Keys Fail to Work in MDI Child Forms

• Microsoft Visual Basic Learning, Professional, and Enterprise Editions for Windows, versions 5.0, 6.0

SYMPTOMS

In MDI child forms, accelerator keys such as CTRL+TAB, CTRL+F6, and CTRL+F4 will not work when the focus is set to the following controls:

Combobox
Tabstrip
Slider
Listview
Treeview
MaskedEdit Control
DBGrid
DBCombo
DBList
few non-intrinsic controls.

The accelerator keys will work for the following controls:

CommandButton
Textbox
Listbox
Picturebox
Checkbox
OptionButton
Vertical Scroll Bar
Horizontal Scroll Bar
DriveListBox
DirListBox
FileListBox

RESOLUTION

The workaround is to trap the keys in the KeyDown event of each child form and to simulate the right behavior by sending the WM_SYSCOMMAND message. See the MORE INFORMATION section below for a step-by-step example that describes how to implement this workaround if many forms are present in a project.

STATUS

This behavior is by design.

MORE INFORMATION

Steps to Reproduce Behavior

1. Create a new Standard EXE project in Visual Basic. Form1 is created by default.



2. From the Project menu, add Form2 and a MDI Form. For Form1 and Form2, set the MDI child property to True.



3. Place a CommandButton and a ComboBox in Form2. Add more controls in Form1 and Form2 as desired.



4. Paste the following code in the MDI form's General Declaration section:

   
         Private Sub MDIForm_Load()
            Form1.Show
            Form2.Show
         End Sub
    




5. Run the application. When the focus is on CommandButton, the keys CTRL+TAB and CTRL+F4 work. But, when the focus is on a ComboBox, the above keys fail. Note that for a ComboBox, F4 and CTRL+F4 will drop the list as expected. Experiment with other controls.

Steps to Resolve the Problem

1. Paste the following code in any existing module. If there is no module, add a module from the Project menu, and paste in the following code:

   
         Option Explicit
   
         Declare Function SendMessage Lib "user32" Alias "SendMessageA" _
         (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, _
         ByVal lParam As Long) As Long
   
         Public Const SC_CLOSE = &HF060
         Public Const SC_NEXTWINDOW = &HF040
         Public Const WM_SYSCOMMAND = &H112
   
         Public Sub NextWin(KeyCode As Integer, Shift As Integer, sCtl _
         As String, hWin As Long)
         If (KeyCode = vbKeyTab And (Shift And vbCtrlMask)) Or (KeyCode = _
               vbKeyF6 And (Shift And vbCtrlMask)) Then
             If Not (sCtl = "CommandButton" Or sCtl = "OptionButton" Or _
                sCtl = "TextBox" Or sCtl = "CheckBox" Or _
                sCtl = "ListBox") Then ' This line is to save CPU time. _
                   ' Code will work even without this If block
                   ' Modify the If block to include other controls as needed
                Call SendMessage(hWin, WM_SYSCOMMAND, SC_NEXTWINDOW, 0)
             End If
         ElseIf KeyCode = vbKeyF4 And (Shift And vbCtrlMask) Then
            Call SendMessage(hWin, WM_SYSCOMMAND, SC_CLOSE, 0)
         End If
         End Sub 




2. For each child form, change the KeyPreview property to True and add the following to their code windows:

   
         Private Sub Form_KeyDown(KeyCode As Integer, Shift As Integer)
            ' Any key processing code specific to project.
            ' Check for CTRL+TAB, CTRL+F6 and
            ' CTRL+F4 here itself for Forms with intense key processing
            NextWin KeyCode, Shift, TypeName(Me.ActiveControl), Me.hwnd
         End Sub
    




3. Run the project. All the forms should now function properly irrespective of which control has the focus.

REFERENCES

For additional information, please see the following articles in the Microsoft Knowledge Base:

Q189779 : BUG: Enabling Accelerator Keys in Visual Basic ActiveX Controls

Q99688 : How to Trap Keystrokes in the Form Instead of Form's Controls

Q190353 : FIX: Form Receives Keyboard Events When KeyPreview Is True

Q113328 : PRB: Form KeyDown Displays Inconsistent Behavior

Q189616 : BUG: DateTimePicker Overrides ALT+F4 Key Combination

Q149273 : BUG: Form Key Events Fire Twice with Some Controls

Additional query words: kbDSupport kbDSD kbVBp kbVBp500 kbVBp600 kbCtrl

Keywords : kbGrpVB
Version : WINDOWS:5.0,6.0
Platform : WINDOWS
Issue type : kbprb