McBasic™ 0.7.881 · Build 881 · 17 min read

Hands-on tutorial · Layout & Forms

Build a multi-document workspace

Host related document windows while keeping independent windows separate.

4 Form / control designs4 complete BASIC filesGuided sample project

Download complete project Complete event code

MDI is a Form relationship, not merely a window style. The sample distinguishes child documents from an independent Form. Track each instance’s lifetime and test how closing a document differs from closing the workspace.

Step 1Prepare a safe practice project#

Extract the archive into a new writable folder, separate from your own application. Open MdiForms.mcproj in McBasic™. Keep every declared source, layout, resource and migration file together.

To reconstruct it yourself, create a DesktopApp project and add the files declared below. In the complete project, follow these steps as a guided rebuild: replace each named source file once and Check after all its procedures are present.

Exact project configuration

MdiForms.mcproj

{
  "schemaVersion": 1,
  "projectId": "357c7963-827f-484a-b5a8-3714b1d6ea04",
  "name": "MdiForms",
  "kind": "DesktopApp",
  "language": {
    "dialect": "McBasic1",
    "requireExplicit": true,
    "compare": "Binary",
    "defaultArrayBase": 0
  },
  "application": {
    "bundleIdentifier": "com.mcbasic.samples.mdiforms",
    "version": "0.1.0",
    "buildNumber": "1",
    "startupFormId": "form-main",
    "shutdownMode": "OnStartupFormClosed"
  },
  "forms": [
    {
      "id": "form-main",
      "typeName": "frmMain",
      "layout": "Forms/frmMain.form.json",
      "code": "Forms/frmMain.bas"
    },
    {
      "id": "form-details",
      "typeName": "frmDetails",
      "layout": "Forms/frmDetails.form.json",
      "code": "Forms/frmDetails.bas"
    },
    {
      "id": "form-independent",
      "typeName": "frmIndependent",
      "layout": "Forms/frmIndependent.form.json",
      "code": "Forms/frmIndependent.bas"
    },
    {
      "id": "form-other",
      "typeName": "frmOther",
      "layout": "Forms/frmOther.form.json",
      "code": "Forms/frmOther.bas"
    }
  ],
  "modules": [],
  "classes": [],
  "tests": [],
  "references": [],
  "resources": [],
  "targets": [
    "osx-arm64"
  ],
  "capabilities": []
}

Step 2Build the Form and set its properties#

frmMain

Select the Form first and set its properties. Add containers before their children. These are initial Designer values, not statements to paste into a procedure.

Form property	Value
`Caption`	`"MDI Forms"`
`Width`	`900`
`Height`	`600`
`MinWidth`	`520`
`MinHeight`	`480`
`MDIForm`	`True`
`MDIClientTop`	`288`

Type	Name	Parent
Label	`lblIntro`	Form
CommandButton	`cmdAlpha`	Form
CommandButton	`cmdBeta`	Form
Label	`lblStatus`	Form
CommandButton	`cmdClose`	Form
CommandButton	`cmdIndependent`	Form

lblIntro · exact Inspector values

Property	Value
`Left`	`24`
`Top`	`24`
`Width`	`500`
`Height`	`44`
`Caption`	`"Two child forms share this window; another form stays independent."`
Anchor edges	Left, Top

cmdAlpha · exact Inspector values

Property	Value
`Left`	`24`
`Top`	`92`
`Width`	`160`
`Height`	`38`
`Caption`	`"Open Alpha"`
`TabIndex`	`0`
Anchor edges	Left, Top

cmdBeta · exact Inspector values

Property	Value
`Left`	`200`
`Top`	`92`
`Width`	`160`
`Height`	`38`
`Caption`	`"Open Beta"`
`TabIndex`	`1`
Anchor edges	Left, Top

lblStatus · exact Inspector values

Property	Value
`Left`	`24`
`Top`	`158`
`Width`	`500`
`Height`	`52`
`Caption`	`"Ready. No secondary Forms are open."`
Anchor edges	Left, Top

cmdClose · exact Inspector values

Property	Value
`Left`	`24`
`Top`	`236`
`Width`	`160`
`Height`	`38`
`Caption`	`"Close main Form"`
`TabIndex`	`2`
Anchor edges	Left, Top

cmdIndependent · exact Inspector values

Property	Value
`Left`	`376`
`Top`	`92`
`Width`	`160`
`Height`	`38`
`Caption`	`"Show independent"`
`TabIndex`	`3`
Anchor edges	Left, Top

frmDetails

Select the Form first and set its properties. Add containers before their children. These are initial Designer values, not statements to paste into a procedure.

Form property	Value
`Caption`	`"Details window"`
`Width`	`360`
`Height`	`220`
`MinWidth`	`320`
`MinHeight`	`190`
`MDIChild`	`True`

Type	Name	Parent
Label	`lblName`	Form
CommandButton	`cmdHide`	Form
CommandButton	`cmdUnload`	Form

lblName · exact Inspector values

Property	Value
`Left`	`24`
`Top`	`24`
`Width`	`300`
`Height`	`44`
`Caption`	`"Details window"`
Anchor edges	Left, Top

cmdHide · exact Inspector values

Property	Value
`Left`	`24`
`Top`	`96`
`Width`	`140`
`Height`	`36`
`Caption`	`"Hide window"`
`TabIndex`	`0`
Anchor edges	Left, Top

cmdUnload · exact Inspector values

Property	Value
`Left`	`176`
`Top`	`96`
`Width`	`140`
`Height`	`36`
`Caption`	`"Unload window"`
`TabIndex`	`1`
Anchor edges	Left, Top

frmIndependent

Select the Form first and set its properties. Add containers before their children. These are initial Designer values, not statements to paste into a procedure.

Form property	Value
`Caption`	`"Independent form"`
`Width`	`420`
`Height`	`420`
`MinWidth`	`420`
`MinHeight`	`420`

Type	Name	Parent
Label	`lblName`	Form
CommandButton	`cmdHide`	Form
CommandButton	`cmdUnload`	Form
CommandButton	`cmdCascade`	Form
CommandButton	`cmdTileHorizontal`	Form
CommandButton	`cmdTileVertical`	Form
CommandButton	`cmdCheckActive`	Form
CommandButton	`cmdHideActive`	Form

lblName · exact Inspector values

Property	Value
`Left`	`24`
`Top`	`24`
`Width`	`300`
`Height`	`44`
`Caption`	`"Details window"`
Anchor edges	Left, Top

cmdHide · exact Inspector values

Property	Value
`Left`	`24`
`Top`	`96`
`Width`	`140`
`Height`	`36`
`Caption`	`"Hide window"`
`TabIndex`	`0`
Anchor edges	Left, Top

cmdUnload · exact Inspector values

Property	Value
`Left`	`176`
`Top`	`96`
`Width`	`140`
`Height`	`36`
`Caption`	`"Unload window"`
`TabIndex`	`1`
Anchor edges	Left, Top

cmdCascade · exact Inspector values

Property	Value
`Left`	`24`
`Top`	`160`
`Width`	`220`
`Height`	`36`
`Caption`	`"Cascade"`
`TabIndex`	`2`
Anchor edges	Left, Top

cmdTileHorizontal · exact Inspector values

Property	Value
`Left`	`24`
`Top`	`205`
`Width`	`220`
`Height`	`36`
`Caption`	`"Tile horizontal"`
`TabIndex`	`3`
Anchor edges	Left, Top

cmdTileVertical · exact Inspector values

Property	Value
`Left`	`24`
`Top`	`250`
`Width`	`220`
`Height`	`36`
`Caption`	`"Tile vertical"`
`TabIndex`	`4`
Anchor edges	Left, Top

cmdCheckActive · exact Inspector values

Property	Value
`Left`	`24`
`Top`	`295`
`Width`	`220`
`Height`	`30`
`Caption`	`"Check active child"`
`TabIndex`	`5`
Anchor edges	Left, Top

cmdHideActive · exact Inspector values

Property	Value
`Left`	`24`
`Top`	`340`
`Width`	`220`
`Height`	`32`
`Caption`	`"Hide active child"`
`TabIndex`	`6`
Anchor edges	Left, Top

frmOther

Select the Form first and set its properties. Add containers before their children. These are initial Designer values, not statements to paste into a procedure.

Form property	Value
`Caption`	`"Other child"`
`Width`	`360`
`Height`	`220`
`MinWidth`	`320`
`MinHeight`	`190`
`MDIChild`	`True`

Type	Name	Parent
Label	`lblName`	Form
CommandButton	`cmdHide`	Form
CommandButton	`cmdUnload`	Form
CommandButton	`cmdCancelClose`	Form
CommandButton	`cmdFailClose`	Form

lblName · exact Inspector values

Property	Value
`Left`	`24`
`Top`	`24`
`Width`	`300`
`Height`	`44`
`Caption`	`"Details window"`
Anchor edges	Left, Top

cmdHide · exact Inspector values

Property	Value
`Left`	`24`
`Top`	`96`
`Width`	`140`
`Height`	`36`
`Caption`	`"Hide window"`
`TabIndex`	`0`
Anchor edges	Left, Top

cmdUnload · exact Inspector values

Property	Value
`Left`	`176`
`Top`	`96`
`Width`	`140`
`Height`	`36`
`Caption`	`"Unload window"`
`TabIndex`	`1`
Anchor edges	Left, Top

cmdCancelClose · exact Inspector values

Property	Value
`Left`	`24`
`Top`	`144`
`Width`	`140`
`Height`	`36`
`Caption`	`"Cancel next close"`
`TabIndex`	`2`
Anchor edges	Left, Top

cmdFailClose · exact Inspector values

Property	Value
`Left`	`176`
`Top`	`144`
`Width`	`140`
`Height`	`36`
`Caption`	`"Error next close"`
`TabIndex`	`3`
Anchor edges	Left, Top

Step 3Connect the events explicitly#

frmMain

Object	Event	Procedure	Parameters
`cmdAlpha`	`Click`	`cmdAlpha_Click`	`Click()`
`cmdBeta`	`Click`	`cmdBeta_Click`	`Click()`
`cmdClose`	`Click`	`cmdClose_Click`	`Click()`
`cmdIndependent`	`Click`	`cmdIndependent_Click`	`Click()`
Form	`Shown`	`Form_Shown`	`()`

frmDetails

Object	Event	Procedure	Parameters
`cmdHide`	`Click`	`cmdHide_Click`	`Click()`
`cmdUnload`	`Click`	`cmdUnload_Click`	`Click()`
Form	`Initialize`	`Form_Initialize`	`()`
Form	`Load`	`Form_Load`	`()`
Form	`Shown`	`Form_Shown`	`()`
Form	`QueryUnload`	`Form_QueryUnload`	`(ByRef Cancel As Integer, ByVal UnloadMode As Integer)`
Form	`Unload`	`Form_Unload`	`()`

frmIndependent

Object	Event	Procedure	Parameters
`cmdHide`	`Click`	`cmdHide_Click`	`Click()`
`cmdUnload`	`Click`	`cmdUnload_Click`	`Click()`
`cmdCascade`	`Click`	`cmdCascade_Click`	`Click()`
`cmdTileHorizontal`	`Click`	`cmdTileHorizontal_Click`	`Click()`
`cmdTileVertical`	`Click`	`cmdTileVertical_Click`	`Click()`
`cmdCheckActive`	`Click`	`cmdCheckActive_Click`	`Click()`
`cmdHideActive`	`Click`	`cmdHideActive_Click`	`Click()`
Form	`Initialize`	`Form_Initialize`	`()`
Form	`Load`	`Form_Load`	`()`
Form	`Shown`	`Form_Shown`	`()`
Form	`QueryUnload`	`Form_QueryUnload`	`(ByRef Cancel As Integer, ByVal UnloadMode As Integer)`
Form	`Unload`	`Form_Unload`	`()`

frmOther

Object	Event	Procedure	Parameters
`cmdHide`	`Click`	`cmdHide_Click`	`Click()`
`cmdUnload`	`Click`	`cmdUnload_Click`	`Click()`
`cmdCancelClose`	`Click`	`cmdCancelClose_Click`	`Click()`
`cmdFailClose`	`Click`	`cmdFailClose_Click`	`Click()`
Form	`Initialize`	`Form_Initialize`	`()`
Form	`Load`	`Form_Load`	`()`
Form	`Shown`	`Form_Shown`	`()`
Form	`QueryUnload`	`Form_QueryUnload`	`(ByRef Cancel As Integer, ByVal UnloadMode As Integer)`
Form	`Unload`	`Form_Unload`	`()`

Step 4Enter the complete behavior#

Open the named source file. Enter declarations first, then every procedure. Expand a procedure for its full body, or copy the complete file. Helpers are required: do not stop after entering the first Click handler.

`Forms/frmMain.bas`

Enter these declarations at file scope, before the procedures.

Forms/frmMain.bas · declarations

Option Explicit

Public ActiveAlpha As frmDetails
Public ActiveBeta As frmOther

Private Sub Form_Shown()

Initialize state before enabling dependent actions. Keep the shared declarations and startup dependencies with this procedure.

Forms/frmMain.bas · Form_Shown

Private Sub Form_Shown()
    Dim alpha As frmDetails
    Dim beta As frmOther
    Dim active As Form
    Set alpha = New frmDetails
    Set beta = New frmOther
    Set ActiveAlpha = alpha
    Set ActiveBeta = beta
    alpha.DisplayName = "Alpha"
    beta.DisplayName = "Beta"
    Debug.Print "active-empty:" & (Me.ActiveForm Is Nothing)
    alpha.Show
    Set active = Me.ActiveForm
    Debug.Print "active-alpha:" & (active Is alpha)
    beta.Show
    Set active = Me.ActiveForm
    Debug.Print "active-beta:" & (active Is beta)
    Me.Arrange vbCascade
    frmIndependent.Show
    lblStatus.Caption = "Two MDI children and one independent window."
End Sub

Private Sub cmdAlpha_Click()

Enter the complete action, including its input checks and calls to helper procedures.

Forms/frmMain.bas · cmdAlpha_Click

Private Sub cmdAlpha_Click()
    Dim alpha As frmDetails
    Set alpha = New frmDetails
    alpha.DisplayName = "Alpha"
    alpha.Show
    lblStatus.Caption = "Another Alpha child opened inside MDI Forms."
End Sub

Private Sub cmdBeta_Click()

Enter the complete action, including its input checks and calls to helper procedures.

Forms/frmMain.bas · cmdBeta_Click

Private Sub cmdBeta_Click()
    Dim beta As frmOther
    Set beta = New frmOther
    beta.DisplayName = "Beta"
    beta.Show
    lblStatus.Caption = "Another Beta child opened inside MDI Forms."
End Sub

Private Sub cmdClose_Click()

Enter the complete action, including its input checks and calls to helper procedures.

Forms/frmMain.bas · cmdClose_Click

Private Sub cmdClose_Click()
    Unload Me
End Sub

Private Sub cmdIndependent_Click()

Enter the complete action, including its input checks and calls to helper procedures.

Forms/frmMain.bas · cmdIndependent_Click

Private Sub cmdIndependent_Click()
    frmIndependent.Show
    lblStatus.Caption = "Independent window shown outside the MDI container."
End Sub

Copy the complete Forms/frmMain.bas file

Replace the file once; do not append duplicate procedures.

Forms/frmMain.bas

Option Explicit

Public ActiveAlpha As frmDetails
Public ActiveBeta As frmOther

Private Sub Form_Shown()
    Dim alpha As frmDetails
    Dim beta As frmOther
    Dim active As Form
    Set alpha = New frmDetails
    Set beta = New frmOther
    Set ActiveAlpha = alpha
    Set ActiveBeta = beta
    alpha.DisplayName = "Alpha"
    beta.DisplayName = "Beta"
    Debug.Print "active-empty:" & (Me.ActiveForm Is Nothing)
    alpha.Show
    Set active = Me.ActiveForm
    Debug.Print "active-alpha:" & (active Is alpha)
    beta.Show
    Set active = Me.ActiveForm
    Debug.Print "active-beta:" & (active Is beta)
    Me.Arrange vbCascade
    frmIndependent.Show
    lblStatus.Caption = "Two MDI children and one independent window."
End Sub

Private Sub cmdAlpha_Click()
    Dim alpha As frmDetails
    Set alpha = New frmDetails
    alpha.DisplayName = "Alpha"
    alpha.Show
    lblStatus.Caption = "Another Alpha child opened inside MDI Forms."
End Sub

Private Sub cmdBeta_Click()
    Dim beta As frmOther
    Set beta = New frmOther
    beta.DisplayName = "Beta"
    beta.Show
    lblStatus.Caption = "Another Beta child opened inside MDI Forms."
End Sub

Private Sub cmdClose_Click()
    Unload Me
End Sub

Private Sub cmdIndependent_Click()
    frmIndependent.Show
    lblStatus.Caption = "Independent window shown outside the MDI container."
End Sub

`Forms/frmDetails.bas`

Enter these declarations at file scope, before the procedures.

Forms/frmDetails.bas · declarations

Option Explicit

Public DisplayName As String

Private Sub Form_Initialize()

Initialize state before enabling dependent actions. Keep the shared declarations and startup dependencies with this procedure.

Forms/frmDetails.bas · Form_Initialize

Private Sub Form_Initialize()
    Debug.Print "initialize:" & DisplayName
End Sub

Private Sub Form_Load()

Initialize state before enabling dependent actions. Keep the shared declarations and startup dependencies with this procedure.

Forms/frmDetails.bas · Form_Load

Private Sub Form_Load()
    Debug.Print "load:" & DisplayName
End Sub

Private Sub Form_Shown()

Initialize state before enabling dependent actions. Keep the shared declarations and startup dependencies with this procedure.

Forms/frmDetails.bas · Form_Shown

Private Sub Form_Shown()
    lblName.Caption = "Details window: " & DisplayName
    Debug.Print "shown:" & DisplayName
End Sub

Private Sub cmdHide_Click()

Enter the complete action, including its input checks and calls to helper procedures.

Forms/frmDetails.bas · cmdHide_Click

Private Sub cmdHide_Click()
    Me.Hide
    Debug.Print "hidden:" & DisplayName
End Sub

Private Sub cmdUnload_Click()

Enter the complete action, including its input checks and calls to helper procedures.

Forms/frmDetails.bas · cmdUnload_Click

Private Sub cmdUnload_Click()
    Unload Me
End Sub

Private Sub Form_QueryUnload(ByRef Cancel As Integer, ByVal UnloadMode As Integer)

This is the lifetime boundary. Preserve the cancellation signature where present and release resources owned by this Form.

Forms/frmDetails.bas · Form_QueryUnload

Private Sub Form_QueryUnload(ByRef Cancel As Integer, ByVal UnloadMode As Integer)
    Debug.Print "query:" & DisplayName & ":" & UnloadMode
End Sub

Private Sub Form_Unload()

This is the lifetime boundary. Preserve the cancellation signature where present and release resources owned by this Form.

Forms/frmDetails.bas · Form_Unload

Private Sub Form_Unload()
    Debug.Print "unload:" & DisplayName
End Sub

Copy the complete Forms/frmDetails.bas file

Replace the file once; do not append duplicate procedures.

Forms/frmDetails.bas

Option Explicit

Public DisplayName As String

Private Sub Form_Initialize()
    Debug.Print "initialize:" & DisplayName
End Sub

Private Sub Form_Load()
    Debug.Print "load:" & DisplayName
End Sub

Private Sub Form_Shown()
    lblName.Caption = "Details window: " & DisplayName
    Debug.Print "shown:" & DisplayName
End Sub

Private Sub cmdHide_Click()
    Me.Hide
    Debug.Print "hidden:" & DisplayName
End Sub

Private Sub cmdUnload_Click()
    Unload Me
End Sub

Private Sub Form_QueryUnload(ByRef Cancel As Integer, ByVal UnloadMode As Integer)
    Debug.Print "query:" & DisplayName & ":" & UnloadMode
End Sub

Private Sub Form_Unload()
    Debug.Print "unload:" & DisplayName
End Sub

`Forms/frmIndependent.bas`

Enter these declarations at file scope, before the procedures.

Forms/frmIndependent.bas · declarations

Option Explicit

Public DisplayName As String

Private Sub Form_Initialize()

Initialize state before enabling dependent actions. Keep the shared declarations and startup dependencies with this procedure.

Forms/frmIndependent.bas · Form_Initialize

Private Sub Form_Initialize()
    Debug.Print "initialize:" & DisplayName
End Sub

Private Sub Form_Load()

Initialize state before enabling dependent actions. Keep the shared declarations and startup dependencies with this procedure.

Forms/frmIndependent.bas · Form_Load

Private Sub Form_Load()
    Debug.Print "load:" & DisplayName
End Sub

Private Sub Form_Shown()

Initialize state before enabling dependent actions. Keep the shared declarations and startup dependencies with this procedure.

Forms/frmIndependent.bas · Form_Shown

Private Sub Form_Shown()
    lblName.Caption = "Details window: " & DisplayName
    Debug.Print "shown:" & DisplayName
End Sub

Private Sub cmdHide_Click()

Enter the complete action, including its input checks and calls to helper procedures.

Forms/frmIndependent.bas · cmdHide_Click

Private Sub cmdHide_Click()
    Me.Hide
    Debug.Print "hidden:" & DisplayName
End Sub

Private Sub cmdUnload_Click()

Enter the complete action, including its input checks and calls to helper procedures.

Forms/frmIndependent.bas · cmdUnload_Click

Private Sub cmdUnload_Click()
    Unload Me
End Sub

Private Sub cmdCascade_Click()

Enter the complete action, including its input checks and calls to helper procedures.

Forms/frmIndependent.bas · cmdCascade_Click

Private Sub cmdCascade_Click()
    frmMain.Arrange vbCascade
    Debug.Print "arrange:cascade"
End Sub

Private Sub cmdTileHorizontal_Click()

Enter the complete action, including its input checks and calls to helper procedures.

Forms/frmIndependent.bas · cmdTileHorizontal_Click

Private Sub cmdTileHorizontal_Click()
    frmMain.Arrange vbTileHorizontal
    Debug.Print "arrange:horizontal"
End Sub

Private Sub cmdTileVertical_Click()

Enter the complete action, including its input checks and calls to helper procedures.

Forms/frmIndependent.bas · cmdTileVertical_Click

Private Sub cmdTileVertical_Click()
    frmMain.Arrange vbTileVertical
    Debug.Print "arrange:vertical"
End Sub

Private Sub cmdCheckActive_Click()

Enter the complete action, including its input checks and calls to helper procedures.

Forms/frmIndependent.bas · cmdCheckActive_Click

Private Sub cmdCheckActive_Click()
    Debug.Print "active-alpha-now:" & (frmMain.ActiveForm Is frmMain.ActiveAlpha)
    Debug.Print "active-beta-now:" & (frmMain.ActiveForm Is frmMain.ActiveBeta)
    Debug.Print "active-none-now:" & (frmMain.ActiveForm Is Nothing)
End Sub

Private Sub cmdHideActive_Click()

Enter the complete action, including its input checks and calls to helper procedures.

Forms/frmIndependent.bas · cmdHideActive_Click

Private Sub cmdHideActive_Click()
    If Not (frmMain.ActiveForm Is Nothing) Then
        frmMain.ActiveForm.Hide
        Debug.Print "hide-active"
    End If
End Sub

Private Sub Form_QueryUnload(ByRef Cancel As Integer, ByVal UnloadMode As Integer)

This is the lifetime boundary. Preserve the cancellation signature where present and release resources owned by this Form.

Forms/frmIndependent.bas · Form_QueryUnload

Private Sub Form_QueryUnload(ByRef Cancel As Integer, ByVal UnloadMode As Integer)
    Debug.Print "query:" & DisplayName & ":" & UnloadMode
End Sub

Private Sub Form_Unload()

This is the lifetime boundary. Preserve the cancellation signature where present and release resources owned by this Form.

Forms/frmIndependent.bas · Form_Unload

Private Sub Form_Unload()
    Debug.Print "unload:" & DisplayName
End Sub

Copy the complete Forms/frmIndependent.bas file

Replace the file once; do not append duplicate procedures.

Forms/frmIndependent.bas

Option Explicit

Public DisplayName As String

Private Sub Form_Initialize()
    Debug.Print "initialize:" & DisplayName
End Sub

Private Sub Form_Load()
    Debug.Print "load:" & DisplayName
End Sub

Private Sub Form_Shown()
    lblName.Caption = "Details window: " & DisplayName
    Debug.Print "shown:" & DisplayName
End Sub

Private Sub cmdHide_Click()
    Me.Hide
    Debug.Print "hidden:" & DisplayName
End Sub

Private Sub cmdUnload_Click()
    Unload Me
End Sub

Private Sub cmdCascade_Click()
    frmMain.Arrange vbCascade
    Debug.Print "arrange:cascade"
End Sub

Private Sub cmdTileHorizontal_Click()
    frmMain.Arrange vbTileHorizontal
    Debug.Print "arrange:horizontal"
End Sub

Private Sub cmdTileVertical_Click()
    frmMain.Arrange vbTileVertical
    Debug.Print "arrange:vertical"
End Sub

Private Sub cmdCheckActive_Click()
    Debug.Print "active-alpha-now:" & (frmMain.ActiveForm Is frmMain.ActiveAlpha)
    Debug.Print "active-beta-now:" & (frmMain.ActiveForm Is frmMain.ActiveBeta)
    Debug.Print "active-none-now:" & (frmMain.ActiveForm Is Nothing)
End Sub

Private Sub cmdHideActive_Click()
    If Not (frmMain.ActiveForm Is Nothing) Then
        frmMain.ActiveForm.Hide
        Debug.Print "hide-active"
    End If
End Sub

Private Sub Form_QueryUnload(ByRef Cancel As Integer, ByVal UnloadMode As Integer)
    Debug.Print "query:" & DisplayName & ":" & UnloadMode
End Sub

Private Sub Form_Unload()
    Debug.Print "unload:" & DisplayName
End Sub

`Forms/frmOther.bas`

Enter these declarations at file scope, before the procedures.

Forms/frmOther.bas · declarations

Option Explicit

Public DisplayName As String
Private CancelNextClose As Boolean
Private FailNextClose As Boolean

Private Sub Form_Initialize()

Initialize state before enabling dependent actions. Keep the shared declarations and startup dependencies with this procedure.

Forms/frmOther.bas · Form_Initialize

Private Sub Form_Initialize()
    Debug.Print "initialize:" & DisplayName
End Sub

Private Sub Form_Load()

Initialize state before enabling dependent actions. Keep the shared declarations and startup dependencies with this procedure.

Forms/frmOther.bas · Form_Load

Private Sub Form_Load()
    Debug.Print "load:" & DisplayName
End Sub

Private Sub Form_Shown()

Initialize state before enabling dependent actions. Keep the shared declarations and startup dependencies with this procedure.

Forms/frmOther.bas · Form_Shown

Private Sub Form_Shown()
    lblName.Caption = "Details window: " & DisplayName
    Debug.Print "shown:" & DisplayName
End Sub

Private Sub cmdHide_Click()

Enter the complete action, including its input checks and calls to helper procedures.

Forms/frmOther.bas · cmdHide_Click

Private Sub cmdHide_Click()
    Me.Hide
    Debug.Print "hidden:" & DisplayName
End Sub

Private Sub cmdUnload_Click()

Enter the complete action, including its input checks and calls to helper procedures.

Forms/frmOther.bas · cmdUnload_Click

Private Sub cmdUnload_Click()
    Unload Me
End Sub

Private Sub cmdCancelClose_Click()

Enter the complete action, including its input checks and calls to helper procedures.

Forms/frmOther.bas · cmdCancelClose_Click

Private Sub cmdCancelClose_Click()
    CancelNextClose = True
    lblName.Caption = "Next close will be cancelled."
End Sub

Private Sub cmdFailClose_Click()

Enter the complete action, including its input checks and calls to helper procedures.

Forms/frmOther.bas · cmdFailClose_Click

Private Sub cmdFailClose_Click()
    FailNextClose = True
    lblName.Caption = "Next close will report an error."
End Sub

Private Sub Form_QueryUnload(ByRef Cancel As Integer, ByVal UnloadMode As Integer)

This is the lifetime boundary. Preserve the cancellation signature where present and release resources owned by this Form.

Forms/frmOther.bas · Form_QueryUnload

Private Sub Form_QueryUnload(ByRef Cancel As Integer, ByVal UnloadMode As Integer)
    Debug.Print "query:" & DisplayName & ":" & UnloadMode
    If CancelNextClose Then
        CancelNextClose = False
        Cancel = 1
        Debug.Print "cancel-close:" & DisplayName
    End If
    If FailNextClose Then
        FailNextClose = False
        Debug.Print "error-close:" & DisplayName
        Err.Raise 513, "MdiForms", "Requested child close failure"
    End If
End Sub

Private Sub Form_Unload()

This is the lifetime boundary. Preserve the cancellation signature where present and release resources owned by this Form.

Forms/frmOther.bas · Form_Unload

Private Sub Form_Unload()
    Debug.Print "unload:" & DisplayName
End Sub

Copy the complete Forms/frmOther.bas file

Replace the file once; do not append duplicate procedures.

Forms/frmOther.bas

Option Explicit

Public DisplayName As String
Private CancelNextClose As Boolean
Private FailNextClose As Boolean

Private Sub Form_Initialize()
    Debug.Print "initialize:" & DisplayName
End Sub

Private Sub Form_Load()
    Debug.Print "load:" & DisplayName
End Sub

Private Sub Form_Shown()
    lblName.Caption = "Details window: " & DisplayName
    Debug.Print "shown:" & DisplayName
End Sub

Private Sub cmdHide_Click()
    Me.Hide
    Debug.Print "hidden:" & DisplayName
End Sub

Private Sub cmdUnload_Click()
    Unload Me
End Sub

Private Sub cmdCancelClose_Click()
    CancelNextClose = True
    lblName.Caption = "Next close will be cancelled."
End Sub

Private Sub cmdFailClose_Click()
    FailNextClose = True
    lblName.Caption = "Next close will report an error."
End Sub

Private Sub Form_QueryUnload(ByRef Cancel As Integer, ByVal UnloadMode As Integer)
    Debug.Print "query:" & DisplayName & ":" & UnloadMode
    If CancelNextClose Then
        CancelNextClose = False
        Cancel = 1
        Debug.Print "cancel-close:" & DisplayName
    End If
    If FailNextClose Then
        FailNextClose = False
        Debug.Print "error-close:" & DisplayName
        Err.Raise 513, "MdiForms", "Requested child close failure"
    End If
End Sub

Private Sub Form_Unload()
    Debug.Print "unload:" & DisplayName
End Sub

Step 5Keep resources and storage reproducible#

No external resource or migration files are declared. Any inline migration, seed data or local JSON is present in the code above. Runtime application data and private preferences are not included in the archive.

Step 6Check, run and test the result#

Save all files and run Check. Resolve diagnostics before Run. Developer CLI users can work from the extracted folder:

Developer CLI

mcbasic check MdiForms.mcproj
mcbasic run MdiForms.mcproj

Acceptance checklist

Open two document Forms in the workspace.
Open the independent Form and compare its behavior.
Hide and unload a document, then reopen it.
Close the workspace and inspect the resulting application lifetime.

Step 7Make one change and repeat the tests#

Give each document a distinct public title before showing it.

Save a working Git checkpoint first. Change one behavior, Check again and repeat the acceptance checklist. Compare with the downloaded solution if a regression appears.

Source baseline 20f4bfed6b · Build manifest

Build a multi-document workspace

Step 1Prepare a safe practice project#

Step 2Build the Form and set its properties#

frmMain

frmDetails

frmIndependent

frmOther

Step 3Connect the events explicitly#

frmMain

frmDetails

frmIndependent

frmOther

Step 4Enter the complete behavior#

Forms/frmMain.bas

Forms/frmDetails.bas

Forms/frmIndependent.bas

Forms/frmOther.bas

Step 5Keep resources and storage reproducible#

Step 6Check, run and test the result#

Acceptance checklist

Step 7Make one change and repeat the tests#

Continue learning#

`Forms/frmMain.bas`

`Forms/frmDetails.bas`

`Forms/frmIndependent.bas`

`Forms/frmOther.bas`