McBasic™Get McBasic™ ↗Select from a compact list
Populate a ComboBox and handle selection changes.
A selection index identifies a position, not a stable business ID. Use the initial items to understand Change first; then use the ChoiceBinding lesson for typed values backed by records. Handle the unselected state before reading an item.
Step 1Prepare a safe practice project#
Extract the archive into a new writable folder, separate from your own application. Open ComboBox.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
{
"schemaVersion": 1,
"projectId": "4e306f3b-4a6d-4a89-bf54-16fb3cc6db32",
"name": "ComboBoxSample",
"kind": "DesktopApp",
"language": {
"dialect": "McBasic1",
"requireExplicit": true,
"compare": "Binary",
"defaultArrayBase": 0
},
"application": {
"bundleIdentifier": "com.mcbasic.samples.combobox",
"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"
}
],
"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 | "ComboBox — McBasic" |
Width | 520 |
Height | 260 |
MinWidth | 420 |
MinHeight | 220 |
cboChoice · exact Inspector values
| Property | Value |
|---|---|
Left | 36 |
Top | 48 |
Width | 260 |
Height | 36 |
Items | "First choice\nSecond choice\nThird choice" |
Sorted | True |
DropDownStyle | "DropDownList" |
MaxDropDownItems | 6 |
Padding | "8,4,8,4" |
SelectedIndex | 0 |
TabIndex | 0 |
TabStop | True |
| Anchor edges | Left, Top |
lblStatus · exact Inspector values
| Property | Value |
|---|---|
Left | 36 |
Top | 112 |
Width | 420 |
Height | 40 |
Caption | "Choose an item from the list." |
| Anchor edges | Left, Top |
Step 3Connect the events explicitly#
frmMain
| Object | Event | Procedure | Parameters |
|---|---|---|---|
cboChoice | Change | cboChoice_Change | Change() |
| Form | Load | Form_Load | () |
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.
Option ExplicitPrivate Sub Form_Load()
Initialize state before enabling dependent actions. Keep the shared declarations and startup dependencies with this procedure.
Private Sub Form_Load()
cboChoice.Items.Add "Fourth choice"
cboChoice.Items.RemoveAt 1
cboChoice.SelectedItem = "Fourth choice"
cboChoice.DropDownStyle = "DropDown"
cboChoice.Text = "Custom entry"
lblStatus.Caption = CStr(cboChoice.Items.Count) & " items — sorted=" & CStr(cboChoice.Sorted) & " — " & cboChoice.Text & " — max " & CStr(cboChoice.MaxDropDownItems) & " — padding " & cboChoice.Padding
End SubPrivate Sub cboChoice_Change()
Read the current value or selection and update its dependent interface. The binding above determines which object calls this handler.
Private Sub cboChoice_Change()
Dim itemList As Collection
Dim selected As Variant
Set itemList = cboChoice.Items
selected = cboChoice.SelectedItem
If cboChoice.SelectedIndex >= 0 Then
lblStatus.Caption = "Selection changed in the ComboBox."
Else
lblStatus.Caption = "No item is selected."
End If
End SubCopy the complete Forms/frmMain.bas file
Replace the file once; do not append duplicate procedures.
Option Explicit
Private Sub Form_Load()
cboChoice.Items.Add "Fourth choice"
cboChoice.Items.RemoveAt 1
cboChoice.SelectedItem = "Fourth choice"
cboChoice.DropDownStyle = "DropDown"
cboChoice.Text = "Custom entry"
lblStatus.Caption = CStr(cboChoice.Items.Count) & " items — sorted=" & CStr(cboChoice.Sorted) & " — " & cboChoice.Text & " — max " & CStr(cboChoice.MaxDropDownItems) & " — padding " & cboChoice.Padding
End Sub
Private Sub cboChoice_Change()
Dim itemList As Collection
Dim selected As Variant
Set itemList = cboChoice.Items
selected = cboChoice.SelectedItem
If cboChoice.SelectedIndex >= 0 Then
lblStatus.Caption = "Selection changed in the ComboBox."
Else
lblStatus.Caption = "No item is selected."
End If
End SubStep 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:
mcbasic check ComboBox.mcproj
mcbasic run ComboBox.mcprojAcceptance checklist
- Select each item and verify the result.
- Use the keyboard to move through the choices.
- Inspect the initial selection before the first user action.
Step 7Make one change and repeat the tests#
Add one choice and ensure the handler does not depend on the old item count.
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.
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