Instruction file imported from alxayo/vb-migration-harness (.github/instructions/webforms-vb.instructions.md). Copyright stays with the author.

VB WebForms Code-Behind: Extraction Rules

Reading & Understanding First

• Treat each Page_Load, Button_Click, GridView_RowCommand etc. as an entry point.
• For each entry point, identify:
  • Inputs: form fields, Request.QueryString, ViewState, Session variables
  • Outputs: UI bindings, Response.Redirect, Label.Text, GridView data sources
  • Side effects: DB writes, SOAP calls, file I/O
  • Hidden invariants: conditional branches, null checks, default values applied silently
• Do not assume two event handlers that look similar DO the same thing — verify each one.
• The custom expression evaluator / transformation module is a critical black box: do not modify it without golden-master tests in place.

Before Any Edit

• Confirm a characterization test exists that covers the event handler's workflow.
• If no test exists, stop and create one first.
• Use #codebase and #usages to find all callers of any method you intend to move.

Extraction Pattern (for each event handler)

1. Enumerate the handler's inputs, outputs, and side-effects.
2. Extract pure logic (validation, calculation, transformation) into C# in /src/Domain/.
3. Extract use-case orchestration (call domain + call infra) into C# in /src/App/.
4. Leave the VB code-behind as a thin adapter:

   ' After extraction — VB event handler should look like this:
   Protected Sub btnSubmit_Click(sender As Object, e As EventArgs)
       Dim request = New MyRequest(txtField.Text, ddlOption.SelectedValue)
       Dim result = _myService.Execute(request)   ' C# service via COM-interop or side-by-side
       lblResult.Text = result.Message
   End Sub

5. Verify tests still pass; fix regressions before proceeding.

Do NOT Do

• Do not refactor VB to be "cleaner" unless it helps extraction.
• Do not move logic in the same file without a test oracle in place.
• Do not silently drop ViewState or Session usage — catalog it; some hold genuine state.
• Do not convert DataSet/DataTable to something else in the VB layer; leave that for the C# Data Modernizer step.

AjaxControlToolkit

• Document every control used and what user action it enables.
• Do not attempt in-place replacement; note it in the workflow inventory for Phase 6 (UI Rebuild).
• During extraction, treat AJAX behaviors as UI concerns only — they don't affect the business rules being extracted.