fix(mfcwx): stop deferred tab activation from using a deleted main frame

port/mfcwx/src/app.cpp

@@ -236,6 +236,7 @@ int main(int argc, char** argv) { return wxEntry(argc, argv); }
 IMPLEMENT_DYNAMIC(CWinApp, CWinThread)
 
 BEGIN_MESSAGE_MAP(CWinApp, CWinThread)
+    ON_COMMAND(ID_APP_EXIT, &CWinApp::OnAppExit)
     ON_COMMAND_EX_RANGE(ID_FILE_MRU_FILE1, ID_FILE_MRU_FILE16, &CWinApp::OnOpenRecentFile)
     ON_UPDATE_COMMAND_UI(ID_FILE_MRU_FILE1, &CWinApp::OnUpdateRecentFileMenu)
 END_MESSAGE_MAP()

port/mfcwx/src/docview.cpp

@@ -88,6 +88,14 @@ wxAuiNotebook* ClientNotebook(CMDIFrameWnd* frame) {
     return frame && frame->m_hWndMDIClient ? wxDynamicCast(ToWx(frame->m_hWndMDIClient), wxAuiNotebook) : nullptr;
 }
 
+// Resolves a frame by its window at call time, so deferred calls never use a deleted frame object.
+CMDIFrameWnd* LiveMDIFrame(HWND hWnd) {
+    if (!hWnd || !IsWindow(hWnd))
+        return nullptr;
+    CWnd* wnd = PermanentWnd(ToWx(hWnd));
+    return wnd && wnd->IsKindOf(RUNTIME_CLASS(CMDIFrameWnd)) ? static_cast<CMDIFrameWnd*>(wnd) : nullptr;
+}
+
 CMDIFrameWnd* MainMDIFrame() {
     CWinApp* app = AfxGetApp();
     CWnd* main = app ? app->m_pMainWnd : nullptr;
@@ -893,9 +901,11 @@ BOOL CMDIFrameWnd::OnCreateClient(LPCREATESTRUCT, CCreateContext*) {
         auto* sizer = new wxBoxSizer(wxVERTICAL);
         sizer->Add(book, 1, wxEXPAND);
         frame->SetSizer(sizer);
-        book->Bind(wxEVT_AUINOTEBOOK_PAGE_CHANGED, [this](wxAuiNotebookEvent& e) {
+        HWND frameWnd = m_hWnd;
+        book->Bind(wxEVT_AUINOTEBOOK_PAGE_CHANGED, [frameWnd](wxAuiNotebookEvent& e) {
             e.Skip();
-            OnChildActivated();
+            if (CMDIFrameWnd* mdi = LiveMDIFrame(frameWnd))
+                mdi->OnChildActivated();
         });
         book->Bind(wxEVT_AUINOTEBOOK_PAGE_CLOSE, [book](wxAuiNotebookEvent& e) {
             e.Veto();
@@ -1117,11 +1127,13 @@ BOOL CMDIChildWnd::DestroyWindow() {
                 book->RemovePage(static_cast<size_t>(index));
         }
         DestroyWxWindow(panel);
-        if (mdi)
-            PostToMainThread([mdi] {
-                if (mdi->m_hWnd)
-                    mdi->OnChildActivated();
+        if (mdi) {
+            HWND frameWnd = mdi->m_hWnd;
+            PostToMainThread([frameWnd] {
+                if (CMDIFrameWnd* live = LiveMDIFrame(frameWnd))
+                    live->OnChildActivated();
             });
+        }
         return TRUE;
     });
 }

port/mfcwx/src/snapshot.cpp

@@ -129,6 +129,7 @@ wxWindow* ActiveDialog() {
 // Development aid: MFCWX_AUTOMATION=file runs one step per line on a timer, for UI tests:
 //   command <id>        WM_COMMAND to the main window
 //   button <id>         WM_COMMAND (BN_CLICKED) to the topmost dialog
+//   close               WM_CLOSE to the main window
 //   text <id> <text>    sets the text of a control of the topmost dialog
 //   tab <n> / closetab <n>   clicks the n-th MDI tab or its close button
 //   tabs                print the MDI tabs
@@ -161,6 +162,10 @@ class AutomationTimer : public wxTimer {
                 target->PostMessage(WM_COMMAND, MAKEWPARAM(id, BN_CLICKED), 0);
             else
                 fprintf(stderr, "mfcwx automation: no target window\n");
+        } else if (op == "close") {
+            CWnd* main = AfxGetMainWnd();
+            if (main && main->m_hWnd)
+                main->PostMessage(WM_CLOSE, 0, 0);
         } else if (op == "text") {
             int id = 0;
             in >> id;