Implement EmptyUndoBuffer() for wxTextCtrl in wxMSW too

The relevant code was already present in MSWCreateText(), so just
extract it into its own function.

include/wx/msw/textctrl.h

@@ -64,6 +64,9 @@ public:
 
     virtual void Redo() wxOVERRIDE;
     virtual bool CanRedo() const wxOVERRIDE;
+#if wxUSE_RICHEDIT
+    virtual void EmptyUndoBuffer() wxOVERRIDE;
+#endif // wxUSE_RICHEDIT
 
     virtual void SetInsertionPointEnd() wxOVERRIDE;
     virtual long GetInsertionPoint() const wxOVERRIDE;

interface/wx/textentry.h

@@ -168,8 +168,9 @@ public:
     /**
         Delete the undo history.
 
-        Currently only implemented under macOS and only for multiline text
+        Currently only implemented in wxMSW (for controls using wxTE_RICH2
-        controls, does nothing in the other ports.
+        style only) and wxOSX (for multiline text controls only), does nothing
+        in the other ports or for the controls not using the appropriate styles.
 
         @since 3.1.6
     */

src/msw/textctrl.cpp

@@ -690,33 +690,16 @@ bool wxTextCtrl::MSWCreateText(const wxString& value,
         ::SendMessage(GetHwnd(), EM_SETMARGINS, wParam, lParam);
     }
 
-#if wxUSE_RICHEDIT && wxUSE_OLE && defined(wxHAS_TOM_H)
+#if wxUSE_RICHEDIT
     // For RichEdit >= 4, SetFont(), called above from MSWCreateControl(), uses
     // EM_SETCHARFORMAT which affects the undo buffer, meaning that CanUndo()
-    // for a newly created control returns true, which is unexpected. To avoid
+    // for a newly created control returns true, which is unexpected, so clear
-    // this, we explicitly use Undo(tomFalse) here to clear the undo buffer.
+    // the undo buffer.
-    // And since Undo(tomFalse) also disables the undo buffer, we need to
-    // enable it again immediately after clearing by calling Undo(tomTrue).
     if ( GetRichVersion() >= 4 )
     {
-        wxCOMPtr<IRichEditOle> pRichEditOle;
+        EmptyUndoBuffer();
-        if ( SendMessage(GetHwnd(), EM_GETOLEINTERFACE,
-                         0, (LPARAM)&pRichEditOle) && pRichEditOle )
-        {
-            wxCOMPtr<ITextDocument> pDoc;
-            HRESULT hr = pRichEditOle->QueryInterface
-                                       (
-                                        wxIID_PPV_ARGS(ITextDocument, &pDoc)
-                                       );
-            if ( SUCCEEDED(hr) )
-            {
-                hr = pDoc->Undo(tomFalse, NULL);
-                if ( SUCCEEDED(hr) )
-                    pDoc->Undo(tomTrue, NULL);
-            }
-        }
     }
-#endif // wxUSE_RICHEDIT && wxHAS_TOM_H
+#endif // wxUSE_RICHEDIT
 
     return true;
 }
@@ -2012,6 +1995,37 @@ bool wxTextCtrl::CanRedo() const
     return wxTextEntry::CanRedo();
 }
 
+#if wxUSE_RICHEDIT
+
+void wxTextCtrl::EmptyUndoBuffer()
+{
+#if wxUSE_OLE && defined(wxHAS_TOM_H)
+    // We need to use Undo(tomFalse) to clear the undo buffer, but calling it
+    // also disables the undo buffer, so we need to enable it again immediately
+    // after clearing by calling Undo(tomTrue).
+    if ( GetRichVersion() >= 4 )
+    {
+        wxCOMPtr<IRichEditOle> pRichEditOle;
+        if ( SendMessage(GetHwnd(), EM_GETOLEINTERFACE,
+                         0, (LPARAM)&pRichEditOle) && pRichEditOle )
+        {
+            wxCOMPtr<ITextDocument> pDoc;
+            HRESULT hr = pRichEditOle->QueryInterface
+                                       (
+                                        wxIID_PPV_ARGS(ITextDocument, &pDoc)
+                                       );
+            if ( SUCCEEDED(hr) )
+            {
+                hr = pDoc->Undo(tomFalse, NULL);
+                if ( SUCCEEDED(hr) )
+                    pDoc->Undo(tomTrue, NULL);
+            }
+        }
+    }
+#endif // wxUSE_OLE && wxHAS_TOM_H
+}
+#endif // wxUSE_RICHEDIT
+
 // ----------------------------------------------------------------------------
 // caret handling (Windows only)
 // ----------------------------------------------------------------------------