Fix unwanted message boxes in widgets sample once and for all

Add IsUsingLogWindow() that can be used to check if the log messages go
into the listbox instead of being shown in a message box, which was
annoying when starting or quitting the sample.

This is a bit more complicated than the hack previously used in
TextWidgetsPage::OnText(), but more general and can be easily reused for
the focus loss messages, for example.

samples/widgets/widgets.cpp

@@ -139,6 +139,13 @@ const wxChar *WidgetsCategories[MAX_PAGES] = {
 class WidgetsApp : public wxApp
 {
 public:
+    WidgetsApp()
+    {
+#if USE_LOG
+        m_logTarget = NULL;
+#endif // USE_LOG
+    }
+
     // override base class virtuals
     // ----------------------------
 
@@ -146,8 +153,20 @@ public:
     // initialization (doing it here and not in the ctor allows to have an error
     // return: if OnInit() returns false, the application terminates)
     virtual bool OnInit() wxOVERRIDE;
+
+    // real implementation of WidgetsPage method with the same name
+    bool IsUsingLogWindow() const;
+
+private:
+#if USE_LOG
+    wxLog* m_logTarget;
+#endif // USE_LOG
+
+    wxDECLARE_NO_COPY_CLASS(WidgetsApp);
 };
 
+wxDECLARE_APP(WidgetsApp); // This provides a convenient wxGetApp() accessor.
+
 // Define a new frame type: this is going to be our main frame
 class WidgetsFrame : public wxFrame
 {
@@ -375,9 +394,22 @@ bool WidgetsApp::OnInit()
     wxFrame *frame = new WidgetsFrame(title + " widgets demo");
     frame->Show();
 
+#if USE_LOG
+    m_logTarget = wxLog::GetActiveTarget();
+#endif // USE_LOG
+
     return true;
 }
 
+bool WidgetsApp::IsUsingLogWindow() const
+{
+#if USE_LOG
+    return wxLog::GetActiveTarget() == m_logTarget;
+#else // !USE_LOG
+    return false;
+#endif // USE_LOG
+}
+
 // ----------------------------------------------------------------------------
 // WidgetsFrame construction
 // ----------------------------------------------------------------------------
@@ -1200,8 +1232,13 @@ void WidgetsFrame::OnSetHint(wxCommandEvent& WXUNUSED(event))
 
 void WidgetsFrame::OnWidgetFocus(wxFocusEvent& event)
 {
-    wxLogMessage("Widgets %s focus",
-                 event.GetEventType() == wxEVT_SET_FOCUS ? "got" : "lost");
+    // Don't show annoying message boxes when starting or closing the sample,
+    // only log these events in our own logger.
+    if ( wxGetApp().IsUsingLogWindow() )
+    {
+        wxLogMessage("Widgets %s focus",
+                     event.GetEventType() == wxEVT_SET_FOCUS ? "got" : "lost");
+    }
 
     event.Skip();
 }
@@ -1384,3 +1421,9 @@ wxCheckBox *WidgetsPage::CreateCheckBoxAndAddToSizer(wxSizer *sizer,
 
     return checkbox;
 }
+
+/* static */
+bool WidgetsPage::IsUsingLogWindow()
+{
+    return wxGetApp().IsUsingLogWindow();
+}