Improve wxListBox::GetCountPerPage() in wxGTK and wxOSX

Provide native implementation of this function instead of using the ad hoc one
in common code, which didn't really work -- so remove it completely now.

Closes #17189.

include/wx/gtk/listbox.h

@@ -75,6 +75,7 @@ public:
     virtual void EnsureVisible(int n) wxOVERRIDE;
 
     virtual int GetTopItem() const wxOVERRIDE;
+    virtual int GetCountPerPage() const wxOVERRIDE;
 
     virtual void Update() wxOVERRIDE;
 

include/wx/listbox.h

@@ -73,7 +73,7 @@ public:
     virtual void EnsureVisible(int n);
 
     virtual int GetTopItem() const { return wxNOT_FOUND; }
-    virtual int GetCountPerPage() const;
+    virtual int GetCountPerPage() const { return -1; }
 
     // a combination of Append() and EnsureVisible(): appends the item to the
     // listbox and ensures that it is visible i.e. not scrolled out of view
@@ -136,8 +136,6 @@ protected:
     // single selection mode on platforms other than MSW).
     void UpdateOldSelections();
 
-    wxCoord GetLineHeight() const;
-
 private:
     wxDECLARE_NO_COPY_CLASS(wxListBoxBase);
 };

include/wx/osx/core/private.h

@@ -615,6 +615,7 @@ public:
 
     virtual void            ListScrollTo( unsigned int n ) = 0;
     virtual int             ListGetTopItem() const = 0;
+    virtual int             ListGetCountPerPage() const = 0;
     virtual void            UpdateLine( unsigned int n, wxListWidgetColumn* col = NULL ) = 0;
     virtual void            UpdateLineToEnd( unsigned int n) = 0;
 

include/wx/osx/listbox.h

@@ -109,6 +109,7 @@ public:
     virtual void EnsureVisible(int n) wxOVERRIDE;
 
     virtual int GetTopItem() const wxOVERRIDE;
+    virtual int GetCountPerPage() const wxOVERRIDE;
 
     virtual wxVisualAttributes GetDefaultAttributes() const wxOVERRIDE
     {

interface/wx/listbox.h

@@ -301,7 +301,9 @@ public:
         Return the number of items that can fit vertically in the visible area of
         the listbox.
 
-        Returns -1 if the number of items per page couldn't be determined.
+        Returns -1 if the number of items per page couldn't be determined. On
+        wxGTK this method can only determine the number of items per page if
+        there is at least one item in the listbox.
 
         @since 3.1.0
     */

src/common/lboxcmn.cpp

@@ -34,15 +34,6 @@
     #include "wx/dcclient.h"
 #endif
 
-// the spacing between the lines (in report mode)
-static const int LINE_SPACING = 0;
-
-#ifdef __WXGTK__
-static const int EXTRA_HEIGHT = 6;
-#else
-static const int EXTRA_HEIGHT = 4;
-#endif
-
 extern WXDLLEXPORT_DATA(const char) wxListBoxNameStr[] = "listBox";
 
 // ============================================================================
@@ -349,24 +340,4 @@ void wxListBoxBase::EnsureVisible(int WXUNUSED(n))
     // the base class version does nothing (the only alternative would be to
     // call SetFirstItem() but this is probably even more stupid)
 }
-
-wxCoord wxListBoxBase::GetLineHeight() const
-{
-    wxListBoxBase *self = wxConstCast(this, wxListBoxBase);
-
-    wxClientDC dc( self );
-    dc.SetFont( GetFont() );
-
-    wxCoord y;
-    dc.GetTextExtent(wxT("H"), NULL, &y);
-
-    y += EXTRA_HEIGHT;
-
-    return y + LINE_SPACING;
-}
-
-int wxListBoxBase::GetCountPerPage() const
-{
-    return GetClientSize().y / GetLineHeight();
-}
 #endif // wxUSE_LISTBOX

src/gtk/listbox.cpp

@@ -780,6 +780,37 @@ int wxListBox::GetTopItem() const
     return idx;
 }
 
+int wxListBox::GetCountPerPage() const
+{
+    wxGtkTreePath path;
+    GtkTreeViewColumn *column;
+
+    if ( !gtk_tree_view_get_path_at_pos
+          (
+            m_treeview,
+            0,
+            0,
+            path.ByRef(),
+            &column,
+            NULL,
+            NULL
+          ) )
+    {
+        return -1;
+    }
+
+    GdkRectangle rect;
+    gtk_tree_view_get_cell_area(m_treeview, path, column, &rect);
+
+    if ( !rect.height )
+        return -1;
+
+    GdkRectangle vis;
+    gtk_tree_view_get_visible_rect(m_treeview, &vis);
+
+    return vis.height / rect.height;
+}
+
 // ----------------------------------------------------------------------------
 // hittest
 // ----------------------------------------------------------------------------

src/osx/cocoa/listbox.mm

@@ -130,6 +130,7 @@ public :
     virtual void            ListScrollTo( unsigned int n ) wxOVERRIDE ;
 
     virtual int             ListGetTopItem() const wxOVERRIDE;
+    virtual int             ListGetCountPerPage() const wxOVERRIDE;
 
     // accessing content
 
@@ -548,6 +549,13 @@ int wxListWidgetCocoaImpl::ListGetTopItem() const
     return range.location;
 }
 
+int wxListWidgetCocoaImpl::ListGetCountPerPage() const
+{
+    NSScrollView *scrollView = [m_tableView enclosingScrollView];
+    NSRect visibleRect = scrollView.contentView.visibleRect;
+    return (int) (visibleRect.size.height / [m_tableView rowHeight]);
+}
+
 void wxListWidgetCocoaImpl::UpdateLine( unsigned int WXUNUSED(n), wxListWidgetColumn* WXUNUSED(col) )
 {
     // TODO optimize

src/osx/listbox_osx.cpp

@@ -150,6 +150,11 @@ int wxListBox::GetTopItem() const
     return GetListPeer()->ListGetTopItem();
 }
 
+int wxListBox::GetCountPerPage() const
+{
+    return GetListPeer()->ListGetCountPerPage();
+}
+
 void wxListBox::DoDeleteOneItem(unsigned int n)
 {
     wxCHECK_RET( IsValid(n), wxT("invalid index in wxListBox::Delete") );