Add wxDataViewRendererBase::PrepareForItem() helper.

For calling SetValue() and SetAttr() consistently, instead of having the
same code duplicated all over the place.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65950 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/dvrenderers.h

@@ -118,6 +118,10 @@ public:
 
     wxString GetVariantType() const             { return m_variantType; }
 
+    // helper that calls SetValue and SetAttr:
+    void PrepareForItem(const wxDataViewModel *model,
+                        const wxDataViewItem& item, unsigned column);
+
     // renderer properties:
     virtual void SetMode( wxDataViewCellMode mode ) = 0;
     virtual wxDataViewCellMode GetMode() const = 0;