Use wxGridCellAttrPtr instead of manual DecRef() calls

Provide GetAttrPtr() and GetCellAttrPtr() convenience functions that can
be used instead of the original Ptr-less versions to avoid the need to
manually call DecRef() on the returned wxGridCellAttr pointers.

No real changes, just simplify the code and make it safer.

interface/wx/grid.h

@@ -976,6 +976,10 @@ public:
     changing their attributes from the defaults. An object of this class may be
     returned by wxGridTableBase::GetAttr().
 
+    Note that objects of this class are reference-counted and it's recommended
+    to use wxGridCellAttrPtr smart pointer class when working with them to
+    avoid memory leaks.
+
     @library{wxcore}
     @category{grid}
 */
@@ -1257,6 +1261,20 @@ protected:
     virtual ~wxGridCellAttr();
 };
 
+/**
+    Smart pointer wrapping wxGridCellAttr.
+
+    wxGridCellAttrPtr takes ownership of wxGridCellAttr passed to it on
+    construction and calls DecRef() on it automatically when it is destroyed.
+    It also provides transparent access to wxGridCellAttr methods by allowing
+    to use objects of this class as if they were wxGridCellAttr pointers.
+
+    @since 3.1.4
+
+    @category{grid}
+*/
+typedef wxObjectDataPtr<wxGridCellAttr> wxGridCellAttrPtr;
+
 /**
     Base class for header cells renderers.
 
@@ -1459,7 +1477,7 @@ public:
         the cell attribute having the highest precedence.
 
         Notice that the caller must call DecRef() on the returned pointer if it
-        is non-@NULL.
+        is non-@NULL. GetAttrPtr() method can be used to do this automatically.
 
         @param row
             The row of the cell.
@@ -1474,6 +1492,17 @@ public:
     virtual wxGridCellAttr *GetAttr(int row, int col,
                                     wxGridCellAttr::wxAttrKind kind) const;
 
+    /**
+        Get the attribute to use for the specified cell.
+
+        This method is identical to GetAttr(), but returns a smart pointer,
+        which frees the caller from the need to call DecRef() manually.
+
+        @since 3.1.4
+     */
+    wxGridCellAttrPtr GetAttrPtr(int row, int col,
+                                 wxGridCellAttr::wxAttrKind kind) const;
+
     /*!
         @name Setting attributes.
 
@@ -2121,10 +2150,24 @@ public:
         By default this function is simply forwarded to
         wxGridCellAttrProvider::GetAttr() but it may be overridden to handle
         attributes directly in the table.
+
+        Prefer to use GetAttrPtr() to avoid the need to call DecRef() on the
+        returned pointer manually.
      */
     virtual wxGridCellAttr *GetAttr(int row, int col,
                                     wxGridCellAttr::wxAttrKind kind);
 
+    /**
+        Return the attribute for the given cell.
+
+        This method is identical to GetAttr(), but returns a smart pointer,
+        which frees the caller from the need to call DecRef() manually.
+
+        @since 3.1.4
+     */
+    wxGridCellAttrPtr GetAttrPtr(int row, int col,
+                                 wxGridCellAttr::wxAttrKind kind);
+
     /**
         Set attribute of the specified cell.
 
@@ -4939,10 +4982,24 @@ public:
         attribute is created, associated with the cell and returned. In any
         case the caller must call DecRef() on the returned pointer.
 
+        Prefer to use GetOrCreateCellAttrPtr() to avoid the need to call
+        DecRef() on the returned pointer.
+
         This function may only be called if CanHaveAttributes() returns @true.
     */
     wxGridCellAttr *GetOrCreateCellAttr(int row, int col) const;
 
+    /**
+        Returns the attribute for the given cell creating one if necessary.
+
+        This method is identical to GetOrCreateCellAttr(), but returns a smart
+        pointer, which frees the caller from the need to call DecRef()
+        manually.
+
+        @since 3.1.4
+     */
+    wxGridCellAttrPtr GetOrCreateCellAttrPtr(int row, int col) const;
+
     /**
         Returns a base pointer to the current table object.