Associate an opaque user pointer with the row at index.
The pointer is stored inside the native control, where the D garbage
collector cannot see it. To keep GC-allocated data from being collected
out from under the control, Deft also retains a reference internally for the
control's lifetime; the retained references are released by clear(). (The
native control owns the canonical copy returned by getItemData.)
Associate an opaque user pointer with the row at index.
The pointer is stored inside the native control, where the D garbage collector cannot see it. To keep GC-allocated data from being collected out from under the control, Deft also retains a reference internally for the control's lifetime; the retained references are released by clear(). (The native control owns the canonical copy returned by getItemData.)