computePrefix
⚠️ Deprecated ⚠️
This is deprecated since version 4.10.
GtkEntryCompletion will be removed in GTK 5.
---Computes the common prefix that is shared by all rows in @completion that start with @key.
If no row matches @key, null will be returned. Note that a text column must have been set for this function to work, see method@Gtk.EntryCompletion.set_text_column for details.
Return
The common prefix all rows starting with @key
Parameters
key
The text to complete for