During the Manchu-led Qing dynasty, an emperor would write an edict to select one of his sons in secret. An emperor could have numerous sons by women of various ranks, so the heir might not be obvious until it was announced.
In the Qing dynasty under Manchu leadership, an emperor would issue a private proclamation to designate one of his sons as the next ruler. Given that emperors often had many sons from different social backgrounds, the chosen successor might not become clear until the official declaration.