If your opponent declares a direct attack and you activate call of the haunted to bring back a monster is the direct attack negated since a monster appeared on your side of the field?

Answer 1

If a potential attack target appears or disappears after the attack is declared, but before the damage step, then a 'replay' occurs. A replay is the continuation or discontinuation of the attack - the attacker is allowed to continue the attack (against a new target if it wishes, or sometimes it might have to choose a new one) or it can forfeit its attack completely for that turn.

So, the opponent declares a direct attack, and you respond with CotH. CotH will resolve and summon a monster, causing a replay. The attacking monster may continue its attack, however it is not possible to perform a direct attack now, so will have to attack the newly summoned monster. Or, it can cancel its attack for that turn.