In BitShares 2 your transactions gets and id once included into the blockchain. There actually is no "txhash".
The id is of the form 1.11.x
something like this:
locked >>> get_object 1.11.1000
get_object 1.11.1000
[{
    "id": "1.11.1000",
    "op": [
      37,{
        "fee": {
          "amount": 0,
          "asset_id": "1.3.0"
        },
        "deposit_to_account": "1.2.11268",
        "balance_to_claim": "1.15.28529",
        "balance_owner_key": "BTS8jcFd3ZNYvW11Sh2uYivWQb17Yd2zuxe7Ee4EDag9gjA9YqSJH",
        "total_claimed": {
          "amount": 1199997594,
          "asset_id": "1.3.0"
        }
      }
    ],
    "result": [
      0,{}
    ],
    "block_num": 6073,
    "trx_in_block": 0,
    "op_in_trx": 8,
    "virtual_op": 32500
  }
]
and there is no way of known the id before it has been included in a block .. thus the callback ..