test

ToolTalk User's Guide

Adding Message Callbacks

When a request contains a message callback routine, the callback routine is automatically called when the reply is received to examine the results of the reply and take appropriate actions.

Note -

Callbacks are called in reverse order of registration (for example, the most recently added callback is called first).

You use tt_message_callback_add to add the callback routine to your request. When the reply comes back and the reply message has been processed through the callback routine, the reply message must be destroyed before the callback function returns TT_CALLBACK_PROCESSED. To destroy the reply message, use tt_message_destroy, as illustrated in Example 8-4.

Example 8-4 Destroying a Message

Tt_callback_action
sample_msg_callback(Tt_message m, Tt_pattern p)
{
	... process the reply msg ...

	tt_message_destroy(m);
	return TT_CALLBACK_PROCESSED;
}

The following code sample is a callback routine, cntl_msg_callback, that examines the state field of the reply and takes action if the state is started, handled, or failed.

/*
 * Default callback for all the ToolTalk messages we send.
 */

Tt_callback_action
cntl_msg_callback(m, p)
     Tt_message m;
     Tt_pattern p;
{
	int		mark;
	char		msg[255];
	char		*errstr;


	mark = tt_mark();
	switch (tt_message_state(m)) {
	      case TT_STARTED:
		    xv_set(cntl_ui_base_window, FRAME_LEFT_FOOTER,
		       "Starting editor...", NULL);
		    break;
	      case TT_HANDLED:
		    xv_set(cntl_ui_base_window, FRAME_LEFT_FOOTER, "", NULL);
		    break;
	      case TT_FAILED:
		    errstr = tt_message_status_string(m);
		    if (tt_pointer_error(errstr) == TT_OK && errstr) {
			sprintf(msg,"%s failed: %s", tt_message_op(m), errstr);
		    } else if (tt_message_status(m) == TT_ERR_NO_MATCH) {
			sprintf(msg,"%s failed: Couldn't contact editor",
				tt_message_op(m),
				tt_status_message(tt_message_status(m)));
		    } else {
			sprintf(msg,"%s failed: %s",
				tt_message_op(m),
				tt_status_message(tt_message_status(m)));
		    }
		    xv_set(cntl_ui_base_window, FRAME_LEFT_FOOTER, msg, NULL);
		    break;
	      default:
		    break;
	}
	/*
	 * no further action required for this message. Destroy it
	 * and return TT_CALLBACK_PROCESSED so no other callbacks will
	 * be run for the message.
	 */
	tt_message_destroy(m);
	tt_release(mark);
	return TT_CALLBACK_PROCESSED;
}

You can also add callbacks to static patterns by attaching a callback to the opnum of a signature in a ptype. When a message is delivered because it matched a static pattern with an opnum, the ToolTalk service checks for any callbacks attached to the opnum and runs them.