Passing Parse objectID created on prepareForSegue - swift

Question

I am trying to pass the Parse Class "Conversation" objectId after it's created to another View Controller. When I check the data does not pass to the variable I point to.
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject!) {
// Get the new view controller using [segue destinationViewController].
// Pass the selected object(s) to the new view controller.
let selectedIndex = self.tableView.indexPathForSelectedRow()?.row
let destinationVC = segue.destinationViewController as ConversationViewController
//Save Conversation Data
var convo = PFObject(className: "Conversation")
convo.saveInBackgroundWithBlock{
(success: Bool!, error: NSError!) -> Void in
if (success != nil) {
//Save Selected Person
participant["conversationId"] = convo.objectId as String!
participant.saveInBackground()
}
else{
NSLog("%#", error)
}
}
//Trying to Pass convo.objectId
destinationVC.newConversationId = convo.objectId as String!
}

Answer 1

The problem with the code is that convo.objectId is not set at the point where you use it. It gets set in the completion block of saveInBackgroundWithBlock:, but that block runs after the code that appears underneath it.
So what to do? If the next vc needs the convo object to be saved before it runs, then the correct pattern is to run the segue after the save. Find the point in your code where you are initiating the segue and replace it with the convo.saveInBackgroundWithBlock. Then do the performSegue from within that block.
Edit - Here's how doing this looks in objective-C. In either language, in order to do this, you must initiate the segue from code. Say you have the segue painted from a table view cell in IB (or storyboard) to the next view controller. Delete that segue, and control-drag a new one starting from the view controller which contains the table. (Select the view controller in IB and drag from there. Then, using the attributes inspector, give that segue and identifier, say, "ConvoSegue").
// since a table selection that starts the action, implement the selection delegate method
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
// we decide here that the convo object must be saved, and
// a segue should happen to another vc that needs the convo object:
var convo = PFObject(className: "Conversation")
convo saveInBackgroundWithBlock:^(BOOL success, NSError *error) {
if (!error) {
// now that convo is saved, we can start the segue
[self performSegueWithIdentifier:#"ConvoSegue" sender:convo];
} else {
// don't segue, stay here and deal with the error
}
}];
}
Notice in the above, we passed convo as the sender of the segue. This allows access to it in prepareForSegue. You can skip that if convo is a property of this view controller.
Now prepare for segue looks like yours, except without the asynch save...
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject!) {
// we don't need the selected row from the table view, because we have
// the convo object as the sender
// let selectedIndex = self.tableView.indexPathForSelectedRow()?.row
let destinationVC = segue.destinationViewController as ConversationViewController
// sorry, back to objective-c here:
PFObject *convo = (PFObject)AnyObject; // need a cast to use properly in objective-c
// deleted your save logic. just pass convo's id
//Trying to Pass convo.objectId
destinationVC.newConversationId = convo.objectId as String!
}