传递在prepareForSegue上创建的Parse objectID

Question

我正在尝试将Parse Class“Conversation”objectId传递给另一个View Controller。当我检查数据没有传递给我指向的变量。

 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

代码的问题是convo.objectId未设置在您使用它的位置。它在saveInBackgroundWithBlock:的完成块中设置，但该块在显示在其下方的代码之后运行。

那该怎么办？如果下一个vc需要在运行之前保存convo对象，那么正确的模式是在保存后运行segue。在代码中找到启动segue的位置，并将其替换为convo.saveInBackgroundWithBlock。然后从该块中执行performSegue。

编辑 - 以下是在Objective-C中执行此操作的方法。在任何一种语言中，为了做到这一点，你必须从代码中启动segue。假设你有从IB（或故事板）中的表格视图单元格绘制到下一个视图控制器的segue。删除该segue，然后从包含表的视图控制器开始控制拖动一个新的。 （在IB中选择视图控制器并从那里拖动。然后，使用属性检查器，给出该segue和标识符，例如“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
        }
    }];
}

注意上面，我们通过convo作为segue的发送者。这允许在prepareForSegue中访问它。如果convo是此视图控制器的属性，则可以跳过此步骤。

现在准备看起来像你的segue，除非没有asynch保存......

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!
}