ios - 在 ViewWillAppear 完成运行之前调用 CellForRowAtIndexPath

Question

我有一个从 Parse 数据库中提取信息并将其显示在 UITableView 中的应用程序。我从 viewWillAppear 函数中的解析中提取信息，并将其显示在 tableView(cellForRowAtIndexPath) 函数中。有时我收到一个错误，因为存储 Parse 信息的数组的长度为 0，并且我尝试访问数组边界之外的索引处的信息。我相信这是因为在 viewWillAppear 完成运行之前调用了 cellForRowAtIndexPath。这是可能的还是我的错误肯定来自其他地方？

编辑:错误不会每次都发生，我找不到重现它的方法

override func viewWillAppear(animated: Bool) {

    //begin ignoring events until the information is finished being pulled
    UIApplication.sharedApplication().beginIgnoringInteractionEvents()

    resultsArray.removeAll(keepCapacity: false)

    //run query
    let query = PFQuery(className: "Answers")
    query.findObjectsInBackgroundWithBlock { (objects, error) -> Void in

        if let objects = objects {

                    //append information to the resultsArray 
                }
            }
            self.tableView.reloadData()
        }
    }
    //information is now pulled, so allow interaction 
   UIApplication.sharedApplication().endIgnoringInteractionEvents()

}


override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCellWithIdentifier("cell", forIndexPath: indexPath) as! answerCell

    // THIS IS WHERE THE ERROR OCCURS
    resultsArray[indexPath.row].imageFile.getDataInBackgroundWithBlock { (data, error) -> Void in

        //set image within cell
    }
    return cell
}

Answer 1

我建议您将数据从 Parse 加载到一个临时数组中，然后在您调用 reloadData 之前将其分配给您的属性数组 - 这将避免任何潜在的竞争条件并消除对removeAll 这可能是您问题的重要组成部分；

override func viewWillAppear(animated: Bool) {

    //begin ignoring events until the information is finished being pulled
    UIApplication.sharedApplication().beginIgnoringInteractionEvents()



    //run query
    let query = PFQuery(className: "Answers")
    query.findObjectsInBackgroundWithBlock { (objects, error) -> Void in

        var localArray=[SomeType]()

        if let objects = objects {

                    //append information to the localArray 
                }
            }
            self.resultsArray=localArray
            self.tableView.reloadData()
        }
    }
    //information is now pulled, so allow interaction 
   UIApplication.sharedApplication().endIgnoringInteractionEvents()

}