如何使用Swift在異步完成塊中的特定索引處將數據添加到數組中

Question

對此併發性有困難，最後我試圖按照請求的順序將異步獲取對象添加到數組中，即第一次獲取應該添加到數組[0]，第二次獲取應該添加到數組[1]等等。問題是，到獲取完成時，我的索引計數已經改變了，我怎樣才能將索引計數傳遞給異步塊，所以它使用正確的？

class BATableViewController: UITableViewController { 
    var paymentArray = [[AnyObject]]() 
    var keepCount = 0 


func buildPaymentsArray(expenses: Array<AnyObject>!){ 
    for (index, expense) in enumerate(expenses) { 
     // query for all Payments for that expense 
     var paymentQuery = PFQuery(className: "Payment") 
     paymentQuery.whereKey("expense", equalTo: expense) 
     paymentQuery.findObjectsInBackgroundWithBlock({ (objects: [AnyObject]!, error: NSError!) -> Void in 
      self.paymentArray[self.keepCount] = objects 
      self.keepCount++ 
     }) 
    } 
} 

Answer 1

只是預擴展你的陣列，以及要將其插入他們：

func buildPaymentsArray(expenses: Array<AnyObject>!){ 
    // Pre-allocate your array. (This *really* shouldn't be AnyObject if you can at all help it) 
    self.paymentArray = [[AnyObject]](count: expenses.count repeatedValue: []) 

    for (index, expense) in enumerate(expenses) { 
     // query for all Payments for that expense 
     var paymentQuery = PFQuery(className: "Payment") 
     paymentQuery.whereKey("expense", equalTo: expense) 
     paymentQuery.findObjectsInBackgroundWithBlock({ (objects: [AnyObject]!, error: NSError!) -> Void in 
      self.paymentArray[index] = objects // <=== write it to the index location from expenses 
      self.keepCount++ // <== I assume you shouldn't need this 
     }) 
    } 
}