在我点击另一个标签并返回之前，tableView不会更新-swift

Question

我是iOS的新手，我通过解析JSON数据从Web源动态填充tableView数据。 但是问题是，当我第一次访问该标签时，它什么也没显示。 在我访问另一个选项卡并返回后，它在tableView上正确显示了数据。

这是我的代码

import UIKit

class BranchViewController: UITableViewController , UISearchBarDelegate, UISearchDisplayDelegate {

    var branches = [Branch]()
    var filteredBranch = [Branch]()
    var BranchArray = [BranchTable]()
    var BranchLocationArray = [BranchLocation]()


    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        self.tableView!.delegate = self
        self.tableView!.dataSource = self

        let url = NSURL(string: "http://rana.ninja/branches.php")

        let task = NSURLSession.sharedSession().dataTaskWithURL(url!) {(data, response, error) in
            println(NSString(data: data, encoding: NSUTF8StringEncoding))
            var error: NSError?
            let jsonData: NSData = data /* get your json data */
            let json = NSJSONSerialization.JSONObjectWithData(jsonData, options: nil, error: &error) as NSDictionary

            if let name: AnyObject = json["name"]  {
                for var index = 0; index < name.count; ++index {
                    var Name : String  = name[index] as NSString
                    self.branches.append(Branch(name: Name))
                    println(Name)
                }
            }
        }

        task.resume()

        BranchArray =
            [BranchTable(BranchTitle: ["FirstFirst","SecondFirst","ThirdFirst"]),
                BranchTable(BranchTitle: ["FirstSecond","SecondSecond","ThirdSecond"]),
                BranchTable(BranchTitle: ["FirstThird","SecondThird","ThirdThird"]),
                BranchTable(BranchTitle: ["FirstFourth"])]

        BranchLocationArray = [BranchLocation(BranchLocationValues: ["asdfasd","asdfasd","asdfas"]),
            BranchLocation(BranchLocationValues: ["asdkljf","asdfasd","asdfas"]),
            BranchLocation(BranchLocationValues: ["asdkljf","asdfasd","asdfas"]),
            BranchLocation(BranchLocationValues: ["asdkljf","asdfasd","asdfas"])]

            // Reload the table
            self.tableView.reloadData()
            }

Answer 1

更新数据结构后，需要调用tableView.reloadData 。 这必须在主线程中完成，因此：

 let task = NSURLSession.sharedSession().dataTaskWithURL(url!) {(data, response, error) in
     println(NSString(data: data, encoding: NSUTF8StringEncoding))
     var error: NSError?
     let jsonData: NSData = data /* get your json data */
     let json = NSJSONSerialization.JSONObjectWithData(jsonData, options: nil, error: &error) as NSDictionary

     if let name: AnyObject = json["name"]  {
         for var index = 0; index < name.count; ++index {
             var Name : String  = name[index] as NSString
             self.branches.append(Branch(name: Name))
             println(Name)
         }
     }
     // NOTE: Calling reloadData in the main thread
     dispatch_async(dispatch_get_main_queue()) {
         self.tableView.reloadData()
     }
}

Answer 2

看来，您的数据加载是异步完成的，但是您要在闭包外部重新加载表，因此它可能在加载完成之前执行。 因此，您可以将表重新加载到闭包内部。

而且，建议的排队方式也不错，您可以在Apple Doc中阅读GCD：

dispatch_async(dispatch_get_main_queue()) { // Assign Job To The Main Queue }

dispatch_async提交一个块，以在调度队列上异步执行并立即返回。 它有两个参数- queue ; 提交阻止的队列和block要提交的作业。