自动搜索时快速取消 URLSession

Question

我的 moto 是自动搜索，我一直在尝试使用 URLSession，当我尝试缓慢搜索时，请求按预期处理（当没有文本时，响应为空，我的意思是 placesarray）但是当我试图清除文本或快速点击任何搜索文本，然后将先前的请求响应附加到位置数组中。我尝试取消先前的请求但我没有得到结果（即未附加先前的响应）

func autoSearch(text:String){    
   let urlRequest = URLRequest(url: self.getQueryFormedBingURL()!)

   let session = URLSession.shared
   session.getTasksWithCompletionHandler
   {
      (dataTasks, uploadTasks, downloadTasks) -> Void in
      // self.cancelTasksByUrl(tasks: dataTasks     as [URLSessionTask])
      self.cancelTasksByUrl(tasks: uploadTasks   as [URLSessionTask])
      self.cancelTasksByUrl(tasks: downloadTasks as [URLSessionTask])
   }
   let task = session.dataTask(with: urlRequest, completionHandler: { (data, response, error) -> Void in

   print("response \(response)")

   if let data = data {

      let json = try? JSONSerialization.jsonObject(with: data, options: [])

      if let response = response as? HTTPURLResponse , 200...299 ~= response.statusCode {

         if let jsonDic = json as? NSDictionary {

             let status = jsonDic.returnsObjectOrNone(forKey: "statusCode") as! Int

              if status == 200 {

                 if let resourceSetsArr = jsonDic.returnsObjectOrNone(forKey: "resourceSets") as? NSArray {

                    if let placesDict = resourceSetsArr.object(at: 0) as? NSDictionary {
                       if let resourceArr = placesDict.object(forKey: "resources") as? NSArray, resourceArr.count > 0 {

                          if let _ = self.placesArray {
                             self.placesArray!.removeAll()
                          }
                          for loopCounter in 0...resourceArr.count - 1 {
                             let modalClass:BingAutoCompletePlace = BingAutoCompletePlace(responseDict: resourceArr[loopCounter] as! NSDictionary)
                             self.placesArray?.append(modalClass)
                          }
                          completion(self.placesArray!)
                       }
                       else { //URL Success, where there no places with the given search string
                          completion([])
                       }
                    }
                 }
              }
           }
        }
        else if let response = response as? HTTPURLResponse , 400...499 ~= response.statusCode {// When url fails
                if let _ = error {
                   print("error=\(error!.localizedDescription)")
                }
                completion([])
             }
             else {
                if let _ = error {
                   print("error=\(error!.localizedDescription)")
                }
                completion([])
             }
         }
     })
     task.resume()
}

//请求取消

private func cancelTasksByUrl(tasks: [URLSessionTask]) {
   for task in tasks
   {
      task.cancel()
   }
}

Answer 1

不幸的是，框架不保证任务完成的任何顺序——因为这取决于运行时间。也可能是您处于当前已取消任务的完成处理程序中。

要避免这种情况，您可以执行以下操作：

• 创建一个私有实例变量来存储最近的任务
• 像以前一样取消其他所有内容
• 在完成处理程序中
  • 检查任务是否仍然是最近的任务（如if (task !== self.currentTask) {return}）
  • 创建一个本地数组来存储数据
  • 在主线程中更新视图控制器数组 (DispatchQueue.main.async(...))

我清理了你的代码（使用guard 语句来最小化嵌套）。也许你也应该

• 在所有错误/空的情况下清空数组（而不是简单地从guard 语句返回）
• 将任务交给completion 调用并再次检查该任务是否仍然是当前任务。这也是将currentTask 重置为nil 的好方法。

根据您的需要采用它 :-)

var currentTask:URLSessionDataTask?

func autoSearch(text:String){
    let completion:(_ x:[AnyObject])->() =  {_ in }

    let urlRequest = URLRequest(url: self.getQueryFormedBingURL()!)

    let session = URLSession.shared
    session.getTasksWithCompletionHandler
        {
            (dataTasks, uploadTasks, downloadTasks) -> Void in
            //                self.cancelTasksByUrl(tasks: dataTasks     as [URLSessionTask])
            self.cancelTasksByUrl(tasks: uploadTasks   as [URLSessionTask])
            self.cancelTasksByUrl(tasks: downloadTasks as [URLSessionTask])
    }

    var task:URLSessionDataTask!
    task = session.dataTask(with: urlRequest, completionHandler: { (data, response, error) -> Void in

        print("response \(response)")

        if (task !== self.currentTask) {
            print("Ignore this task")
            return
        }

        if let error = error {
            print("response error \(error)")
        }

        guard let data = data else { return }

        let json = try? JSONSerialization.jsonObject(with: data, options: [])

        var newPlacesArray = [AnyObject]() // Empty array of whichever type you want

        if let response = response as? HTTPURLResponse , 200...299 ~= response.statusCode {

            guard let jsonDic = json as? NSDictionary else { return }

            let status = jsonDic.returnsObjectOrNone(forKey: "statusCode") as! Int

            if status == 200 {

                guard let resourceSetsArr = jsonDic.returnsObjectOrNone(forKey: "resourceSets") as? NSArray else { return }
                guard let placesDict = resourceSetsArr.object(at: 0) as? NSDictionary else { return }
                guard let resourceArr = placesDict.object(forKey: "resources") as? NSArray, resourceArr.count > 0 else {
                    //URL Success, where there no places with the given search string
                    DispatchQueue.main.async {completion(newPlacesArray)}
                    return
                }

                for loopCounter in 0...resourceArr.count - 1 {
                    let modalClass:BingAutoCompletePlace = BingAutoCompletePlace(responseDict: resourceArr[loopCounter] as! NSDictionary)
                    newPlacesArray.append(modalClass)
                }
                DispatchQueue.main.async {completion(newPlacesArray)}
            }
        }
        else if let response = response as? HTTPURLResponse , 400...499 ~= response.statusCode {// When url fails
            if let _ = error {
                print("error=\(error!.localizedDescription)")
            }
            DispatchQueue.main.async {completion(newPlacesArray)}
        }
        else {
            if let _ = error {
                print("error=\(error!.localizedDescription)")
            }
            DispatchQueue.main.async {completion(newPlacesArray)}
        }
    })

    self.currentTask = task
    task.resume()
}