我正在开发的视图执行以下操作:
- 向API发送GET请求以检索用户列表
- 向API发送GET请求以从用户列表中检索配置文件图像
- 在TableViewCells 中显示图像
然而，我在管理任务和队列方面遇到了问题。确保在填充表视图之前完成所有请求和任务的最佳方法是什么?
代码如下:
import UIKit
class homeViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {
@IBOutlet weak var tableView: UITableView!
var jsonData : [NSDictionary] = [NSDictionary]()
var imageUrls: NSDictionary = NSDictionary()
var urlsArray: [NSURL] = [NSURL]()
override func viewDidLoad() {
super.viewDidLoad()
let qualityOfServiceClass = QOS_CLASS_BACKGROUND
let backgroundQueue = dispatch_get_global_queue(qualityOfServiceClass, 0)
dispatch_async(backgroundQueue, {
self.refreshData()
self.getImage()
dispatch_async(dispatch_get_main_queue(), { () -> Void in
self.tableView.reloadData()
})
})
}
override func viewWillAppear(animated: Bool) {
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return jsonData.count
}
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
var type = jsonData[indexPath.row]["type"] as! Int
for typej in jsonData {
let t : Int = typej["type"] as! Int
println("type : (t)")
}
if type == 1 {
let cell1 : cellTableViewCell = self.tableView.dequeueReusableCellWithIdentifier("cell") as! cellTableViewCell
/* //If images url are retrieved, load them. Otherwise, load the placeholders
if self.urlsArray.isEmpty == false {
println("Tiè: (self.urlsArray[indexPath.row])")
if let data = NSData(contentsOfURL: self.urlsArray[indexPath.row]) {
cell1.profileImg?.image = UIImage(data: data)
}
} else {
cell1.profileImg?.image = UIImage(named: "placeholder.png")
}*/
let block: SDWebImageCompletionBlock! = {
(image: UIImage!, error: NSError!, cacheType: SDImageCacheType, imageURL: NSURL!) -> Void in
println(self)
}
println("url Array: (self.urlsArray)")
let url = NSURL(string: "http://adall.ga/s/profile-1439584252497.png")
if UIApplication.sharedApplication().canOpenURL(urlsArray[indexPath.row]) {
cell1.profileImg.sd_setImageWithURL(urlsArray[indexPath.row], completed: block)
} else {
cell1.profileImg.sd_setImageWithURL(url, completed: block)
}
cell1.testLbl.text = (self.jsonData[indexPath.row]["author"] as? String)!
return cell1
} else {
let cell2 : cell2TableViewCell = self.tableView.dequeueReusableCellWithIdentifier("cell2") as! cell2TableViewCell
return cell2
}
}
func refreshData() {
let requestURL = NSURL(string:"http://adall.ga/api/feeds/author/mat/0")!
var request = NSMutableURLRequest(URL: requestURL)
request.HTTPMethod = "GET"
request.addValue(userToken, forHTTPHeaderField: "tb-token")
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithRequest(request) {
data, response, error in
println(response)
var dataString = NSString(data: data, encoding: NSUTF8StringEncoding)
println(dataString)
//let jsonResult : NSDictionary = (NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers, error: nil) as? NSDictionary)!
//jsonData = (NSJSONSerialization.JSONObjectWithData(data!, options:NSJSONReadingOptions.MutableContainers , error: nil) as? NSArray)!
self.jsonData = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.AllowFragments, error: nil) as! [NSDictionary]
}
task.resume()
var index: Int
for index = 0; index < 10000; ++index {
print("Index: (index), Task state: (task.state)")
}
}
func getImage() {
var i = 0
for jsonSingleData in jsonData {
let author = jsonSingleData["author"] as! String
let requestURL2 = NSURL(string: "http://adall.ga/api/users/" + author + "/image")!
var request2 = NSMutableURLRequest(URL: requestURL2)
request2.HTTPMethod = "GET"
request2.addValue(userToken!, forHTTPHeaderField: "tb-token")
let session2 = NSURLSession.sharedSession()
let task2 = session2.dataTaskWithRequest(request2) {
data, response, error in
println("response= (response)")
var dataString = NSString(data: data, encoding: NSUTF8StringEncoding)
println(dataString)
self.imageUrls = (NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers, error: nil) as! NSDictionary)
if self.imageUrls["url"] != nil {
//check if exists
let imageUrl = self.imageUrls["url"] as! String
let url = NSURL(string: "http://" + imageUrl)
self.urlsArray.append(url!)
} else {
let imageUrl = "http://shackmanlab.org/wp-content/uploads/2013/07/person-placeholder.jpg"
let url = NSURL(string: imageUrl)
self.urlsArray.append(url!)
}
}
task2.resume()
self.tableView.reloadData()
}
}
/*
// MARK: - Navigation
// In a storyboard-based application, you will often want to do a little preparation before navigation
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
// Get the new view controller using segue.destinationViewController.
// Pass the selected object to the new view controller.
}
*/
}
问题的关键在于以下代码:
dispatch_async(backgroundQueue, {
self.refreshData()
self.getImage()
dispatch_async(dispatch_get_main_queue(), { () -> Void in
self.tableView.reloadData()
})
})
NSURLSession在后台线程中工作，所以当self.getImage()和reloadData执行时，jsonData是空的。
你可以在这行之后调用self.getImage()
self.jsonData = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.AllowFragments, error: nil) as! [NSDictionary]
在session.dataTaskWithRequest的已完成块中，调用session2.dataTaskWithRequest的已完成块中的reloadData(在dispatch_get_main_queue上)。
我想这会解决你的问题。