首先，为了避免我的英语不好，我上传了一个显示我的问题的视频
http://www.mediafire.com/download/j6krsa274o80ik9/Screen_Recording.mov
其次，我有一个UITableViewController，它使用远程API下载数据。数据包含许多图像URL，我的第一个问题是即使我正在执行.reloadData()函数，tableView也没有更新
我的第二个问题是在函数中：
tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
我下载了图片，我从第一次调用中得到了他们的网址，然后事件很好但我看不到图像，除非我点击了行
请看视频，更容易理解
这是我的代码:(我给了你UITableView的完整代码，因为它很简单，因为它有两个功能，而且它们让我有问题）
class Physicst: NSObject {
let image : String
var imageData: UIImage?
let name : NSString
init(image: String, name: NSString) {
self.image = image
self.name = name
}
}
class PhysicistTableViewController: UITableViewController {
var physicsts : [Physicst]?
@IBOutlet var physicstsTableView: UITableView!
override func viewDidLoad() {
super.viewDidLoad()
loadDataFromDBPedia()
}
func loadDataFromDBPedia() {
let session = NSURLSession.sharedSession()
var url = "http://dbpedia.org/sparql/"
let query = "http://dbpedia.org&query=select * {?o dbo:thumbnail ?p . ?o dbo:award dbr:Nobel_Prize_in_Physics} limit 10"
url = url + "?default-graph-uri=" + query.stringByAddingPercentEncodingWithAllowedCharacters(.URLHostAllowedCharacterSet())!
url = url + "&format=JSON&CXML_redir_for_subjs=121&CXML_redir_for_hrefs=&timeout=30000&debug=on"
let request = NSMutableURLRequest(URL: NSURL(string: url)!)
let task = session.dataTaskWithRequest(request, completionHandler: {(data, response ,error) in
if let error = error {
print ("\(error)")
}
if let response = response {
let httpResponse = response as! NSHTTPURLResponse
let statusCode = httpResponse.statusCode
print("Status code = \(statusCode)")
}
if let data = data {
do {
let jsonResponse = try NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions())
let binding = jsonResponse["results"]!!["bindings"] as! NSArray
for oneBinding in binding {
let name = oneBinding["o"]!!["value"] as! NSString
var image = oneBinding["p"]!!["value"] as! String
image = image.stringByAddingPercentEscapesUsingEncoding(NSUTF8StringEncoding)!
let physicst = Physicst(image: image, name: name)
if self.physicsts == nil {
self.physicsts = [Physicst]()
}
self.physicsts!.append(physicst)
}
self.physicstsTableView.reloadData()
}catch _ {
print ("not well json-formatted response")
}
}
})
task.resume()
}
override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
return 1
}
override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
if self.physicsts == nil {
return 0
}else {
return self.physicsts!.count
}
}
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("physicstCell")! as UITableViewCell
let row = indexPath.row
let physicst = self.physicsts![row]
cell.textLabel?.text = physicst.name as String
if (physicst.imageData == nil) {
let session = NSURLSession.sharedSession()
let url = NSURL(string: physicst.image as String)
if let url = url {
let request = NSMutableURLRequest(URL: url)
let task = session.dataTaskWithRequest(request, completionHandler: {(data, response, error) in
if let data = data {
let imageData = UIImage(data: data)
cell.imageView?.image = imageData
physicst.imageData = imageData
self.physicstsTableView.reloadRowsAtIndexPaths([indexPath], withRowAnimation: UITableViewRowAnimation.None)
}
})
task.resume()
}else {
print ("nill URL \(physicst.image)")
}
}else {
cell.imageView?.image = physicst.imageData!
}
return cell
}
}
**可以自由复制/粘贴它，没有自定义单元格，所以它应该可以工作**
答案 0 :(得分：2)
应在主线程上调用tableView reload。 session.dataTaskWithRequest在后台线程上调用完成块，在后台线程上执行UI操作可能会导致严重后果。我相信你面临的问题只是其中一个后果。修改代码如下。
func loadDataFromDBPedia() {
let session = NSURLSession.sharedSession()
var url = "http://dbpedia.org/sparql/"
let query = "http://dbpedia.org&query=select * {?o dbo:thumbnail ?p . ?o dbo:award dbr:Nobel_Prize_in_Physics} limit 10"
url = url + "?default-graph-uri=" + query.stringByAddingPercentEncodingWithAllowedCharacters(.URLHostAllowedCharacterSet())!
url = url + "&format=JSON&CXML_redir_for_subjs=121&CXML_redir_for_hrefs=&timeout=30000&debug=on"
let request = NSMutableURLRequest(URL: NSURL(string: url)!)
let task = session.dataTaskWithRequest(request, completionHandler: {(data, response ,error) in
if let error = error {
print ("\(error)")
}
if let response = response {
let httpResponse = response as! NSHTTPURLResponse
let statusCode = httpResponse.statusCode
print("Status code = \(statusCode)")
}
if let data = data {
do {
let jsonResponse = try NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions())
let binding = jsonResponse["results"]!!["bindings"] as! NSArray
for oneBinding in binding {
let name = oneBinding["o"]!!["value"] as! NSString
var image = oneBinding["p"]!!["value"] as! String
image = image.stringByAddingPercentEscapesUsingEncoding(NSUTF8StringEncoding)!
let physicst = Physicst(image: image, name: name)
if self.physicsts == nil {
self.physicsts = [Physicst]()
}
self.physicsts!.append(physicst)
}
dispatch_async(dispatch_get_main_queue()) { () -> Void in
self.physicstsTableView.reloadData()
}
}catch _ {
print ("not well json-formatted response")
}
}
})
task.resume()
}
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("physicstCell")! as UITableViewCell
let row = indexPath.row
let physicst = self.physicsts![row]
cell.textLabel?.text = physicst.name as String
if (physicst.imageData == nil) {
let session = NSURLSession.sharedSession()
let url = NSURL(string: physicst.image as String)
if let url = url {
let request = NSMutableURLRequest(URL: url)
let task = session.dataTaskWithRequest(request, completionHandler: {(data, response, error) in
if let data = data {
dispatch_async(dispatch_get_main_queue(), { () -> Void in
let imageData = UIImage(data: data)
cell.imageView?.image = imageData
physicst.imageData = imageData
self.physicstsTableView.reloadRowsAtIndexPaths([indexPath], withRowAnimation: UITableViewRowAnimation.None)
})
}
})
task.resume()
}else {
print ("nill URL \(physicst.image)")
}
}else {
cell.imageView?.image = physicst.imageData!
}
return cell
}
提示
为每个单元格手动下载图像，然后将其加载到tableViewCell并处理缓存以提高滚动性能，就像在有无轮胎轮胎时重新发明轮子一样:)请考虑使用SDWebImage或AFNetworking我个人使用了SDWebImage，其缓存功能完美无缺。