在tableView（_：cellForRowAt :)下載圖像導致單元格不停閃爍

我想要在tableView(_:cellForRowAt:)方法上每個UITableViewCell懶懶地下載圖像。當表格視圖顯示在屏幕上時，它不停地在每個單元格上閃爍，我無法滾動tableView。在tableView（_：cellForRowAt :)下載圖像導致單元格不停閃爍

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell { 
    let cell = tableView.dequeueReusableCell(withIdentifier: "MessageCell", for: indexPath) as! MessageCell 
    let row = indexPath.row 

    cell.content.delegate = self 
    cell.content.text = messages[row].content 
    cell.date.text = messages[row].createdDateStrInLocal 
    cell.messageOwner.text = messages[row].user 

    self.fetchUserAvatar(avatarName: messages[row].user, handler: ({ img in 
     cell.profileImageView.image = img 
     tableView.reloadRows(at: [indexPath], with: .automatic) 
    })) 
    return cell 
} 

fileprivate func fetchUserAvatar(avatarName: String, handler: @escaping (UIImage) -> Void){ 
    guard !avatarName.isEmpty, let user = self.user, !user.isEmpty else { return } 
     let url = URL(string: self.url + "/userAvatarURL") 
     var request = URLRequest(url: url!) 
     let body = "username=" + user + "&avatarName=" + avatarName 
     request.httpMethod = "POST" 
     request.setValue("application/x-www-form-urlencoded; charset=utf-8", forHTTPHeaderField: "Content-Type") 
     request.httpBody = body.data(using: .utf8) 
     defaultSession.dataTask(with: request as URLRequest, completionHandler: { data, response, error in 
      guard error == nil else { 
       print(error!) 
       return 
      } 
      if let httpResponse = response as? HTTPURLResponse, 200...299 ~= httpResponse.statusCode, let data = data, let urlStr = String(data: data, encoding: String.Encoding.utf8), urlStr != "NULL", urlStr.contains("http"), let url = URL(string: urlStr) { 
       self.defaultSession.dataTask(with: url, completionHandler:{ data, respone, error in 
        guard error == nil else { 
         print(error!) 
         return 
        } 
        DispatchQueue.main.async { 
         if let httpResponse = response as? HTTPURLResponse, 200...299 ~= httpResponse.statusCode, let data = data, let img = UIImage(data: data) { 
          self.cacheImage.setObject(img, forKey: avatarName as NSString) 
          handler(img) 
         } 
        } 
       }).resume() 
      } 
     }).resume() 
}

來源

2017-05-18 Carl Hung

儘管在這不下載圖像的細胞一種安全的方式，你需要刪除tableView.reloadRows(at: [indexPath], with: .automatic)。這導致無限循環。

並確保更新圖像時更新約束。

來源

2017-05-18 12:18:12

但如果我刪除它，我不能在每個單元格上顯示圖像。 –

編輯答案。您擁有的另一個問題是在更新圖像時不更新單元佈局。 –

對於fetchUserAvatar使它在單獨的後臺線程中。在完成塊中，返回主線程並更新表格單元格縮略圖。不要在`cellForRowAt indexPath：IndexPath'中重新加載表視圖。因爲它已經重新加載單元格。

來源

2017-05-18 13:16:34 byJeevan

在tableView（_：cellForRowAt :)下載圖像導致單元格不停閃爍

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