QLPreviewController freezing while donwload and set images using the observer

Question

Created Mar ’24

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I am using QlPreviewController in my applications, I am download the data one by one using observer, The observer detects currentIndexItem in the preview controller, The image is only download when the currentIndexItem will changed ,After downloading i will refresh the currentPreviewItem , My Problem is , while downloading an files in first item and i am moving to the next items , which also downloading an files,And both screens are freezing , after click the menu button, in the sections show images is loaded , but not reflected.

While i am calling download data, The thread is changed to Background thread

            DispatchQueue.global().async {
                interactor.processData(kbPath: categoriesPath)
            }
        }else{
            interactor.processData(kbPath: categoriesPath)
            
        }

This is the downloading file which will happens in Background thread, The above code will change

        
        let url = fileData.contentUrl
        let fileName = fileData.name
        let contentUrl = fileData.contentUrl
        
        
        let documentsURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
        let destinationURL = documentsURL.appendingPathComponent(fileName)
        
            
            // Check if the file already exists at the destination URL
            if FileManager.default.fileExists(atPath: destinationURL.path){
                return completion(.success(File(data: destinationURL, name: fileName, contentUrl: contentUrl, hasData: true)))
            }
            
            // If the file doesn't exist, proceed with downloading
            let request = URLRequest(url: URL(string: url)!)
            let task = URLSession.shared.downloadTask(with: request) {(tempFileURL, response, error) in
                
                if let error = error {
                    print("Error downloading file: \(error)")
                    completion(.failure(.FailedToDownload))
                    return
                }
                
                guard let httpResponse = response as? HTTPURLResponse , httpResponse.statusCode == 200,let tempFileURL = tempFileURL  else {
                    print("Failed to download file. Invalid response.")
                    completion(.failure(.FailedToDownload))
                    return
                }
                
                do {
                    try FileManager.default.moveItem(at: tempFileURL, to: destinationURL)
                    completion(.success(File(data: destinationURL, name: fileName, contentUrl: url, hasData: true)))
                } catch {
                    print("Error moving file: \(error)")
                    completion(.failure(.FailedToDownload))
                }
            }
            
            task.resume()
        
        }

After Downloading the data , it will inform to the viewcontroller to check the thread and call

            DispatchQueue.main.async {
                handler()
            }
        }else{
                handler()
        }

This is my Observer

        if context == &previewControllerContext{
            if keyPath == "currentPreviewItemIndex" {
                let currentIndex = preview.currentPreviewItemIndex
                //api calls for the specific files 
                if currentIndex < previewData.count && !previewData[currentIndex].hasData {
                    self.loadingView.startAnimating()
                    let builder = Builder()
                    self.previewData[currentIndex].hasData = true
                    builder.build(instance: self, categoriesPath: .KBDownloadFile(fileData: self.previewData[currentIndex]))
                }
            }
        }else {
            super.observeValue(forKeyPath: keyPath, of: object, change: change, context: context)
        }

After downloaded image the result will notify and i will refresh the current previewItem self.preview.refreshCurrentPreviewItem()

The Issue video link -> https://drive.google.com/file/d/18pBZawbvcUU3SA5vS53X9R9q-AGMG5Sv/view

Any one facing this issues with this ,my thought this issues is thread based , but i will handle the thread

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