如何知道何时使用PDFKit渲染
如何知道何时使用PDFKit渲染
提问于 2019-04-10 08:29:08
当屏幕上还没有显示PDF时，我正在尝试显示加载。问题是，我的加载总是在文档呈现之前停止，有时它不能花2到3秒，我需要知道什么时候PDF已经呈现来停止activyIndicator。是否可以使用PDFKIT？我的代码：
class PDFViewController: URLSessionDownloadDelegate {
@IBOutlet weak var pdfView: PDFView!
var pdfDocument: PDFDocument!
override func viewDidLoad() {
super.viewDidLoad()
setupPDFView()
setupNavigationBar()
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
self.startLoading()
}
override func viewDidAppear(_ animated: Bool) {
super.viewWillAppear(animated)
loadPDF()
}
private func loadPDF() {
DispatchQueue.main.async {
guard let url = URL(string: self.viewModel.pdfURL) else {
self.showAlert(with: self.viewModel.strings.invalidInvoice)
return
}
let urlSession = URLSession(configuration: .default, delegate: self, delegateQueue: OperationQueue())
let downloadTask = urlSession.downloadTask(with: url)
downloadTask.resume()
}
}
private func setupPDFView() {
self.pdfView.displayMode = .singlePageContinuous
self.pdfView.autoScales = true
}
func startLoading() {
guard let window = UIApplication.shared.keyWindow,
!window.subviews.contains(where: { $0 is LoadingView }) else { return }
let loadingView = LoadingView(frame: window.bounds)
window.addSubview(loadingView)
Thread.performUIUpdate {
loadingView.startAnimation()
}
}
func stopLoading() {
guard let window = UIApplication.shared.keyWindow,
let view = window.subviews.first(where: { $0 is LoadingView }),
let loadingView = view as? LoadingView else { return }
Thread.performUIUpdate {
loadingView.stopAnimation()
loadingView.removeFromSuperview()
}
}
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {
DispatchQueue.main.async {
self.pdfDocument = PDFDocument(url: location)
if let pdfDocument = self.pdfDocument {
self.pdfView.document = pdfDocument
}
self?.stopLoading()
}
}
}回答 2
Stack Overflow用户
发布于 2019-04-10 08:49:40
这似乎是一个非常糟糕的想法：
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {
DispatchQueue.main.async {
self.pdfDocument = PDFDocument(url: location)问题是，当您离开当前线程并启动异步代码时，该方法结束，location处的临时文档可能会被销毁。我建议这样写：
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {
let pdf = PDFDocument(url: location)
DispatchQueue.main.async {
self.pdfDocument = pdf我并不是说这会解决你的问题，但它似乎比你正在做的事情要危险得多。
至于你的实际问题，我建议注册一个通知，比如this one，看看它是否在正确的时间到达。
Stack Overflow用户
发布于 2019-09-20 10:45:55
要知道PDFView页面何时可见，必须观察PDFViewVisiblePagesChanged通知，将代码添加到该方法中。
NotificationCenter.default.addObserver(self, selector: #selector(pdfViewVisiblePagesChanged(sender:)), name: .PDFViewVisiblePagesChanged, object: nil)
@objc func pdfViewVisiblePagesChanged(sender: Notification) {
//Add your code here
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/55603064
复制相关文章
相似问题