swift 如何使用UIPrintInteractionController从URL异步打印PDF文件？

xuo3flqw  于 2023-03-22  发布在  Swift
关注(0)|答案(1)|浏览(363)

在我的应用程序中，我有一个打印送货单的选项。当我点击这个选项时，我会收到一个带有URL的服务器响应（PDF文件的URL）。收到响应后，应用程序会立即导航到一个屏幕，其中包含一个执行打印操作的按钮。在此之前，一切正常。但当我点击打印按钮时，视图冻结。我收到警告，这是一个同步的URL加载，导致应用程序的UI无响应。它建议使用一些异步URL加载，如URLSession。但我不知道如何在这种情况下使用它。任何帮助都将不胜感激。我提供了下面的代码示例。

  1. public enum PrintingResult {
  2.   case success
  3.   case failure(Error)
  4.   case userCancelled
  5. }
  7. public func presentPrintInteractionController(url: URL?, jobName: String? = nil, completion: ((PrintingResult) -> Void)? = nil) {
  8.   let printController = UIPrintInteractionController()
  9.   let printInfo = UIPrintInfo.printInfo()
  10.   if let jobName = jobName {
  11.     printInfo.jobName = jobName
  12.   }
  13.   printController.printInfo = printInfo
  15.   if let url = url {
  16.     printController.printingItem = url
  17.   }
  18.   printController.present(animated: true) { _, completed, error in
  19.     guard let completion = completion else { return }
  20.     if completed {
  21.         completion(.success)
  22.     } else {
  23.         if let error = error {
  24.             completion(.failure(error))
  25.         } else {
  26.             completion(.userCancelled)
  27.         }
  28.     }
  29.   }
  30. }

查看：

  1. import SwiftUI
  3. struct ReportView: View {
  4.    var reportUrl: String
  6.    init(reportUrl: String) {
  7.       self.reportUrl = reportUrl
  8.    }
  10.    var body: some View {
  11.       VStack {
  12.           Button {
  13.             presentPrintInteractionController(url: URL(string: reportUrl), jobName: "Print a pdf report") { result in
  14.                 switch result {
  15.                 case .success:
  16.                     print("Print Successful")
  17.                 case .failure(let error):
  18.                     print("Error: \(error)")
  19.                 case .userCancelled:
  20.                     print("Printing job cancelled.")
  21.                 }
  22.             }
  23.         } label: {
  24.             Text("Print")
  25.         }
  26.      }
  27.   }
  28. }
  30. struct ReportView_Previews: PreviewProvider {
  31.    static var previews: some View {
  32.        ReportView(reportUrl: "")
  33.    }
  34. }

swift

1条答案

按热度按时间
bpsygsoo

bpsygsoo1#

似乎UIPrintInteractionController正在尝试从远程URL同步获取数据。解决这个问题的一种方法是异步获取数据 * 自己 *，并将Data交给UIPrintInteractionController。
其基本思想是：

  1. URLSession.shared.dataTask(with: URLRequest(url: url)) { data, response, error in
  2.     // do some error handling...
  3.     
  4.     printController.printingItem = data
  5.     
  6.     printController.present(animated: true) { _, completed, error in
  7.         // call your completion handler here...
  8.     }
  9. }.resume()

我建议将presentPrintInteractionController转换为async throws函数，并去掉完成处理程序参数。
这种嵌套方式要少得多。

  1. // you don't need to wrap the built-in errors that can be thrown
  2. // so the only case left is userCancelled.
  3. // perhaps consider renaming this 
  4. public enum PrintingResult: Error {
  5.   case userCancelled
  6. }
  8. // assuming this is a global function, you'd need @MainActor
  9. @MainActor
  10. public func presentPrintInteractionController(url: URL?, jobName: String? = nil) async throws {
  11.     let printController = UIPrintInteractionController()
  12.     let printInfo = UIPrintInfo.printInfo()
  13.     if let jobName = jobName {
  14.         printInfo.jobName = jobName
  15.     }
  16.     printController.printInfo = printInfo
  18.     if let url = url {
  19.         // fetching the data asynchronously
  20.         let (data, response) = try await URLSession.shared.data(from: url)
  21.         // you might add some error handling here by inspecting response
  22.         printController.printingItem = data
  23.     }
  24.     
  25.     try await withCheckedThrowingContinuation { continuation in
  26.         printController.present(animated: true) { _, completed, error in
  27.             if completed {
  28.                 continuation.resume()
  29.             } else if let e = error {
  30.                 continuation.resume(with: .failure(e))
  31.             } else {
  32.                 continuation.resume(with: .failure(PrintingResult.userCancelled))
  33.             }
  34.         }
  35.     }
  36. }

然后，您可以在Button代码中使用do...catch来处理以下三种情况：

  1. Button {
  2.     Task {
  3.         do {
  4.             try await presentPrintInteractionController(url: URL(string: reportUrl), jobName: "Print a pdf report")
  5.             print("Print Successful")
  6.         } catch PrintingResult.userCancelled {
  7.             print("Printing job cancelled.")
  8.         } catch {
  9.             print("Error: \(error)")
  10.         }
  11.     }
  12. } label: {
  13.     Text("Print")
  14. }
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