为什么 PDFKit .beginFindStrings 的结果为零？

Question

这里是自学新手。

我的最终目标：

加载 PDF 目录的 iOS/Mac 应用程序，在每个目录中搜索字符串数组，并列出哪些 PDF 包含哪些字符串。

只有一个 PDF 的原型设计问题：

我从加载选定的 PDF、运行 .beginFindStrings(["and", "the"], withOptions: .caseInsensitive) 并等待通知 .PDFDocumentDidEndFind 检查 [PDFSelection] 收到一个令人困惑的 nil。

那不应该。内存显示 PDF 已加载。我在线程上做错了吗？我想我在这里遵循了async 的建议：PDFKit background search

代码

import UIKit
import MobileCoreServices
import PDFKit

class ViewController: UIViewController, UIDocumentPickerDelegate {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    var matchesFound: PDFSelection?

    @IBOutlet weak var resultsLabel: UILabel!

    @IBAction func importPDF(_ sender: Any) {
        let picker = UIDocumentPickerViewController(documentTypes: [kUTTypePDF as String], in: .import)
        picker.delegate = self
        picker.allowsMultipleSelection = false
        self.present(picker, animated: true)
    }

    func documentPicker(_ controller: UIDocumentPickerViewController, didPickDocumentsAt urls: [URL]) {
        guard urls.count == 1 else {return}
        let data = try! Data(contentsOf: urls[0])
        let subjectPDF = PDFDocument.init(data: data)
        guard subjectPDF!.isLocked == false else {return}

        subjectPDF!.beginFindStrings(["the", "and"], withOptions: .caseInsensitive)

        NotificationCenter.default.addObserver(self, selector: #selector(onDidFindMatch(_:)), name: Notification.Name.PDFDocumentDidEndFind, object: nil)
    }

    @objc func onDidFindMatch(_ notification: Notification) {
        resultsLabel.text = "\(String(describing: matchesFound?.string))"
    }

    func documentPickerWasCancelled(_ controller: UIDocumentPickerViewController) {
            dismiss(animated: true, completion: nil)
    }

}

带标记的代码

import UIKit
import MobileCoreServices
import PDFKit

class ViewController: UIViewController, UIDocumentPickerDelegate {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

//Array of PDFSelection search results
    var matchesFound: PDFSelection?

//Temporary display for search result strings
    @IBOutlet weak var resultsLabel: UILabel!

//Choose a PDF to import, temporarily limited to one
    @IBAction func importPDF(_ sender: Any) {
        let picker = UIDocumentPickerViewController(documentTypes: [kUTTypePDF as String], in: .import)
        picker.delegate = self
        picker.allowsMultipleSelection = false
        self.present(picker, animated: true)
    }

//Load the picked PDF as subjectPDF, if unlocked
    func documentPicker(_ controller: UIDocumentPickerViewController, didPickDocumentsAt urls: [URL]) {
        guard urls.count == 1 else {return}
        let data = try! Data(contentsOf: urls[0])
        let subjectPDF = PDFDocument.init(data: data)
        guard subjectPDF!.isLocked == false else {return}

//Find temporary array of strings
        subjectPDF!.beginFindStrings(["the", "and"], withOptions: .caseInsensitive)

//Trigger results readout upon search competion
        NotificationCenter.default.addObserver(self, selector: #selector(onDidFindMatch(_:)), name: Notification.Name.PDFDocumentDidEndFind, object: nil)
    }

//Readout found strings to temporary label
    @objc func onDidFindMatch(_ notification: Notification) {
        resultsLabel.text = "\(String(describing: matchesFound?.string))"
    }

    func documentPickerWasCancelled(_ controller: UIDocumentPickerViewController) {
            dismiss(animated: true, completion: nil)
    }

}

Answer 1

这个问题是在 7 个月前提出的，但我希望你已经找到了解决方案。 无论如何解决您的问题：

1-将下面的行移到viewDidLoad()，因为你是在触发beginFindString()方法后添加观察者。

NotificationCenter.default.addObserver(self, selector: #selector(onDidFindMatch(_:)), name: Notification.Name.PDFDocumentDidEndFind, object: nil)

2- 您永远不会为 matchesFound 变量分配任何值，因此它始终为 nil。

3- 要从beginFindString 方法获取匹配，您需要为PDFDocumentDidFindMatch 添加一个观察者，并从userInfo 而不是PDFDocumentDidEndFind 获取数据。 PDFDocumentDidEndFindobserver 将在搜索完成时被调用，你可以使用这个观察者来移除你正在加载的视图。

这是正确实现的示例代码：

var matchesFound = [PDFSelection]()

// MARK: Life cycle

override func viewDidLoad() {
    super.viewDidLoad()
    
    NotificationCenter.default.addObserver(self, selector: #selector(didFindMatch(_:)), name: NSNotification.Name.PDFDocumentDidFindMatch, object: nil)
}

deinit {
    NotificationCenter.default.removeObserver(self)
}

// This method will get called every-time a match has been found.
@objc private func didFindMatch(_ sender: Notification) {
    guard let selection = sender.userInfo?["PDFDocumentFoundSelection"] as? PDFSelection else { return }

    self.matchesFound.append(selection)
}