QuickLook框架详细解析（五） —— QuickLook预览和缩略图扩展的实现（二）

版本记录

版本号	时间
V1.0	2021.03.22 星期一

前言

QuickLook框架提供了文档的预览功能。接下来几篇我们就一起看一下这个框架。感兴趣的可以看下面几篇。
1. QuickLook框架详细解析（一） —— 基本概览（一）
2. QuickLook框架详细解析（二） —— QuickLook 预览简单示例（一）
3. QuickLook框架详细解析（三） —— QuickLook 预览简单示例（二）
4. QuickLook框架详细解析（四） —— QuickLook预览和缩略图扩展的实现（一）

源码

1. Swift

首先看下工程组织文件

下面就是源码了

1. AppMain.swift

import SwiftUI

@main
struct AppMain: App {
  var body: some Scene {
    WindowGroup {
      ContentView()
    }
  }
}

2. ContentView.swift

import SwiftUI

struct ContentView: View {
  let documents = Document.documents
  let title = "Thumbs"

  var body: some View {
    NavigationView {
      ScrollView(.vertical) {
        LazyVGrid(
          columns: [GridItem(.adaptive(minimum: 150, maximum: 150), spacing: 44)],
          spacing: 10
        ) {
          ForEach(documents) { document in
            NavigationLink(destination: DocumentPreviewView(document: document)) {
              DocumentThumbnailView(document: document)
            }
          }
        }
      }
      .navigationBarTitle(title)
    }
  }
}

struct ContentView_Previews: PreviewProvider {
  static var previews: some View {
    ContentView()
  }
}

3. Document.swift

import Foundation
import QuickLook

struct Document {
  let url: URL

  var name: String {
    url.lastPathComponent
  }
}

extension Document: Identifiable {
  var id: URL {
    url
  }
}

// MARK: - Static helper methods
extension Document {
  static let documents = [
    Bundle.main.url(forResource: "zombiethumb", withExtension: "jpg"),
    Bundle.main.url(forResource: "humanthumb", withExtension: "pdf"),
    Bundle.main.url(forResource: "thumbsup", withExtension: "txt"),
    Bundle.main.url(forResource: "thumbsdown", withExtension: "md"),
    Bundle.main.url(forResource: "thumbsdown", withExtension: "html"),
    Bundle.main.url(forResource: "greenthumb", withExtension: "thumb")
  ]
  .compactMap { $0 }
  .map { Document(url: $0) }
}

// MARK: - QLThumbnailGenerator
extension Document {
  func generateThumbnail(
    size: CGSize,
    scale: CGFloat,
    completion: @escaping (UIImage) -> Void
  ) {
    let request = QLThumbnailGenerator.Request(
      fileAt: url,
      size: size,
      scale: scale,
      representationTypes: .all
    )

    let generator = QLThumbnailGenerator.shared
    generator.generateRepresentations(for: request) { thumbnail, _, error in
      if let thumbnail = thumbnail {
        print("\(name) thumbnail generated")
        completion(thumbnail.uiImage)
      } else if let error = error {
        print("\(name) - \(error)")
      }
    }
  }
}

4. DocumentThumbnailView.swift

import SwiftUI

struct DocumentThumbnailView: View {
  let document: Document
  var thumbnailSize = CGSize(width: 150, height: 150)
  @State var thumbnail = Image(systemName: "doc")
  @Environment(\.displayScale) var displayScale: CGFloat

  var body: some View {
    GroupBox(label: Text(verbatim: document.name).font(.system(size: 12))) {
      thumbnail
        .font(.system(size: 120))
        .foregroundColor(Color(.label))
        .frame(width: thumbnailSize.width, height: thumbnailSize.height, alignment: .center)
        .clipShape(RoundedRectangle(cornerRadius: 8, style: .continuous))
        .padding()
    }
    .groupBoxStyle(PlainGroupBoxStyle())
    .onAppear {
      document.generateThumbnail(
        size: thumbnailSize,
        scale: displayScale
      ) { uiImage in
        DispatchQueue.main.async {
          self.thumbnail = Image(uiImage: uiImage)
        }
      }
    }
  }
}

struct PlainGroupBoxStyle: GroupBoxStyle {
  func makeBody(configuration: Configuration) -> some View {
    VStack(alignment: .center) {
      configuration.label
        .padding()
      configuration.content
    }
    .background(Color(.systemGroupedBackground))
    .clipShape(RoundedRectangle(cornerRadius: 8, style: .continuous))
  }
}

5. DocumentPreviewView.swift

import SwiftUI
import QuickLook

struct DocumentPreviewView: View {
  let document: Document

  var body: some View {
    QLPreviewView(previewItem: document.url as QLPreviewItem)
      .navigationBarTitle(document.name, displayMode: .inline)
  }
}

6. ThumbFile.swift

import Foundation
import UIKit.UIImage

struct ThumbFile: Codable {
  let title: String
  let imageBase64: String

  init?(from fileURL: URL) {
    guard
      let data = FileManager.default.contents(atPath: fileURL.path),
      let thumb = try? JSONDecoder().decode(Self.self, from: data)
    else {
      return nil
    }

    self = thumb
  }

  var uiImage: UIImage? {
    return Data(base64Encoded: imageBase64)
      .flatMap { UIImage(data: $0) }
  }
}

7. ThumbFileViewController.swift

import UIKit

class ThumbFileViewController: UIViewController {
  private lazy var titleLabel: UILabel = {
    let label = UILabel()
    label.translatesAutoresizingMaskIntoConstraints = false
    label.textAlignment = .center
    label.font = UIFont.preferredFont(forTextStyle: .title1)
    label.text = title
    return label
  }()

  private lazy var imageView: UIImageView = {
    let imageView = UIImageView()
    imageView.translatesAutoresizingMaskIntoConstraints = false
    return imageView
  }()

  override func viewDidLoad() {
    super.viewDidLoad()

    view.backgroundColor = .systemBackground
    view.addSubview(titleLabel)
    view.addSubview(imageView)

    NSLayoutConstraint.activate([
      titleLabel.topAnchor.constraint(equalTo: view.layoutMarginsGuide.topAnchor, constant: 30),
      titleLabel.trailingAnchor.constraint(equalTo: view.layoutMarginsGuide.trailingAnchor),
      titleLabel.leadingAnchor.constraint(equalTo: view.layoutMarginsGuide.leadingAnchor),
      imageView.topAnchor.constraint(equalTo: titleLabel.bottomAnchor, constant: 50.0),
      imageView.centerXAnchor.constraint(equalTo: view.centerXAnchor)
    ])
  }

  var thumbFile: ThumbFile? {
    didSet {
      titleLabel.text = thumbFile?.title
      imageView.image = thumbFile?.uiImage
    }
  }

  static func generateThumbnail(for thumbFile: ThumbFile, size: CGSize) -> UIImage {
    dispatchPrecondition(condition: .onQueue(.main))

    let viewController = ThumbFileViewController()
    viewController.thumbFile = thumbFile
    viewController.view.frame = CGRect(origin: .zero, size: CGSize(width: 450, height: 450))
    viewController.view.updateConstraintsIfNeeded()
    viewController.view.layoutIfNeeded()

    let renderer = UIGraphicsImageRenderer(bounds: viewController.view.bounds)
    return renderer.image { context in
      viewController.view.layer.render(in: context.cgContext)
    }
  }
}

8. QLPreviewView.swift

import SwiftUI
import QuickLook

struct QLPreviewView: UIViewControllerRepresentable {
  var previewItem: QLPreviewItem

  func makeCoordinator() -> Coordinator {
    Coordinator(parent: self)
  }

  func updateUIViewController(
    _ viewController: QLPreviewController,
    context: UIViewControllerRepresentableContext
  ) {
    viewController.reloadData()
  }

  func makeUIViewController(context: Context) -> QLPreviewController {
    // For more on using QLPreviewController, check out this tutorial:
    // https://www.raywenderlich.com/10447506-quicklook-previews-for-ios-getting-started
    let controller = QLPreviewController()
    controller.dataSource = context.coordinator
    controller.reloadData()
    return controller
  }

  class Coordinator: NSObject, QLPreviewControllerDataSource {
    var parent: QLPreviewView

    init(parent: QLPreviewView) {
      self.parent = parent
      super.init()
    }

    // MARK: - QLPreviewControllerDataSource
    func numberOfPreviewItems(in controller: QLPreviewController) -> Int {
      return 1
    }

    func previewController(
      _ controller: QLPreviewController,
      previewItemAt index: Int
    ) -> QLPreviewItem {
      return parent.previewItem
    }
  }
}

9. PreviewViewController.swift

import UIKit
import QuickLook

class PreviewViewController: ThumbFileViewController, QLPreviewingController {
  enum ThumbFilePreviewError: Error {
    case unableToOpenFile(atURL: URL)
  }

  func preparePreviewOfFile(
    at url: URL,
    completionHandler handler: @escaping (Error?) -> Void
  ) {
    guard let thumbFile = ThumbFile(from: url) else {
      handler(ThumbFilePreviewError.unableToOpenFile(atURL: url))
      return
    }

    self.thumbFile = thumbFile

    handler(nil)
  }
}

10. ThumbnailProvider.swift

import UIKit
import QuickLookThumbnailing

class ThumbnailProvider: QLThumbnailProvider {
  enum ThumbFileThumbnailError: Error {
    case unableToOpenFile(atURL: URL)
  }

  override func provideThumbnail(
    for request: QLFileThumbnailRequest,
    _ handler: @escaping (QLThumbnailReply?, Error?) -> Void
  ) {
    guard let thumbFile = ThumbFile(from: request.fileURL) else {
      handler(nil, ThumbFileThumbnailError.unableToOpenFile(atURL: request.fileURL))
      return
    }

    DispatchQueue.main.async {
      let image = ThumbFileViewController.generateThumbnail(
        for: thumbFile,
        size: request.maximumSize
      )

      let reply = QLThumbnailReply(contextSize: request.maximumSize) {
        image.draw(in: CGRect(origin: .zero, size: request.maximumSize))
        return true
      }

      handler(reply, nil)
    }
  }
}

后记

本篇主要讲述了QuickLook预览和缩略图扩展的实现，感兴趣的给个赞或者关注~~~