Introduction to plist

The Property List, commonly referred to as plist, is a versatile data format primarily used on the macOS and iOS platforms. The plist format is used to store serialized objects, often utilized for app configurations, user settings, and data persistence.

Common plist APIs

1. Reading a plist file:

To read a plist file in Swift, you can use the `PropertyListDecoder` class:

  import Foundation

  struct MyData: Codable {
    let name: String
    let age: Int
  }

  if let url = Bundle.main.url(forResource: "data", withExtension: "plist") {
    do {
      let data = try Data(contentsOf: url)
      let decoder = PropertyListDecoder()
      let plistData = try decoder.decode(MyData.self, from: data)
      print(plistData)
    } catch {
      print("Error reading plist: \(error)")
    }
  }
  

2. Writing to a plist file:

Writing data to a plist file involves using the `PropertyListEncoder`:

  import Foundation

  struct MyData: Codable {
    let name: String
    let age: Int
  }
  
  let myData = MyData(name: "John Doe", age: 30)
  
  if let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first {
    let plistURL = documentsDirectory.appendingPathComponent("data.plist")
  
    do {
      let encoder = PropertyListEncoder()
      encoder.outputFormat = .xml
      let data = try encoder.encode(myData)
      try data.write(to: plistURL)
      print("Data written to plist")
    } catch {
      print("Error writing plist: \(error)")
    }
  }
  

3. Modifying plist data:

Modifying a plist can be done by reading it into a mutable structure, updating the data, and then writing it back:

  import Foundation

  struct MyData: Codable {
    var name: String
    var age: Int
  }

  if let url = Bundle.main.url(forResource: "data", withExtension: "plist") {
    do {
      let data = try Data(contentsOf: url)
      var plistData = try PropertyListDecoder().decode(MyData.self, from: data)
      
      // Modify data
      plistData.age = 31
      
      // Write it back
      let encoder = PropertyListEncoder()
      encoder.outputFormat = .xml
      let newData = try encoder.encode(plistData)
      try newData.write(to: url)
      print("Plist data modified")
    } catch {
      print("Error modifying plist: \(error)")
    }
  }
  

Example App Utilizing Plist:

Let’s consider a simple app that uses a plist to save and load user profile data.

  import SwiftUI

  struct UserProfile: Codable {
    var username: String
    var email: String
  }
  
  @MainActor
  class UserProfileViewModel: ObservableObject {
    @Published var profile: UserProfile = UserProfile(username: "", email: "")

    init() {
      loadProfile()
    }

    func loadProfile() {
      if let url = Bundle.main.url(forResource: "UserProfile", withExtension: "plist") {
        do {
          let data = try Data(contentsOf: url)
          let decoder = PropertyListDecoder()
          self.profile = try decoder.decode(UserProfile.self, from: data)
        } catch {
          print("Error loading profile: \(error)")
        }
      }
    }

    func saveProfile() {
      if let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first {
        let plistURL = documentsDirectory.appendingPathComponent("UserProfile.plist")
  
        do {
          let encoder = PropertyListEncoder()
          encoder.outputFormat = .xml
          let data = try encoder.encode(self.profile)
          try data.write(to: plistURL)
        } catch {
          print("Error saving profile: \(error)")
        }
      }
    }
  }

  struct ContentView: View {
    @StateObject private var viewModel = UserProfileViewModel()

    var body: some View {
      VStack {
        TextField("Username", text: $viewModel.profile.username)
          .padding()
        TextField("Email", text: $viewModel.profile.email)
          .padding()
        Button("Save Profile") {
          viewModel.saveProfile()
        }
        .padding()
      }
      .padding()
    }
  }

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

This simple app demonstrates how to load, display, update, and save user profile data using plist files.