Basic data storage (Swift)

Prepared and tested with Xcode 9.2 and Swift 4 (2018-04-24)

In this tutorial we cover the following topics

General information
- Sandbox
- Getting the right path
General app
- Step 1: create a new project
- Step 2: add components
Property list with deprecated NSArray write(to:atomically:)
Property list with Codable protocol
- Step 1: add/modify code
- Step 2: run app
Bundle property list with Codable
Encode and decode with a custom type
Sources

General information

There are many different methods we can use to save our data in iOS devices. Here we will examine the most basic, adequate to save small amount of data.

Sandbox

Every application has its own, independent and restricted, area in file system space, called sandbox. Generaly speaking, no other applications are allowed to get an access to this area. When working with simulator and Xcode, we can find this sandbox in



[YOUR_HOME_DIRECTORY]/Library/Developer/CoreSimulator/Devices/

Let's test it. Open a Finder window and navigate to your home directory. If you can't see your Library folder, hold down the Alt key and select Go | Library from top main menu. Having Library displayed, select Developer/CoreSimulator/Devices/.

Within that directory, there is one subdirectory for each simulator in Xcode installation. The subdirectory names are GUIDs (globally unique identifiers) generated automatically by Xcode, so it’s impossible to know just by looking at them which directory corresponds to which simulator. To find out we should examine a file called device.plist in any of the simulator directories and open it.

We can also examine device_set.plist located in Devices



pc18:Devices fulmanp$ pwd

/Users/fulmanp/Library/Developer/CoreSimulator/Devices

pc18:Devices fulmanp$ ls

017F1FAA-A538-4B05-99DD-56005B2A781E	8DE4F1A7-E3C2-473E-81A4-522DD7A07CC0

033BC02B-C984-44A5-BAF6-858E8521B879	8DFEAA23-D012-4FAB-A7F4-B5D000F2078B

[... cut to save some space ...]

89EF7B1E-0902-4CA6-8FE9-19EB5B99D1E0	FF38963D-624D-423E-8B93-6989F334A20A

8C70AEA1-A42A-42CB-A513-93EF80591E5D	device_set.plist

8D3575AE-DBDC-474E-8652-4E2420833DBB

pc18:Devices fulmanp$



[USER_HOME_DIRECTORY]/Library/Developer/CoreSimulator/Devices/device_set.plist

Every application sandbox contains three directories

Documents Our application can store data in Documents directory. Use this directory to store user-generated content. If iTunes file sharing is enabled for our application, the user can see the contents of this directory and its subdirectories in iTunes and can also upload files to it.
Library This directory is used to store files that we do not want to share with others. This is the top-level directory for any files that are not user data files.
tmp This directory is a place where an application can store temporary files. Files written into it will not be backed up by iTunes.

Getting the right path

As we have seen, path to the applicaton folder is somehow random. To get the right one, we have to use one of the function prepared for this occasion.

        // To get Documents directory
        let dirPaths = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)
        let documentDirectory = dirPaths[0]
        
        // To get tmp directory
        let tmpDirectory = NSTemporaryDirectory();
        
        // To create a full path to a file "someFile.txt" located in "directory" directory
        let filePathString = directory + "/" + "someFile.txt"

// To get Documents directory

let dirPaths = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)

let documentDirectory = dirPaths[0]

// To get tmp directory

let tmpDirectory = NSTemporaryDirectory();

// To create a full path to a file "someFile.txt" located in "directory" directory

let filePathString = directory + "/" + "someFile.txt"

The same in more Swifty way

	let documentDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first
    let filePathURL = documentDirectory!.appendingPathComponent("someFile.txt")

1 2	let documentDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first let filePathURL = documentDirectory!.appendingPathComponent("someFile.txt")

General app

Step 1: create a new project
Create a new project
1. Select File | New | Project...
2. Select Single View Application on the template selection sheet.
3. As the product name enter Swift iOS Basic Data Storage
4. Set the Language to Swift. Because we will not use tests in this tutorial, you can leave both test check boxes unchecked as well as make sure the check box labeled Use Core Data is also unchecked.

Step 2: add components

Select Main.storyboard and from the Object library drag
- one Text field
- two Buttons
- one Text view
Set all the constraints required for a correc layout.
- Set Title for a left button as Save.
- Set Title for a right button as Load.
Create outlets for all components so we can use them in the future
- for Text field creat textField outlet
- for left (Save) Button creat buttonSave outlet
- for right (Load) Button creat buttonLoad outlet
- for Text view creat textView outlet
Create actions for button
- for left (Save) Button creat buttonPressSave action
- for right (Load) Button creat buttonPressLoad action

Now our code should look like below

//
//  ViewController.swift
//  Swift iOS Basic Data Storage
//
//  Created by Piotr Fulmański on 2018.04.24.
//  Copyright © 2018 Piotr Fulmański. All rights reserved.
//

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var textField: UITextField!
    @IBOutlet weak var buttonSave: UIButton!
    @IBOutlet weak var buttonLoad: UIButton!
    @IBOutlet weak var textView: UITextView!
    
    @IBAction func buttonPressSave(_ sender: UIButton) {
    }
    
    @IBAction func buttonPressLoad(_ sender: UIButton) {
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

// ViewController.swift

// Swift iOS Basic Data Storage

// Created by Piotr Fulmański on 2018.04.24.

import UIKit

class ViewController: UIViewController {

@IBOutlet weak var textField: UITextField!

@IBOutlet weak var buttonSave: UIButton!

@IBOutlet weak var buttonLoad: UIButton!

@IBOutlet weak var textView: UITextView!

@IBAction func buttonPressSave(_ sender: UIButton) {

}

@IBAction func buttonPressLoad(_ sender: UIButton) {

}

override func viewDidLoad() {

super.viewDidLoad()

// Do any additional setup after loading the view, typically from a nib.

}

override func didReceiveMemoryWarning() {

super.didReceiveMemoryWarning()

// Dispose of any resources that can be recreated.

}

Property list with deprecated NSArray write(to:atomically:)

In case we want to use property lists to persist our data, we have to use either an NSArray or an NSDictionary as a main data structure to hold the data that needs to be saved. In addition to this we can build our data model from the following objects

NSArray, NSMutableArray
NSDictionary, NSMutableDictionary
NSData, NSMutableData
NSString, NSMutableString
NSNumber
NSDate

Main drawback of this approach is that custom objects cannot be serialized into property lists.

Assuming that all the objects that we put into the NSArray or an NSDictionary are serializable objects from this list, we can write and read a property list, like so

Step 1: add/modify ViewController's code to get path

var pathFull:String?
    
    func getPath() -> String {
        let dirPaths = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)
        let documentDirectory = dirPaths[0]

        return documentDirectory + "/" + "test.plist"
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        pathFull = getPath()
    }

var pathFull:String?

func getPath() -> String {

let dirPaths = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)

let documentDirectory = dirPaths[0]

return documentDirectory + "/" + "test.plist"

}

override func viewDidLoad() {

super.viewDidLoad()

// Do any additional setup after loading the view, typically from a nib.

pathFull = getPath()

}

Step 2: add/modify code

    @IBAction func buttonPressSave(_ sender: UIButton) {
        savePList()
    }
    
    @IBAction func buttonPressLoad(_ sender: UIButton) {
        loadPList()
    }
    
    func loadPList() {
        if let path = pathFull {
            let data:NSArray = NSArray(contentsOfFile: path)!
            print(data)
        }
    }
    
    func savePList() {
        if let path = pathFull {
            // It is not possible to save dictionary which basically can
            // store any key-value (for example [String:Any]) pair
            // It must be for example [String:Int]
            let data = [["name": "List 1", "items": "1", "0": "1"],
                        ["name": "List 2", "items": "2", "0": "2", "1": "test2"],
                        ["name": "List 3", "items": "3", "0": "2", "2": "test3", "3": "3.21"]]

            let pathUrl = URL(fileURLWithPath: path)
            textView.text = pathUrl.absoluteString
            // Method below works, however according to
            // https://developer.apple.com/documentation/foundation/nsarray/1411480-write
            // write(to:atomically:) is deprecated
            (data as NSArray).write(to: pathUrl, atomically: true)
        }
    }

@IBAction func buttonPressSave(_ sender: UIButton) {

savePList()

}

@IBAction func buttonPressLoad(_ sender: UIButton) {

loadPList()

}

func loadPList() {

if let path = pathFull {

let data:NSArray = NSArray(contentsOfFile: path)!

print(data)

}

func savePList() {

if let path = pathFull {

// It is not possible to save dictionary which basically can

// store any key-value (for example [String:Any]) pair

// It must be for example [String:Int]

let data = [["name": "List 1", "items": "1", "0": "1"],

["name": "List 2", "items": "2", "0": "2", "1": "test2"],

["name": "List 3", "items": "3", "0": "2", "2": "test3", "3": "3.21"]]

let pathUrl = URL(fileURLWithPath: path)

textView.text = pathUrl.absoluteString

// Method below works, however according to

// https://developer.apple.com/documentation/foundation/nsarray/1411480-write

// write(to:atomically:) is deprecated

(data as NSArray).write(to: pathUrl, atomically: true)

}

Step 3: run app
Executed an application and press Save button. A path smilar to the following should be printed as an output in the Text view



file:///Users/fulmanp/Library/Developer/CoreSimulator/Devices/7CF76BA3-51AB-461C-8AE5-B890E6971352/

data/Containers/Data/Application/6D3282F2-343B-40BC-A0DB-C12FF847F1AC/Documents/test.plist

We can check its contents

MacBook-Air-Piotr:Documents fulmanp$ pwd
/Users/fulmanp/Library/Developer/CoreSimulator/Devices/7CF76BA3-51AB-461C-8AE5-B890E6971352/
data/Containers/Data/Application/6D3282F2-343B-40BC-A0DB-C12FF847F1AC/Documents
MacBook-Air-Piotr:Documents fulmanp$ ls -l
total 8
-rw-r--r--  1 fulmanp  staff  720 24 kwi 22:20 test.plist
MacBook-Air-Piotr:Documents fulmanp$ cat test.plist 
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<array>
	<dict>
		<key>0</key>
		<string>1</string>
		<key>items</key>
		<string>1</string>
		<key>name</key>
		<string>List 1</string>
	</dict>
	<dict>
		<key>0</key>
		<string>2</string>
		<key>1</key>
		<string>test2</string>
		<key>items</key>
		<string>2</string>
		<key>name</key>
		<string>List 2</string>
	</dict>
	<dict>
		<key>0</key>
		<string>2</string>
		<key>2</key>
		<string>test3</string>
		<key>3</key>
		<string>3.21</string>
		<key>items</key>
		<string>3</string>
		<key>name</key>
		<string>List 3</string>
	</dict>
</array>
</plist>

MacBook-Air-Piotr:Documents fulmanp$ pwd

/Users/fulmanp/Library/Developer/CoreSimulator/Devices/7CF76BA3-51AB-461C-8AE5-B890E6971352/

data/Containers/Data/Application/6D3282F2-343B-40BC-A0DB-C12FF847F1AC/Documents

MacBook-Air-Piotr:Documents fulmanp$ ls -l

total 8

-rw-r--r-- 1 fulmanp staff 720 24 kwi 22:20 test.plist

MacBook-Air-Piotr:Documents fulmanp$ cat test.plist

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">

<array>

<dict>

<key>items</key>

</dict>

<dict>

<key>items</key>

</dict>

<dict>

<key>items</key>

</dict>

</array>

</plist>

When Load is pressed, the following text should be printed as an output in the Debug area



(

        {

        0 = 1;

        items = 1;

        name = "List 1";

    },

        {

        0 = 2;

        1 = test2;

        items = 2;

        name = "List 2";

    },

        {

        0 = 2;

        2 = test3;

        3 = "3.21";

        items = 3;

        name = "List 3";

    }

)

Property list with Codable protocol

NSArray write(to:atomically:) is deprecated and the Codable protocol which is new to Swift in iOS 11 should be used instead. In some sense Code is a logical consequence of preceding NSCoding protocol.
Some good materials are

Step 1: add/modify code

    @IBAction func buttonPressSave(_ sender: UIButton) {
        //savePList()
        savePListWithCodable()
    }
    
    @IBAction func buttonPressLoad(_ sender: UIButton) {
        //loadPList()
        loadPListWithCodable()
    }
    
    func loadPListWithCodable() {
        if let path = pathFull {
            let pathUrl = URL(fileURLWithPath: path)
            do {
                let dataToDecode = try Data(contentsOf: pathUrl)
                let decoder = PropertyListDecoder()
                let data = try decoder.decode([[String:String]].self, from: dataToDecode)
                print(data)
                print(data[1]["name"]!)
            } catch {
                // Handle error
                print(error)
            }
        }
    }
    
    func savePListWithCodable() {
        if let path = pathFull {
            // It is not possible to save dictionary which basically can
            // store any key-value (for example [String:Any]) pair
            // It must be for example [String:Int]
            let data = [["name": "List 1", "items": "1", "0": "1"],
                        ["name": "List 2", "items": "2", "0": "2", "1": "test2"],
                        ["name": "List 3", "items": "3", "0": "2", "2": "test3", "3": "3.21"]]
            
            let pathUrl = URL(fileURLWithPath: path)
            textView.text = pathUrl.absoluteString

             let encoder = PropertyListEncoder()
             encoder.outputFormat = .xml
             do {
                let dataEncoder = try encoder.encode(data)
                try dataEncoder.write(to: pathUrl)
             } catch {
                print(error)
             }
        }
    }

@IBAction func buttonPressSave(_ sender: UIButton) {

//savePList()

savePListWithCodable()

}

@IBAction func buttonPressLoad(_ sender: UIButton) {

//loadPList()

loadPListWithCodable()

}

func loadPListWithCodable() {

if let path = pathFull {

let pathUrl = URL(fileURLWithPath: path)

do {

let dataToDecode = try Data(contentsOf: pathUrl)

let decoder = PropertyListDecoder()

let data = try decoder.decode([[String:String]].self, from: dataToDecode)

print(data)

print(data[1]["name"]!)

} catch {

// Handle error

print(error)

}

func savePListWithCodable() {

if let path = pathFull {

// It is not possible to save dictionary which basically can

// store any key-value (for example [String:Any]) pair

// It must be for example [String:Int]

let data = [["name": "List 1", "items": "1", "0": "1"],

["name": "List 2", "items": "2", "0": "2", "1": "test2"],

["name": "List 3", "items": "3", "0": "2", "2": "test3", "3": "3.21"]]

let pathUrl = URL(fileURLWithPath: path)

textView.text = pathUrl.absoluteString

let encoder = PropertyListEncoder()

encoder.outputFormat = .xml

do {

let dataEncoder = try encoder.encode(data)

try dataEncoder.write(to: pathUrl)

} catch {

print(error)

}

Step 2: run app
Executed an application and press Save button. A path smilar to the following should be printed as an output in the Text view



file:///Users/fulmanp/Library/Developer/CoreSimulator/Devices/7CF76BA3-51AB-461C-8AE5-B890E6971352/

data/Containers/Data/Application/2A5CB84C-D982-4FE0-AACD-E69813E905E4/Documents/test.plist

We can check its contents

MacBook-Air-Piotr:Documents fulmanp$ pwd
/Users/fulmanp/Library/Developer/CoreSimulator/Devices/7CF76BA3-51AB-461C-8AE5-B890E6971352/
data/Containers/Data/Application/2A5CB84C-D982-4FE0-AACD-E69813E905E4/Documents
MacBook-Air-Piotr:Documents fulmanp$ ls -l
total 8
-rw-r--r--  1 fulmanp  staff  720 24 kwi 23:37 test.plist
MacBook-Air-Piotr:Documents fulmanp$ cat test.plist 
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<array>
	<dict>
		<key>0</key>
		<string>1</string>
		<key>items</key>
		<string>1</string>
		<key>name</key>
		<string>List 1</string>
	</dict>
	<dict>
		<key>0</key>
		<string>2</string>
		<key>1</key>
		<string>test2</string>
		<key>items</key>
		<string>2</string>
		<key>name</key>
		<string>List 2</string>
	</dict>
	<dict>
		<key>0</key>
		<string>2</string>
		<key>2</key>
		<string>test3</string>
		<key>3</key>
		<string>3.21</string>
		<key>items</key>
		<string>3</string>
		<key>name</key>
		<string>List 3</string>
	</dict>
</array>
</plist>

MacBook-Air-Piotr:Documents fulmanp$ pwd

/Users/fulmanp/Library/Developer/CoreSimulator/Devices/7CF76BA3-51AB-461C-8AE5-B890E6971352/

data/Containers/Data/Application/2A5CB84C-D982-4FE0-AACD-E69813E905E4/Documents

MacBook-Air-Piotr:Documents fulmanp$ ls -l

total 8

-rw-r--r-- 1 fulmanp staff 720 24 kwi 23:37 test.plist

MacBook-Air-Piotr:Documents fulmanp$ cat test.plist

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">

<array>

<dict>

<key>items</key>

</dict>

<dict>

<key>items</key>

</dict>

<dict>

<key>items</key>

</dict>

</array>

</plist>

When Load is pressed, the following text should be printed as an output in the Debug area



[["items": "1", "0": "1", "name": "List 1"], ["items": "2", "name": "List 2", "1": "test2",

"0": "2"], ["items": "3", "name": "List 3", "2": "test3", "0": "2", "3": "3.21"]]

List 2

Bundle property list with Codable protocol

Codable and bundle property list works exactly the same way as property lists. The only true diference is how we get the path to a bundle propert list.

Step 1: cerate bundle property list
- In the Project Navigator, right-click the Swift iOS Basic Data Storage group and select New File....
- Choose Property List from the iOS | Resources section in the template dialog and then press Next
- Name the property list Settings.plist and press Create. We should see a blank property list
Step 2: add property list items
- When hover over the root entry we will find a + button to add an entry
- When the + button is clicked a new entry appears, with a default type of String
- By analogy, add some items

Step 3: add/modify code

    @IBAction func buttonPressSave(_ sender: UIButton) {
        //savePList()
        //savePListWithCodable()
        savePListBoundle()
    }
    
    @IBAction func buttonPressLoad(_ sender: UIButton) {
        //loadPList()
        //loadPListWithCodable()
        loadPListBoundle()
    }
    
    func loadPListBoundle() {
        pathFull = Bundle.main.path(forResource:"Settings", ofType: "plist")
        if let path = pathFull {
            let pathUrl = URL(fileURLWithPath: path)
            do {
                let dataToDecode = try Data(contentsOf: pathUrl)
                let decoder = PropertyListDecoder()
                let data = try decoder.decode([String:String].self, from: dataToDecode)
                print(data)
                if let d = data["Setting 1"] {
                    print(d)
                }
            } catch {
                print(error)
            }
        }
    }
    
    func savePListBoundle() {
        pathFull = Bundle.main.path(forResource:"Settings", ofType: "plist")
        if let path = pathFull {
            // It is not possible to save dictionary which basically can
            // store any key-value (for example [String:Any]) pair
            // It must be for example [String:Int]
            let data = ["name": "List 3", "items": "3", "0": "2", "2": "test3", "3": "3.21"]
            
            let pathUrl = URL(fileURLWithPath: path)
            textView.text = pathUrl.absoluteString
            
            let encoder = PropertyListEncoder()
            encoder.outputFormat = .xml
            do {
                let dataEncoder = try encoder.encode(data)
                try dataEncoder.write(to: pathUrl)
            } catch {
                print(error)
            }
        }
    }

@IBAction func buttonPressSave(_ sender: UIButton) {

//savePList()

//savePListWithCodable()

savePListBoundle()

}

@IBAction func buttonPressLoad(_ sender: UIButton) {

//loadPList()

//loadPListWithCodable()

loadPListBoundle()

}

func loadPListBoundle() {

pathFull = Bundle.main.path(forResource:"Settings", ofType: "plist")

if let path = pathFull {

let pathUrl = URL(fileURLWithPath: path)

do {

let dataToDecode = try Data(contentsOf: pathUrl)

let decoder = PropertyListDecoder()

let data = try decoder.decode([String:String].self, from: dataToDecode)

print(data)

if let d = data["Setting 1"] {

print(d)

}

} catch {

print(error)

}

func savePListBoundle() {

pathFull = Bundle.main.path(forResource:"Settings", ofType: "plist")

if let path = pathFull {

// It is not possible to save dictionary which basically can

// store any key-value (for example [String:Any]) pair

// It must be for example [String:Int]

let data = ["name": "List 3", "items": "3", "0": "2", "2": "test3", "3": "3.21"]

let pathUrl = URL(fileURLWithPath: path)

textView.text = pathUrl.absoluteString

let encoder = PropertyListEncoder()

encoder.outputFormat = .xml

do {

let dataEncoder = try encoder.encode(data)

try dataEncoder.write(to: pathUrl)

} catch {

print(error)

}

Step 4: run app

Executed an application and press Load button. The following text should be printed as an output in the Debug area
```
["Setting 1": "Value 1"]

Value 1
```

Press Save button. A path smilar to the following should be printed as an output in the Text view



file:///Users/fulmanp/Library/Developer/CoreSimulator/Devices/7CF76BA3-51AB-461C-8AE5-B890E6971352/

data/Containers/Bundle/Application/689888CB-3540-457C-952B-4A2D8E29B941/Swift%20iOS%20Basic%20Data%

20Storage.app/Settings.plist

We can check its contents

MacBook-Air-Piotr:Swift iOS Basic Data Storage.app fulmanp$ pwd
/Users/fulmanp/Library/Developer/CoreSimulator/Devices/7CF76BA3-51AB-461C-8AE5-B890E6971352/
data/Containers/Bundle/Application/689888CB-3540-457C-952B-4A2D8E29B941/Swift iOS Basic Data Storage.app
MacBook-Air-Piotr:Swift iOS Basic Data Storage.app fulmanp$ ls -l
total 1920
drwxr-xr-x   4 fulmanp  staff     128 25 kwi 00:52 Base.lproj
drwxr-xr-x  15 fulmanp  staff     480 25 kwi 00:52 Frameworks
-rw-r--r--   1 fulmanp  staff    1180 24 kwi 13:10 Info.plist
-rw-r--r--   1 fulmanp  staff       8 24 kwi 13:10 PkgInfo
-rw-r--r--   1 fulmanp  staff     720 25 kwi 00:52 Settings.plist
-rwxr-xr-x   1 fulmanp  staff  116032 25 kwi 00:52 Swift iOS Basic Data Storage
drwxr-xr-x   3 fulmanp  staff      96 25 kwi 00:52 _CodeSignature
-rw-r--r--   1 fulmanp  staff  799312 25 kwi 00:52 libswiftRemoteMirror.dylib
MacBook-Air-Piotr:Swift iOS Basic Data Storage.app fulmanp$ cat Settings.plist 
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<array>
	<dict>
		<key>0</key>
		<string>1</string>
		<key>items</key>
		<string>1</string>
		<key>name</key>
		<string>List 1</string>
	</dict>
	<dict>
		<key>0</key>
		<string>2</string>
		<key>1</key>
		<string>test2</string>
		<key>items</key>
		<string>2</string>
		<key>name</key>
		<string>List 2</string>
	</dict>
	<dict>
		<key>0</key>
		<string>2</string>
		<key>2</key>
		<string>test3</string>
		<key>3</key>
		<string>3.21</string>
		<key>items</key>
		<string>3</string>
		<key>name</key>
		<string>List 3</string>
	</dict>
</array>
</plist>

MacBook-Air-Piotr:Swift iOS Basic Data Storage.app fulmanp$ pwd

/Users/fulmanp/Library/Developer/CoreSimulator/Devices/7CF76BA3-51AB-461C-8AE5-B890E6971352/

data/Containers/Bundle/Application/689888CB-3540-457C-952B-4A2D8E29B941/Swift iOS Basic Data Storage.app

MacBook-Air-Piotr:Swift iOS Basic Data Storage.app fulmanp$ ls -l

total 1920

drwxr-xr-x 4 fulmanp staff 128 25 kwi 00:52 Base.lproj

drwxr-xr-x 15 fulmanp staff 480 25 kwi 00:52 Frameworks

-rw-r--r-- 1 fulmanp staff 1180 24 kwi 13:10 Info.plist

-rw-r--r-- 1 fulmanp staff 8 24 kwi 13:10 PkgInfo

-rw-r--r-- 1 fulmanp staff 720 25 kwi 00:52 Settings.plist

-rwxr-xr-x 1 fulmanp staff 116032 25 kwi 00:52 Swift iOS Basic Data Storage

drwxr-xr-x 3 fulmanp staff 96 25 kwi 00:52 _CodeSignature

-rw-r--r-- 1 fulmanp staff 799312 25 kwi 00:52 libswiftRemoteMirror.dylib

MacBook-Air-Piotr:Swift iOS Basic Data Storage.app fulmanp$ cat Settings.plist

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">

<array>

<dict>

<key>items</key>

</dict>

<dict>

<key>items</key>

</dict>

<dict>

<key>items</key>

</dict>

</array>

</plist>

Press Load button. The following text should be printed as an output in the Debug area
```
["items": "3", "name": "List 3", "2": "test3", "0": "2", "3": "3.21"]
```

Encode and decode with a custom type

As we have seen Codable protocols simplify saving our data to propert list. If we want to operate this way with more complex object than for example [String: String] dictionary, preferably something like [String: Any], we have to use custom types. Having custom type, we can save/read our data to/from a property list as well as JSON. Some good materials we can read about this were mentioned in Property list with Codable protocol section. In short, to encode and decode a custom type, we need to make it Codable. The simplest way to make a type codable is to declare its properties using types that are already Codable

Built-in Codable types: String, Int, Double, Data, URL.
Array, Dictionary, Optional are Codable if they contain Codable types.

We will show how it works with JSON files, but the same apprach is used for property list - simply use ideas from the previous sections: Property list with Codable protocol or Bundle property list with Codable protocol.

Step 1: change path generating code to make it more Swifty

    // Old way:
    var pathFull:String?
    
    func getPath() -> String {
        let dirPaths = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)
        let documentDirectory = dirPaths[0]
        return documentDirectory + "/" + "test.plist"
    }

    // The same in more Swifty way:
    var pathUrl:URL?
    
    func getPath() -> URL {
        let documentDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first
        //return documentDirectory.appendingPathComponent("test.plist")
        return documentDirectory!.appendingPathComponent("test.json")
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        pathFull = getPath() // Path as a String
        pathUrl = getPath() // Path as an URL
    }

// Old way:

var pathFull:String?

func getPath() -> String {

let dirPaths = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)

let documentDirectory = dirPaths[0]

return documentDirectory + "/" + "test.plist"

}

// The same in more Swifty way:

var pathUrl:URL?

func getPath() -> URL {

let documentDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first

//return documentDirectory.appendingPathComponent("test.plist")

return documentDirectory!.appendingPathComponent("test.json")

}

override func viewDidLoad() {

super.viewDidLoad()

// Do any additional setup after loading the view, typically from a nib.

pathFull = getPath() // Path as a String

pathUrl = getPath() // Path as an URL

}

Step 2: add custom types to be saved

struct Lists: Codable {
    var count: Int
    var lists: [List]
}

struct List: Codable {
    var name: String
    var itemInt: Int
    var itemString: String
    var itemFloat: Double
    var itemBool: Bool
}

class ViewController: UIViewController {
...
}

struct Lists: Codable {

var count: Int

var lists: [List]

}

struct List: Codable {

var name: String

var itemInt: Int

var itemString: String

var itemFloat: Double

var itemBool: Bool

}

class ViewController: UIViewController {

...

}

Step 3: add/modify code

    @IBAction func buttonPressSave(_ sender: UIButton) {
        //savePList()
        //savePListWithCodable()
        //savePListBoundle()
        saveCustomTypeWithCodable()
    }
    
    @IBAction func buttonPressLoad(_ sender: UIButton) {
        //loadPList()
        //loadPListWithCodable()
        //loadPListBoundle()
        loadCustomTypeWithCodable()
    }
    
    func loadCustomTypeWithCodable() {
        if let pathUrl = pathUrl {
            do {
                let jsonFileContents = try String(contentsOf: pathUrl, encoding: .utf8)
                let lists = try JSONDecoder().decode(Lists.self, from: jsonFileContents.data(using: .utf8)!)
                print(lists.count)
                for list in lists.lists {
                    print("\(list.name): \(list.itemInt) \(list.itemString) \(list.itemFloat) \(list.itemBool)")
                }
            } catch let error {
                print("Encoding error: ", error)
            }
        }
    }
    
    func saveCustomTypeWithCodable() {
        if let pathUrl = pathUrl {
            textView.text = pathUrl.absoluteString
            
            let list1 = List(name: "List 1", itemInt: 1, itemString: "String 1", itemFloat: 1.23, itemBool: true)
            let list2 = List(name: "List 2", itemInt: 2, itemString: "String 2", itemFloat: 2.34, itemBool: false)
            let list3 = List(name: "List 3", itemInt: 3, itemString: "String 3", itemFloat: 3.45, itemBool: true)
            
            let lists = Lists(count: 3, lists: [list1, list2, list3])
            
            let jsonEncoder = JSONEncoder()
            do {
                let jsonData = try jsonEncoder.encode(lists)
                let jsonString = String(data: jsonData, encoding: .utf8)
                print(jsonString!)
                
                try jsonString?.write(to: pathUrl, atomically: true, encoding: .utf8)
            } catch let error {
                print("Encoding error: ", error)
            }
        }
    }

@IBAction func buttonPressSave(_ sender: UIButton) {

//savePList()

//savePListWithCodable()

//savePListBoundle()

saveCustomTypeWithCodable()

}

@IBAction func buttonPressLoad(_ sender: UIButton) {

//loadPList()

//loadPListWithCodable()

//loadPListBoundle()

loadCustomTypeWithCodable()

}

func loadCustomTypeWithCodable() {

if let pathUrl = pathUrl {

do {

let jsonFileContents = try String(contentsOf: pathUrl, encoding: .utf8)

let lists = try JSONDecoder().decode(Lists.self, from: jsonFileContents.data(using: .utf8)!)

print(lists.count)

for list in lists.lists {

print("\(list.name): \(list.itemInt) \(list.itemString) \(list.itemFloat) \(list.itemBool)")

}

} catch let error {

print("Encoding error: ", error)

}

func saveCustomTypeWithCodable() {

if let pathUrl = pathUrl {

textView.text = pathUrl.absoluteString

let list1 = List(name: "List 1", itemInt: 1, itemString: "String 1", itemFloat: 1.23, itemBool: true)

let list2 = List(name: "List 2", itemInt: 2, itemString: "String 2", itemFloat: 2.34, itemBool: false)

let list3 = List(name: "List 3", itemInt: 3, itemString: "String 3", itemFloat: 3.45, itemBool: true)

let lists = Lists(count: 3, lists: [list1, list2, list3])

let jsonEncoder = JSONEncoder()

do {

let jsonData = try jsonEncoder.encode(lists)

let jsonString = String(data: jsonData, encoding: .utf8)

print(jsonString!)

try jsonString?.write(to: pathUrl, atomically: true, encoding: .utf8)

} catch let error {

print("Encoding error: ", error)

}

Step 4: run app
Executed an application and press Save button. A path smilar to the following should be printed as an output in the Debug area



{"count":3,"lists":[{"itemBool":true,"itemString":"String 1","name":"List 1","itemInt":1,"itemFloat":1.23},

{"itemBool":false,"itemString":"String 2","name":"List 2","itemInt":2,"itemFloat":2.3399999999999999},{"ite

mBool":true,"itemString":"String 3","name":"List 3","itemInt":3,"itemFloat":3.4500000000000002}]}

At the same time a path smilar to the following should be printed as an output in the Text view



file:///Users/fulmanp/Library/Developer/CoreSimulator/Devices/7CF76BA3-51AB-461C-8AE5-B890E6971352/data/

Containers/Data/Application/3520AE20-2B0C-4737-80A2-9B5B0902C07D/Documents/test.json

We can check its contents

MacBook-Air-Piotr:Documents fulmanp$ pwd
/Users/fulmanp/Library/Developer/CoreSimulator/Devices/7CF76BA3-51AB-461C-8AE5-B890E6971352/data/
Containers/Data/Application/3520AE20-2B0C-4737-80A2-9B5B0902C07D/Documents
MacBook-Air-Piotr:Documents fulmanp$ ls -l
total 16
-rw-r--r--@ 1 fulmanp  staff  311 25 kwi 14:18 test.json
-rw-r--r--  1 fulmanp  staff  720 24 kwi 23:45 test.plist
MacBook-Air-Piotr:Documents fulmanp$ cat test.json 
{"count":3,"lists":[{"itemBool":true,"itemString":"String 1","name":"List 1","itemInt":1,"itemFloat":1.23},{"itemBool":false,"itemString":"String 2","name":"List 2","itemInt":2,"itemFloat":2.3399999999999999},{"itemBool":true,"itemString":"String 3","name":"List 3","itemInt":3,"itemFloat":3.4500000000000002}]}

MacBook-Air-Piotr:Documents fulmanp$ pwd

/Users/fulmanp/Library/Developer/CoreSimulator/Devices/7CF76BA3-51AB-461C-8AE5-B890E6971352/data/

Containers/Data/Application/3520AE20-2B0C-4737-80A2-9B5B0902C07D/Documents

MacBook-Air-Piotr:Documents fulmanp$ ls -l

total 16

-rw-r--r--@ 1 fulmanp staff 311 25 kwi 14:18 test.json

-rw-r--r-- 1 fulmanp staff 720 24 kwi 23:45 test.plist

MacBook-Air-Piotr:Documents fulmanp$ cat test.json

{"count":3,"lists":[{"itemBool":true,"itemString":"String 1","name":"List 1","itemInt":1,"itemFloat":1.23},{"itemBool":false,"itemString":"String 2","name":"List 2","itemInt":2,"itemFloat":2.3399999999999999},{"itemBool":true,"itemString":"String 3","name":"List 3","itemInt":3,"itemFloat":3.4500000000000002}]}

When Load is pressed, the following text should be printed as an output in the Debug area



3

List 1: 1 String 1 1.23 true

List 2: 2 String 2 2.34 false

List 3: 3 String 3 3.45 true

Sources

Encoding, Decoding and Serialization in Swift 4