How to create a file, write data into it and read data from it on iOS?

Being a software developer we should be always aware of how to play with files, write to a file, read from the file and so on.

In this post we are going to learn the same, we will be creating a file and writing the data to the file and later reading through the same file.

So let’s get started,

Step 1 − Create new Xcode Project → Single View Application → name it “ReadingWritingFile”

Step 2 − Open ViewController.swift and add new function as show below

public func createAndWriteFile() {
}

Now we will create a file and will print the path of the file.

Step 3 − Inside createAndWriteFile function add

let fileName = "sample"
let documentDirectoryUrl = try! FileManager.default.url(
   for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: true
)
let fileUrl = documentDirectoryUrl.appendingPathComponent(fileName).appendingPathExtension("txt")
// prints the file path
print("File path \(fileUrl.path)")

Now your createAndWriteFile function should look like below one

public func createAndWriteFile() {
   let fileName = "sample"
   let documentDirectoryUrl = try! FileManager.default.url(
      for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: true
   )
   let fileUrl = documentDirectoryUrl.appendingPathComponent(fileName).appendingPathExtension("txt")
   // prints the file path
   print("File path \(fileUrl.path)")
   //data to write in file.
   let stringData = "Hello Tutorials Point"
   do {
      try stringData.write(to: fileUrl, atomically: true, encoding: String.Encoding.utf8)
   } catch let error as NSError {
      print (error)
   }
}

Now we will be writing to the file.

Add below code to the existing function

//data to write in file.
let stringData = "Hello Tutorials Point"
do {
   try stringData.write(to: fileUrl, atomically: true, encoding: String.Encoding.utf8)
} catch let error as NSError {
   print (error)
}

Step 4 − Your final function should look like below

// function to create file and write into the same.
public func createAndWriteFile() {
   let fileName = "sample"
   let documentDirectoryUrl = try! FileManager.default.url(
      for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: true
   )
   let fileUrl = documentDirectoryUrl.appendingPathComponent(fileName).appendingPathExtension("txt")
   // prints the file path
   print("File path \(fileUrl.path)")
   //data to write in file.
   let stringData = "Hello Tutorials Point"
   do {
      try stringData.write(to: fileUrl, atomically: true, encoding: String.Encoding.utf8)
   } catch let error as NSError {
      print (error)
   }
}

Step 5 − Run the project by calling the new method from viewDidLoad() and navigate the file path and validate the content.

Step 6 − Now we’re going to read the content, copy the below code in the same function

var readFile = ""
do {
   readFile = try String(contentsOf: fileUrl)
} catch let error as NSError {
   print(error)
}
print (readFile)

And you’re done,

Step 7 − Complete code,

import UIKit
class ViewController: UIViewController {
   override func viewDidLoad() {
      super.viewDidLoad()
      // Do any additional setup after loading the view, typically from a nib.
      self.createReadAndWriteFile()
   }
   override func didReceiveMemoryWarning() {
      super.didReceiveMemoryWarning()
      // Dispose of any resources that can be recreated.
   }
   // function to create file and write into the same.
   public func createReadAndWriteFile() {
      let fileName = "sample"
      let documentDirectoryUrl = try! FileManager.default.url(
         for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: true
         )
      let fileUrl = documentDirectoryUrl.appendingPathComponent(fileName).appendingPathExtension("txt")
      // prints the file path
      print("File path \(fileUrl.path)")
      //data to write in file.
      let stringData = "Hello Tutorials Point."
      do {
         try stringData.write(to: fileUrl, atomically: true, encoding: String.Encoding.utf8)
      } catch let error as NSError {
         print (error)
      }
      var readFile = ""
      do {
         readFile = try String(contentsOf: fileUrl)
      } catch let error as NSError {
         print(error)
      }
      print (readFile)
   }
}