Read a text file line by line in Swift?

Question

Just started learning Swift, I have got my code to read from the text file, and the App displays the content of the Entire Text file. How can I display line by line and call upon that line multiple times?

TextFile.txt contains the following.

1. Banana
2. Apple
3. pear
4. strawberry
5. blueberry
6. blackcurrent

the following is what currently have..

  if let path = NSBundle.mainBundle().pathForResource("TextFile", ofType: "txt"){
        var data = String(contentsOfFile:path, encoding: NSUTF8StringEncoding, error: nil)
            if let content = (data){
                TextView.text = content
    }

also if there is another way, of doing this please let me know. Much appreciated

Answer 1

Swift 3.0

if let path = Bundle.main.path(forResource: "TextFile", ofType: "txt") {
    do {
        let data = try String(contentsOfFile: path, encoding: .utf8)
        let myStrings = data.components(separatedBy: .newlines)
        TextView.text = myStrings.joined(separator: ", ")
    } catch {
        print(error)
    }
}

The variable myStrings should be each line of the data.

The code used is from: Reading file line by line in iOS SDK written in Obj-C and using NSString

Check edit history for previous versions of Swift.

Answer 2

Update for Swift 2.0 / Xcode 7.2

    do {
        if let path = NSBundle.mainBundle().pathForResource("TextFile", ofType: "txt"){
            let data = try String(contentsOfFile:path, encoding: NSUTF8StringEncoding)

            let myStrings = data.componentsSeparatedByCharactersInSet(NSCharacterSet.newlineCharacterSet())
            print(myStrings)
        }
    } catch let err as NSError {
        //do sth with Error
        print(err)
    }

Also worth to mention is that this code reads a file which is in the project folder (since pathForResource is used), and not in e.g. the documents folder of the device

Answer 3

Probably the simplest, and easiest way to do this in Swift 5.0, would be the following:

import Foundation

// Determine the file name
let filename = "main.swift"

// Read the contents of the specified file
let contents = try! String(contentsOfFile: filename)

// Split the file into separate lines
let lines = contents.split(separator:"\n")

// Iterate over each line and print the line
for line in lines {
    print("\(line)")
}

Credit goes to: https://wiki.codermerlin.com/mediawiki/index.php/Code_Snippet:_Print_a_File_Line-by-Line

Answer 4

You probably do want to read the entire file in at once. I bet it's very small.

But then you want to split the resulting string into an array, and then distribute the array's contents among various UI elements, such as table cells.

A simple example:

    var x: String = "abc\ndef"
    var y = x.componentsSeparatedByString("\n")
    // y is now a [String]: ["abc", "def"]

Answer 5

This is not pretty, but I believe it works (on Swift 5). This uses the underlying POSIX getline command for iteration and file reading.

typealias LineState = (
  // pointer to a C string representing a line
  linePtr:UnsafeMutablePointer<CChar>?,
  linecap:Int,
  filePtr:UnsafeMutablePointer<FILE>?
)

/// Returns a sequence which iterates through all lines of the the file at the URL.
///
/// - Parameter url: file URL of a file to read
/// - Returns: a Sequence which lazily iterates through lines of the file
///
/// - warning: the caller of this function **must** iterate through all lines of the file, since aborting iteration midway will leak memory and a file pointer
/// - precondition: the file must be UTF8-encoded (which includes, ASCII-encoded)
func lines(ofFile url:URL) -> UnfoldSequence<String,LineState>
{
  let initialState:LineState = (linePtr:nil, linecap:0, filePtr:fopen(fileURL.path,"r"))
  return sequence(state: initialState, next: { (state) -> String? in
    if getline(&state.linePtr, &state.linecap, state.filePtr) > 0,
      let theLine = state.linePtr  {
      return String.init(cString:theLine)
    }
    else {
      if let actualLine = state.linePtr  { free(actualLine) }
      fclose(state.filePtr)
      return nil
    }
  })
}

Here is how you might use it:

for line in lines(ofFile:myFileURL) {
  print(line)
}