Read a text file line by line in Swift?

问题

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.

Banana
Apple
pear
strawberry
blueberry
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

回答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.

回答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

回答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

回答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"]

回答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)
}

来源：https://stackoverflow.com/questions/31778700/read-a-text-file-line-by-line-in-swift

标签

ios

arrays

swift

text

nsstring