【Swift】シンプルにログをファイルに書き出す

コピペでいけます

ソース

logger.swift

import Foundation
import UIKit


///
///
/// 日時用書式インスタンス
///
///
private class __formatInstance {

    private static var _formatter : DateFormatter?
    
    static var formatter : DateFormatter {
        get {
            if ( _formatter == nil  ){
                _formatter = DateFormatter()
                _formatter!.dateFormat = "yyyy-MM-dd HH:mm:ss.SSS "
            }
            return _formatter!
        }
    }
}

func dateString() -> String {
    return __formatInstance.formatter.string(from:Date())
}

func printLog(_ log: Any) {

    let timestamp = __formatInstance.formatter.string(from:Date())
    print(timestamp, terminator: "")
    let tid = Thread.current

    let logStr = log as? String
    if let str = logStr {
        print("\(tid) : \(str)")
        Logger.getInstance().write(timeStamp: timestamp, text: "\(tid) : \(str)")
    }else{
        print("CAN'T LOG WRITE")
    }
}

class Logger {
    
    private let filename_ : String
    
    private static let instance_ = Logger()
    
    init(){
        
        let date = Date()

        let df = DateFormatter()
        
        df.dateFormat = "yyyyMMddHHmmss"
        self.filename_ = "Log_\(df.string(from: date)).log"
        
        print("log filename:\(self.filename_)")
    }
    
    
    static func getInstance() -> Logger{
        return Logger.instance_
    }

    func write(timeStamp tm: String,  text:String)
    {
        /// DocumentsフォルダURL取得
        guard let dirURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first else {
            fatalError("フォルダURL取得エラー")
        }
        /// 対象のファイルURL取得
        let fileURL = dirURL.appendingPathComponent( self.filename_ )
        if self.write(url: fileURL, text: "\(tm) \(text)") == false{
            printLog("LOG ERROR")
        }
    }
    
    func write(_ text:String)
    {
        let logTimeStamp = __formatInstance.formatter.string(from:Date())

        self.write(timeStamp:logTimeStamp,  text:text)
    }
    
    func write(url: URL, text: String) -> Bool {
        guard let stream = OutputStream(url: url, append: true) else {
            return false
        }
        stream.open()
        
        defer {
            stream.close()
        }
        
        let logText = "\(text)\n"
        
        guard let data = logText.data(using: .utf8) else { return false }
        let byteArray = [UInt8](data)
        let result = stream.write(byteArray , maxLength: byteArray.count)
        return (result > 0)
    }

}

つかいかた

Logger.getInstance().write("test")

ファイルを確認

1. Window > Devices and Simulators
2. デバッグ中のiPhone > デバッグ中のApp > [...] > Download Container...
3. できたContainerを右クリック > パッケージの内容を表示 > AppData > Documents