XCGLogger Swift日志打印

Swift没有C预编译功能，所以我们不能使用调试log #define 宏定义了。 XCGLogger提供给开发者打印详细的内容到控制台。

简单举个例子吧，下面就是使用XCGLogger打印出来的结果：

2014-06-09 06:44:43.600 [Debug] [AppDelegate.swift:40] application(_:didFinishLaunchingWithOptions:): Simple message

介绍一下XCGLogger的使用方法：

1.CocoaPods：
添加下面的几行代码到项目的Podfile文件中。

source 'https://github.com/CocoaPods/Specs.git'
platform :ios, '8.0'
use_frameworks!

pod 'XCGLogger', '~> 3.2'

然后运行 pod install

2.标准使用
在AppDelegate中

import XCGLogger

application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject : AnyObject]?) // iOS, tvOS

在上诉方法中添加一下代码

let log = XCGLogger.defaultInstance()

log.setup(.Debug, showThreadName: true, showLogLevel: true, showFileNames: true, showLineNumbers: true, writeToFile: "path/to/file", fileLogLevel: .Debug)

我来解释一下上面的参数：
The value for writeToFile: can be a String or NSURL. If the file already exists, it will be cleared before we use it. Omit a value or set it to nil to log to the console only. You can optionally set a different log level for the file output using the fileLogLevel parameter. Set it to nil or omit it to use the same log level as the console.

无论你想打印任何日志，你可以使用下面的遍历的方法：

log.verbose("A verbose message, usually useful when working on a specific problem")
log.debug("A debug message")
log.info("An info message, probably useful to power users looking in console.app")
log.warning("A warning message, may indicate a possible error")
log.error("An error occurred, but it's recoverable, just info about what happened")
log.severe("A severe error occurred, we are likely about to crash now")

3.高级使用方法

XCGLogger旨在简单快速的使用，它也允许我们提供给我们更强大更灵活地使用办法。下面是一个配置Apple System Log以及一个文件logger
的例子

// Create a logger object with no destinations
let log = XCGLogger(identifier: "advancedLogger", includeDefaultDestinations: false)

// Create a destination for the system console log (via NSLog)
let systemLogDestination = XCGNSLogDestination(owner: log, identifier: "advancedLogger.systemLogDestination")

// Optionally set some configuration options
systemLogDestination.outputLogLevel = .Debug
systemLogDestination.showLogIdentifier = false
systemLogDestination.showFunctionName = true
systemLogDestination.showThreadName = true
systemLogDestination.showLogLevel = true
systemLogDestination.showFileName = true
systemLogDestination.showLineNumber = true
systemLogDestination.showDate = true

// Add the destination to the logger
log.addLogDestination(systemLogDestination)

// Create a file log destination
let fileLogDestination = XCGFileLogDestination(owner: log, writeToFile: "/path/to/file", identifier: "advancedLogger.fileLogDestination")

// Optionally set some configuration options
fileLogDestination.outputLogLevel = .Debug
fileLogDestination.showLogIdentifier = false
fileLogDestination.showFunctionName = true
fileLogDestination.showThreadName = true
fileLogDestination.showLogLevel = true
fileLogDestination.showFileName = true
fileLogDestination.showLineNumber = true
fileLogDestination.showDate = true

// Process this destination in the background
fileLogDestination.logQueue = XCGLogger.logQueue

// Add the destination to the logger
log.addLogDestination(fileLogDestination)

// Add basic app info, version info etc, to the start of the logs
log.logAppDetails()

自定义时间格式：

let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "MM/dd/yyyy hh:mma"
dateFormatter.locale = NSLocale.currentLocale()
log.dateFormatter = dateFormatter

利用一个闭包（Closure）初始化XCGLogger对象

let log: XCGLogger = {
    let log = XCGLogger.defaultInstance()
    log.setup(.Debug, showThreadName: true, showLogLevel: true, showFileNames: true, showLineNumbers: true, writeToFile: nil, fileLogLevel: .Debug)

    let dateFormatter = NSDateFormatter()
    dateFormatter.dateFormat = "MM/dd/yyyy hh:mma"
    dateFormatter.locale = NSLocale.currentLocale()
    log.dateFormatter = dateFormatter

    return log
}()

调试与发布 配置

通过使用Swift build flags，不同的log 水平能被利用到调试和发布版本。Build setting
-> Swift Compiler -> Customer Flags -> Other Swift Flags 添加-DDEBUG到the Debug entry中

#if DEBUG
    log.setup(.Debug, showThreadName: true, showLogLevel: true, showFileNames: true, showLineNumbers: true, writeToFile: nil)
#else
    log.setup(.Severe, showThreadName: true, showLogLevel: true, showFileNames: true, showLineNumbers: true, writeToFile: nil)
#endif

后台运行打印进程

默认情况下，供给的log destination将运行在我们调用的线程中，这将确保打印的消息会被马上显示当我们调试app的时候。
然而，如果我们不想在当前线程中调试打印的结果。开发者可以特定一个 destination 进程的logs在一个分发队列中（dispatch queue）。

fileLogDestination.logQueue = XCGLogger.logQueue

甚至可以这样

fileLogDestination.logQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0)

这种使用方法可以非常好地和 调试与发布 配置很好的结合使用，如下：

#if DEBUG
    log.setup(.Debug, showThreadName: true, showLogLevel: true, showFileNames: true, showLineNumbers: true, writeToFile: nil)
#else
    log.setup(.Severe, showThreadName: true, showLogLevel: true, showFileNames: true, showLineNumbers: true, writeToFile: nil)
    if let consoleLog = log.logDestination(XCGLogger.Constants.baseConsoleLogDestinationIdentifier) as? XCGConsoleLogDestination {
        consoleLog.logQueue = XCGLogger.logQueue
    }
#endif