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My background is J2EE and one of the things that has been bugging me about the iPhone platform is that nobody seems to care about logging. When you have a complicated application with many layers and subsystems, it is very handy to be able to turn on and off logging for different sections of code.

Log4J is pretty much the industry standard implementation of the commons logging framework for Java. It allows you to have hierarchical logging categories that turn on/off logging at various levels (info,warn,error, etc). There’s a Cocoa port called log4cocoa, but I couldn’t find any documentation describing how to get it to work in an iPhone project.

Here are the steps I took to get log4cocoa to work in my projects

Create a New View-based Application Project

Choose 'View-based Application'

Call it 'L4C-iPhone'

Examine the Project Contents

Check out log4cocoa and Custom Categories

Check out log4cocoa:
svn co https://log4cocoa.svn.sourceforge.net/svnroot/log4cocoa/trunk log4cocoa

A log4cocoa/lib3rd A log4cocoa/lib3rd/OCMock.tgz A log4cocoa/Log4Cocoa_Prefix.pch A log4cocoa/source A log4cocoa/source/L4StringMatchFilter.h A log4cocoa/source/L4LevelRangeFilter.h A log4cocoa/source/L4LevelMatchFilter.h A log4cocoa/source/L4RollingFileAppender.m A log4cocoa/source/L4LoggerStore.h A log4cocoa/source/L4SimpleLayout.m A log4cocoa/source/L4LoggingEvent.m A log4cocoa/source/L4DenyAllFilter.h A log4cocoa/source/L4FileAppender.h A log4cocoa/source/L4StringMatchFilter.m A log4cocoa/source/L4LevelRangeFilter.m A log4cocoa/source/L4LevelMatchFilter.m A log4cocoa/source/L4LoggerStore.m A log4cocoa/source/L4FileAppender.m A log4cocoa/source/L4AppenderProtocols.h A log4cocoa/source/L4AppenderSkeleton.h A log4cocoa/source/L4DenyAllFilter.m A log4cocoa/source/L4BasicConfigurator.h A log4cocoa/source/L4PropertyConfigurator.h A log4cocoa/source/L4AppenderAttachable.h A log4cocoa/source/L4Level.h A log4cocoa/source/L4AppenderSkeleton.m A log4cocoa/source/L4BasicConfigurator.m A log4cocoa/source/L4PatternLayout.h A log4cocoa/source/L4PropertyConfigurator.m A log4cocoa/source/L4AppenderAttachable.m A log4cocoa/source/L4Level.m A log4cocoa/source/L4Layout.h A log4cocoa/source/L4PatternLayout.m A log4cocoa/source/L4ConsoleAppender.h A log4cocoa/source/L4Layout.m A log4cocoa/source/L4LogLog.h A log4cocoa/source/L4LoggerProtocols.h A log4cocoa/source/L4Filter.h A log4cocoa/source/L4ConsoleAppender.m A log4cocoa/source/L4Logging.h A log4cocoa/source/L4LogLog.m A log4cocoa/source/L4Filter.m A log4cocoa/source/L4Logging.m A log4cocoa/source/L4WriterAppender.h A log4cocoa/source/L4Properties.h A log4cocoa/source/L4WriterAppender.m A log4cocoa/source/L4Properties.m A log4cocoa/source/L4DailyRollingFileAppender.h A log4cocoa/source/Log4CocoaDefines.h A log4cocoa/source/Log4Cocoa.h A log4cocoa/source/Tests A log4cocoa/source/Tests/TestL4StringMatchFilter.m A log4cocoa/source/Tests/TestL4LevelMatchFilter.m A log4cocoa/source/Tests/TestL4LevelRangeFilter.m A log4cocoa/source/Tests/TestL4PatternLayout.m A log4cocoa/source/Tests/TestL4Properties.m A log4cocoa/source/Tests/TestL4DenyAllFilter.m A log4cocoa/source/Tests/data A log4cocoa/source/Tests/data/test.properties A log4cocoa/source/L4DailyRollingFileAppender.m A log4cocoa/source/NSObject+Log4Cocoa.h A log4cocoa/source/L4Logger.h A log4cocoa/source/NSObject+Log4Cocoa.m A log4cocoa/source/L4RootLogger.h A log4cocoa/source/L4Logger.m A log4cocoa/source/L4RollingFileAppender.h A log4cocoa/source/L4SimpleLayout.h A log4cocoa/source/L4LoggingEvent.h A log4cocoa/source/L4RootLogger.m A log4cocoa/xcconfig A log4cocoa/xcconfig/Release.xcconfig A log4cocoa/xcconfig/ReleaseLeopardOrLater.xcconfig A log4cocoa/xcconfig/FrameworkTigerOrLater.xcconfig A log4cocoa/xcconfig/Application.xcconfig A log4cocoa/xcconfig/TigerOrLater.xcconfig A log4cocoa/xcconfig/Debug.xcconfig A log4cocoa/xcconfig/DebugLeopardOrLater.xcconfig A log4cocoa/xcconfig/Coverage.xcconfig A log4cocoa/xcconfig/CoverageLeopardOrLater.xcconfig A log4cocoa/xcconfig/Framework.xcconfig A log4cocoa/xcconfig/General.xcconfig A log4cocoa/xcconfig/LeopardOrLater.xcconfig A log4cocoa/xcconfig/Unittest.xcconfig A log4cocoa/TODO.txt A log4cocoa/demo A log4cocoa/demo/AppController.m A log4cocoa/demo/main.m A log4cocoa/demo/Log4CocoaDemo-Info.plist A log4cocoa/demo/LoggingThread.h A log4cocoa/demo/log4cocoa.properties A log4cocoa/demo/LoggingThread.m A log4cocoa/demo/AppController.h A log4cocoa/demo/English.lproj A log4cocoa/demo/English.lproj/InfoPlist.strings A log4cocoa/demo/English.lproj/MainMenu.xib A log4cocoa/Info.plist A log4cocoa/Tests-Info.plist A log4cocoa/doc A log4cocoa/doc/Doxyfile A log4cocoa/COPYRIGHT.txt A log4cocoa/Log4Cocoa.xcodeproj A log4cocoa/Log4Cocoa.xcodeproj/treaves.pbxuser A log4cocoa/Log4Cocoa.xcodeproj/eric.perspectivev3 A log4cocoa/Log4Cocoa.xcodeproj/treaves.mode1v3 A log4cocoa/Log4Cocoa.xcodeproj/treaves.mode2v3 A log4cocoa/Log4Cocoa.xcodeproj/eric.pbxuser A log4cocoa/Log4Cocoa.xcodeproj/project.pbxproj A log4cocoa/Log4Cocoa.xcodeproj/treaves.perspectivev3 A log4cocoa/readme.txt A log4cocoa/English.lproj A log4cocoa/English.lproj/InfoPlist.strings U log4cocoa Checked out revision 111.

Check out my category for NSDate to make int compliant with the missing NSCalendarDate:
git clone git://github.com/jeremyprz/categories.git

Initialized empty Git repository in /Users/jeremy/dev/sandbox/L4C-iPhone/categories/.git/ remote: Counting objects: 16, done. Receiving objects: 100% (16/16), done.ceiving objects: 6% (1/16) remote: Compressing objects: 100% (13/13), done. remote: Total 16 (delta 7), reused 7 (delta 3) Resolving deltas: 100% (7/7), done.

Add Empty Source Groups to your Project

One for ‘Categories’
Another for ‘Log4Cocoa’

‘Add > Existing Files…’ to the Categories Group

Add existing files to the Categories group by selecting the categories/NSDate-Calendar.* files.
Add: Existing Files...
Select the NSDate-Calendar.* files

‘Add > Existing Files…’ to the Log4Cocoa Group

Add existing files to the Categories group by selecting the log4cocoa/source/*.* files.
Add: Existing Files...
Select the NSDate-Calendar.* files

Modify _Prefix.pch File

You will need to add a single line to your project’s .pch file. In this project, the file is named ‘L4C_iPhone_Prefix.pch’. We are adding a single line to the file: #import "NSDate-Calendar.h"
This line will ensure that the unmodified log4cocoa files will our NSDate category instead of the NSCalendarDate, which is not available on the iPhone.
Add one line to the _prefix.pch file

Add Log4Cocoa Code to the Application

At this point, your project should be fully able to use log4cocoa. Here is the plain vanilla AppDelegate from this example: #import "L4C_iPhoneAppDelegate.h" #import "L4C_iPhoneViewController.h" #import "Log4Cocoa.h"


@implementation L4C_iPhoneAppDelegate
@synthesize window;

@synthesize viewController;
- (void)applicationDidFinishLaunching:(UIApplication *)application {    
    // Override point for customization after app launch

    [window addSubview:viewController.view];

    [window makeKeyAndVisible];
	[[L4Logger rootLogger] setLevel:[L4Level all]];

	[[L4Logger rootLogger] addAppender: [[L4ConsoleAppender alloc]

										 initTarget:YES

										 withLayout:[L4Layout simpleLayout]]];

	L4Logger *theLogger = [L4Logger loggerForClass:[L4FunctionLogger class]];

	[theLogger setLevel:[L4Level debug]];

	log4CDebug(@"The logging system has been initialized.");

}
- (void)dealloc {

    [viewController release];

    [window release];

    [super dealloc];

}

@end
Example AppDelegate

Run your App

You should now be able to run the application and see log4cocoa output in the console.
Run your App

Barking Minds Software and Crowd Map

Log4Cocoa in an iPhone Project