Avoid Excessive Retaining Mistake

When I ran "Analyze" on my project, I got a lot of "potential leak" warnings. I thought I was carefully managing object retaining but I did stupid mistakes everywhere.

part of the sample header file

@property (nonatomic, retain) ClassA objA;

part of the sample source file

@synthesize objA;
...
self.objA = [[ClassA alloc] init];
...
// done using objA instance
[self.objA release];

Above example seems good and there is no places for mistake. But actually retaining is happened twice.

• objA has "retain" attribute
• it will retain anything with assigning operator ("=")
• "alloc" method will increase retain count too

Corrected code

Class *tmpA = [[ClassA alloc] init];
self.objA = tmpA;
[tmpA release];
...
// done using objA instance
[self.objA release];

Objective-C Singleton Class

Singleton class is really awesome when I need to share some data throughout many places. If I use normal way which is passing object pointer around, I have to care about a lot of object assigning tasks. With singleton class, it is really simple to use shared class object.

• no instanciation
• one class method do the all necessary job
• first time of the class method call > create single instance
• other class method calls > return already created instance
• how to use?
• include singleton class's header file
• use class method to obtain class instance

Sample Class's header file

@interface SampleClass : NSObject

+ (SampleClass*)sharedInstance;

@end

Sample Class's source file

@implementation SampleClass

static SampleClass *sharedInstance = nil;   // shared instance

+ (SampleClass*)sharedInstance
{
    @synchronized(self)
    {
        if (sharedInstance == nil)
            sharedInstance = [[super allocWithZone:nil] init];

        return sharedInstance;
    }
}

+ (id)allocWithZone:(NSZone*)zone
{
    return [[self sharedInstance] retain];
}

- (id)copyWithZone:(NSZone*)zone
{
    return self;
}

- (id)retain
{
    return self;
}

- (NSUInteger)retainCount
{
    return NSUIntegerMax;  // object cannot be released
}

- (oneway void)release
{
    // do nothing
}

- (id)autorelease
{
    return self;
}

Use Code Block in Blogspot

I got all of these informations form here

1. go to "Template Designer" of your blog
2. select Advanced > Add CSS
3. add css code

pre.code
{
font-size:12px;
border:1px dashed #CCCCCC;
width:99%;
height:auto;
overflow:auto;
color:#000000;
background:#f0f0f0;
background-image:URL(http://2.bp.blogspot.com/_z5ltvMQPaa8/SjJXr_U2YBI/AAAAAAAAAAM/46OqEP32CJ8/s320/codebg.gif);
padding:0px;
padding-left:2px;
text-align:left;
line-height:20px;
word-wrap:normal;
}

You can use them with <pre class="code"> tag

Working with Static Libraries in Xcode

Layout

• single workspace
• app project AProj
• static library project BProj

Configurations

• In BProj
• Target > Build Phase > Copy Headers
• add header files
• Project > Build Settings > Public Headers Folder Path
• set to header folder name (ex. LIBA for )
• Project > Build Settings > Skip Install
• Yes
• In AProj
• Target > Build Phase > Link Binary With Libraries
• add library file (ex. lib.a)
• Project > Build Settings > Header Search Paths
• ../../**

Readable Terminal Colors for OSX Snow Leopard

1. edit .bash_profile

• add "export CLICOLOR=1"
• unlike Linux, .bashrc is not default bash config file (will not be loaded automatically) -- use .bash_profile instead

2. install SIMBL

3. install plugins for SIMBL

• download plugin
• extract to ~/Library/Application Support/SIMBL/Plugins

4. set Terminal.app to 32bit mode

• goto Application/Utilities
• Terminal -> right click -> Get Info
• Check "Open in 32-bit mode"
• reference

5. install color theme for Terminal

• download IR_Black theme
• reference

Workaround for Wireless Disconnection Issue (Linux)

I wanted to run ubuntu server with wireless connection. But it is disconnected randomly. I have no idea and I couldn’t find any solution online. So, I made cron job, which ping to router every 2 minute, and restart networking if there is 0 response.

1. prepare script file to run every 2 minutes

# wireless_check.sh
# ping check and log time and result
#!/bin/bash
a=`ping -q -c 3 192.168.1.1 | grep "0 received"`
b=`date "+%Y%d%m %T"`
if $a then 
 echo "$b it's connected" >> /home/sean/wireless_status
else
 echo "$b it's not connected" >> /home/sean/wireless_status 
 sudo /etc/init.d/networking restart 
fi

2. run cron editor

$ sudo crontab -e

3. add new cron job

*/2 * * * * /home/sean/wireless_check.sh

4. New cron job starts automatically and you can check your log file. Here is my log file.

20091904 01:08:13 it's not connected 
20091904 01:10:13 it's not connected 
20091904 01:12:13 it's not connected 
20091904 01:14:13 it's not connected 
20091904 01:16:13 it's not connected 
20091904 01:18:13 it's not connected 
20091904 01:20:04 it's connected 
20091904 01:22:13 it's not connected 
20091904 01:24:13 it's not connected 
20091904 01:26:03 it's connected 
20091904 01:28:03 it's connected 
20091904 01:30:04 it's connected 
20091904 01:32:03 it's connected 
20091904 01:34:03 it's connected 
20091904 01:36:03 it's connected 
20091904 01:38:03 it's connected 
20091904 01:40:03 it's connected 
20091904 01:42:03 it's connected 
20091904 01:44:13 it's not connected 
20091904 01:46:04 it's connected 
20091904 01:48:04 it's connected 
20091904 01:50:03 it's connected