錯誤訊息：
Finishing up a navigation transition in an unexpected state. Navigation Bar subview tree might get corrupted.

原來手腳太快也是會有問題的，
在使用navigation時，要注意push的間隔，
如果在很短的時間連續push就會發生上述錯誤，
這時候記得延遲一下就可以解決這問題的。

可以用這個來解決：

// 在原先要push的地方加上，取代原先的push
[self performSelector:@selector(showView) withObject:nil afterDelay:0.7];

// Push View
- (void)showView{

    UIViewController *viewController = [[UIViewController alloc] initWithNibName:@"UIViewController" bundle:nil];
    [self.navigationController pushViewController:viewController animated:YES];
}

參考文件：
http://www.cocoachina.com/bbs/read.php?tid=110206

Debug Area Commands

在Debug Area中可以輸入help後，列出的Commands有以下這些，
不過我認為應該是不只啦！先記錄下來。
後面有找到在另外補充。

The following is a list of built-in, permanent debugger commands:

_regexp-attach    -- Attach to a process id if in decimal, otherwise treat the
                     argument as a process name to attach to.
_regexp-break     -- Set a breakpoint using a regular expression to specify the
                     location, where  is in decimal and 

 is
                     in hex.
_regexp-bt        -- Show a backtrace.  An optional argument is accepted; if
                     that argument is a number, it specifies the number of
                     frames to display.  If that argument is 'all', full
                     backtraces of all threads are displayed.
_regexp-display   -- Add an expression evaluation stop-hook.
_regexp-down      -- Go down "n" frames in the stack (1 frame by default).
_regexp-tbreak    -- Set a one shot breakpoint using a regular expression to
                     specify the location, where  is in decimal and
                     

 is in hex.
_regexp-undisplay -- Remove an expression evaluation stop-hook.
_regexp-up        -- Go up "n" frames in the stack (1 frame by default).
apropos           -- Find a list of debugger commands related to a particular
                     word/subject.
breakpoint        -- A set of commands for operating on breakpoints. Also see
                     _regexp-break.
command           -- A set of commands for managing or customizing the debugger
                     commands.
disassemble       -- Disassemble bytes in the current function, or elsewhere in
                     the executable program as specified by the user.
expression        -- Evaluate a C/ObjC/C++ expression in the current program
                     context, using user defined variables and variables
                     currently in scope.
frame             -- A set of commands for operating on the current thread's
                     frames.
gdb-remote        -- Connect to a remote GDB server.  If no hostname is
                     provided, localhost is assumed.
help              -- Show a list of all debugger commands, or give details
                     about specific commands.
kdp-remote        -- Connect to a remote KDP server.  udp port 41139 is the
                     default port number.
log               -- A set of commands for operating on logs.
memory            -- A set of commands for operating on memory.
platform          -- A set of commands to manage and create platforms.
plugin            -- A set of commands for managing or customizing plugin
                     commands.
process           -- A set of commands for operating on a process.
quit              -- Quit out of the LLDB debugger.
register          -- A set of commands to access thread registers.
script            -- Pass an expression to the script interpreter for
                     evaluation and return the results. Drop into the
                     interactive interpreter if no expression is given.
settings          -- A set of commands for manipulating internal settable
                     debugger variables.
source            -- A set of commands for accessing source file information
target            -- A set of commands for operating on debugger targets.
thread            -- A set of commands for operating on one or more threads
                     within a running process.
type              -- A set of commands for operating on the type system
version           -- Show version of LLDB debugger.
watchpoint        -- A set of commands for operating on watchpoints.

For more information on any particular command, try 'help '.

iOS 6 Status Bar Color

在iOS 6，Status Bar的顏色會改變，
原來是受到了Navigation Bar顏色的影響，
之前都沒有注意到這個狀況。

這是為了讓App與整體更加融合，
不過話說回來這功能有時候也是會挺困擾的。
調整的方式如下：

在這邊改變一下設定就行啦！
如果是Default，在iOS 6系統會自動變更Status Bar顏色，iOS 6以下版本則不會。
附上相關程式設定

[[UIApplication sharedApplication] setStatusBarStyle:UIStatusBarStyleDefault];
[[UIApplication sharedApplication] setStatusBarStyle:UIStatusBarStyleBlackTranslucent];
[[UIApplication sharedApplication] setStatusBarStyle:UIStatusBarStyleBlackOpaque];

參考資料：
http://blog.jiwo.in/post/28621527054
http://stackoverflow.com/questions/12931749/status-bar-color-in-ios-6

Multi Thread 散記

UI更新必須在主線程
很多文章使用detachNewThreadSelector或performSelectorInBackground啓動Thread，
然後呼叫performSelectorOnMainThread，通知主線程更新UI。

// 主線程呼叫
[self performSelectorInBackground:<#(SEL)#> withObject:<#(id)#>];
[NSThread detachNewThreadSelector:<#(SEL)#> toTarget:<#(id)#> withObject:<#(id)#>];
// 更新UI
[self performSelectorOnMainThread:<#(SEL)#> withObject:<#(id)#> waitUntilDone:<#(BOOL)#>];

使用NSOperationQueue的過程：

1. 建立一个NSOperationQueue的實體 
2. 建立一个NSOperation的實體 
3. 將operation加入到NSOperationQueue中 
4. release掉operation

NSURLConnection 相關紀錄

紀錄NSURLConnection 相關資訊

1. NSURLRequest 預設timeoutInterval為60.0秒