1. NSUserDefaults
个人认为ios这个方法有点类似于c#中Properties.Settings.Default，NSUserDefaults只支持： NSString, NSNumber, NSDate, NSArray, NSDictionary.
创建一个user defaults方法有多个，最简单得快速创建方法:
NSUserDefaults *accountDefaults = [NSUserDefaults standardUserDefaults];
添加数据到 user defaults:
[accountDefaults setObject:nameField.text forKey:UserDefaultNameKey];
也可以添加基本数据类型int, float, bool等，有相应得方法
[accountDefaults setBool:YES forKey:UserDefaultBoolKey];
从user defaults中获取数据:
[accountDefaults objectForKey:NCUserDefaultNameKey]
[accountDefaults boolForKey: UserDefaultBoolKey];
针对同一个关键字对应的对象或者数据，可以对它进行重写，重写之后关键字就对应新的对象或者数据，旧的对象或者数据会被自动清理。
2. NSDateFormatter
格式化日期字符串，copy一份常用参数：
a: AM/PM (上午/下午)
A: 0~86399999 (一天的第A微秒)
c/cc: 1~7 (一周的第一天, 周天为1)
ccc: Sun/Mon/Tue/Wed/Thu/Fri/Sat (星期几简写)
cccc: Sunday/Monday/Tuesday/Wednesday/Thursday/Friday/Saturday (星期几全拼)
d: 1~31 (月份的第几天, 带0)
D: 1~366 (年份的第几天,带0)
e: 1~7 (一周的第几天, 带0)
E~EEE: Sun/Mon/Tue/Wed/Thu/Fri/Sat (星期几简写)
EEEE: Sunday/Monday/Tuesday/Wednesday/Thursday/Friday/Saturday (星期几全拼)
F: 1~5 (每月的第几周, 一周的第一天为周一)
g: Julian Day Number (number of days since 4713 BC January 1) 未知
G~GGG: BC/AD (Era Designator Abbreviated) 未知
GGGG: Before Christ/Anno Domini 未知
h: 1~12 (0 padded Hour (12hr)) 带0的时, 12小时制
H: 0~23 (0 padded Hour (24hr)) 带0的时, 24小时制
k: 1~24 (0 padded Hour (24hr) 带0的时, 24小时制
K: 0~11 (0 padded Hour (12hr)) 带0的时, 12小时制
L/LL: 1~12 (0 padded Month) 第几月
LLL: Jan/Feb/Mar/Apr/May/Jun/Jul/Aug/Sep/Oct/Nov/Dec 月份简写
LLLL: January/February/March/April/May/June/July/August/September/October/November/December 月份全称
m: 0~59 (0 padded Minute) 分钟
M/MM: 1~12 (0 padded Month) 第几月
MMM: Jan/Feb/Mar/Apr/May/Jun/Jul/Aug/Sep/Oct/Nov/Dec
MMMM: January/February/March/April/May/June/July/August/September/October/November/December
q/qq: 1~4 (0 padded Quarter) 第几季度
qqq: Q1/Q2/Q3/Q4 季度简写
qqqq: 1st quarter/2nd quarter/3rd quarter/4th quarter 季度全拼
Q/QQ: 1~4 (0 padded Quarter) 同小写
QQQ: Q1/Q2/Q3/Q4 同小写
QQQQ: 1st quarter/2nd quarter/3rd quarter/4th quarter 同小写
s: 0~59 (0 padded Second) 秒数
S: (rounded Sub-Second) 未知
u: (0 padded Year) 未知
v~vvv: (General GMT Timezone Abbreviation) 常规GMT时区的编写
vvvv: (General GMT Timezone Name) 常规GMT时区的名称
w: 1~53 (0 padded Week of Year, 1st day of week = Sunday, NB: 1st week of year starts from the last Sunday of last year) 一年的第几周, 一周的开始为周日,第一周从去年的最后一个周日起算
W: 1~5 (0 padded Week of Month, 1st day of week = Sunday) 一个月的第几周
y/yyyy: (Full Year) 完整的年份
yy/yyy: (2 Digits Year) 2个数字的年份
Y/YYYY: (Full Year, starting from the Sunday of the 1st week of year) 这个年份未知干嘛用的
YY/YYY: (2 Digits Year, starting from the Sunday of the 1st week of year) 这个年份未知干嘛用的
z~zzz: (Specific GMT Timezone Abbreviation) 指定GMT时区的编写
zzzz: (Specific GMT Timezone Name) Z: +0000 (RFC 822 Timezone) 指定GMT时区的名称
实例：
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setAMSymbol:@"AM"];
[formatter setPMSymbol:@"PM"];
[formatter setDateFormat:@"MM/dd/yyyy hh:mm:a"];
// [NSString stringWithFormat:@"Last Updated: %@", [formatter stringFromDate:[NSDate date]]];
3. backgroundView
UIView* backgroundView= = [[TESTCellView alloc] initWithFrame:CGRectZero];
backgroundView.opaque = YES;
backgroundView.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:@"list-gap.png"]];
backgroundView = backgroundView;
[backgroundView release];
4. NSParameterAssert
字面意思是带参数的断点，条件为假时执行，主要用于程序调试
NSParameterAssert( 1== 2 );
5. Reachability
类似于一个网络状况的探针。
[[NSNotificationCenter defaultCenter] addObserver: self selector: @selector(reachabilityChanged:) name: kReachabilityChangedNotification object: nil];
hostReach = [[Reachability reachabilityWithHostName: @"hubj.cnblogs.com"] retain];
[hostReach startNotifier];
wifiReach=[[Reachability reachabilityForLocalWiFi]retain];
[wifiReach startNotifier];
- (void)reachabilityChanged: (NSNotification* )note {
Reachability* curReach = [note object];
NSParameterAssert([curReach isKindOfClass: [Reachability class]]);
NetworkStatus netStatus = [curReach currentReachabilityStatus];
switch (netStatus)
{
case NotReachable:
{
NSLog(@"Access Not Available");
break;
}
case ReachableViaWWAN:
{
NSLog(@"Reachable WWAN");
break;
}
case ReachableViaWiFi:
{
NSLog(@"Reachable WiFi");
break;
}
}
}