iOS 常用类转换

NSDate 获取当前日期及时间 [NSDate date]获取的时间是标准时区的时间

转换成系统时间：

NSDate *date = [NSDate date];

NSTimeZone *zone=[NSTimeZone systemTimeZone];

NSTimeInterval timeInt=[zone secondsFromGMTForDate:date];

date = [date dateByAddingTimeInterval:timeInt];

NSString 转换成NSData 对象:

NSData* xmlData = [@"testdata" dataUsingEncoding:NSUTF8StringEncoding];

NSData 转换成NSString对象:

NSData * data;

NSString *result = [[NSString alloc] initWithData:data  encoding:NSUTF8StringEncoding];

NSData 转换成char*

NSData *data;

charchar *test=[data bytes];

char* 转换成NSData对象

byte* tempData = malloc(sizeof(byte)*16);

NSData *content=[NSData dataWithBytes:tempData length:16];

NSString和NSURL 转换

//NSString->NSURL

NSString *urlString=[@"http://www.google.com" stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

NSURL *url=[NSURL URLWithString:urlString];

//NSURL->NSString

NSString *urlString=[[url absoluteString] stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

NSString和NSData转换（即可作json串互相转换）

//NSData－> NSString

NSString *testString = [[NSString alloc] initWithData:testData encoding:NSUTF8StringEncoding];

//NSString－>NSData

NSString *aString = @"我是NSString";

NSData *testData = [testString dataUsingEncoding: NSUTF8StringEncoding];

NSData和NSImage转换

//NSData－>UIImage

UIImage *testImage = [UIImage imageWithData: imageData];

//UIImage->NSData

NSData *imageData = UIImagePNGRepresentation(testImage)

//或者

NSData *imageData = UIImageJPEGRepresentation(testImage,1.0)

NSData和NSDictionary转换

//NSData-->NSDictionary

NSDictionary *testDict = [NSJSONSerialization JSONObjectWithData:testData options:NSJSONReadingMutableContainers error:nil]

//或者

NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:testData];

NSDictionary *myDictionary = [[unarchiver decodeObjectForKey:@"Some Key Value"] retain];

[unarchiver finishDecoding];

//NSDictionay --> NSData

NSMutableData *data = [[NSMutableData alloc] init];

NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];

[archiver encodeObject:params forKey:@"Some Key Value"];

[archiver finishEncoding];

NSDictionary和JSON转换

JSON:  //这个方法是SBJson类库里的，需要导入SBJson.h

NSString *jsonStr=[dict JSONRepresentation];

//或者原生类库中

NSData      *data = [NSJSONSerialization dataWithJSONObject:dict options:NSJSONWritingPrettyPrinted error:nil];

NSString    *string = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];

//建议（特别是http取回来的jsonStr转换如下）

//JSON->NSDictionary:

NSData *jsonData = [testJsonStr dataUsingEncoding:NSUTF8StringEncoding];

NSDictionary *dict = [NSJSONSerialization JSONObjectWithData:jsonData options:NSJSONReadingMutableContainers error:nil]

IOS 系统API---NSJSONSerialization四个枚举什么意思

NSJSONReadingMutableContainers：返回可变容器，NSMutableDictionary或NSMutableArray。

NSJSONReadingMutableLeaves：返回的JSON对象中字符串的值为NSMutableString，目前在iOS 7上测试不好用，应该是个bug，参见：

http://stackoverflow.com/questions/19345864/nsjsonreadingmutableleaves-option-is-not-working

NSJSONReadingAllowFragments：允许JSON字符串最外层既不是NSArray也不是NSDictionary，但必须是有效的JSON Fragment。例如使用这个选项可以解析 @“123” 这样的字符串。参见：

http://stackoverflow.com/questions/16961025/nsjsonserialization-nsjsonreadingallowfragments-reading

NSJSONWritingPrettyPrinted：的意思是将生成的json数据格式化输出，这样可读性高，不设置则输出的json字符串就是一整行。

NSUserDefaults 简介，使用 NSUserDefaults 存储自定义对象(参考下面链接)

http://my.oschina.net/u/1245365/blog/294449