NSData，NSImage,NSDictionary,NSString，NSURL 等等互相转换

一：NSString和NSURL 转换

//NSString->NSURL
NSString *urlString=[@"http://www.baidu.com" stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
NSURL *url=[NSURL URLWithString:urlString];
//NSURL->NSString
NSString *urlString=[[url absoluteString] stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringE

二：NSString和NSData转换

//NSData－> NSString
NSString *testString = [[NSString alloc] initWithData:testData encoding:NSUTF8StringEncoding];
//NSString－>NSData
NSString *aString = @"str to data<span style="font-family: 'Comic Sans MS';">";  </span>

NSData *testData = [testString dataUsingEncoding: NSUTF8StringEncoding];

三：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)

四：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];

五：NSDictionary和JSON转换
//NSDictionary -> JSON: //这个方法是SBJson类库里的，需要导入SBJson.h
NSString *jsonStr=[dict JSONRepresentation];
//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]