NSData 转 NSString
NSData *data = [NSData data];
NSString *dataStr = [[NSString alloc] initWithData:data];
NSString 转 NSData
NSData *data = [@"123" dataUsingEncoding:NSUTF8StringEncoding];
NSData *data = [NSData data];
NSString *dataStr = [[NSString alloc] initWithData:data];
NSData *data = [@"123" dataUsingEncoding:NSUTF8StringEncoding];