NSData

1. NSData 与 NSString
NSData－> NSString
NSString *aString = [[NSString alloc] initWithData:adataencoding:NSUTF8StringEncoding];
NSString－>NSData
NSString *aString = @"1234abcd";
NSData *aData = [aString dataUsingEncoding: NSUTF8StringEncoding]; 
//将data类型的数据,转成UTF8的数据
+(NSString *)dataToUTF8String:(NSData *)data
{
 NSString *buf = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
 return [buf autorelease];
}
//将string转换为指定编码 
+(NSString *)changeDataToEncodinString:(NSData *)data encodin:(NSStringEncoding )encodin{
    NSString *buf = [[[NSString alloc] initWithData:data encoding:encodin] autorelease];
    return buf;
}
2. NSData 与 UIImage
NSData－>UIImage
UIImage *aimage = [UIImage imageWithData: imageData];
 
//例：从本地文件沙盒中取图片并转换为NSData
NSString *path = [[NSBundle mainBundle] bundlePath];
NSString *name = [NSString stringWithFormat:@"ceshi.png"];
NSString *finalPath = [path stringByAppendingPathComponent:name];
NSData *imageData = [NSData dataWithContentsOfFile: finalPath];
UIImage *aimage = [UIImage imageWithData: imageData];
//sdk中提供了方法可以直接调用  
UIImage *img = [UIImage imageNamed:@"some.png"];  
NSData *dataObj = UIImageJPEGRepresentation(img, 1.0);  
  
//下面是sdk中UIImage.h头文件中的内容  
UIKIT_EXTERN NSData *UIImagePNGRepresentation(UIImage *image);                               // return image as PNG. May return nil if image has no CGImageRef or invalid bitmap format  
UIKIT_EXTERN NSData *UIImageJPEGRepresentation(UIImage *image, CGFloat compressionQuality);  // return image as JPEG. May return nil if image has no CGImageRef or invalid bitmap format. compression is 0(most)..1(least) 

3.NSData与NSArray  NSDictionary
+(NSString *)getLocalFilePath:(NSString *) fileName
{
 return [NSString stringWithFormat:@"%@/%@%@", NSHomeDirectory(),@“Documents”,fileName];
}
包括将NSData写进Documents目录
从Documents目录读取数据
在进行网络数据通信的时候，经常会遇到NSData类型的数据。在该数据是dictionary结构的情况下，系统没有提供现成的转换成NSDictionary的方法，为此可以通过Category对NSDictionary进行扩展，以支持从NSData到NSDictionary的转换。声明和实现如下：
 
+ (NSDictionary *)dictionaryWithContentsOfData:(NSData *)data {     
    CFPropertyListRef list = CFPropertyListCreateFromXMLData(kCFAllocatorDefault, (CFDataRef)data, kCFPropertyListImmutable, NULL);
    if(list == nil) return nil; 
    if ([(id)list isKindOfClass:[NSDictionary class]]) { 
         return [(NSDictionary *)list autorelease]; 
        } 
    else { 
         CFRelease(list); 
         return nil; 
        } 
}

NSDate
//函数作用 :date根据formatter转换成string
+(NSString*)dateToString:(NSString *)formatter date:(NSDate *)date
{
    NSDateFormatter *dateFormatter = [[[NSDateFormatter alloc] init] autorelease];
    [dateFormatter setDateFormat:formatter];
    return[dateFormatter stringFromDate:date];
}
//函数作用 :string类型的时间戳转换成时间
+(NSString*)dateStringToString:(NSString *)dateStr
{
    if ([dateStr isKindOfClass:[NSNull class]]) {
        return nil;
    }
    else{
        NSInteger time = [dateStr intValue];
        NSDate *date = [NSDate dateWithTimeIntervalSince1970:time];
        NSString *timestr = [NSString stringWithFormat:@"%@",date];
        NSRange rang;
        rang.location = 0;
        rang.length = 10;
        NSString *needtime = [timestr substringWithRange:rang];
        return needtime;
    }
}

//函数作用 :将日期从原格式转换成需要的格式
+(NSString*)convertDateFormatter:(NSString*)sourceFormatter 
                  targetFormatter:(NSString*)targetFormatter  
                       dateString:(NSString*)dateString
{   
    NSDateFormatter *dateFormatter = [[[NSDateFormatter alloc] init] autorelease];
    [dateFormatter setDateFormat:sourceFormatter];
    NSDate *date = [dateFormatter dateFromString:dateString];
    [dateFormatter setDateFormat:targetFormatter];
    return[dateFormatter stringFromDate:date];
}
//函数作用 :将日期字符串转换成date
+(NSDate *)stringToDate:(NSString *)formatter dateString:(NSString *)dateString{
 NSDateFormatter *dateFormatter= [[[NSDateFormatter alloc] init] autorelease];
 [dateFormatter setDateFormat:formatter];
 return [dateFormatter dateFromString:dateString];
}

//时间戳转换成时间
                NSInteger time = [[dic objectForKey:@"press_date"] intValue];
                NSDate *date = [NSDate dateWithTimeIntervalSince1970:time];
                NSString *timestr = [NSString stringWithFormat:@"%@",date];
                NSRange rang;
                rang.location = 0;
                rang.length = 10;
                NSString *needtime = [timestr substringWithRange:rang];