我封装好了2个方法，用来字典和data相互转换的，直接复制方法拿来用就可以了，注意2点：

1.我是用的mrc，用arc的同学把autorelease去掉即可。

2.第二个我是路径文件转的字典，想data转的话自己把方法改一下就行了。

//字典转data

+(NSData *)returnDataWithDictionary:(NSDictionary *)dict

{

    NSMutableData * data = http://www.mamicode.com/[[NSMutableDataalloc] init];

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

    [archiverencodeObject:dict forKey:@"talkData"];

    [archiverfinishEncoding];

    [dataautorelease];

    [archiverautorelease];

   return data;

}

//路径文件转dictonary

+(NSDictionary *)returnDictionaryWithDataPath:(NSString *)path

{

    NSData * data = http://www.mamicode.com/[[NSMutableDataalloc] initWithContentsOfFile:path];

    NSKeyedUnarchiver * unarchiver = [[NSKeyedUnarchiveralloc] initForReadingWithData:data];

   NSDictionary * myDictionary = [[unarchiver decodeObjectForKey:@"talkData"] retain];

    [unarchiverfinishDecoding];

//    NSLog(@"%@", myDictionary);

    [unarchiverautorelease];

    [dataautorelease];

   return myDictionary;

}

NSDictionary和NSData之间的相互转换