How to create a custom file type that holds text and images?

I know this is going to be somewhat hard to answer, but I need to save text and images into a single file (like photoshop does). Should I make a custom file type, or is there another way to do this?

If I need a custom file type, would somebody please give me link to something that may help me make the file type store the data properly? If there is another way, how can I do t开发者_开发知识库his?

NOTE: I am using this in a application that imports three images, and lets users put text over them, so I may not be able to get the information needed to store the images as text in any way. If it is what I have to do, I will need a link to some helpful information.

An easy way to save objects to a file is to add them to an NSDictionary and then use NSArchiver to archive the dictionary into data.

For example in a document based app:

- (NSData *)dataOfType:(NSString *)typeName error:(NSError **)outError {
    if ([typeName isEqualToString:@"YourTypeName"]) {
          //Create a Dictionary
          NSMutableDictionary *dictToSave = [NSMutableDictionary dictionary];
          //Add the first image to the dictionary
          [dictToSave setObject:image1 forKey:@"Image1"];
          //Add the first image's text
          [dictToSave setObject:image1text forKey:@"Image1Text"];
          //etc.
          [dictToSave setObject:image2 forKey:@"Image2"];
          [dictToSave setObject:image2text forKey:@"Image2Text"];              
          [dictToSave setObject:image3 forKey:@"Image3"];
          [dictToSave setObject:image3text forKey:@"Image3Text"];
          //Return the archived data
          return [NSArchiver archivedDataWithRootObject:dictToSave];
    }
    //Don't generate an error
    outError = NULL;
    return nil;
}

To read this data, just unarchive the dictionary and set the objects:

- (BOOL)readFromData:(NSData *)data ofType:(NSString *)typeName
error:(NSError **)outError {
    if ([typeName isEqualToString:@"MyTypeName"]) {
        NSMutableDictionary *readDict = 
        [NSUnarchiver unarchiveRootObjectWithData:data];
        image1 = [readDict objectForKey:@"Image1"];
        image1text = [readDict objectForKey:@"Image1Text"];
        image2 = [readDict objectForKey:@"Image2"];
        image2text = [readDict objectForKey:@"Image2Text"];
        image3 = [readDict objectForKey:@"Image3"];
        image3text = [readDict objectForKey:@"Image3Text"];
    }
    outError = NULL;
    return YES;
}

You will also need to define your custom file type in your app's plist file.