Quickies for NSCoder

---

General

• Archiving a document using keyed archiving [permalink]
  This uses the new Tiger NSDocument load/store. For real code you'll want to handle errors and create an appropriate NSError object. This also saves the document in an XML format.

  - (NSData *) dataOfType: (NSString *) typeName
                    error: (NSError **) error
  {
      *error = nil;
  
      NSMutableData *data = [[NSMutableData alloc] init];
  
      NSKeyedArchiver *archiver;
      archiver = [[NSKeyedArchiver alloc]
                     initForWritingWithMutableData: data];
      [archiver setOutputFormat: NSPropertyListXMLFormat_v1_0];
  
      [archiver encodeObject: stitches  forKey: @"stitches"];
      // and archive other stuff you want
  
      [archiver finishEncoding];
      [archiver release];
  
      return ([data autorelease]);
  
  } // dataOfType
  
  
  - (BOOL) readFromData: (NSData *) data
                ofType: (NSString *) typeName
                 error: (NSError **) error
  {
      *error = nil;
  
      NSKeyedUnarchiver *archiver;
      archiver = [[NSKeyedUnarchiver alloc]
                     initForReadingWithData: data];
  
      [stitches release];
  
      stitches = [archiver decodeObjectForKey: @"stitches"];
      // decode other stuff of interest
  
      [stitches retain];
  
      return (YES);
  
  } // readFromData

• Decoding one class as another [permalink]
  If you change the name of a class, and then try to use NSUnarchiver to expand an archived stream, you'll get an error like this (in this case "BWRawPath" was renamed to "BWSymbol"):

  StitchEdit[3522] *** class error for 'BWRawPath': class not loaded

  In a convenient place (like in the +load method of your class), use NSUnarchiver's decodeClassName:asClassName:

  @implementation BWSymbol
  
  + (void) load
  {
      [NSUnarchiver decodeClassName: @"BWRawPath"
                    asClassName: @"BWSymbol"];
   
      // No need to [super load] - the superclass +load has already
      // been invoked automatically by the runtime.
  
  } // load

  Note that this won't help you if you're wanting to rename something that was added via encodeValueOfObjCType:. You'll have to write some code to unarchive your data using the old @encode(oldName) and then re-archive it as @encode(newName)

  (Thanks to Greg Miller for spotting an error in this quickie)

• Simple archiving [permalink]
  To archive a single object (which can be something like an array or dictionary that contains other object), such as saving your document, do:

  - (NSData *) dataRepresentationOfType: (NSString *) aType
  {
      NSData *data;
      data = [NSArchiver archivedDataWithRootObject: group];
  
      return (data);
  
  } // dataRepresentationOfType
  

• Simple unarchiving [permalink]
  To unarchive a single object (which can be something like an array or dictionary that contains other object), such as loading your document, do:

  - (BOOL) loadDataRepresentation: (NSData *) data
                           ofType: (NSString *) aType
  {
      // replace the moedl
      [group release];
      group = [NSUnarchiver unarchiveObjectWithData: data];
      [group retain];
  
      // make any associations to hook the new data into your document
  
      return (YES);
  
  } // loadDataRepresentation
  
  

• Supporting NSKeyedArchiving in your objects [permalink]
  They should conform to the NSCoding protocol.

  - (void) encodeWithCoder: (NSCoder *) coder
  {
      [coder encodeInt: x  forKey: @"x"];
      [coder encodeInt: y  forKey: @"y"];
      [coder encodeObject: color1  forKey: @"color1"];
      [coder encodeObject: color2  forKey: @"color2"];
      [coder encodeInt: direction  forKey: @"direction"];
  
  } // encodeWithCoder
  
  
  - (id) initWithCoder: (NSCoder *) coder
  {
      if (self = [super init]) {
          x = [coder decodeIntForKey: @"x"];
          y = [coder decodeIntForKey: @"y"];
          color1 = [coder decodeObjectForKey: @"color1"];
          color2 = [coder decodeObjectForKey: @"color2"];
          direction = [coder decodeIntForKey: @"direction"];
      }
  
      return (self);
  
  } // initWithCoder

• Supporting decoding [permalink]
  

  - (id) initWithCoder: (NSCoder *) aDecoder
  {
      if (self = [super init]) {
          // or else [super initWithCoder: aDecoder] if your superclass
          // supports it.  NSObject does not.
  
          // decoding a C type
          [aDecoder decodeValueOfObjCType: @encode(int)
                    at: &itemCount];
  
          // decoding an array of C structs
          if (items != NULL) {
              free (items);
          }
          items = malloc (sizeof(BWRawPathItem) * itemCount);
  
          int i;
          for (i = 0; i < itemCount; i++) {
              [aDecoder decodeValueOfObjCType: @encode(BWRawPathItem)
                        at: &items[i]];
          }
  
          // decoding an object
          name = [aDecoder decodeObject];
          [name retain];
  
          // any other random initializations that don't come from
          // the encoder
          fooby = -1;
      }
  
      return (self);
  
  } // initWithCoder

• Supporting encoding [permalink]
  

  - (void) encodeWithCoder: (NSCoder *) aCoder
  {
      // [super encodeWithCoder:] if you inherit from a class
      // that supports encoding.  NSObject does not.
  
      // encoding a C type
      [aCoder encodeValueOfObjCType: @encode(int)
              at: &itemCount];
  
      // encoding an array of C structs
      int i;
      for (i = 0; i < itemCount; i++) {
          [aCoder encodeValueOfObjCType: @encode(BWRawPathItem)
                  at: &items[i]];
      }
  
      // encoding an object
      [aCoder encodeObject: name];
  
  } // encodeWithCoder

---