Python for Bioinformatics: Cocoa: More about archiving

Tuesday, September 29, 2009

Cocoa: More about archiving

This post is the result from some more tests I've run on archiving. Some interesting points:

• I'm compiling and running the tests from the command line. I've enabled garbage collection as you can see in the compiler invocation on the first line of the listing.

• The object to be archived is an instance of NSColor. In order to use this class, I need to not only import the AppKit but also link against it. I missed that at first.

• Just for fun, I get a color from the "Crayons" color list.

• The last example used NSKeyedArchiver, but since we're not using a key, we can just use NSArchiver.

• The interesting part is where the action happens in:

[archiver encodeObject:maroon];

Essentially, the archiver says to the object: encode yourself! Since NSColor conforms to NSCoding, it should (and fortunately, is) able to do that.

• The encoded color is an NSMutableData object, and can now be added to an array and written to a plist file.

Output:

2009-09-29 16:13:04.573 test[1077:10b] color NSCalibratedRGBColorSpace 0.501961 0 0.25098 1
2009-09-29 16:13:04.576 test[1077:10b] data <040b7374 7265616d 74797065 6481e803 84014084 8484074e 53436f6c 6f720084 84084e53 4f626a65 63740085 84016301 84046666 66668381 80003f00 83818080 3e0186>
2009-09-29 16:13:04.582 test[1077:10b] array1 (
    <040b7374 7265616d 74797065 6481e803 84014084 8484074e 53436f6c 6f720084 84084e53 4f626a65 63740085 84016301 84046666 66668381 80003f00 83818080 3e0186>
)
2009-09-29 16:13:04.582 test[1077:10b] filename /Users/te/Desktop/a.plist
2009-09-29 16:13:04.585 test[1077:10b] color NSCalibratedRGBColorSpace 0.501961 0 0.25098 1

Code listing:

// gcc -o test test2.m -framework Foundation -framework AppKit -fobjc-gc-only
// ./test
#import <Foundation/Foundation.h>
#import <AppKit/AppKit.h>

int main (int argc, const char * argv[]) {
  NSColor *maroon;
  NSColorList *CL;
  CL = [NSColorList colorListNamed:@"Crayons"];
  maroon = [CL colorWithKey:@"Maroon"];
  NSLog(@"color %@", maroon);

  NSMutableData *mdata;
  mdata = [[NSMutableData alloc] initWithCapacity:100];
  NSArchiver *archiver;
  archiver = [[NSArchiver alloc]
              initForWritingWithMutableData:mdata];
  [archiver encodeObject:maroon];
  NSLog(@"data %@", [mdata description]);

  NSArray *arr;  
  arr = [NSArray arrayWithObject:mdata];
 NSLog(@"array1 %@", arr);
 
  NSString *fn;
  bool result;
  fn = NSHomeDirectory();
  fn = [fn stringByAppendingString:
         @"/Desktop/a.plist"];
  NSLog(@"filename %@", fn);
  [arr writeToFile:fn atomically:YES];

  NSArray *arr2;
  arr2 = [NSArray arrayWithContentsOfFile:fn];
  NSColor *color;
  NSData *data = [arr2 objectAtIndex:0];
  color = [NSUnarchiver unarchiveObjectWithData:data];
  NSLog(@"color %@", color);
  return 0;
}