Question

the background: I’m adding a print panel accessory view to a print dialog (using addAccessoryController:), with controls binded to NSPrintInfo printSettings values so the values are saved in the print presets. I’m having troubles observing printSettings changes. I’m building with SDK 10.6, testing on OS X 10.7.

Here is a code sample that should work in my understanding, but observeValueForKeyPath: is never called:

- (void)testKVO
{
  NSPrintInfo *printInfo = [NSPrintInfo sharedPrintInfo];
  [printInfo addObserver:self forKeyPath:@"printSettings.foo" options:0 context:NULL];
  [printInfo setValue:@"bar" forKeyPath:@"printSettings.foo"]; // observeValueForKeyPath:ofObject:change:context: not called
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
  NSLog(@"%s %@ :: %@", _cmd, keyPath, object);
}

I also tried observing printSettings directly, with no more success, the observer method is not called either (the printSettings returned by NSPrintInfo is in fact of class NSPrintInfoDictionaryProxy):

- (void)testKVO
{
  NSMutableDictionary *printSettings = [[NSPrintInfo sharedPrintInfo] printSettings];
  [printSettings addObserver:self forKeyPath:@"foo" options:0 context:NULL];
  [printSettings setValue:@"bar" forKey:@"foo"]; // observeValueForKeyPath:ofObject:change:context: not called
}

I double checked that my KVO system works in normal conditions and calls the observer method:

- (void)testKVO
{
  NSMutableDictionary *printSettings = [NSMutableDictionary dictionary];
  [printSettings addObserver:self forKeyPath:@"foo" options:0 context:NULL];
  [printSettings setValue:@"bar" forKey:@"foo"]; // observeValueForKeyPath:ofObject:change:context: called at last!
}

So the question is: how can I observe printSettings modifications, especially to know when the user has chosen a print preset?

I’d also like the preview to be updated automatically with

- (NSSet *)keyPathsForValuesAffectingPreview
{
  return [NSSet setWithObjects:
          @"representedObject.printSettings.foo",
          nil];
}

there is an easy workaround for the preview update: adding an indirection level by redeclaring the properties directly on the NSViewController itself. But for the print preset change I have no clue.

In the end, here is the comment in NSPrintInfo.h:

- (NSMutableDictionary *)printSettings;

The print info’s print settings. You can put values in this dictionary to store them in any preset that the user creates while editing this print info with a print panel. Such values must be property list objects. This class is key-value coding (KVC) and key-value observing (KVO) compliant for “printSettings” so you can often bind controls in print panel accessory views directly to entries in this dictionary. You can also use this dictionary to get values that have been set by other parts of the printing system, like a printer driver’s print dialog extension (the same sort of values that are returned by the Carbon Printing Manager’s PMPrintSettingsGetValue() function). Other parts of the printing system often use key strings like “com.apple.print.PrintSettings.PMColorSyncProfileID” but dots like those in key strings wouldn’t work well with KVC, so those dots are replaced with underscores in keys that appear in this dictionary, as in “com_apple_print_PrintSettings_PMColorSyncProfileID”. You should use the same convention when adding entries to this dictionary.

Any help appreciated

Thanks

Answer 1

Well I found a way. There is an undocumented notification that is being sent when selecting a print preset or changing paper format, all that you have to do is add an observer:

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(printInfoDidChange:) name:@"NSPrintInfoDidChange" object:nil];

That is not as straightforward as binding to printSettings keypaths, and I really don’t like using an undocumented notification (almost as bad as using private API in term of maintainability) but that’s the only way I could figure out to do the job.