Learning Cocoa

Implement Archiving and Unarchiving (Save and Open)

Now that you have implemented and debugged all of To Do’s major features, it’s time to finish up by adding support for saving and opening documents to ToDoDocument.m.

Implement dataRepresentationOfType:

As you learned previously, this method is responsible for archiving the document’s data and returning it in the form of an NSData instance. It’s very simple:

- (NSData *)dataRepresentationOfType:(NSString *)aType
{
    [self saveDocItems];
    return [NSArchiver archivedDataWithRootObject:activeDays];
}

This method saves the current day’s items to the activeDays dictionary and archives it.

Implement loadDataRepresentation:ofType:

This method checks to see if calendar exists before deciding how to proceed. If calendar does exist, it means that the nib file has already been loaded and the document controller is being asked to display the data (this is what happens when Revert is selected from the File menu). If calendar doesn’t yet exist (meaning the nib file has not yet been loaded), the method saves a reference to the document data in the dataFromFile instance variable. When windowControllerDidLoadNib is called, that method checks to see if any data is pending, and if it is, that data is loaded into the document.

1. Add the instance variable dataFromFile to ToDoDocument.h. Statically type the variable as an NSData*.

2. Add the following method definition to ToDoDocument.m:

   - (BOOL)loadDataRepresentation:(NSData *)data ofType:(NSString *)aType ...