Objective-C Programming: The Big Nerd Ranch Guide

Saving and loading data

To add the ability to save and reopen a task list, you need to override two methods inherited from BNRDocument’s superclass, NSDocument:

- (NSData *)dataOfType:(NSString *)typeName
                 error:(NSError **)outError
{
    // This method is called when our document is being saved
    // You are expected to hand the caller an NSData object wrapping our data
    // so that it can be written to disk
    // If there is no array, write out an empty array
    if (!self.tasks) {
        self.tasks = [NSMutableArray array];
    }

    // Pack the tasks array into an NSData object
    NSData *data = [NSPropertyListSerialization
                         dataWithPropertyList:self.tasks
                                       format:NSPropertyListXMLFormat_v1_0
                                      options:0
                                        error:outError];

    // Return the newly-packed NSData object