I am trying to work out an issue with undo in a few places in my application, and think
if I "get it" with one of the places, I should be able to apply the same theory
elsewhere.
I have a parent and children relationship, and need to have a few things happen
during the process of adding and deleting a child so that the rest of the
application stays in sync. The core data side of things manages the undoability
of the data, but of course it doesn't know how to send the other messages at
the right times, so I have tried to add the notification messages in the
reverse order on the undo stack (prepareWithInvocationTarget), but then redo
doesn't work properly All the undo and redo for the rest of my application is
working fine (just fairly simple relationships and attributes), but I think
there's a design pattern I'm missing here for the more complex case.
It's probably best for me to just post the things that need to happen during a
normal add of a child and deletion of a child, and hopefully someone will be
able to give me guidance on how to make it undoable and redoable.
- (MyNode *)createChild {
MyNode *child = [NSEntityDescription
insertNewObjectForEntityForName:@"MyNodeEntity" inManagedObjectContext:[self
managedObjectContext]];
// Set a bunch of properties on the new child.
...
[[self mutableSetValueForKey:@"children"] addObject:child];
// Set a bunch more properties on the new child and other core data
managed objects
...
// Let the front end of the application know about it
[[NSNotificationCenter defaultCenter]
postNotificationName:@"ChildNodeAddedNotification" object:... userInfo:...];
return child;
}
- (void)deleteChild:(MyNode *)aChild {
NSArray *affectedChildren = [aChild selfAndAllDescendants];
[[NSNotificationCenter defaultCenter]
postNotificationName:@"NodesWillBeRemovedNotification" object:self
userInfo:[NSDictionarydictionaryWithObjectsAndKeys:affectedChildren, @"affectedChildren",
nil]];
[[self mutableSetValueForKey:@"children"] removeObject:aChild];
if (self.parent) {
// Do some things that could affect some ancestor values
...
}
for (MyNode *tn in affectedChildren) {
// Do some special processing to clean up things that might be
pointing to the descendants
...
// Set a non-persistent property on the tn node which will be
picked up by KVO to show that the node will be removed, so we can kill
observing etc.
...
[[self managedObjectContext] deleteObject:tn];
}
aChild.parent = nil;
// Do some post-processing to make sure some other values are kept in
sync.
...
// Post a notification so the front end can be updated.
[[NSNotificationCenter defaultCenter] postNotificationName:@"NodeRemovedNotification" object:self
userInfo:[NSDictionarydictionaryWithObjectsAndKeys:aChild, @"node", self, @"parent",
affectedChildren, @"affectedChildren", nil]];
}
I have looked at some of the previous posts on related things, but haven't seen
an answer that would explain what to do for this kind of thing (and some posts
were suggesting turning off core data's undo completely and doing your own etc,
which would not be good for me since I have a *lot* of places where it is
working just fine for me and only about 6 places where it's not).
Thanks in advance for any advice on this.
Ken
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