macOS Undo / Redo Issue

[stadidas]

Hi everybody.

I've been having a small issue getting a new feature in a program I've made to work correctly.
Currently the methods do exactly what I want them to, and when I hit undo, the action is undone as I would expect. However, when I try to redo the action, nothing happens. Hopefully this will be an easy problem to solve that I just can't see, even Aaron Hillegas says the UndoManager makes his head spin! Anyway, here's the troublesome code:

- (void)add:(double)d:(NSString *)s
{
	Log *l = [[Log alloc] init];
	[l setDescription:s];
	[l setAmount:d];
	[self doAdd:d:s:l];
	[l release];
}

- (void)addAmount:(double)d
{
	double tempBalance = [myBalance doubleValue];
	double newBalance = tempBalance + d;
	[detailsController setMyBalance:newBalance];
}

- (void)doAdd:(double)d:(NSString *)s:(Log *)l
{
	[self addAmount:d];
	[self addLog:l];
	[tableView reloadData];
	
	NSUndoManager *undo = [self undoManager];
	[[undo prepareWithInvocationTarget:self]
		removeLog:l];
	
	[[undo prepareWithInvocationTarget:self]
		subtractAmount:d];
	
	if (![undo isUndoing]) {
		[undo setActionName:@"Add to Balance"];
	}
}

- (void)subtract:(double)d:(NSString *)s
{
	Log *l = [[Log alloc] init];
	double inverseD = - d;
	[l setDescription:s];
	[l setAmount:inverseD];
	[self doSubtract:d:s:l];
	[l release];
}

- (void)subtractAmount:(double)d
{
	double tempBalance = [myBalance doubleValue];
	double newBalance = tempBalance - d;
	[detailsController setMyBalance:newBalance];
}

- (void)doSubtract:(double)d:(NSString *)s:(Log *)l
{
	[self subtractAmount:d];
	[self addLog:l];
	[tableView reloadData];
	
	NSUndoManager *undo = [self undoManager];
	[[undo prepareWithInvocationTarget:self]
		removeLog:l];
	
	[[undo prepareWithInvocationTarget:self]
		addAmount:d];
	
	if (![undo isUndoing]) {
		[undo setActionName:@"Subtract From Balance"];
	}
	
}

I hacked this code out a few nights ago, so I'm sure it's probably just a fault from trying several different approaches and maybe not thinking it through correctly.
As always any help is very much appreciated!

 

[stadidas]

No-one has any ideas?