1. A How-To for
an Easy Undo

2. Last Time
• Objective C
• Tutorial resources
• XCode projects

3. This Time
• A simple, common pattern with
Cocoa

4. Undo/Redo
• You should have undo in your app.

5. The Theory of Undo
@interface dot : NSObject
{
int x;
int y;
}

6. The Theory of Undo
History of X
@interface dot : NSObject
{ • x = 100;
int x;
int y;
}

7. The Theory of Undo
History of X
@interface dot : NSObject
{ • x = 100;
int x;
int y;
• x = 22;
}

8. The Theory of Undo
History of X
@interface dot : NSObject
{ • x = 100;
int x;
int y;
• x = 22;
} •x=

9. The Theory of Undo
History of X
@interface dot : NSObject
{
int x; x = 22;
•
int y;
} • x = 100; •x=

10. The Theory of Undo
History of X
x = 22;
x = 100; •x=

11. The Theory of Undo
Undo Stack
x = 22;
x = 100; •x=

12. The Theory of Undo
Undo Stack
x = 22; •x=
x = 100;

13. The Theory of Undo
Undo Stack
x = 22; •x=
x = 100;

14. The Theory of Undo
Undo Stack
x = 22; x=
x = 100;

15. The Theory of Undo
Undo Stack
x = 22; x=
x = 100;

16. The Theory of Undo
Undo Stack Redo Stack
x = 22; x=
x = 100;

17. Undo Stack Redo Stack
x = 22; x=
x = 100;

18. Undo Stack Redo Stack

19. NSUndoManager
Undo Stack Redo Stack

20. NSUndoManager

21. NSUndoManager

22. NSUndoManager
Q: How many
managers?

23. NSUndoManager
Q: How many
managers?
A1: It depends.

24. NSUndoManager
Q: How many managers?
A1: It depends...
A2: ...but often one per
doc.

25. NSUndoManager
Q: How many managers?
A1: It depends...
A2: ...but often one per
doc.
NSDocument

26. NSUndoManager
Q: How many managers?
A1: It depends...
A2: ...but often one per
doc.
NSDocument
eebie # 472:
Co coa fr saved
arked as un
doc m not empty
if undo stack

27. Registering Undos
1. Simple Undo
2. Invocation-based Undo

28. Simple Undo
[self.document.undoManager registerUndoWithTarget: target
selector: aSelector
object: anObject];

29. Simple Undo:
Example
- (void) setX: (int) newX
{
NSUndoManager undoManager = self.document.undoManager;
if (x != newX) {
[undoManager registerUndoWithTarget: self
selector: @selector(setX:)
object: x];
[myObject setX:newX];
}
}

30. Simple Undo:
Example
- (void) setX: (int) newX
{
NSUndoManager undoManager = self.document.undoManager;
if (x != newX) {
[undoManager registerUndoWithTarget: self
selector: @selector(setX:)
object: x];
ject
[myObject setX:newX];
}
}
N ot a n ob

31. Simple Undo:
Example
- (void) setX: (NSNumber *) newX
{
NSUndoManager undoManager = self.document.undoManager;
if (![x isEqual:newX]) {
[undoManager registerUndoWithTarget: self
selector: @selector(setX:)
object: x];
[myObject setX:newX];
}
}

32. Simple Undo:
Example
- (void) setX: (NSNumber *) newX
{
NSUndoManager undoManager = self.document.undoManager;
if (![x isEqual:newX]) {
[undoManager registerUndoWithTarget: self
selector: @selector(setX:)
object: x];
[myObject setX:newX];
}
} Tip: Cocoa uses objects.
You usually should too.

33. Invocation-based
Undo
[[undoManager prepareWithInvocationTarget: target] <any method>];

34. Invocation-based
Undo
[[undoManager prepareWithInvocationTarget: target] <any method>];
Magic

35. Invocation-based
Undo
[[undoManager prepareWithInvocationTarget: target] <any method>];
NSInvocation Magic

36. Invocation-based
Undo
[[undoManager prepareWithInvocationTarget: target] <any method>];
NSInvocation Magic

37. Invocation-based
Undo
[[undoManager prepareWithInvocationTarget: target] <any method>];
NSInvocation
Magic

38. Invocation-based
Undo
[[undoManager prepareWithInvocationTarget: target] <any method>];
NSInvocation
• “An action turned into an object.”

39. Invocation-based
Undo
[[undoManager prepareWithInvocationTarget: target] <any method>];
NSInvocation
• “An action turned into an object.”
• Contains: target, selector,
arguments, etc.

40. Invocation-based
Undo
[[undoManager prepareWithInvocationTarget: target] <any method>];
NSInvocation
• “An action turned into an object.”
• Contains: target, selector,
arguments, etc.

41. Invocation-based
Undo
[[undoManager prepareWithInvocationTarget: target] <any method>];
NSInvocation
• “An action turned into an object.”
• Contains: target, selector,
arguments, etc.
byte level

42. Invocation-based
Undo
[[undoManager prepareWithInvocationTarget: target] <any method>];
What happens:

43. Invocation-based
Undo
[[undoManager prepareWithInvocationTarget: target] <any method>];
What happens:
• Prepare target - “incoming!”

44. Invocation-based
Undo
[[undoManager prepareWithInvocationTarget: target] <any method>];
What happens:
• Prepare target - “incoming!”
• becomes an NSInvocation
<any method>
object

45. Invocation-based
Undo
[[undoManager prepareWithInvocationTarget: target] <any method>];
What happens:
• Prepare target - “incoming!”
• becomes an NSInvocation
<any method>
object
• NSUndoManager doesn’t respond to
method>
<any

46. Invocation-based
Undo
[[undoManager prepareWithInvocationTarget: target] <any method>];
What happens:
• Prepare target - “incoming!”
• becomes an NSInvocation
<any method>
object
• NSUndoManager doesn’t respond to
method>
<any

47. Invocation-based
Undo
[[undoManager prepareWithInvocationTarget: target] <any method>];
What happens:
• Prepare target - “incoming!”
• becomes an NSInvocation
<any method>
object
• NSUndoManager doesn’t respond to
method>
<any
• calls with the NSInvocation
forwardInvocation:

48. Invocation Undo:
Example
- (void) setX: (int) newX
{
NSUndoManager undoManager = self.document.undoManager;
if (oldX != newX) {
[[undoManager prepareWithInvocationTarget:self] setX:oldX];
[myObject setX:newX];
}
}

49. Invocation Undo:
Example
- (void) setX: (int) newX
{
NSUndoManager undoManager = self.document.undoManager;
if (oldX != newX) {
[[undoManager prepareWithInvocationTarget:self] setX:oldX];
[myObject setX:newX];
}
}
OK

50. Undo Details

51. Undo Details
1. [undoManager setActionName:@”What’s Changing”];

52. Undo Details
1. [undoManager setActionName:@”What’s Changing”];
2. Memory management: what’s going
on?

53. Undo Details
1. [undoManager setActionName:@”What’s Changing”];
2. Memory management: what’s going
on?
• Simple - retains object, not target

54. Undo Details
1. [undoManager setActionName:@”What’s Changing”];
2. Memory management: what’s going
on?
• Simple - retains object, not target
• Invocation - Probably retained?

55. Undo Details
1. [undoManager setActionName:@”What’s Changing”];
2. Memory management: what’s going
on?
• Simple - retains object, not target
• Invocation - Probably retained?
3. Undo groupings

56. Undo Architecture
• How do we make sure all changes
are captured?
• Parallel controller objects?
• ...that gets repetitive...

57. Ta da!

58. Key/Value
Observation (K

59. Key/Value
*
Observation (K
(the basics)

61. K VO: What is it?
• Built into base NSObject

62. K VO: What is it?
• Built into base NSObject
• Automated notifications of
property changes

63. K VO: What is it?
• Built into base NSObject
• Automated notifications of
property changes...
• ...but allows for manual override

65. K VO: What’s a key?
• A string that identifies a property

66. K VO: What’s a key?
• A string that identifies a property
• e.g. via an accessor method or
instance variable

67. K VO: What’s a key?
• A string that identifies a property
• e.g. via an accessor method or
instance variable
These accessors...
- (void) setHeight: (NSNumber *) newHeight;
- (NSNumber *) height;

68. K VO: What’s a key?
• A string that identifies a property
• e.g. via an accessor method or
instance variable
These accessors... ...correspond to this key.
- (void) setHeight: (NSNumber *) newHeight;
@"height"
- (NSNumber *) height;

70. K VO: How to use it.
1. Must be KVO compliant for
properties you want to observe

71. K VO: How to use it.
1. Must be KVO compliant for
properties you want to observe
2. Must register for each property

72. K VO: How to use it.
1. Must be KVO compliant for
properties you want to observe
2. Must register for each property
3. Observer must handle the
notification

74. 1. K VO Compliance
Depends on what kind of property.
• To-one
• To-many (indexed)
• To-many (unordered)

75. 1. K VO Compliance
Depends on what kind of property:
e.g. - (void
• To-one
) setHe
- (NSNu ight: (
mber *) NSNumbe
height; r *) ne
wHeight
;
• To-many (indexed)
• To-many (unordered)

76. 1. K VO Compliance
Depends on what kind of property:
e.g. - (void
• To-one
) setHe
- (NSNu ight: (
mber *) NSNumbe
height; r *) ne
wHeight
;
• To-many (indexed)
• To-many (unordered)
- (NSUI
e.g. - (NSEn
- (id)
nteger)
umerato
countOf
r *) en
MySet;
memberO umerato
fMySet: rOfMySe
(id) an t;
Object;

78. 2. K VO Registration
[object addObserver: (NSObject *) anObserver
forKeyPath: (NSString *) keyPath
options: (NSKeyValueObservingOptions) options
context: (void *) context];

80. 3. K VO
Notifications
- (void) observeValueForKeyPath: (NSString *) keyPath
ofObject: (id) object
change: (NSDictionary *) change
context: (void *) context

81. 3. K VO
Notifications
- (void) observeValueForKeyPath: (NSString *) keyPath
ofObject: (id) object
change: (NSDictionary *) change
context: (void *) context
{
int kindOfChange = [[change objectForKey:NSKeyValueChangeKindKey] intValue];
id oldValue = [change objectForKey:NSKeyValueChangeOldKey];
id newValue = [change objectForKey:NSKeyValueChangeNewKey];
NSIndexSet *indexSet = [change objectForKey:NSKeyValueChangeIndexesKey];
...

82. Put it all
together...