iOS Gems Some jewels for your glory box My talk from Swipe 2011.

1. iOS Gems
Some jewels for your glory box
Kevin O’Neill
Delivery Manager – Mobile
REA Group
twitter: @kevinoneill
This is not a con dential session — please stream, blog, tweet and take pictures :)

2. Roadmap
• Enhancing NSArray
• View size and layout
• Simple gestures handling
• Closing thoughts

3. Enhancing NSArray

4. NSArray
Great Core Support

5. But …

6. It’s verbose
- (NSIndexSet *)indexesOfObjectsWithOptions:
(NSEnumerationOptions)opts passingTest:(BOOL
(^)(id obj, NSUInteger idx, BOOL *stop))
predicate

7. Difficult to combine
- (NSIndexSet *)indexesOfObjectsAtIndexes:
(NSIndexSet *)indexes options:
(NSEnumerationOptions)opts passingTest:(BOOL
(^)(id obj, NSUInteger idx, BOOL
*stop))predicate;

8. We Can Do Better
• Enumeration
• Filtering
• Transformation

9. Enumeration
- (void)each:
(void (^)(id item))block;
- (void)eachWithIndex:
(void (^)(id, NSUInteger))block;

10. Consider carefully

11. Results by side effect only

12. Huh?

13. Enumerations produce no
‘value’

14. They mutate state of the
world around them

15. EG
NSMutableSet *uniqueNames = [NSMutableSet
set];
[names each: ^ (id name) {
[uniqueNames addObject:name];
}];

16. OR
[[view subviews] eachWithIndex:^ (id subview,
NSUInteger position) {
CGRect cell_frame =
CGRectMake(subview_width * position,
0,
requested_subview_size.width,
requested_subview_size.height);

17. Demo
Enumeration
Use and implementation

18. A for loop may often be a
better choice

19. Useful at the tail of
transform operations

20. Filtering
- (NSArray *)filter:(BOOL (^)(id item))block;
- (NSArray *)pick:(BOOL (^)(id item))block;
- (id)first:(BOOL (^)(id))block;
- (id)last:(BOOL (^)(id))block;

21. Filter removes matching
elements

22. Filter
NSArray *names = [NSArray arrayWithObjects:
@"Kevin", @"Sue", @"Aaron",
@"Jack", @"Maddie", nil];
[[names filter:^BOOL(id name) {
return [name length] < 5;
}] each:^(id name) {
NSLog(@"%@", name);
}];
"Kevin"
"Aaron"
"Maddie"

23. Pick selects matching
elements

24. Pick
NSArray *names = [NSArray arrayWithObjects:
@"Kevin", @"Sue", @"Aaron",
@"Jack", @"Maddie", nil];
[[names pick:^BOOL(id name) {
return [name length] < 5;
}] each:^(id name) {
NSLog(@"%@", name);
}];
"Sue"
"Jack"

25. First returns the first
element matched

26. First
NSArray *names = [NSArray arrayWithObjects:
@"Kevin", @"Sue", @"Aaron",
@"Jack", @"Maddie", nil];
NSLog(@"%@", [names first:^BOOL(id name) {
return [name length] < 5;
}]);
"Sue"

27. Last returns the last
element matched

28. Last
NSArray *names = [NSArray arrayWithObjects:
@"Kevin", @"Sue", @"Aaron",
@"Jack", @"Maddie", nil];
NSLog(@"%@", [names last:^BOOL(id name) {
return [name length] < 5;
}]);
"Jack"

29. Demo
Filter, Pick, First and Last
Use and implementation

30. Transformation
- (NSArray *)map:(id (^)(id item))block;
- (id)reduce:(id (^)(id current, id item))block
initial:(id)initial;
- (NSArray *)intersperse:(id (^) (void))separator;

31. Map applies the block to
each element

32. Map
NSArray *names = [NSArray arrayWithObjects:
@"Kevin", @"Sue", @"Aaron",
@"Jack", @"Maddie", nil];
[[names map:^id(id name) {
return [NSNumber numberWithInteger:
[name length]];
}] each:^(id length) {
NSLog(@"%@", length);
}];
"5"
"3"
"5"
…

33. Reduce applies the block
to each element passing
the result along

34. Reduce
NSArray *names = [NSArray arrayWithObjects:
@"Kevin", @"Sue", @"Aaron",
@"Jack", @"Maddie", nil];
NSLog(@"%@",
[names reduce:^id(id current, id item) {
NSInteger result = [current integerValue]
+ [item length];
return [NSNumber numberWithInteger:result];
} initial:[NSNumber numberWithInteger:0]]);
"23"

35. Place the result of the
block between elements

36. Intersperse
NSArray *names = [NSArray arrayWithObjects:
@"Kevin", @"Sue", @"Aaron",
@"Jack", @"Maddie", nil];
[[names intersperse:^id(id current, id next) {
return [current length] > [next length]
? @">" : @"<";
}] each:^(id item) {
NSLog(@"%@", item);
}];
"Kevin"
">"
"Sue"
"<"
…

37. Demo
Map, Reduce, Intersperse
Use and implementation

38. View size and layout

39. How to size and layout
subviews without pain

40. I have a confession

41. I’m an interface builder
muppet

42. Two methods are key

43. Two methods are key
- (void)layoutSubviews;
- (CGSize)sizeThatFits:(CGSize)size;

44. A diversion.
Paired methods.

45. sizeThatFits: and
layoutSubviews are loosely
paired

46. They must be sympathetic
to one and other

47. - (void)layoutSubviews;
• Does nothing by default
• Used to position subviews
• Called when the layout is dirty
• Don’t call it manually– I’ve seen to
many times
• Don’t resize self – I’ve seen to many
times

48. - (CGSize)sizeThatFits:
(CGSize)size;
• Returns current size by default
• Return ‘best’ size to fit given size
• Doesn’t resize the view
• Don’t resize the view – I’ve seen to
many times
• Don’t layout view – I’ve seen to many
times

49. But here’s the rub

50. The calculations used are
often the same, just
applied differently

51. EG
- (CGSize)sizeThatFits:(CGSize)size;
{
float width = size.width;
float height = [[[self subviews] reduce: ^ id (id current, id item) {
CGSize item_size = [item sizeThatFits:CGSizeMake(width, 0.)];
return [NSNumber numberWithFloat:
ceilf([current floatValue] +
(item_size.height + [self spacingForSubview:item]))];
} initial:[NSNumber numberWithFloat:0.]] floatValue];
CGSize result = CGSizeMake(width, height);
return result;
}

52. And
- (void)layoutSubviews;
{
float width = [self width];
__block StackedView *block_self = self;
[[self subviews] reduce: ^ id (id current, id item) {
CGSize item_size = [item sizeThatFits:CGSizeMake(width, 0.)];
[item setFrame:
CGRectMake(0,
[current floatValue] + [block_self spacingForSubview:item],
item_size.width,
item_size.height)];
return [NSNumber numberWithFloat:ceilf([item bottom])];
} initial:[NSNumber numberWithFloat:0.]];
}

53. The only real variance here
is the action

54. And that’s a simple
example

55. We can do better

56. Demo
Size and Layout

57. The layout algorithm is
coded once

58. Then applied appropriately

59. Simple gestures handling

60. Gesture recognisers rock

61. But maintaining pairing
between selectors and
actions is a little tedious

62. EG
- (void)cancelRequest
{
[self displayCancelMessage];
}
UITapGestureRecognizer *tapRecognizer =
[[UITapGestureRecognizer alloc]
initWithTarget:self
action:@selector(cancelRequest)];

63. We can do better

64. Can you guess what makes
gesture handling easier?

65. Demo
Gesture recognisers

66. Blocks make gesture setup
much easier

67. Closing thoughts

68. Take from this what you will

69. Understanding blocks will
make you more productive

70. New Core API’s are taking
advantage of blocks

71. So should you

72. Categories are a key
method of partitioning
behaviour

73. Blocks are a key method of
partitioning algorithms

74. Associated objects should
be part of your toolkit

75. But

76. Don’t use these tools
because they are there

77. Use them to make your
code …

78. Simpler

79. Easier to maintain

80. Useful Bits
Open source libraries used
https://github.com/kevinoneill/Useful-Bits
https://github.com/kevinoneill/Useful-Swipe
https://github.com/domesticcatsoftware/DCIntrospect
Questions?