Objective-C Sins

I have a confession to make. I've written some terrible Objective-C code. I guess you can say I've sinned. In this talk, I discuss common anti-patterns and how to avoid them.

This talk was originally presented to students of the iOS class at The Flatiron School. Without the actual talking to go with it, these slides are probably missing a lot of context. If you're confused about something, send me a message on twitter (@mb).

Transcript

1. View Slide

2. Objective-C Sins
   

   View Slide

3. sin 1 |sin|
   noun
   an immoral act considered to be a transgression against
   divine law: a sin in the eyes of God | the human capacity for sin.
   !
   • an act regarded as a serious or regrettable fault, offense, or
   omission: he committed the unforgivable sin of refusing to give
   interviews | humorous : with air like this, it's a sin not to go out.
   

   View Slide

4. sin 1 |sin|
   noun
   an immoral act considered to be a transgression against
   divine law: a sin in the eyes of God | the human capacity for sin.
   !
   • an act regarded as a serious or regrettable fault, offense, or
   omission: he committed the unforgivable sin of refusing to give
   interviews | humorous : with air like this, it's a sin not to go out.
   

   View Slide

5. @mb
   

   View Slide

6. matthew bischoff
   

   View Slide

7. matt
   

   View Slide

8. View Slide

9. Velocity
   Quotebook
   

   View Slide

10. View Slide

11. View Slide

12. Sins
    

    View Slide

13. [object retainCount];
    

    View Slide

14. View Slide

15. Why not?
    

    View Slide

16. Object retainCount? Actual retainCount
    [NSNumber numberWithInt:1] 1 2
    @"Matt" 1 1152921504606846975
    [NSString stringWithString:@"Matt"] 1 1152921504606846975
    

    View Slide

17. Key-Value Observing
    

    View Slide

18. Key-Value Observing has the
    worst API in all of Cocoa. It’s
    awkward, verbose, and confusing.
    Mattt Thompson
    

    View Slide

19. “Stringly Typed”
    

    View Slide

20. Refactoring is scary.
    

    View Slide

21. Throws Exceptions
    

    View Slide

22. ARC == garbage collection
    

    View Slide

23. You still have to pay attention.
    

    View Slide

24. . Syntax
    [ ] Syntax
    

    View Slide

25. What’s the obvious thing to do, the easiest
    way to agree? Just do what the headers say. If
    it’s a property, treat it as such. If it’s not, don’t.
    !
    And when in doubt, look it up.
    Brent Simmons
    

    View Slide

26. Dot syntax is for properties.
    

    View Slide

27. Bracket syntax is for methods.
    

    View Slide

28. UIColor.clearColor;
    array.count;
    object.hash;
    

    View Slide

29. More than 1 Class per file
    

    View Slide

30. View Slide

31. performSelector:
    afterDelay:
    

    View Slide

32. It’s a crash waiting to happen.
    

    View Slide

33. Missing or improper reuse
    

    View Slide

34. Always reuse cells.
    

    View Slide

35. Don’t keep track of cells.
    

    View Slide

36. Architecture-dependent
    primitive types
    

    View Slide

37. int
    float
    double
    

    View Slide

38. NSInteger / NSUInteger
    CGFloat
    NSTimeInterval
    

    View Slide

39. Violating MVC
    

    View Slide

40. Models that do networking
    

    View Slide

41. Views that know about models
    

    View Slide

42. Controllers that do layout
    

    View Slide

43. NSDictionary
    

    View Slide

44. Not a replacement for a model
    

    View Slide

45. ✨"
    

    View Slide

46. Magic numbers
    

    View Slide

47. Repeating yourself
    Repeating yourself
    Repeating yourself
    Repeating yourself
    Repeating yourself
    Repeating yourself
    

    View Slide

48. Every piece of knowledge must
    have a single, unambiguous,
    authoritative representation
    within a system.
    Andy Hunt and Dave Thomas
    

    View Slide

49. if (taylorSwift) {
    taylorSwift.age = 22;
    }
    

    View Slide

50. id
    

    View Slide

51. Singletons
    

    View Slide

52. Blocking the main queue
    

    View Slide

53. Low level APIs
    

    View Slide

54. CoreFoundation
    CoreText
    CoreGraphics
    CoreAnimation
    

    View Slide

55. Foundation
    TextKit
    UIKit
    UIView Animations
    

    View Slide

56. @property (nonatomic, strong, readwrite) NSString *title;
    

    View Slide

57. @property (nonatomic) NSString *title;
    

    View Slide

58. @property NSString *title;
    

    View Slide

59. Warnings
    

    View Slide

60. Unused Variable ‘sin’
    !
    

    View Slide

61. Unused Variable ‘sin’
    !
    

    View Slide

62. Public and readwrite
    

    View Slide

63. Missing #pragma marks
    

    View Slide

64. #pragma mark - NSObject
    !
    - (void)dealloc {}
    !
    #pragma mark - UIViewController
    !
    - (void)viewDidLoad {}
    !
    #pragma mark - LCKDocumentsTableViewController
    !
    - (void)setupRefreshControl {}
    

    View Slide

65. Bad names
    

    View Slide

66. UIImage *img;
    UIButton *btn;
    NSString *str;
    NSArray *arr;
    NSDictionary *dict;
    NSInteger i;
    

    View Slide

67. UIImage *avatar;
    UIButton *signupButton;
    NSString *name;
    NSArray *people;
    NSDictionary *userInfo;
    NSInteger count;
    

    View Slide

68. Two-letter prefixes
    

    View Slide

69. NS
    UI
    CG
    CA
    AC
    ST
    XC
    SK
    MF
    AD
    

    View Slide

70. Two-letter prefixes…are reserved by
    Apple for use in framework classes.
    !
    Your own classes should use three
    letter prefixes.
    

    View Slide

71. Inconsistent style
    

    View Slide

72. View Slide

73. Not overriding the
    designated initializer
    

    View Slide

74. - (instancetype)initWithPerson:(LCKPerson *)person {
    self = [super initWithStyle:UITableViewStylePlain];
    if (self) {
    _person = person;
    _dataStore = [NSMutableDictionary dictionary];
    }
    return self;
    }
    

    View Slide

75. - (id)initWithStyle:(UITableViewStyle)style {
    return [self initWithPerson:nil];
    }
    !
    - (instancetype)initWithPerson:(LCKPerson *)person {
    self = [super initWithStyle:UITableViewStylePlain];
    if (self) {
    _person = person;
    _dataStore = [NSMutableDictionary dictionary];
    }
    return self;
    }
    

    View Slide

76. UITapGestureRecognizer
    

    View Slide

77. Just use a UIButton.
    

    View Slide

78. UISwipeGestureRecognizer
    

    View Slide

79. Just use a UIPanGestureRecognizer.
    

    View Slide

80. Inaccessibility
    

    View Slide

81. View Slide

82. Property Description Example
    accessibilityLabel
    Identifies the accessibility element, but does not include the
    type of the control or view
    “Share”
    accessibilityValue
    The value is a localized string that contains the current value
    of an element
    “35 %”
    accessibilityHint
    Description of the result of performing an action on the
    element.
    “Selects the
    message”
    

    View Slide

83. Missing Localization
    

    View Slide

84. View Slide

85. // Unnecessary comments
    

    View Slide

86. Comments explain why.
    Not what or how.
    

    View Slide

87. true && false
    

    View Slide

88. YES and and NO
    

    View Slide

89. Profiling at the end
    

    View Slide

90. View Slide

91. [[[[[too much] code] on] one] line]
    

    View Slide

92. #import
    

    View Slide

93. #define
    

    View Slide

94. retain cycles
    

    View Slide

95. Object Object
    strong
    

    View Slide

96. [self.queue addOperationWithBlock:^{
    [self download];
    }];
    

    View Slide

97. __weak typeof(self) weakSelf = self;
    [self.queue addOperationWithBlock:^{
    [weakSelf download];
    }];
    

    View Slide

98. (assign) delegates
    

    View Slide

99. self.webView.delegate = nil;
    

    View Slide

100. Blended layers
     

     View Slide

101. View Slide

102. View Slide

103. Mixing up nothing
     

     View Slide

104. nil, Nil, NULL, NSNull
     

     View Slide

105. Symbol Value Meaning
     NULL (void *)0 literal null value for C pointers
     nil (id)0 literal null value for Objective-C objects
     Nil (Class)0 literal null value for Objective-C classes
     NSNull [NSNull null] singleton object used to represent null
     

     View Slide

106. Ignoring crash logs
     

     View Slide

107. View Slide

108. Special Thanks
     •Ash Furrow
     •Brent Simmons
     •Mattt Thompson
     •Brian Capps
     

     View Slide

109. Thank you.
     

     View Slide

110. Questions?
     

     View Slide