Objective-C for C# Devs

Objective-C for C# Devs

My evolved talk on intro to Obj-C and iOS for .NET savvy people.

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Mark Wilkinson

March 18, 2013
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Transcript

  1. 2.

    Me Mark Wilkinson UH grad in EE Former DotNetter, now

    full- time mobile and rails developer. Head of the C#UG for the last 2 years.
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    Objective-C Created in 1986 by Tom Love and Brad Cox

    Marriage of C with Smalltalk Dynamic language, runs natively not on/in a virtual machine. Simply put, it’s a superset of C, with OO and dynamic features. Steve Jobs at Next adopted it, later Mac OSX was based on it.
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    Language Basics It is C, so you can use all

    the features and libraries available to C. Basic building blocks: Classes, defined by interfaces Value types (Structs, primitives, etc.) Pointers are needed when referring to objects. Function pointers are achieved through Blocks pointers...
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    Messaging? Yes, in the dynamic world you’re sending a message

    to an object, and at runtime the system will try to find a method (or property) with that matching name and params to then execute. A good analogy is to think of a class as a dictionary, with a key-value system.
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    Making a class Start with an interface file The @

    symbol Declare properties, methods and instance vars (optional)
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    Make an implementation file Notice the #import statements, there are

    no namespaces in Obj-C. What we’re used to. Remember, no need for interface in C# to create a class
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    must be defined in the interface Implementation follows standard practice

    of setting self to result of base init must return self Constructors are called Initializers in Obj-C
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    Allocating and Initializing a Class must call alloc first on

    the class then call init with the result of alloc custom initializer id can be used to represent any type
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    What would a OO language be without inheritance? Syntax is

    the same as C# goes in the interface section not implementation
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    Notes on Obj-C inheritance It’s like (if not the same)

    as Ruby. if you want to override a base method, simply name it the same, have the same return type and params. No need to mark things virtual, or use the new keyword, override, etc. Inheritance is everywhere in Objective-C/Cocoa, where as in C# interfaces and Composition are encouraged.
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    Back to methods - indicates the method is an instance

    method + indicates a “class” method, static in the C# lingo. All methods and properties in the interface section are visible to the caller or subclass. @private at the top of the implementation section can list methods you want to be private.
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    Properties Here’s the equivalent of auto implemented properties in C#.

    tells compiler to create getter and setters attributes type variable name
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    Extending a class How is it done in C#? Objective-C

    calls them Categories, they work in the same way extending in Ruby works (almost). ( catName ) tells compiler it’s a category will add DoFoo to any instance of Base
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    If @required or @optional are not marked above methods in

    the protocol (the 2 can be mixed), then it’s required by default. if the method was marked @optional, then the adopter/conformer doesn’t have to implement the method But caller of the class needs to check if the method is implemented use reflection to test conformity and implementation of an optional method
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    Memory mgt. at 1000ft Pre-ARC: you had to release an

    obj when you were finished retain it to increase the retain count so it won’t be deallocated
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    You were in charge of managing objects on your own

    with the pre-defined rules on when to retain, release and/or set to nil. Doing this incorrectly could cause memory leaks. iOS 5 brought ARC, or Automatic Reference Counting. Simply put, the compiler adds the appropriate release, retains where they’re needed.
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    nil is special desc will now be nil, no exception

    is thrown. can’t do this in C#, unless it was a bool if statements fail if condition is nil or null (works on value and object types)
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    KeyValueObserving This is a feature added by the Foundation framework,

    but it’s cool enough to be on the list *”KVO provides a mechanism that allows objects to be notified of changes to specific properties of other objects.” - Apple documentation
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    call addObserver method from NSObject to setup the KVO implement

    observeValueForKeyPath to complete the functionality method will catch all changes of any properties, so set logic for change you’re interested in
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    Blocks => Lambdas In Obj-C we have blocks to create

    anonymous functions, used in the same way anon/lambdas are used in C#.
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    C# Obj-C interface protocol ext. method category method call message

    send TRUE YES FALSE NO null nil (for objects) null (for values) this self static method class method Anonymous method Block
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    There’s not an equivalent to Generics in C#. Mainly because

    of the dynamic nature, much like Ruby. Obj-C discourages method chaining, because it becomes more unreadable unlike other languages. Less hand holding than what VS and the C# compiler offers. Like Rails, CocoaTouch has MVC baked in, it’s the preferred way to build applications. Because iOS apps generally aren’t enterprise, you won’t see complex DDD layers and architectures.
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    Cocoapods is the NuGet/Gems equivalent. The standard Unit Test framework

    that ships is called OCUnit. Much like NUnit, JUnit, etc. There’s also plenty of BDD, Specification testing options as well. Apple documentation is great, much better than MSDN.
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