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Introduction to Design Patterns

2:32 with Pasan Premaratne

Delegation is not finished code per se, but a design pattern. Let’s talk about what a design pattern is and where delegates fit in.

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    [SOUND] Hi, I'm Pasan and welcome to this

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    course on delegation at Treehouse.

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    In software development since people have been at it for

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    a fairly long time now, we've run into some common problems.

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    There are lots of these kinds of problems.

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    How to create flexible objects.

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    How to communicate between objects without tight coupling and

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    how to facilitate relationships between objects.

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    During the early days of software development,

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    engineers figured out their own ways around these problems.

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    But as it became evident that these problems occurred in almost all domains

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    and weren't specific to the task at hand,

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    more general purpose solutions began to emerge.

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    Today we call these solutions design patterns.

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    A design pattern is a general reusable solution to commonly occurring

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    problems within a given context, regardless of a particular domain.

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    Design patterns aren't finished code per se.

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    They aren't something you can plug into your project and be done with.

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    Instead they're templates for

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    solving problems that occur in many different situations.

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    A design pattern makes it easier to reuse successful software development

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    architectures and solve problems without having to reinvent the wheel.

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    As I mentioned there are different problems for

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    which there are different design patterns.

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    In this course we're going to focus on just one that is very prevalent in our

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    domain and good to understand before we run into it when we use various IOS APIs.

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    That pattern is the delegate pattern.

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    The delegate pattern is a variation of a design pattern

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    that is more commonly called the decorator pattern.

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    The decorator pattern is a structural pattern, that is it is a pattern that is

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    focused on how we can compose objects to form larger structures.

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    The decorator pattern in particular is concerned with how we can add

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    responsibilities to an object dynamically.

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    That is at runtime rather than statically at compile time.

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    Before we get into any of this though, I'd like to walk us through an example and

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    try to solve it without any knowledge of delegation.

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    And you will see that the resulting code is not as flexible as we'd like it to be

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    or reusable.

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    This should help illustrate the problem we're trying to solve and

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    show how delegation makes it much easier.

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