mirror of
https://github.com/Instagram/IGListKit
synced 2026-05-05 06:28:22 +00:00
f2a9d93be8
Summary: Added migration guide for `IGListDiffable` changes. Closes #221 Closes https://github.com/Instagram/IGListKit/pull/274 Differential Revision: D4265446 Pulled By: rnystrom fbshipit-source-id: b98a975a9ef65bca0d46a1011e76834ecf08c681
354 lines
25 KiB
HTML
354 lines
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<a href='#getting-started' class='anchor' aria-hidden=true><span class="header-anchor"></span></a><h1 id='getting-started'>Getting Started</h1>
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<p>This guide provides a brief overview for how to get started using <code>IGListKit</code>.</p>
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<a href='#creating-your-first-list' class='anchor' aria-hidden=true><span class="header-anchor"></span></a><h2 id='creating-your-first-list'>Creating your first list</h2>
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<p>After installing <code>IGListKit</code>, creating a new list is easy.</p>
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<a href='#creating-a-section-controller' class='anchor' aria-hidden=true><span class="header-anchor"></span></a><h3 id='creating-a-section-controller'>Creating a section controller</h3>
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<p>Creating a new section controller is simple. You subclass <code>IGListSectionController</code> and conform to the <code>IGListSectionType</code> protocol. Once you conform to <code>IGListSectionType</code>, the compiler will make sure you implement all of the required methods.</p>
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<p>Take a look at <a href="https://raw.githubusercontent.com/Instagram/IGListKit/master/Examples/Examples-iOS/IGListKitExamples/SectionControllers/LabelSectionController.swift">LabelSectionController</a> for an example section controller that handles a <code>String</code> and configures a single cell with a <code>UILabel</code>.</p>
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<pre class="highlight swift"><code><span class="kd">class</span> <span class="kt">LabelSectionController</span><span class="p">:</span> <span class="kt">IGListSectionController</span><span class="p">,</span> <span class="kt">IGListSectionType</span> <span class="p">{</span>
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<span class="c1">// ...</span>
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<span class="p">}</span>
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</code></pre>
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<a href='#creating-the-ui' class='anchor' aria-hidden=true><span class="header-anchor"></span></a><h3 id='creating-the-ui'>Creating the UI</h3>
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<p>After creating at least one section controller, you must create an <code>IGListCollectionView</code> and <code>IGListAdapter</code>.</p>
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<pre class="highlight swift"><code><span class="k">let</span> <span class="nv">layout</span> <span class="o">=</span> <span class="kt">UICollectionViewFlowLayout</span><span class="p">()</span>
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<span class="k">let</span> <span class="nv">collectionView</span> <span class="o">=</span> <span class="kt">IGListCollectionView</span><span class="p">(</span><span class="nv">frame</span><span class="p">:</span> <span class="o">.</span><span class="n">zero</span><span class="p">,</span> <span class="nv">collectionViewLayout</span><span class="p">:</span> <span class="n">layout</span><span class="p">)</span>
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<span class="k">let</span> <span class="nv">updater</span> <span class="o">=</span> <span class="kt">IGListAdapterUpdater</span><span class="p">()</span>
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<span class="k">let</span> <span class="nv">adapter</span> <span class="o">=</span> <span class="kt">IGListAdapter</span><span class="p">(</span><span class="nv">updater</span><span class="p">:</span> <span class="n">updater</span><span class="p">,</span> <span class="nv">viewController</span><span class="p">:</span> <span class="k">self</span><span class="p">,</span> <span class="nv">workingRangeSize</span><span class="p">:</span> <span class="mi">0</span><span class="p">)</span>
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<span class="n">adapter</span><span class="o">.</span><span class="n">collectionView</span> <span class="o">=</span> <span class="n">collectionView</span>
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</code></pre>
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<blockquote>
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<p><strong>Note:</strong> This example is done within a <code>UIViewController</code> and uses both a stock <code>UICollectionViewFlowLayout</code> and <code>IGListAdapterUpdater</code>. You can use your own layout and updater if you need advanced features!</p>
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</blockquote>
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<a href='#connecting-the-data-source' class='anchor' aria-hidden=true><span class="header-anchor"></span></a><h3 id='connecting-the-data-source'>Connecting the data source</h3>
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<p>The last step is the <code>IGListAdapter</code>’s data source and returning some data.</p>
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<pre class="highlight swift"><code><span class="kd">func</span> <span class="nf">objects</span><span class="p">(</span><span class="k">for</span> <span class="nv">listAdapter</span><span class="p">:</span> <span class="kt">IGListAdapter</span><span class="p">)</span> <span class="o">-></span> <span class="p">[</span><span class="kt">IGListDiffable</span><span class="p">]</span> <span class="p">{</span>
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<span class="c1">// this can be anything!</span>
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<span class="k">return</span> <span class="p">[</span> <span class="s">"Foo"</span><span class="p">,</span> <span class="s">"Bar"</span><span class="p">,</span> <span class="mi">42</span><span class="p">,</span> <span class="s">"Biz"</span> <span class="p">]</span>
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<span class="p">}</span>
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<span class="kd">func</span> <span class="nf">listAdapter</span><span class="p">(</span><span class="n">_</span> <span class="nv">listAdapter</span><span class="p">:</span> <span class="kt">IGListAdapter</span><span class="p">,</span> <span class="n">sectionControllerFor</span> <span class="nv">object</span><span class="p">:</span> <span class="kt">Any</span><span class="p">)</span> <span class="o">-></span> <span class="kt">IGListSectionController</span> <span class="p">{</span>
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<span class="k">if</span> <span class="n">object</span> <span class="k">is</span> <span class="kt">String</span> <span class="p">{</span>
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<span class="k">return</span> <span class="kt">LabelSectionController</span><span class="p">()</span>
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<span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
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<span class="k">return</span> <span class="kt">NumberSectionController</span><span class="p">()</span>
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<span class="p">}</span>
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<span class="p">}</span>
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<span class="kd">func</span> <span class="nf">emptyView</span><span class="p">(</span><span class="k">for</span> <span class="nv">listAdapter</span><span class="p">:</span> <span class="kt">IGListAdapter</span><span class="p">)</span> <span class="o">-></span> <span class="kt">UIView</span><span class="p">?</span> <span class="p">{</span>
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<span class="k">return</span> <span class="kc">nil</span>
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<span class="p">}</span>
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</code></pre>
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<p>You can return an array of <em>any</em> type of data, as long as it conforms to <code>IGListDiffable</code>.</p>
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<a href='#diffing' class='anchor' aria-hidden=true><span class="header-anchor"></span></a><h2 id='diffing'>Diffing</h2>
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<p><code>IGListKit</code> uses an algorithm adapted from a paper titled <a href="http://dl.acm.org/citation.cfm?id=359467&dl=ACM&coll=DL">A technique for isolating differences between files</a> by Paul Heckel. This algorithm uses a technique known as the <em>longest common subsequence</em> to find a minimal diff between collections in linear time <code>O(n)</code>. It finds all <strong>inserts</strong>, <strong>deletes</strong>, <strong>updates</strong>, and <strong>moves</strong> between arrays of data.</p>
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<p>To add custom, diffable models, you need to conform to the <code>IGListDiffable</code> protocol and implement <code>diffIdentifier()</code> and <code>isEqual(toDiffableObject:)</code>.</p>
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<p>For an example, consider the following model:</p>
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<pre class="highlight swift"><code><span class="kd">class</span> <span class="kt">User</span> <span class="p">{</span>
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<span class="k">let</span> <span class="nv">primaryKey</span><span class="p">:</span> <span class="kt">Int</span>
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<span class="k">let</span> <span class="nv">name</span><span class="p">:</span> <span class="kt">String</span>
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<span class="c1">// implementation, etc</span>
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<span class="p">}</span>
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</code></pre>
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<p>The user’s <code>primaryKey</code> uniquely identifies user data, and the <code>name</code> is just the value for that user.</p>
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<p>Let’s say a server returns a <code>User</code> object that looks like this:</p>
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<pre class="highlight swift"><code><span class="k">let</span> <span class="nv">shayne</span> <span class="o">=</span> <span class="kt">User</span><span class="p">(</span><span class="nv">primaryKey</span><span class="p">:</span> <span class="mi">2</span><span class="p">,</span> <span class="nv">name</span><span class="p">:</span> <span class="s">"Shayne"</span><span class="p">)</span>
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</code></pre>
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<p>But sometime after the client receives <code>shayne</code>, someone changes their name:</p>
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<pre class="highlight swift"><code><span class="k">let</span> <span class="nv">ann</span> <span class="o">=</span> <span class="kt">User</span><span class="p">(</span><span class="nv">primaryKey</span><span class="p">:</span> <span class="mi">2</span><span class="p">,</span> <span class="nv">name</span><span class="p">:</span> <span class="s">"Ann"</span><span class="p">)</span>
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</code></pre>
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<p>Both <code>shayne</code> and <code>ann</code> represent the same <em>unique</em> data because they share the same <code>primaryKey</code>, but they are not <em>equal</em> because their names are different.</p>
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<p>To represent this in <code>IGListKit</code>’s diffing, add and implement the <code>IGListDiffable</code> protocol:</p>
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<pre class="highlight swift"><code><span class="kd">extension</span> <span class="kt">User</span><span class="p">:</span> <span class="kt">IGListDiffable</span> <span class="p">{</span>
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<span class="kd">func</span> <span class="nf">diffIdentifier</span><span class="p">()</span> <span class="o">-></span> <span class="kt">NSObjectProtocol</span> <span class="p">{</span>
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<span class="k">return</span> <span class="n">primaryKey</span>
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<span class="p">}</span>
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<span class="kd">func</span> <span class="nf">isEqual</span><span class="p">(</span><span class="n">toDiffableObject</span> <span class="nv">object</span><span class="p">:</span> <span class="kt">Any</span><span class="p">?)</span> <span class="o">-></span> <span class="kt">Bool</span> <span class="p">{</span>
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<span class="k">if</span> <span class="k">let</span> <span class="nv">object</span> <span class="o">=</span> <span class="n">object</span> <span class="k">as?</span> <span class="kt">User</span> <span class="p">{</span>
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<span class="k">return</span> <span class="n">name</span> <span class="o">==</span> <span class="n">object</span><span class="o">.</span><span class="n">name</span>
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<span class="p">}</span>
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<span class="k">return</span> <span class="kc">false</span>
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<span class="p">}</span>
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<span class="p">}</span>
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</code></pre>
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<p>The algorithm will skip updating two <code>User</code> objects that have the same <code>primaryKey</code> and <code>name</code>, even if they are different instances! You now avoid unnecessary UI updates in the collection view even when providing new instances.</p>
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<blockquote>
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<p><strong>Note:</strong> Remember that <code>isEqual(toDiffableObject:)</code> should return <code>false</code> when you want to reload the cells in the corresponding section controller.</p>
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</blockquote>
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<a href='#diffing-outside-of-iglistkit' class='anchor' aria-hidden=true><span class="header-anchor"></span></a><h3 id='diffing-outside-of-iglistkit'>Diffing outside of IGListKit</h3>
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<p>If you want to use the diffing algorithm outside of <code>IGListAdapter</code> and <code>UICollectionView</code>, you can! The diffing algorithm was built with the flexibility to be used with any models that conform to <code>IGListDiffable</code>.</p>
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<pre class="highlight swift"><code><span class="k">let</span> <span class="nv">result</span> <span class="o">=</span> <span class="kt">IGListDiff</span><span class="p">(</span><span class="n">oldUsers</span><span class="p">,</span> <span class="n">newUsers</span><span class="p">,</span> <span class="o">.</span><span class="n">equality</span><span class="p">)</span>
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</code></pre>
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<p>With this you have all of the deletes, reloads, moves, and inserts! There’s even a function to generate <code>NSIndexPath</code> results.</p>
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<a href='#advanced-features' class='anchor' aria-hidden=true><span class="header-anchor"></span></a><h2 id='advanced-features'>Advanced Features</h2>
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<a href='#working-range' class='anchor' aria-hidden=true><span class="header-anchor"></span></a><h3 id='working-range'>Working Range</h3>
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<p>A <em>working range</em> is a range of section controllers who aren’t yet visible, but are near the screen. Section controllers are notified of their entrance and exit to this range. This concept lets your section controllers <strong>prepare content</strong> before they come on screen (e.g. download images).</p>
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<p>The <code>IGListAdapter</code> must be initialized with a range value in order to work. This value is a multiple of the visible height or width, depending on the scroll-direction.</p>
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<pre class="highlight swift"><code><span class="k">let</span> <span class="nv">adapter</span> <span class="o">=</span> <span class="kt">IGListAdapter</span><span class="p">(</span><span class="nv">updater</span><span class="p">:</span> <span class="kt">IGListAdapterUpdater</span><span class="p">(),</span>
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<span class="nv">viewController</span><span class="p">:</span> <span class="k">self</span><span class="p">,</span>
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<span class="nv">workingRangeSize</span><span class="p">:</span> <span class="mi">1</span><span class="p">)</span> <span class="c1">// 1 before/after visible objects</span>
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</code></pre>
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<p><img src="https://raw.githubusercontent.com/Instagram/IGListKit/master/Resources/workingrange.png" alt="working-range"></p>
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<p>You can set the weak <code>workingRangeDelegate</code> on a section controller to receive events.</p>
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|
<a href='#supplementary-views' class='anchor' aria-hidden=true><span class="header-anchor"></span></a><h3 id='supplementary-views'>Supplementary Views</h3>
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<p>Adding supplementary views to section controllers is as simple as setting the (weak) <code>supplementaryViewSource</code> and implementing the <code>IGListSupplementaryViewSource</code> protocol. This protocol works nearly the same as returning and configuring cells.</p>
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<a href='#display-delegate' class='anchor' aria-hidden=true><span class="header-anchor"></span></a><h3 id='display-delegate'>Display Delegate</h3>
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<p>Section controllers can set the weak <code>displayDelegate</code> delegate to an object, including <code>self</code>, to receive display events about a section controller and individual cells.</p>
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|
<a href='#custom-updaters' class='anchor' aria-hidden=true><span class="header-anchor"></span></a><h3 id='custom-updaters'>Custom Updaters</h3>
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<p>The default <code>IGListAdapterUpdater</code> should handle any <code>UICollectionView</code> update that you need. However, if you find the functionality lacking, or want to perform updates in a very specific way, you can create an object that conforms to the <code>IGListUpdatingDelegate</code> protocol and initialize a new <code>IGListAdapter</code> with it.</p>
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<p>Check out the updater <code>IGListReloadDataUpdater</code> (used in unit tests) for an example.</p>
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</section>
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</section>
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<section id="footer">
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<p>© 2016 <a class="link" href="https://twitter.com/fbOpenSource" target="_blank" rel="external">Instagram</a>. All rights reserved. (Last updated: 2016-12-02)</p>
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<p>Generated by <a class="link" href="https://github.com/realm/jazzy" target="_blank" rel="external">jazzy ♪♫ v0.7.2</a>, a <a class="link" href="http://realm.io" target="_blank" rel="external">Realm</a> project.</p>
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