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<!DOCTYPE html>
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<title>Content Updates Reference</title>
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<a href="index.html">CollectionView Docs</a>
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Content Updates Reference
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<section>
<section class="section">
<h1 id='insert-delete-move-and-reload' class='heading'>Insert, Delete, Move and Reload</h1>
<p>As data changes a collection view displaying that data will need to update as well. New content could be pulled from a remote service or the user could take an action. Collection view supports inserting, deleting, moving, and reloading sections and items.</p>
<hr>
<h2 id='single-updates' class='heading'>Single Updates</h2>
<p>To perform a single update operation you can use any of the update functions directly.</p>
<pre class="highlight swift"><code><span class="kd">public</span> <span class="kd">func</span> <span class="nf">insertSections</span><span class="p">(</span><span class="n">_</span> <span class="nv">sections</span><span class="p">:</span> <span class="kt">IndexSet</span><span class="p">,</span> <span class="nv">animated</span><span class="p">:</span> <span class="kt">Bool</span><span class="p">)</span>
<span class="kd">public</span> <span class="kd">func</span> <span class="nf">deleteSections</span><span class="p">(</span><span class="n">_</span> <span class="nv">sections</span><span class="p">:</span> <span class="kt">IndexSet</span><span class="p">,</span> <span class="nv">animated</span><span class="p">:</span> <span class="kt">Bool</span><span class="p">)</span>
<span class="kd">public</span> <span class="kd">func</span> <span class="nf">moveSection</span><span class="p">(</span><span class="n">_</span> <span class="nv">section</span><span class="p">:</span> <span class="kt">Int</span><span class="p">,</span> <span class="n">to</span> <span class="nv">newSection</span><span class="p">:</span> <span class="kt">Int</span><span class="p">,</span> <span class="nv">animated</span><span class="p">:</span> <span class="kt">Bool</span><span class="p">)</span>
<span class="kd">public</span> <span class="kd">func</span> <span class="nf">insertItems</span><span class="p">(</span><span class="n">at</span> <span class="nv">indexPaths</span><span class="p">:</span> <span class="p">[</span><span class="kt">IndexPath</span><span class="p">],</span> <span class="nv">animated</span><span class="p">:</span> <span class="kt">Bool</span><span class="p">)</span>
<span class="kd">public</span> <span class="kd">func</span> <span class="nf">deleteItems</span><span class="p">(</span><span class="n">at</span> <span class="nv">indexPaths</span><span class="p">:</span> <span class="p">[</span><span class="kt">IndexPath</span><span class="p">],</span> <span class="nv">animated</span><span class="p">:</span> <span class="kt">Bool</span><span class="p">)</span>
<span class="kd">public</span> <span class="kd">func</span> <span class="nf">reloadItems</span><span class="p">(</span><span class="n">at</span> <span class="nv">indexPaths</span><span class="p">:</span> <span class="p">[</span><span class="kt">IndexPath</span><span class="p">],</span> <span class="nv">animated</span><span class="p">:</span> <span class="kt">Bool</span><span class="p">)</span>
<span class="kd">public</span> <span class="kd">func</span> <span class="nf">moveItem</span><span class="p">(</span><span class="n">at</span> <span class="nv">indexPath</span> <span class="p">:</span> <span class="kt">IndexPath</span><span class="p">,</span> <span class="n">to</span> <span class="nv">destinationIndexPath</span><span class="p">:</span> <span class="kt">IndexPath</span><span class="p">,</span> <span class="nv">animated</span><span class="p">:</span> <span class="kt">Bool</span><span class="p">)</span>
</code></pre>
<p>Before doing so you must be sure that your data source will report the change. For example, if inserting an item your data source must report 1 more item than the collection view currently has.</p>
<blockquote>
<p>Note that these operations currently reload the entire layout object and should not be called excessivly.</p>
</blockquote>
<h2 id='batch-updates' class='heading'>Batch Updates</h2>
<p>Multiple updates can be performed simultaneously use <code>performBatchUpdates(_:completion:)</code>. Any changes made in the first closure will be batched together and commited as a single operation.</p>
<pre class="highlight swift"><code><span class="n">myData</span><span class="o">.</span><span class="nf">remove</span><span class="p">(</span><span class="nv">at</span><span class="p">:</span> <span class="mi">1</span><span class="p">)</span>
<span class="n">myData</span><span class="o">.</span><span class="nf">append</span><span class="p">(</span><span class="s">"Another Entry"</span><span class="p">)</span>
<span class="n">collectionView</span><span class="o">.</span><span class="nf">performBatchUpdates</span><span class="p">({</span>
<span class="n">collectionView</span><span class="o">.</span><span class="nf">deletItems</span><span class="p">(</span><span class="nv">at</span><span class="p">:</span> <span class="p">[</span><span class="kt">IndexPath</span><span class="o">.</span><span class="k">for</span><span class="p">(</span><span class="nv">item</span><span class="p">:</span> <span class="mi">1</span><span class="p">,</span> <span class="nv">section</span><span class="p">:</span> <span class="mi">0</span><span class="p">)])</span>
<span class="n">collectionView</span><span class="o">.</span><span class="nf">insertITems</span><span class="p">(</span><span class="nv">at</span><span class="p">:</span> <span class="p">[[</span><span class="kt">IndexPath</span><span class="o">.</span><span class="k">for</span><span class="p">(</span><span class="nv">item</span><span class="p">:</span> <span class="n">myData</span><span class="o">.</span><span class="n">count</span> <span class="o">-</span> <span class="mi">1</span><span class="p">,</span> <span class="nv">section</span><span class="p">:</span> <span class="mi">0</span><span class="p">)]])</span>
<span class="p">})</span> <span class="p">{</span> <span class="p">(</span><span class="n">completed</span><span class="p">)</span> <span class="k">in</span>
<span class="c1">// Animation is complete!</span>
<span class="p">}</span>
</code></pre>
<p>Note that delete and reload updates use index paths prior to any changes, inserts refer to index paths after all changes are made, and moves go from a pre-update index path fo a post-updates index path. The following illustrates this</p>
<pre class="highlight swift"><code><span class="kt">Section</span> <span class="kt">A</span>
<span class="p">[</span><span class="kt">H</span><span class="p">]</span> <span class="p">[</span><span class="kt">J</span><span class="p">]</span> <span class="p">[</span><span class="kt">K</span><span class="p">]</span>
<span class="kt">Section</span> <span class="kt">B</span>
<span class="p">[</span><span class="kt">X</span><span class="p">]</span> <span class="p">[</span><span class="kt">Y</span><span class="p">]</span> <span class="p">[</span><span class="kt">Z</span><span class="p">]</span>
<span class="n">move</span> <span class="n">section</span> <span class="kt">A</span> <span class="n">to</span> <span class="mi">1</span>
<span class="kt">Move</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">]</span> <span class="n">to</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">]</span>
<span class="kt">Section</span> <span class="kt">B</span>
<span class="p">[</span><span class="kt">X</span><span class="p">]</span> <span class="p">[</span><span class="kt">Z</span><span class="p">]</span>
<span class="kt">Section</span> <span class="kt">A</span>
<span class="p">[</span><span class="kt">H</span><span class="p">]</span> <span class="p">[</span><span class="kt">Y</span><span class="p">]</span> <span class="p">[</span><span class="kt">J</span><span class="p">]</span> <span class="p">[</span><span class="kt">K</span><span class="p">]</span>
</code></pre>
<p>Notice that the second move at [1, 1] moves [Y] from its starting index path [1, 1] to its final index path after changes [1, 1].</p>
<p>Managing these changes can be tricky to understand especially when making many changes together. This is why we create ResultsController to help connect your collection view to your data.</p>
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