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<!DOCTYPE HTML>
<html lang="zh-tw" >
<head>
<meta charset=utf-8"UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=11; IE=10; IE=9; IE=8; IE=7; IE=EDGE" />
<title>利用 Live Text API 从图片中撷取文本 | 精通 SwiftUI - iOS 16 版</title>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
<meta name="description" content="">
<meta name="generator" content="GitBook 2.0.1">
<meta name="author" content="Simon Ng">
<meta name="HandheldFriendly" content="true"/>
<meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=no">
<meta name="apple-mobile-web-app-capable" content="yes">
<meta name="apple-mobile-web-app-status-bar-style" content="black">
<link rel="apple-touch-icon-precomposed" sizes="152x152" href="gitbook/images/apple-touch-icon-precomposed-152.png">
<link rel="shortcut icon" href="gitbook/images/favicon.ico" type="image/x-icon">
<link rel="next" href="./swiftui-sharelink.html" />
<link rel="prev" href="./swiftui-charts.html" />
</head>
<body>
<link rel="stylesheet" href="gitbook/style.css">
<link rel="stylesheet" href="gitbook/plugins/gitbook-plugin-image-captions/image-captions.css">
<link rel="stylesheet" href="././styles/website.css">
<div class="book" data-level="39" data-basepath="." data-revision="Thu Dec 01 2022 17:36:55 GMT+0800 (HKT)">
<div class="book-summary">
<div class="book-search">
<input type="text" placeholder="输入并搜寻" class="form-control" />
</div>
<ul class="summary">
<li>
<a href="https://www.appcoda.com.tw" target="blank" class="custom-link">Made by AppCoda</a>
</li>
<li>
<a href="https://www.appcoda.com.tw/contact" target="blank" class="custom-link">Contact us / Support</a>
</li>
<li>
<a href="http://twitter.com/share?text=Mastering%20SwiftUI%20via%20@appcodamobile&url=https://www.appcoda.com.tw/swiftui/&hashtags=swiftlang" target="blank" class="custom-link">Tweet this book</a>
</li>
<li class="divider"></li>
<li class="chapter " data-level="0" data-path="index.html">
<a href="./index.html">
<i class="fa fa-check"></i>
序言
</a>
</li>
<li class="chapter " data-level="1" data-path="swiftui-basics.html">
<a href="./swiftui-basics.html">
<i class="fa fa-check"></i>
<b>1.</b>
SwiftUI 介绍
</a>
</li>
<li class="chapter " data-level="2" data-path="swiftui-text.html">
<a href="./swiftui-text.html">
<i class="fa fa-check"></i>
<b>2.</b>
SwiftUI 入门 - 文字的处理
</a>
</li>
<li class="chapter " data-level="3" data-path="swiftui-images.html">
<a href="./swiftui-images.html">
<i class="fa fa-check"></i>
<b>3.</b>
图片的处理
</a>
</li>
<li class="chapter " data-level="4" data-path="swiftui-stacks.html">
<a href="./swiftui-stacks.html">
<i class="fa fa-check"></i>
<b>4.</b>
以堆叠布局使用者介面
</a>
</li>
<li class="chapter " data-level="5" data-path="swiftui-scrollview.html">
<a href="./swiftui-scrollview.html">
<i class="fa fa-check"></i>
<b>5.</b>
ScrollView 与 Carousel UI 的建立
</a>
</li>
<li class="chapter " data-level="6" data-path="swiftui-buttons.html">
<a href="./swiftui-buttons.html">
<i class="fa fa-check"></i>
<b>6.</b>
SwiftUI 按钮与渐层
</a>
</li>
<li class="chapter " data-level="7" data-path="swiftui-state.html">
<a href="./swiftui-state.html">
<i class="fa fa-check"></i>
<b>7.</b>
状态(State)与绑定(Binding)
</a>
</li>
<li class="chapter " data-level="8" data-path="swiftui-path-shape.html">
<a href="./swiftui-path-shape.html">
<i class="fa fa-check"></i>
<b>8.</b>
实现路径(Path)与形状(Shape)来画线与圆饼图
</a>
</li>
<li class="chapter " data-level="9" data-path="swiftui-animation.html">
<a href="./swiftui-animation.html">
<i class="fa fa-check"></i>
<b>9.</b>
基础动画与转场
</a>
</li>
<li class="chapter " data-level="10" data-path="swiftui-list.html">
<a href="./swiftui-list.html">
<i class="fa fa-check"></i>
<b>10.</b>
动态列表、 ForEach 与 Identifiable 的使用方法
</a>
</li>
<li class="chapter " data-level="11" data-path="swiftui-navigation.html">
<a href="./swiftui-navigation.html">
<i class="fa fa-check"></i>
<b>11.</b>
导航UI与导航列客制化运用
</a>
</li>
<li class="chapter " data-level="12" data-path="swiftui-modal.html">
<a href="./swiftui-modal.html">
<i class="fa fa-check"></i>
<b>12.</b>
强制回应视图、浮动按钮与提示的实现
</a>
</li>
<li class="chapter " data-level="13" data-path="swiftui-form.html">
<a href="./swiftui-form.html">
<i class="fa fa-check"></i>
<b>13.</b>
以选取器(Picker)、开关(Toggle)与步进器(Stepper)来建立一个表单
</a>
</li>
<li class="chapter " data-level="14" data-path="swiftui-form-data.html">
<a href="./swiftui-form-data.html">
<i class="fa fa-check"></i>
<b>14.</b>
使用 Combine 与 Environment 物件进行数据分享
</a>
</li>
<li class="chapter " data-level="15" data-path="swiftui-form-registration.html">
<a href="./swiftui-form-registration.html">
<i class="fa fa-check"></i>
<b>15.</b>
以 Combine 与 视图模型建立一个注册表单
</a>
</li>
<li class="chapter " data-level="16" data-path="swiftui-actionsheet-context.html">
<a href="./swiftui-actionsheet-context.html">
<i class="fa fa-check"></i>
<b>16.</b>
滑动删除、内容菜单与动作列表
</a>
</li>
<li class="chapter " data-level="17" data-path="swiftui-gestures.html">
<a href="./swiftui-gestures.html">
<i class="fa fa-check"></i>
<b>17.</b>
认识手势(Gestures)
</a>
</li>
<li class="chapter " data-level="18" data-path="swiftui-bottom-sheet.html">
<a href="./swiftui-bottom-sheet.html">
<i class="fa fa-check"></i>
<b>18.</b>
以SwiftUI 手势与 GeometryReader 建立一个底部展开式页面
</a>
</li>
<li class="chapter " data-level="19" data-path="swiftui-trip-tinder.html">
<a href="./swiftui-trip-tinder.html">
<i class="fa fa-check"></i>
<b>19.</b>
使用手势与动画建立 Tinder 风格的 UI
</a>
</li>
<li class="chapter " data-level="20" data-path="swiftui-advanced-animations.html">
<a href="./swiftui-advanced-animations.html">
<i class="fa fa-check"></i>
<b>20.</b>
建立像 Apple Wallet App 的动画和转场效果
</a>
</li>
<li class="chapter " data-level="21" data-path="swiftui-json.html">
<a href="./swiftui-json.html">
<i class="fa fa-check"></i>
<b>21.</b>
JSON、滑杆的运用与数据过滤
</a>
</li>
<li class="chapter " data-level="22" data-path="swiftui-core-data.html">
<a href="./swiftui-core-data.html">
<i class="fa fa-check"></i>
<b>22.</b>
如何使用 Core Data 建立 ToDo App
</a>
</li>
<li class="chapter " data-level="23" data-path="swiftui-uikit.html">
<a href="./swiftui-uikit.html">
<i class="fa fa-check"></i>
<b>23.</b>
利用 UIViewRepresentable 整合UIKit 组件
</a>
</li>
<li class="chapter " data-level="24" data-path="swiftui-searchbar.html">
<a href="./swiftui-searchbar.html">
<i class="fa fa-check"></i>
<b>24.</b>
建立搜寻栏视图并使用自订绑定(Custom Binding)
</a>
</li>
<li class="chapter " data-level="25" data-path="swiftui-real-world-app.html">
<a href="./swiftui-real-world-app.html">
<i class="fa fa-check"></i>
<b>25.</b>
把所学应用出来!构建个人理财App
</a>
</li>
<li class="chapter " data-level="26" data-path="swiftui-appstoreanimation.html">
<a href="./swiftui-appstoreanimation.html">
<i class="fa fa-check"></i>
<b>26.</b>
创建类似App Store使用的动画视图转换
</a>
</li>
<li class="chapter " data-level="27" data-path="swiftui-carousel.html">
<a href="./swiftui-carousel.html">
<i class="fa fa-check"></i>
<b>27.</b>
如何建立图像轮播(Image Carousel)
</a>
</li>
<li class="chapter " data-level="28" data-path="swiftui-expandable-list.html">
<a href="./swiftui-expandable-list.html">
<i class="fa fa-check"></i>
<b>28.</b>
如何建立展开式列表视图和大纲视图
</a>
</li>
<li class="chapter " data-level="29" data-path="swiftui-gridlayout.html">
<a href="./swiftui-gridlayout.html">
<i class="fa fa-check"></i>
<b>29.</b>
使用 LazyVGrid 和 LazyHGrid 构建集合视图
</a>
</li>
<li class="chapter " data-level="30" data-path="swiftui-progress-ring.html">
<a href="./swiftui-progress-ring.html">
<i class="fa fa-check"></i>
<b>30.</b>
使用 Shape 和 Animatable 开发带动画的环形进度条
</a>
</li>
<li class="chapter " data-level="31" data-path="swiftui-library.html">
<a href="./swiftui-library.html">
<i class="fa fa-check"></i>
<b>31.</b>
如何使用 AnimatableModifier 和 LibraryContentProvider
</a>
</li>
<li class="chapter " data-level="32" data-path="swiftui-texteditor.html">
<a href="./swiftui-texteditor.html">
<i class="fa fa-check"></i>
<b>32.</b>
使用 TextEditor 支持多行文字输入
</a>
</li>
<li class="chapter " data-level="33" data-path="swiftui-matchedgeometry.html">
<a href="./swiftui-matchedgeometry.html">
<i class="fa fa-check"></i>
<b>33.</b>
使用 matchedGeometryEffect为 App 建立绚丽的视图动画
</a>
</li>
<li class="chapter " data-level="34" data-path="swiftui-grid-animation.html">
<a href="./swiftui-grid-animation.html">
<i class="fa fa-check"></i>
<b>34.</b>
ScrollViewReader 和网格动画
</a>
</li>
<li class="chapter " data-level="35" data-path="swiftui-tabview.html">
<a href="./swiftui-tabview.html">
<i class="fa fa-check"></i>
<b>35.</b>
标签视图的运用与自订标签列
</a>
</li>
<li class="chapter " data-level="36" data-path="swiftui-asyncimage.html">
<a href="./swiftui-asyncimage.html">
<i class="fa fa-check"></i>
<b>36.</b>
利用 AsyncImage 非同步加载和显示图像
</a>
</li>
<li class="chapter " data-level="37" data-path="swiftui-searchable.html">
<a href="./swiftui-searchable.html">
<i class="fa fa-check"></i>
<b>37.</b>
利用 Searchable 建立搜寻栏
</a>
</li>
<li class="chapter " data-level="38" data-path="swiftui-charts.html">
<a href="./swiftui-charts.html">
<i class="fa fa-check"></i>
<b>38.</b>
利用 Charts 框架建立图表
</a>
</li>
<li class="chapter active" data-level="39" data-path="swiftui-live-text.html">
<a href="./swiftui-live-text.html">
<i class="fa fa-check"></i>
<b>39.</b>
利用 Live Text API 从图片中撷取文本
</a>
</li>
<li class="chapter " data-level="40" data-path="swiftui-sharelink.html">
<a href="./swiftui-sharelink.html">
<i class="fa fa-check"></i>
<b>40.</b>
通过 ShareLink 来分享文本和图像等数据
</a>
</li>
<li class="chapter " data-level="41" data-path="swiftui-imagerenderer.html">
<a href="./swiftui-imagerenderer.html">
<i class="fa fa-check"></i>
<b>41.</b>
利用 ImageRenderer API 轻松把 SwiftUI 视图转换为图像
</a>
</li>
<li class="chapter " data-level="42" data-path="swiftui-pdf-doc.html">
<a href="./swiftui-pdf-doc.html">
<i class="fa fa-check"></i>
<b>42.</b>
如何把 SwiftUI 视图转换为 PDF 文件
</a>
</li>
<li class="chapter " data-level="43" data-path="swiftui-gauge.html">
<a href="./swiftui-gauge.html">
<i class="fa fa-check"></i>
<b>43.</b>
使用 Gauge 视图显示进度并创建速度计
</a>
</li>
<li class="chapter " data-level="44" data-path="swiftui-grid.html">
<a href="./swiftui-grid.html">
<i class="fa fa-check"></i>
<b>44.</b>
使用Grid API 创建网格布局
</a>
</li>
<li class="chapter " data-level="45" data-path="swiftui-anylayout.html">
<a href="./swiftui-anylayout.html">
<i class="fa fa-check"></i>
<b>45.</b>
利用 AnyLayout 切换 UI 布局
</a>
</li>
<li class="chapter " data-level="46" data-path="swiftui-navigationstack.html">
<a href="./swiftui-navigationstack.html">
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<a href="./" >精通 SwiftUI - iOS 16 版</a>
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<h1 id="%E7%AC%AC-39-%E7%AB%A0-br-%E5%88%A9%E7%94%A8-live-text-api-%E5%BE%9E%E5%9C%96%E7%89%87%E4%B8%AD%E6%93%B7%E5%8F%96%E6%96%87%E6%9C%AC">第 39 章<br>利用 Live Text API 从图片中撷取文本</h1>
<p>去年,iOS 15 新增了一个非常有用的功能 ── Live Text。你可能也有听过 OCR(光学字元辨识的缩写)一词,这是一个将文本图像转换为机器可读的文本格式的过程;这就是 Live Text 所做的事。</p>
<p>Live Text 内置在相机 App 和相片 App 中。如果你还没有尝试过这个功能,现在就来打开相机 App 试试吧!当我们把电话的镜头对准文本图像,右下角就会出现一个 Live Text 按钮。点击按钮后,iOS 就会自动撷取文本。然后,你就可以将其复制,并粘贴到其他 App(例如备忘录 App)中。</p>
<p>对于使用者来说,这是一个非常强大又方便的功能。而对于开发者来说,我们都会希望把这个 Live Text 功能加到自己的 App 中。在 iOS 16,Apple 发布了 Live Text API,让开发者可以在自己的 App 中加入 Live Text 功能。在这个章节中,让我们一起来看看如何在 SwiftUI 中使用 Live Text API。</p>
<h3 id="%E5%88%A9%E7%94%A8-datascannerviewcontroller-%E5%95%9F%E7%94%A8-live-text">利用 DataScannerViewController 启用 Live Text</h3>
<p>在 WWDC 的 <a href="https://developer.apple.com/videos/play/wwdc2022-10025" target="_blank"><em>Capturing Machine-readable Codes and Text with VisionKit</em></a> Session 中,Apple 工程师展示了以下图片:</p>
<figure id="fig39.1"><img src="images/livetext/swiftui-live-text-avfoundation.png" alt="图 39.1. AVfoundation 和 Vision 框架提供的 API"><figcaption>图 39.1. AVfoundation 和 Vision 框架提供的 API</figcaption></figure>
<p>文本辨识 (Text Recognization) 不是 iOS 16 的新功能。在旧版本的 iOS 上,我们已经可以使用 AVFoundation 和 Vision 框架中的 API,来侦测和辨识文本。但是,实现起来十分复杂,尤其是对于那些刚接触 iOS 开发的人来说。</p>
<p>在新版本的 iOS 中,以上所有的步骤都被简化为 VisionKit 中的一个新类别 <code>DataScannerViewController</code>。我们在 App 内使用这个视图控制器,就可以自动显示有 Live Text 功能的相机 UI。</p>
<p>要使用这个类别,让我们先汇入 <code>VisionKit</code> 框架,并检查设备是否支持数据扫描器功能:</p>
<pre><code class="lang-swift"><span class="hljs-type">DataScannerViewController</span>.isSupported
</code></pre>
<p>Live Text API 只支持 2018 年后推出、有 Neural Engine 的设备。另外,我们也要检查 availability,来确保使用者批准 App 使用数据扫描器:</p>
<pre><code class="lang-swift"><span class="hljs-type">DataScannerViewController</span>.isAvailable
</code></pre>
<p>通过两项检查后,我们就可以开始扫描了。让我们看看以下示例代码,来启用有 Live Text 功能的相机:</p>
<pre><code class="lang-swift"><span class="hljs-keyword">let</span> dataScanner = <span class="hljs-type">DataScannerViewController</span>(
recognizedDataTypes: [.text()],
qualityLevel: .balanced,
isHighlightingEnabled: <span class="hljs-built_in">true</span>
)
present(dataScanner, animated: <span class="hljs-built_in">true</span>) {
try? dataScanner.startScanning()
}
</code></pre>
<p>我们只需要创建一个 <code>DataScannerViewController</code> 实例,并指定要辨识的数据类型即可。在示例中,我们要辨识的是文本,因此我们会把数据类型指定为 <code>.text()</code>。准备好实例之后,我们就可以调用 <code>startScanning()</code> 方法来开始扫描。</p>
<h3 id="%E5%9C%A8-swiftui-%E4%BD%BF%E7%94%A8-datascannerviewcontroller">在 SwiftUI 使用 DataScannerViewController</h3>
<p><code>DataScannerViewController</code> 类别现时只支持 UIKit,因此在 SwiftUI 我们需要多做几个步骤。我们需要采用 <code>UIViewControllerRepresentable</code> 协议,才可以在 SwiftUI 项目中使用这个类别。在这个情况下,让我们创建一个新的 <code>DataScanner</code>结构:</p>
<pre><code class="lang-swift"><span class="hljs-keyword">import</span> <span class="hljs-type">SwiftUI</span>
<span class="hljs-keyword">import</span> <span class="hljs-type">VisionKit</span>
<span class="hljs-class"><span class="hljs-keyword">struct</span> <span class="hljs-title">DataScanner</span>: <span class="hljs-title">UIViewControllerRepresentable</span> </span>{
.
.
.
}
</code></pre>
<p>这个结构会接受两个 binding 变量 (variable):一个用于触发数据扫描,另一个则用来储存扫描到的文本的 binding。</p>
<pre><code class="lang-swift">@<span class="hljs-type">Binding</span> <span class="hljs-keyword">var</span> startScanning: <span class="hljs-type">Bool</span>
@<span class="hljs-type">Binding</span> <span class="hljs-keyword">var</span> scanText: <span class="hljs-type">String</span>
</code></pre>
<p>让我们实现以下方法,来采用 <code>UIViewControllerRepresentable</code> 协议:</p>
<pre><code class="lang-swift"><span class="hljs-func"><span class="hljs-keyword">func</span> <span class="hljs-title">makeUIViewController</span><span class="hljs-params">(context: Context)</span> -> <span class="hljs-title">DataScannerViewController</span> </span>{
<span class="hljs-keyword">let</span> controller = <span class="hljs-type">DataScannerViewController</span>(
recognizedDataTypes: [.text()],
qualityLevel: .balanced,
isHighlightingEnabled: <span class="hljs-built_in">true</span>
)
<span class="hljs-keyword">return</span> controller
}
<span class="hljs-func"><span class="hljs-keyword">func</span> <span class="hljs-title">updateUIViewController</span><span class="hljs-params">(<span class="hljs-number">_</span> uiViewController: DataScannerViewController, context: Context)</span> </span>{
<span class="hljs-keyword">if</span> startScanning {
try? uiViewController.startScanning()
} <span class="hljs-keyword">else</span> {
uiViewController.stopScanning()
}
}
</code></pre>
<p>在 <code>makeUIViewController</code> 方法中,我们回传了一个 <code>DataScannerViewController</code>的实例。在 <code>updateUIViewController</code> 中,我们会根据 <code>startScanning</code> 的数值来开始或停止扫描。</p>
<p>然后,我们要实现以下的 <code>DataScannerViewControllerDelegate</code> 方法,来撷取扫描到的文本。</p>
<pre><code class="lang-swift"><span class="hljs-func"><span class="hljs-keyword">func</span> <span class="hljs-title">dataScanner</span><span class="hljs-params">(<span class="hljs-number">_</span> dataScanner: DataScannerViewController, didTapOn item: RecognizedItem)</span> </span>{
.
.
.
}
</code></pre>
<p>当使用者点击侦测到的文本时,就会调用这个方法,因此我们会这样实现它:</p>
<pre><code class="lang-swift"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Coordinator</span>: <span class="hljs-title">NSObject</span>, <span class="hljs-title">DataScannerViewControllerDelegate</span> </span>{
<span class="hljs-keyword">var</span> parent: <span class="hljs-type">DataScanner</span>
<span class="hljs-keyword">init</span>(<span class="hljs-number">_</span> parent: <span class="hljs-type">DataScanner</span>) {
<span class="hljs-keyword">self</span>.parent = parent
}
<span class="hljs-func"><span class="hljs-keyword">func</span> <span class="hljs-title">dataScanner</span><span class="hljs-params">(<span class="hljs-number">_</span> dataScanner: DataScannerViewController, didTapOn item: RecognizedItem)</span> </span>{
<span class="hljs-keyword">switch</span> item {
<span class="hljs-keyword">case</span> .text(<span class="hljs-keyword">let</span> text):
parent.scanText = text.transcript
<span class="hljs-keyword">default</span>: <span class="hljs-keyword">break</span>
}
}
}
<span class="hljs-func"><span class="hljs-keyword">func</span> <span class="hljs-title">makeCoordinator</span><span class="hljs-params">()</span> -> <span class="hljs-title">Coordinator</span> </span>{
<span class="hljs-type">Coordinator</span>(<span class="hljs-keyword">self</span>)
}
</code></pre>
<p>我们会检查辨别到的物件,如果辨别到任何文本,就会把它储存。最后,在 <code>makeUIViewController</code> 方法中插入这行代码来配置 delegate:</p>
<pre><code class="lang-swift">controller.delegate = context.coordinator
</code></pre>
<p>现在,控制器已经可以在 SwiftUI 视图中使用了。</p>
<h3 id="%E5%88%A9%E7%94%A8-datascanner-%E6%93%B7%E5%8F%96%E6%96%87%E6%9C%AC">利用 DataScanner 撷取文本</h3>
<p>举个例子,我们会构建一个 UI 简单的文本扫描器 App。在启动 App 之后,它会自动显示 Live Text 的相机视图。当侦测到文本时,使用者可以点击文本来撷取它。扫描到的文本会在显示在屏幕的下半部分。</p>
<figure id="fig39.2"><img src="images/livetext/swiftui-live-text-demo.png" alt="图 39.2. Live text 示范"><figcaption>图 39.2. Live text 示范</figcaption></figure>
<p>创建好一个标准的 SwiftUI 项目后,让我们打开 <code>ContentView.swift</code> 和 <code>VisionKit</code>框架。</p>
<pre><code class="lang-swift"><span class="hljs-keyword">import</span> <span class="hljs-type">VisionKit</span>
</code></pre>
<p>然后,我们要声明几个变量,来控制数据扫描器和扫描到的文本的操作。</p>
<pre><code class="lang-swift">@<span class="hljs-type">State</span> private <span class="hljs-keyword">var</span> startScanning = <span class="hljs-built_in">false</span>
@<span class="hljs-type">State</span> private <span class="hljs-keyword">var</span> scanText = <span class="hljs-string">""</span>
</code></pre>
<p>在 <code>body</code> 的部分,让我们这样修改代码:</p>
<pre><code class="lang-swift"><span class="hljs-type">VStack</span>(spacing: <span class="hljs-number">0</span>) {
<span class="hljs-type">DataScanner</span>(startScanning: $startScanning, scanText: $scanText)
.frame(height: <span class="hljs-number">400</span>)
<span class="hljs-type">Text</span>(scanText)
.frame(minWidth: <span class="hljs-number">0</span>, maxWidth: .infinity, maxHeight: .infinity)
.background(<span class="hljs-keyword">in</span>: <span class="hljs-type">Rectangle</span>())
.backgroundStyle(<span class="hljs-type">Color</span>(uiColor: .systemGray6))
}
.task {
<span class="hljs-keyword">if</span> <span class="hljs-type">DataScannerViewController</span>.isSupported && <span class="hljs-type">DataScannerViewController</span>.isAvailable {
startScanning.toggle()
}
}