![]() ![]() Next, let’s focus on how you write them and the kinds of content you can preview. That’s a quick look at how previews work. Similarly, you can have previews for views that encompass a lot of your application, and you can have previews that show individual leaf views. For example, with tests, you can have high level UI tests that exercise a significant portion of your app’s functionality, and you can have smaller unit tests that test individual components. Third, you can test and preview different layers of your app. Secondly, investing in writing tests and previews, they ultimately help you develop faster. This means you have confidence that what you’re testing and previewing represents what the people who will use your app will experience, too. We're not emulating or interpreting code. Like tests, previews run real code in your real project. This isn’t a perfect analogy, but it might be helpful to think of previews similar to tests. For example, you can test it in dark mode or different type sizes and orientations. And, once you have a preview defined, Xcode can run that preview in different contexts automatically without you needing to write any additional code. This means that you can focus on writing and iterating on your code, and Xcode will automatically handle building, running, and updating your previews. First, it'll examine the change you made and recompile the minimal amount of code. When you edit any of the Swift code in your project, Xcode will do two things automatically. ![]() But previews are also about iterating faster. You can do whatever you need to set up a preview for any view in your app and it will appear right in the canvas in Xcode. Because your previews can access these symbols and resources, previews are really flexible. Previews are compiled into your app, right alongside the rest of your app code and your resources. You use the #Preview macro, and return a view. They are written at the top level of a source file, meaning they are not nested inside of any types or functions. So what are previews? A preview is a snippet of code that makes and configures a view. I want to give you a couple of tips and tricks to help take previews further in your project. And finally, as you start to adopt previews in your project, there are some common scenarios or questions you’re bound to encounter. I’ll show you how to write these and some of their unique workflows in Xcode. Second, there are two different ways you can provide content for your previews: views and widgets. It’s helpful to understand a little bit of how they work and how they relate to the rest of the code in your project. Whether you’re new to previews, or you’ve been using them for a while, I want to help you make the most of them. You can use them across your entire app with different kinds of views, data, and devices. That’s why we made previews so you can have that near-instant visual feedback so you can focus on being creative. Building software, and especially apps, is a really iterative and creative process, so you want the fastest way to test your code and experience what you’re making come to life. ♪ ♪ Kevin Cathey: Hi, my name is Kevin, and I work on Previews. Search the forums for tag wwdc2023-10252. ![]()
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