![]() Source codeĮxample source code for this article is available on my GitHub. = true //design mode is by default false in Release :-) Let’s utilize this to build a DesignTimeHelper class: public static class DesignTimeHelper The app will crash immediately, but the previewer will work flawlessly. But it turns out, there is a workaround!Īlthough the App instance is created and the constructor is executed, other app lifecycle methods are not! You can verify it quite easily, if you throw an exception inside the OnStart() method override in your App class. This has however changed with Xamarin.Forms 6.2 which “fixed” this “bug”. Previously it was quite easy to check for design mode, by inspecting the Application.Current property for null as the previewer did not instantiate it. This is very annoying and time consuming and bound to cause frustration in case you accidentally try to actually debug the application in the Preview configuration.īut there is a better way! The pleasant way Whenever you want to use the Previewer, you not only have to switch the build configuration (which can take a moment depending on the size of your solution), but you also need to rebuild the PCL as well as the platform projects (Android or iOS) for which you want to preview. This certainly works, but has a number of drawbacks. code you don't want to run in design mode Whenever you need to prevent design mode from running, you can use the #if preprocessor directive: public MainPage() You can create a new build configuration based on Debug, name it “ Preview” for example, and then define a DESIGNMODE preprocessor flag for the Xamarin.Forms PCL project in this configuration. If you enjoy waiting for builds to finish, there is a simple solution you can use – preprocessor flag. Checking for design mode in Android ( isInEditMode) or iOS ( TARGET_INTERFACE_BUILDER macro) platform projects does not work with Xamarin Previewer. It is strange that this has been not yet added, but it seems, we have to work around this fact for now. If you check the Xamarin.Forms API, you will find out that there is not yet any class that would allow you to directly check for design mode, nothing in the likes of UWP DesignMode class. Can we easily check if the app is in preview (design) mode? XAML Previewer Unfortunately, there are times when your page constructor contains code that cannot be run in design mode (for example service resolution, etc.) and causes the previewer to crash. Visual Studio for Windows and Mac now includes Xamarin XAML Previewer, which allows you to preview your Xamarin.Forms XAML without having to launch the app.
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