When you have a specific version of your app installed on your device, but you are working on another layout that is not connected to that version, the "Preview" feature allows you to view the new layout without having to uninstall and reinstall the new layout on to your device.
i- Go to App UI Builder
ii- Click on the 'Layouts' section from the left panel.
iii- On the top bar actions, click on 'Preview'
iv- Once you click on Preview, you will get a QR code that you can scan to your device and see what you did in your layout in the app level.
* You also have the option of sending the QR code via mail.
This QR Code will be relevant to the specific layer you hace selected.
For example: In this case, the layout is called "Test App"
You can switch layouts, and preview a Different Layout by:
i- Click on the Dropdown arrow, to the right of the Layout Name:
ii- This will bring upon a popup menu with the available Layouts for this app.
iii- Select the relevant layout by clicking on the Date to the right of the App Name
For example: If I want to preview the "TV Demo" Layout, I will click on:
iv- Once selected, you will see that the layout in te upper-top bar, has now changed to the Layout we have just selected:
v- Click on "Preview": You will get a popup screen with a QR code that you can scan to your device and see Preview the relevant layout: