I would like to load all pages inside UIPageViewController at the beginning. It's easy in Android with setOffScreenPageLimit method of view pager. Is it possible to achieve this in swift?
Yes and no. You can manually pass on or two controllers at a time to your UIPageViewController or implement UIPageViewControllerDataSource that would call and fetch the controllers when needed.
When defining a page view controller interface, you can provide the content view controllers one at a time (or two at a time, depending upon the spine position and double-sided state) or as-needed using a data source. When providing content view controllers one at a time, you use the
setViewControllers(_:direction:animated:completion:)method to set the current content view controllers. To support gesture-based navigation, you must provide your view controllers using a data source object. The data source for a page view controller is responsible for providing the content view controllers on demand and must conform to theUIPageViewControllerDataSourceprotocol. The delegate object—an object that conforms to theUIPageViewControllerDelegateprotocol—provides some appearance-related information and receives notifications about gesture-initiated transitions. This class is generally used as-is, but can also be subclassed.
https://developer.apple.com/documentation/uikit/uipageviewcontroller