Main part of the development process requires adaptation of the application to different screen sizes and resolutions on different devices, just like the different screen sizes of iPhone 4/4S (3.5″), iPhone 5/5S (4″), iPhone 6S/7/8/SE (4.7″) and iPhone 7/8 Plus (5.5″).
Click here for more information on online iOS and Android emulation and simulation on Windows and any other desktop OS