Android development is comparatively hard because of the fragmentation of devices. The main reasons are the following:
- Different screen resolutions across devices. You need to design your app at least for several popular screen resolutions to succeed.
- Different Android versions across devices. Different versions of Android maintain different libraries, that is why it is a common situation when one method is unavailable for one of the Android version you are developing for.
You can find more detailed information about Android fragmentation on the Android official page.