Consider the following sentence:
I am developing an application to be installed on Android.
This has been a major flaw in Android...
To be clear I am unsure of the usage of "in" vs. "on". When should I use "in" and when to use "on"?
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Install software on a platform. Find defects in a program.
If you are developing an application to be installed in Android, then it's going to be incorporated into that software and form part of the platform.
If you find a major flaw on Android, you are not talking about Android itself, but something else which is running on that platform (and which works well on other platforms).