Question

Can I rely on statement the Application’s Context is not changing during application’s lifecycle? What if I store a context somewhere using singleton pattern and then use wherever I need?

Answer 1

To answer your second question first: If you need to store some state in a singleton, then you can use the Android Application class and your Application becomes your singleton (it is also a Context). There would be no need to store it.

To the first question, as to whether the Context can be changed at runtime: sort of related to your other question, I think we can figure that out by looking at ContextWrapper.attachBaseContext:

 protected void attachBaseContext(Context base) {
     if (mBase != null) {
         throw new IllegalStateException("Base context already set");
     }
     mBase = base;
 }

So, yes, you can rely on it; it can’t be changed, and if you try, it will throw an IllegalStateException.