Develop Reference

How can we access an android activity from within context?

Trying to call a function from an activity, but I need the specific instance of that activity to do so.
Is there a way to call that specific activity from the application?
If not, is there a way to start an activity from the application so that I always have access to the instance I start running? I tried this, and edited the manifest, but the app never started...

As concerned with the limited details in this question, I think your requirement is to call a function in an activity that needs that activity itself as the parameter. I think you can do it like this.
Activity actiity=this;
yourMethode(activity)
{
//body of your methode
}
Whenever you use the variable "activity", you can get an instance to the current activity.

I think you are talking about casting the context to get the type of activity it represents. You can do it like this. But be careful if the context is not of that type you will most likely cause a crash.
((MainActivity) mContext).myMethod();
This is not really recommended as it will cause some tight coupling between the class and the activity.

Android Fragments: how do I save and pass data back to parent activity once the user closes the current activity?

I have a SearchFragment and a PersonFragment which are hosted by different FragmentActivitys
The user will navigate from the SearchFragment to the PersonFragment. When the user is done with the PersonFragment (such as when they press the back button), I would like to send data back to SearchFragment so it can update its UI with any changes the user made while in PersonFragment.
I read the best way to do this is in the Activity's finish() method. However, since I'm using fragments I'm not sure how to accomplish this.

You first communicate from PersonFragment to the associated activity using interface as a callback.
Then you can use intent to pass values between activities. From activity you can communicate to SearchFragment.
http://developer.android.com/training/basics/fragments/communicating.html

According to the tutorial on the Android developers site (link), you should declare a listener interface in your PersonFragment, implement it in your FragmentActivity and in that implementation, update your SearchFragment's UI.
Edit: Another approach would be to use LocalBroadcastManager, if you can package your relevant data in an Intent, this approach uses a bit less boilerplate code.

you dont need it, all you need to do is some ContentObserver that notifies you about the content changes, see ContentResolver and its methods: registerContentObserver() and notifyChange()

Ended up using EventBus for this

Where is FragmentActivity#onDetachFragment?

Every time I attach a fragment to my activity, I want to register it to receive events from the activity. This is easy, because I can override FragmentActivity#onAttachFragment(Fragment). When the fragment is removed from the activity, I want to unregister it from receiving events. I expected there to be a onDetachFragment event that I could use in a similar manner, but I'm not finding it.
Is there another way to accomplish what I'm trying to do? I'd like to keep the registering/unregistering in the activity, as opposed to moving it to a base fragment class (where I could just use onAttach/onDetach).

its better to use the onStart(), onStop() method from your fragment. Just cast getActivity() to your calling activity class.

Android: How to Pass WebView from one Activity to another Activity

I want to pass the WebView from One activity to another Activity.
how to do that. I referred How do I pass an object from one activity to another on Android?
but still not getting any idea for this. Please help me to get this....

Sounds to me like you may want a broadcast receiever...
try looking here: BroadcastReceiver
That will let one activity send a message to another

either u try to use finish() an the passed Activity or you simply call finish() in the activity after it's done with it's calculations

Are you sure you want that in an Android activity, not just a normal Java class?

Fragment lifecycle with respect to it's activity

Situation
My activity waits on an Async operation and after it hears back from async operation, it needs to pass information to 2 fragments inside it.
Requirement
1. Both fragments need their onCreateView calls to be done for them to have their layouts loaded,
2. They need for themselves to be attached to their activity so that getActivity() works.
I wrote a setData() method in both the fragments and am looking for the "correct" place in the activity's lifecycle to invoke them.
onCreate() of the activity does not work, onStart() of the activity does not work and onStart() of the fragment does not work.
Nothing works, what am I missing here?

The official documentation for the Fragment lifecycle explains this clearly - please refer to it and then ask follow-up questions if something is unclear.

This Image will be helpful to understand both life cycles together.
As many people complaints and it is somewhat valid argument that this life cycle is too complicated, in Google I/O 2018,They have suggested to use Architecture component Framework. Please check this Docs

when you are at Activity2---->backpress--->Fragment2(Activity1)---means Activity1 again attach from fragment2 so on OnAactivityCreated() method Activity1 is completely loaded ....so at that we can call setData() method of your Activity1...

onAttachFragment()-activity is called before onCreate()-activity and after onAttach()-fragment

Call onDestroy on onStop of your fragment. This should call onCreate when the fragment is launched.
Let me know if works as an ideal solution for your problem.