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Use onClick Listener for a button located in one of tab fragment, in Main Activity?

Can I use onClick Listener for a button located in one of tab fragment, in Main Activity?

I think you want to perform some action in your MAIN ACTIVITY when a button is clicked in your fragment. If I am right, then just create a interface callback from your fragment to the activity and use the over-ridden method to perform whatever action you require.
Have a look at this
http://developer.android.com/training/basics/fragments/communicating.html
or this
onAttach callback from fragment to activity
Hope this helps.

Yes, you can think of a Fragment as a stand alone user interface that contains it's own animations and logic. So an onClickListener for a Button in a Fragment is no different than in an Activity.

Though the method using Interface is sufficient, this is the simple way to do it.
You can pass context("getActivity()") of MainActivity while calling
the fragment.
Create a method in MainActivity to change the fragment.
call the MainActivity method to set the Fragment.
((MainActivity) context).setFragment(fragment);
you are done.

Refreshing a fragment view from MainActivity

So I currently have an app that has 4 tabs (fragments). They are fragments A,B,C,D, in that order.
Fragment A is the first view opened (along with B because viewPager loads the view before and after the current view).
When I click a button in Fragment A, it sends Data back to MainActivity and then sends that data out to Fragments B and C.
However, this is where the issue comes into play. Since Fragment B was already called, the View isn't updated once I click the button and send the data over, but Fragment C is because the view wasn't called before.
Is there any way that I can remedy this?

You can do it a few ways right.
Just set the data to the fragment and have it update its views
Have all the fragments like B and C register themselves to recieve data from the MainActivity and when MainActivity gets it's data set you tell all the registered receivers of the new data
Recreate the fragment
Use an event bus and tell all subsribers of the new data and MainActivity, Fragment B would get notified of new data. Fragment C would get its data when created by MainActivity
I think this list is pretty endless tbh
The key here is the fragments need to fetch the data from the actvitiy aswell as be updated by the activity. In which case you need to break your UI update behaviour out of onCreateView and into its own updateUI() function. updateUI(MyData) can then be called from onCreateView and also called in a setMyData() on the fragment. Just make sure you check the isAdded flag in setMyData.
This pretty much says it all:
http://developer.android.com/training/basics/fragments/communicating.html

I used a simple fragment communicator that allows the activity to call the fragment, and the same for a fragment to talk to the activity.
You can change the views with the new data based on calling the method from within the activity. The way I do it is set the fragments in the activity then pass them into the page adapter this way I can call the methods within the fragment and implement the fragmentcommunicator interface on the fragments.
You can honestly even avoid the interface if you want, but if you are going to include the same method in all the fragments to talk to them it is easiest.
If you show code, I can show you a quick example.

Activity/Fragment to Activity/Fragment to Activity/Fragment

Looking for a best practices solution to this issue.
Activity1 contains Fragment1 with a spinner of valid products
Activity1 contains an action bar menu option 'products' which launches Activity2 containing Fragment2 (list fragment).
From Fragment2 you can add/edit products using Activity3/Fragment3.
Changes made in Fragment3 I am getting back to Fragment2 with ActivityResult, and I know I could also achieve the same with an Interface.
The question is: What is the best way to get changes made in Fragment 3 reflected in the Fragment1 spinner?
I know I could reload the spinner values in Fragment1 in onResume() but if I didn't make any changes in Fragment3 this would be unnecessary.

I would use an Observer pattern. Implement an Interface with something like
public void onInputChanged(yourStuff);
let your first Fragment implement this Interface and Add the Fragment to a Listener Pool.
and from your Activity where the change happened, do something like
EventManager.fireOnInPutChanged(yourData)
EventManager would b the calls your listeners sign up to.
like this you wont need Activity forResult and you always know if something has changed.

How to make call backs between Fragments of the same Ativity

I have 4 tabs in an Activity.
Each of them is a Fragment. And every Fragment has a ListView.
So, if i change the ListView in Fragment, it must change the ListView in all other Fragments ie.., Tabs.
The problem i face is while creating the interface instance.
It takes it's own onClick() method.
In case i want a callback to the parent activity i could have done that by overriding onAttach. But how to make a callback to a Fragment?
From Developers site:
Often you will want one Fragment to communicate with another, for example to change the content based on a user event. All Fragment-to-Fragment communication is done through the associated Activity. Two Fragments should never communicate directly.
So, make a callback to the Activity which in turn makes a callback to other fragments??
Thank You

It's pretty simple,all You need is steps below:
1) From onClick method in your first fragment make a function call of activity:
((IYourActivityInterface) getActivty()).activityMethod();
2) In your activity find fragment by tag or id and run it's method:
public void activityMethod(){
Fragment tabFragment = getFragmentManager().findFragmentByTag("second_fragment");
// or Fragment tabFragment = getFragmentManager().findFragmentById(R.id.frag);
if (tabFragment!=null){
((IFragmentInterface) tabFragment).fragmentMethod();
}
}
Hope this is what you are looking for.)

Call fragment events from activity

So, I got the event in my fragment to pass to the activity, so how do I make it so the activity in turns, notifies fragment B to do something. I want to fragment B to populate a custom list when fragment A has a list item clicked on. So, it sends the event to the activity, now how do I get the activity to call events in fragment B?

One way to do it would be like this in your activity:
FragmentB fragmentB = (FragmentB)getFragmentManager().findFragmentById(R.id.fragmentBId);
fragmentB.performSomeTask();
This is of course assuming that you have a publicly accessibly method in FragmentB called performSomeTask();
Hope that helps!

The best practice is probably to create interfaces for both fragments and then have the activity implement the interfaces. You want to have good decoupling between fragments so that you can reuse them in other places.