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ViewPager and Fragment lifecycle with Activity

I'm using an Activity which has a ViewPager holding 2 fragments, the pager handler is some implementation of FragmentPagerAdapter.
As I understand, pager adapter handles the lifecycle of the fragments inside it.
I found out that my Activity onResume() method already gets called but the fragment onStart() method didn't even started.
how in the world can I fix that? it destroy the whole point of lifecycle interactions between activity an fragments...
Since pager adapter handles the lifecycle of the Fragment, does this means I can no longer depend on interaction with the Activity? I mean, if I want the Activity to do something in the onResume() but after the Fragment onStart() is called, I just can't do it...
Edited:
To make things clear:
Google says lifecycle of activity and fragment are going together, once one gets called, the other also gets called, e.g
Activiy -> onCreate() , and then, Fragment -> onCreate()
Activiy -> onResume() , and then, Fragment -> onResume()
BUT! in my case I get:
Activity -> onCreate() -> onStart() -> onResume() -> onPostResume()
And then:
Fragment -> onAttach() -> onCreateView() -> ... ->onResume().
and to be clear, I am using a pager adapter (not "state" pager) and I have an abstract base activiy in my app which all activities should extend.
public abstract class AbsLoginAppCompatActivity extends AppCompatActivity {
.............
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Log.d(TAG, "*******************onCreate");
//do some general stuff like check for updates on server
}
And in my extend activity:
public class A extends AbsLoginAppCompatActivity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Log.e(TAG, "*******************onCreate");
setContentView(R.layout.activity_a);
//also set pager + adapter + give it getSupportFragmentManager()
}
I am using:
android.support.v4.view.ViewPager
android.support.v4.app.FragmentPagerAdapter
android.support.v4.app.Fragment
android.support.v7.app.AppCompatActivity (for abs activity)

The Fragment[State]PagerAdapter uses the activities FragmentManager - or in case of a nested ViewPager in a parent fragment - that fragment's child FragmentManager to manage the fragments, just like normal fragments would do. Really, the only thing that these adapter implementations do is that they hide the nasty FragmentTransaction stuff for you.
I had never problems that particular lifecycle callbacks weren't called for me in my fragments, so I cannot say anything about that. One thing however that is important to understand and that many people get wrong is that the adapter's getItem() method is called only when a fragment is freshly created; if it is restored from a saved state this method is not called again and people tend to do all fancy things there to initialize their just "created" fragment, while they should really look into instantiateItem(), which either returns the instance you give the adapter via getItem() or returns the reference of the fragment that was automatically re-created for you.
Another thing that is good to know about fragments in pager is the method setUserVisibleHint(boolean). Since fragments are usually recreated and resumed all at once (non-state adapter) or on demand (state adapter), its usually important to know when one instance is actually visible to the user. This can be achieved by overriding the aforementioned method in a custom fragment.

Notifying fragments in a viewpager

I am using ViewPager in my app. In each fragment there is a toolbar. On a single tap on the image the the toolbar is animated to the top out of the screen. But I have to notify all the remaining fragments to do the same thing. So that when the user scrolls to the next fragment he doesn't see the toolbar.
I tried adding setUserVisibleHint(), but it did not work as it was called only when the fragment was completely visible, thus showing the toolbar exiting to the user.
Then I tried it in onResume and setting pager.offscreenpagelimit=1, it worked fine for the fragment next to next but did not work for the next fragment.
Thanks!!

First Notify your activity from fragment using:
In Fragment on Animation End:
((YourActivity)getActivity()).hideToolbar();
In Activity:
public void hideToolbar() {
// Redraw view pager without toolbar (notify your adapter create pager without toolbar)
}
Well, why don't you get your toolbar out of your fragments and just create one in activity and change its state on page change (definitely it will not slide but may

You have 2 problems to face.
How to call existing fragments to hide/show their toolbars.
How to create another fragments with hidden toolbar.
First problem can be easly done by using Otto event library found here. Just paste this code in your viewpager fragments:
Bus bus = new Bus();
#Override
protected void onResume() {
super.onResume();
bus.register(this);
}
#Override
protected void onPause() {
super.onPause();
bus.unregister(this);
}
#Subscribe
public void onToolbarEvent(ToolbarEvent event) {
//do your toolbar logic
}
Then in your onClick event on image just put (of course creating bus object before)
bus.post(new ToolbarEvent());
ToolbarEvent can be just empty class. If you read about Otto events you will understand how it works.
Another problem is how to know that the toolbar should be hidden/shown, when viewpager instantiates new fragments? Simply add a boolean flag in your shared prefferences, so every time fragment is created, it can check if it can show toolbar or not e.g. in onViewCreated() method. The example how to use shared prefferences can be found here
Hope I helped a little bit.

Which method to override in android fragment to populate a listview

I have an activity which holds the fragment A and Fragment A hold a list view and button, when I pressed the button it directs to another fragment B.
My question is which method I need to override in fragment A so when I pressed the back button, I can re-populate the list view inside. Or is there another simple way I can make it ?
Until now I tried to override the onResume and onStart, it didnt work. Btw I cant override the back button pressed in Fragment B because in that case I cant reach ui components in fragment B and getting a null pointer normally.
Thanks in Advance.

Your will get NO notice when the previous fragment is show again.
But you can override the onBackPressed() method of the fragment's parent activity like this:
#Override
public void onBackPressed() {
//1.find your fragment A by tag, this tag is supplied
//when you using FragmentTransaction.add(int id, Fragment fragment, String tag)
//the you can find fragment by this way
//FragmentA fragment = getSupportFragmentManager().findFragmentByTag(name)
//2.call some method of it!
}

Force Main view to recreate after preferences

So I have my main activity that has some views and I have an activity that has the preferences.
I want to, when the activity of the preferences is destroyed, to recreate my main activity, because some views depend on the preferences.
I don't see a way to do this.
Thanks.

Check what's changed in onResume() of your main Activity. Then, based on whatever your logic is, set the contentView to the appropriate Views or manipulate whatever Views you need to.

for me I always make all work in separated method and call it in onCreate()..
i.e:
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//here call method contains views initializing, logic, etc..
initializingPro();
}
private void initializingPro(){
//....
webview=(WebView)findById(R.id.webb);
//....
}
now in you case you want to recreate those components, just call this method again initializingPro() ,, no need to destroy activity..
good luck,

onCreate not called

I have 2 Activities : First activity user clicks on a button which launches the 2nd activity. The 2nd Activity does all the work.
I launch the 2nd Activity as follows which is inside a onClickListener Inner Class and I have tried explicitly calling it with (FirstActivity.this,Simple.Class) but same thing happens.
Intent test = new Intent(arg0.getContext(),Simple.class);
startActivity(test);
On the emulator, I see the screen move over like its calling the 2nd activity but all I get is a black screen but nothing is loaded from my layout. I looked at logcat and I do see some binder thread failed messages. This is the onCreate function from my 2nd activity but I do not get any results from either the screen or logcat showing me that the Log functions were called:
public void onCreate(Bundle savedState)
{
Log.d("SimpleActivity","OnCreate Started");
super.onCreate(savedState);
setContentView(R.layout.simple);
Log.d("SimpleActivity","OnCreate Ended");
}
Note : I have called the base constructor in OnCreate() with super.onCreate(savedState) in my code above.

What happened to me was I was overriding the wrong onCreate method. I was overriding public void onCreate(Bundle savedInstanceState, PersistableBundle persistentState) when I really needed to override protected void onCreate(#Nullable Bundle savedInstanceState). Maybe this might help someone!

It's possible that onCreate doesn't get called, if the activity has never been destroyed,
if for some reason an activity hangs around, next time its instantiated it is not recreated but resumed instead...
At least that's what im Dealing with right now in my code... Life cycle of Activities seem a good logical explanation.. However 99% of time I do rely on onCreate being called when startingActivity and it doesn't fail me....
Edit: And of course its because I wasn't calling finish() when exiting the activity. Doh.

This is not related to this certain issue, but also this can happen when activity is not declared in manifest file)

Be careful that if your method belongs to AppCompatActivity or Activity .
It is up to what you implemented to your Class
If you want to add lifecycle or any override methods, I recommend you to press
CTRL+O or do Code > Override methodsand there you can see where the method belongs

remove android:launchMode="singleTask" from manifest

you should #Override onCreate and add super.onCreate() in it
#Override
public void onCreate(Bundle savedState)
{
super.onCreate(savedState);
Log.d("SimpleActivity","OnCreate Started");
setContentView(R.layout.simple);
Log.d("SimpleActivity","OnCreate Ended");
}

my case
(1) mainActivity -> (2) open Adaptor - startActivity -> (3) mainActivity onCreate() doesn't get to triggered.
I resolved this by adding finish();. in mainActivity.
follow the below steps to check your application.
1.did you override the right method? if not overriding the below method, this method will be triggered, when you startActivity.
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
2.Make sure that you registered the activity in manifest.xml
2.1 is your activity has android:launchMode="singleInstance" ?
(if your application doesn't need to be singleinstance, consider to remove.
but my case I need singleinstance. hence i moved to the next step)
use finish()
public void openSearch(View view) {
Intent intent = new Intent(this, BookInfoActivity.class);
intent.putExtra(...);
startActivity(intent);
finish(); // add like this.}
why do we need to use "finish()"?
Screen A -> click button on A -> Screen B -> click button on B -> screen A with some new data that you get from Screen B
if you don't call finish() method(in A button) , that means the A is still in your background
even you are seeing the screen B.
hence, when you trigger startActivity on screen B, it just simply shows the running A screen.
however if you use finish() method (in A button), when you go to B Screen,
it destroys the A screen, so when you go back to A screen by clicking B method( 'StartActivity') it creates A screen and trigger onCreate() Method .

You need to call the super.onCreate(savedState) method. Take a look at Activity doc.
public void onCreate(Bundle savedState)
{
super.onCreate(savedState);
}