Develop Reference

When will a dynamically added fragment be re-added?

The Fragment documentation shows an example of an activity dynamically adding a fragment in onCreate(...):
if (savedInstanceState == null) {
// During initial setup, plug in the details fragment.
DetailsFragment details = new DetailsFragment();
details.setArguments(getIntent().getExtras());
getFragmentManager().beginTransaction().add(android.R.id.content, details).commit();
}
This almost makes sense to me, except for one detail. I thought the reason for checking savedInstanceState == null was that if the activity is being re-created, we can expect the framework to re-add the fragment for us. However, I thought the framework would only do this if the fragment has a tag, and the example uses the version of FragmentTransaction#add(...) that does not take a tag. So as I understand it, if this activity were recreated, it would not have a DetailsFragment.
Is my understanding wrong? And if the framework does re-add the fragment, at what point in the activity's lifecycle is it guaranteed to have done so?

I thought the framework would only do this [re-add the fragment] if the fragment has a tag
No. According to the documentation in "Adding a fragment to an activity" section:
each fragment requires a unique identifier that the system can use to restore the fragment if the activity is restarted.
Thus, you have 3 possibilities to handle this: using an unique id, unique tag or none of them. Yes, neither of the previous two requirements.The purpose of adding a tag is to capture the fragment. This is useful if you want to retrieve it easily and play with it (such as performing transactions). However, it's not required.
When you use add(int, Fragment), it calls add(int, Fragment, String) with a null tag at the 3rd parameter. Therefore, the system will use the ID of the container view instead (1st param in add()). Thus, the fragment is restored without any id or tag that you supplied but correctly handled by the system.
Note: in reference of add(int, Fragment, String), you can see this quote: "Optional tag name for the fragment, to later retrieve the fragment with FragmentManager.findFragmentByTag(String)" - How could it be optional if we need it to restore fragments? ;)
At what point in the activity's lifecycle is it guaranteed to have done so?
I cannot honestly respond on it, maybe someone has the right answer but, here's what I think.
As you can see in "Handling configuration changes", when orientation (or any specific change) occurs on activity, it calls onDestroy() and directly onCreate(). At the point of (activity's) onCreate() is called, the child fragment will receive a callback in onAttach(). Beside, when the activity has received its onCreate() callback, a child fragment receives automatically a onActivityCreated() callback. After that, each method in activity will trigger the "exact" same child methods (onStart(), onResume(), onPause(), onStop()).
Thus, I think the safe point is onStart(), because activity triggers directly the call of the fragment's method, you're sure that the fragment is attached to it and you can handle onRestart() -> onStart() to update the UI.

I don't use tags with my Fragments and mine work just fine, I have the exact same test as you.
if (savedInstanceState == null) {
//fragment needs to be created
}
if (savedInstanceState != null) {
//fragment will automatically be there with no code
}

Where to place application logic in new Activity code generated by ADT 22.6.2

In the latest versions of eclipse (ADT v22.6.2) the create android application now generates an activity_main.xml and a fragment_main.xml. It generates only a single activity class
but this now has an embedded inner static fragment class that is created by the activity in its onCreate method
#Override
protected void onCreate(Bundle savedInstanceState) {
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit();
}
....
public static class PlaceholderFragment extends Fragment
My confusion is how to port old code/examples where there was only 1 activity and the main application
logic is usually put in the Activity onCreate method i.e. stuff like findViewById. Listeners
etc
The way I have approached it is that I put all my user created views as members of the static PlaceHolderFragment class. Then I call this in the fragment onCreateView. I still have some logic in the activity and it stores a pointer to the fragment. It updates the views members by calling getters on the fragment. Is this correct or should all logic be moved to the fragment now ?
All the tutorials/examples use the old approach where logic is placed in the activity
so there is no reference documentation for how to use the new files that Eclipse generates for an Android application. Any help appreciated ?

Don't worry about the files that Eclipse generate automatically: You can do whatever that you want!!!
Fragment is a element between an Activity and a container.That's mean that you can put the logic of your code inside of one fragment with not problems.
In theory, fragments are used when you want to manage screens using different modules, containers. It's a fragment, a module, part of one screen (but also can be used in a full screen looking as an activity and with the same behaviour than one activity.) For example, imagine that you have for mobile phone screens, one list of news in one screen, and when you click, your app go to the next screen for show the content of the news, right? Ok, so you can use for these 2 screens: 2 activities for each one or one parent activity with 2 fragments...whatever that you want...
Imagine the same case, for a tablet version of your app, now the left part of the screen you should show the list of news and in the right part of the screen, the contain of each news clicked, right? In that case, would be completly necessary to use one activity parent with two fragments...in that case, we could reuse almost the same case for the mobile phones or tablet.
And now, focus in your question: if you don't want complicate the life (not too much, because work with fragment is easy too) I will recomend you to use only activities for your app.
But, like your question, you want to port, there isn't any problem. Now imagine that your activity is going to be only the class where you are going to manage the fragments. The logic for each screen has to be in each fragment. Use the activity only for replace fragments, or share information between fragments, etc. The activity will be like the orchestra director.
From each fragment, you can access to methods or public variables of your activity using ((NameOfActivity)getActivity()).
Is it clear for you?
One more stuff, in fragment, normally the method that we used for initialize stuffs is onCreateView (and not onCreate like activities).

Where to put the Fragment functional code?

Just a general question about working with Fragments and Activitys for android development: where does the business end of the functional code go for Fragments loaded into an Activity dynamically? (i.e. a fragment's OnClickListeners, OnCheckedChangedListeners, button logic methods...)
Do they go in the Fragment class, or the Activity class?

All the GUI logic for views attached to a fragment should be contained inside the fragment itself.
Thus a fragment should be as self contained as possible.
You can, though, if necessary do callbacks to your activity based on fragment GUI interaction. This can easily be done like this inside the fragment:
#Override
public void onAttach(Activity activity) {
if (!(activity instanceof SherlockFragmentActivity)) {
throw new IllegalStateException(getClass().getSimpleName()
+ " must be attached to a SherlockFragmentActivity.");
}
mActivity = (SherlockFragmentActivity) activity;
super.onAttach(activity);
}
In this specific case the reason for gaining a reference to SherlockFragmentActivity is to gain access to the support menu inflater mActivity.getSupportMenuInflater(), hence the construction can of course also serve to gain information from the underlying activity.

This probably depends on how much the Fragment's functionalities have in common, and how many, let's say Buttons, have to be handled.
I personally (and it's probably most common practice) handle onClick(...) events separately for each Fragment, meaning that I let each Fragment implement it's own OnClickListener.
Furthermore, when handling everything through the Activity, probably not all the components that react to click-events are in memory at all times and can be reached via findViewById(...), depending on which Fragment is currently displayed and how your user-interface is built up in general.

they always in fragment class because fragment is one type of component in android which we can reuse it. if we put onclick and oncheckchanged in activity then what meaning of reusing that component??
for more information about please go through following step:
Link 1 for basic level of information about fragment and how to handle them
Link 2 for dealing with multi pane fragment
Standard site for fragment

It depends:
If fragment can handle logic which is self sufficient(complete) then that code can be handled by fragment. e.g. on click call phone number.
If fragment have UI whose action is activity specific, then you want to add listener in activity.
e.g. master detail view like email client, on tablet user click on title fragment1 which have list of email titles, then handler on click in activity can show detail fragment2 in activity.
In all you want to keep fragment reusable.

Use Activity or Fragment in Android Application

I am new in android. I often use Activity to change from one screen to another screen with other function. Example from Home Page to Popular page. After that, i know about fragment but i never use it before. So, if i have a application with multi tab on a screen, not use TabHost here. Function of every tab very diffrent, ex : tab Home, tab Popular, tab News, tab Profile ... like Instagram App. I must use that
Activity to change Screen to another Screen, it means: i have Home Activity, Popular Activity, ... and change Activity when change Sreen. Each Activity have each layout.
Use fragment within one Activity. We have multi fragment, example HomeFragment, Popular Fragment... chang replace Fragment when change Screen.
What way is better ?
I want to ask when use only phone screen. ( small size screen, not for tablet).

It's important to think of Android devices as more of a spectrum, than clear "phone" vs. "tablet" buckets. There are many instances where you might want to show more information on screen on medium and large screens. Sometimes, this translates to showing two "Activities" at once.
Using Fragments requires little overhead, but adds measurable flexibility, especially when considered early in the development process. If you use Fragments properly, adapting to larger screens is extremely simple. However, there are a few "gotchas" that may make Fragments appear to be more daunting that they actually are:
Fragment classes must always be declared public (if it's a nested class, it must be static).
In the parent Activity (or FragmentActivity), only add the root Fragment if savedInstanceState == null. If you are managing the state of your Fragment properly, everything is handled for you (scroll position, EditText values, etc).
The parent Activity must call through to onSavedInstanceState in order for the Fragment to properly restore it's state.
setRetainInstance(true) should only be used for "headless" Fragments. This is when you use a Fragment that has no UI, and isn't added to the back stack, which is typically used to do life-cycle dependent work.
Fragments declared in XML cannot be used in a FragmentTransaction (and vice-versa).
Think of a Fragment as a modular view, that provides hooks (callbacks) to it's Activity when something important happens. The Activity decides, based on the available space, whether to launch a new Activity, or show a new Fragment.

You can use either way. If you decide to use the Activity solution, create a base activity class that contains all the Tab functionality. You don't want to implement that in every Activity over and over again.
public class BaseActivity extends Activity {
#Override
public void onCreate(...) {
// Init tabs
}
// Methods for tab handling
}
Every Activity (Popular, Profile, Home, ...) extends BaseActivity
public class PopularActivity extends BaseActivity {
#Override
public void onCreate(...) {
super.onCreate(...);
// Init only the popular activity elements here
}
}
This way you implement the tab functionality only once and get it in every activity.

Android: How to call function of Activity inside of tab from the tabhost

I have a tabhost with three tabs. Each is an activity. I would like to have a button which is in the action bar, the bar along the top with common buttons, call functions of the tab which is active.
For example, an add function which could add something different to each tab depending on what tab was present when you clicked the button.
So, I am aksing how to call a function in Activity A from the tabHost.
And if that wont work, perhaps I can update the database from the tabhost and then refresh the tab content. Would that be easier?
Thank you all for you time and support.

I used the following code within my TabActivity class to switch tab then call a public method defined in the activity of the tab:
getTabHost().setCurrentTab(0);
Activity MyActivity = this.getCurrentActivity();
MyActivity.myMethod();
Hopefully helpful to someone looking for the answer to this question.

Hi Just stumbled across this, not sure if you already found a solution?
I solved this myself recently. I was previously getting around the problem by raising a intent broadcast from the tabhost activity and receiving the broadcast within the sub tab activity. This worked for me but i was sure there is a "better" way.
A cleaner way is to achieve it with something like this:
might have something like this:
parentActivity - my "container"
activity which holds the TabHost
childActivity - my tab activity
which holds tab content and the
public method i want to call from
parentActivity
within parentActivity:
// a method used for onclick callback or whatever you need. within parentActivity (tabhost)
// this will get call huzzah() in the first tab - getChildAt(0)
onClick () {
childActivity childAct = (childActivity) getTabHost().getChildAt(0).getContext();
childAct.huzzah();
}
within childActivity:
// a public method for the parent activity to access
public void huzzah() {
Log.d("stuff", "huzzah() called");
}
Note: Another alternative i believe is to redesign to use views instead of activities in your tabs. This is a better overall alternative because IIRC memory wise you are only storing 1 activity on the stack rather than (n * tabs) number of activities
Hope that helps

Edited as per Peter O request:
I am on API 10, and this problem gave me a huge headache. I have 3 tabs, I want all of them to be aware of changes on the other. The problem I had was that once the activity for a tab is started, there seemed to be no call back so the activity understood the user switched to a different tab, and thus needed to do work to be sure its state was correct.
I found lots of answers to this problem, but none seemed to work.
The one that I finally got to work was the solution offered as #3 for this thread --but it too is confusing. I found that the getTabHost().setCurrentTab(0); does nothing; I implemented OnTabChangeListener() to call a function that used getTabHost().setCurrentTab(0); however, I found the getTabHost().setCurrentTab(0); caused the app to crash for any tab other than 0--e.g, If I chose tab B (index=1) then called getTabHost().setCurrentTab(1); the app crashed.
Using the Debugger, I found the call this.getCurrentActivity(); always returns the activity associated with the tab which the user clicked on--calling getTabHost().setCurrentTab(); did not change that fact, and caused the app to crash.
So I got rid of it and I can now call this.getCurrentActivity(), then call a method in the Actvitity class returned by that call --this lets the activity know it has to update it's state--in my case it does this using the application object.

The above way of calling the method will not work,
Here is the quick answer for the above problem:
getTabHost().setCurrentTab(0);
Activity myActivity=getCurrentActivity();
String name=((Tab1) myActivity).et1.getText().toString();
Here the above code is given in the onclick() method of the activity which has TahHost
where Tab1 is the secondactivity and et1 is the identity of the edittext in the Tab1 activity so you can get all the value of the different fields like this individually.