Develop Reference

Pattern for Activity / Fragment in android

I've a activity which basically is :
public class FragmentContainer extends FragmentActivityBase implements IRefreshListener {
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getIntent().getExtras() == null
|| getIntent().getExtras().get("type") == null) {
showProductList();
}
else
{
if (getIntent().getExtras().get("type").equals("customer"))
showCustomerList();
}
#Override
public void showProductList() {
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager
.beginTransaction();
// load the product list
ProductList fragment = new ProductList();
fragmentTransaction.replace(R.id.fragment_container, fragment)
.addToBackStack(null);
fragmentTransaction.commit();
}
.....
}
in the fragment, I use onCreateView to get intent and then I create my view.
If I need to change the fragment, I get the reference to the parent Activity (taken from onAttach) and I call method referenced by the IRefreshListener.
like :
IRefreshListener mCallback;
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
// This makes sure that the container activity has implemented
// the callback interface. If not, it throws an exception.
try {
mCallback = (IRefreshListener) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString()
+ " must implement IRefreshListener");
}
}
public void callCustomer() {
mCallback.showCustomerList();
}
It works but whne I change the orientation, even I use setRetainInstance(true) it will be reseted.
I have 2 questions :
Do I use the good pattern to manage my application. The big activity which contains one fragment become bigger with the time
How should I handle orientation change ?
Regards

I do not find this pattern is more perfect or best one, although it is or was a suggestion from Google. Because it could be a worse coding style if fragment knows particular activity or listeners, you might write more and more code, when you wanna to let your fragment know more its "container" or "parents". Will the fragment later be used for other activity which has not been implemented with IRefreshListener etc, you will code much more.
My introduce is using Otto-Bus or Event-Bus. You can just send message from one to one. Every one doesn't have to know each other.

Fragment: onCreate being called 4 times

I have a Working model of fragments, when i was debugging the code i saw that the Fragment onCreate is being called 4 times.
Below is my code:
MyFragmentActivity
class MyFragmentActivity extends FragmentActivity{
#Override
public void onCreate(Bundle savedInstanceState) {
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction().replace(fragmentID, new MyListFragmentt())
.replace(detailFragmentID, new MyDetailFragment()).commit();
}
}
#Override
protected void onRestart() {
getSupportFragmentManager().beginTransaction().replace(detailFragmentID, new MyDetailFragment()).commitAllowingStateLoss();
}
}
MyDetailFragment.class
class MyDetailFragment extends Fragment{
// has method like oncreate(),onCreateView(),onSaveInstanceState()
}
How my oncreate of MyDetailFragment is called ? When i go to some other activity and come back and then tilt the device only then oncreate and onSaveInstanceState of MyDetailFragment is called multiple times.
How can i solve this, i have looked into few posts on SO but it says that we need use HIDE,Show methods and other things ? but What is the proper soultion to this ?
EDIT
When i am coming back from previous activity, my data in the MyDetailFragment needs to be refreshed.

Try this
MyDetailFragment fragment = new MyDetailFragment();
#Override
public void onCreate(Bundle savedInstanceState) {
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction().replace(fragmentID, new MyListFragmentt())
.replace(detailFragmentID, fragment).commit();
}
}
#Override
protected void onRestart() {
if(fragment != null) {
getSupportFragmentManager().beginTransaction().replace(detailFragmentID, fragment).commitAllowingStateLoss();
}
}

i think ur recreating fragments multiple times, u do new MyListFragment everytime on onCreate function, call findFragmentByTag to get the existing fragment and set that, if null (first time) then create one
/here is some code mate, if this doesnt work and ur app has single fragment better to just create xml and have only a fragment tag in it, and set that xml in setContentView function*/
// declare following member variable
MyFragment _fragment;
// in onCreate function, call this method
private void setupFragment()
{
_fragment = (MyFragment)getFragmentManager().findFragmentByTag("MyFragment");
if(null == _fragment)
{
_fragment = new MyFragment();
}
// now do the fragment transaction
FragmentTransaction trans = getFragmentManager().beginTransaction();
trans.add(containerId, _fragment, "MyFragment"); // here tag is important
trans.commit();
}

Android fragments - findFragmentByTag always returns null

I've had a look around and found a couple of questions with a similar topic, but nothing that helped in my case.
I'm trying to access an existing active fragment using getSupportFragmentManager().findFragmentByTag(TAG), but it always returns null. Replies on similar questions suggested that it takes a while for the commit to be executed, so calling findFragmentByTag would return null if called too early. I've tried two things:
add getSupportFragmentManager().executePendingTransactions()
immediately after the commit, but still get null.
added a button... pressing this after the activity has been created,
the fragment registered and the view displayed should leave the
system enough time to commit. But i still get null.
Here's my activity:
public class MainActivity extends ActionBarActivity {
private static final String F_SETTINGS = "f_settings";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button btn = (Button) findViewById(R.id.btn);
btn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
debug();
}
});
if (savedInstanceState == null) {
FSettings newFragment = new FSettings();
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.container, newFragment);
ft.addToBackStack(F_SETTINGS);
ft.commit();
// getSupportFragmentManager().executePendingTransactions();
//// Activating this did not make any difference...
}
debug();
}
private void debug() {
String txt = "null";
Fragment frag = getSupportFragmentManager().findFragmentByTag(F_SETTINGS);
if (frag != null) {
txt = frag.toString();
}
Log.i("Testing", txt);
}
}
What am I doing wrong here?
Cheers,
Max

In your code you haven't mentioned tag in replace method So,
Use this structure of replace method of fragment
ft.replace(R.id.container, newFragment,"fragment_tag_String");
Refer this link for more information. fragment replace with tag name

DialogFragment / orientation switch

I have a fairly simple DialogFragment. It looks something like:
import android.support.v4.app.DialogFragment;
public class MyDialogFragment extends DialogFragment {
private String mData = "empty";
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Log.d(LOG_TAG, "onCreate");
setStyle(DialogFragment.STYLE_NO_TITLE, 0);
// setRetainInstance(true);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.mydialog, container);
....
return view;
}
public setData(String _data) {
mData = _data;
}
}
I load this fragment like so from my FragmentActivity:
FragmentManager lFM = getSupportFragmentManager();
MyDialogFragment lDialog = new MyDialogFragment();
lDialog.setData("not empty");
lDialog.show(lFM, "MyDialog");
The code as above works fine. However I would like to retain the fragment on an orientation switch so that the mData field is preserved. If I add setRetainInstance(true); (and after sticking in some debug) I can see that the fragment is indeed retained on an orientation switch - onCreate() is not being called this time. I can see onCreateView() is being called and I return a correct View object, but the dialog is not shown on the screen. What am I missing?

After reading the answer that baboo gave me I implemented the solution as follows .. I hope this is correct (at least it works ok ...)
#Override
public void onCreate(Bundle savedInstanceState) {
// ....
FragmentManager lFM = getSupportFragmentManager();
if(lFM.findFragmentByTag("MyDialog")!=null)
((MyDialogFragment)lFM.findFragmentByTag("MyDialog")).show(lFM, "MyDialog");
// ....
}

Try the following logic in your fragment activity:
Use the put methods to store values in onSaveInstanceState():
protected void onSaveInstanceState(Bundle icicle) {
super.onSaveInstanceState(icicle);
icicle.putBoolean("dialogDisplayed", value); // set value = true when displayin dialog...
}
And restore the values in onCreate():
public void onCreate(Bundle icicle) {
if (icicle != null){
value = icicle.getBoolean("dialogDisplayed");
}
if(value)
//Display Dialog here....
}

The dialog fragment should be preserved automatically as long as you do the following:
If you call an Activity onSaveInstanceState(), make sure you call the super function!!!!. In my case, that was the key. Also make sure you do the same thing in the Fragment.
If you use setRetainInstance, you will need to manually store off the values and re-apply them. Otherwise, you should be able to not worry about it, in most cases. If you're doing something a bit more complicated, you might need to setRetainInstance(true), but otherwise ignore it. In my case, I needed to use it to store a random seed for one of my classes, but otherwise I was okay.
Some people have complained about a bug in the support library, where a dismiss message is sent when it shouldn't be. The latest support library seems to have fixed that, so you shouldn't need to worry about that.
You shouldn't need to do anything fancy like manually store off the fragment, it should be done automatically if you follow these steps.

Fragments, DialogFragment, and Screen Rotation

I have an Activity that calls setContentView with this XML:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="horizontal"
>
<fragment android:name="org.vt.indiatab.GroupFragment"
android:id="#+id/home_groups"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_weight="1" />
<..some other fragments ...>
</LinearLayout>
The GroupFragment extends Fragment, and all is well there. However, I show a DialogFragment from within GroupFragment. This shows correctly, HOWEVER when the screen rotates, I get a Force Close.
What's the proper way to display a DialogFragment from within another Fragment other than DialogFragment.show(FragmentManager, String)?

There's a bug in the compatibility library that can cause this. Try putting this in you dialogfragment:
#Override
public void onDestroyView() {
if (getDialog() != null && getRetainInstance())
getDialog().setOnDismissListener(null);
super.onDestroyView();
}
I also suggest setting your dialogfragment as retained, so it won't get dismissed after the rotation. Put "setRetainInstance(true);" e.g. in the onCreate() method.

OK, while Zsombor's method works, this is due to me being inexperienced with Fragments and his solution causes issues with the saveInstanceState Bundle.
Apparently (at least for a DialogFragment), it should be a public static class. You also MUST write your own static DialogFragment newInstance() method. This is because the Fragment class calls the newInstance method in its instantiate() method.
So in conclusion, you MUST write your DialogFragments like so:
public static class MyDialogFragment extends DialogFragment {
static MyDialogFragment newInstance() {
MyDialogFragment d = new MyDialogFragment();
return d;
}
#Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
...
}
}
And show them with:
private void showMyDialog() {
MyDialogFragment d = MyDialogFragment.newInstance();
d.show(getFragmentManager(), "dialog");
}
This may be unique to the ActionBarSherlock Library, but the official samples in the SDK documentation use this paradigm also.

To overcome the Bundle always being null, I save it to a static field in onSaveInstanceState. It's a code smell, but the only solution I found for both restoring the dialog and saving the state.
The Bundle reference should be nulled in onDestroy.
#Override
public void onCreate(Bundle savedInstanceState)
{
if (savedInstanceState == null)
savedInstanceState = HackishSavedState.savedInstanceState;
setRetainInstance(true);
}
#Override
public Dialog onCreateDialog(Bundle savedInstanceState)
{
if (savedInstanceState == null)
savedInstanceState = HackishSavedState.savedInstanceState;
...
}
#Override
public void onDestroyView() // necessary for restoring the dialog
{
if (getDialog() != null && getRetainInstance())
getDialog().setOnDismissListener(null);
super.onDestroyView();
}
#Override
public void onSaveInstanceState(Bundle outState)
{
...
HackishSavedState.savedInstanceState = outState;
super.onSaveInstanceState(outState);
}
#Override
public void onDestroy()
{
HackishSavedState.savedInstanceState = null;
super.onDestroy();
}
private static class HackishSavedState
{
static Bundle savedInstanceState;
}

I used a mix of the presented solutions and added one more thing.
This is my final solution:
I used setRetainInstance(true) in the onCreateDialog;
I used this:
public void onDestroyView() {
if (getDialog() != null && getRetainInstance())
getDialog().setDismissMessage(null);
super.onDestroyView();
}
And as a workaround of the savedInstanceState not working, I created a private class called StateHolder (the same way a holder is create for a listView):
private class StateHolder {
String name;
String quantity;
}
I save the state this way:
#Override
public void onSaveInstanceState(Bundle savedInstanceState) {
super.onSaveInstanceState(savedInstanceState);
stateHolder = new StateHolder();
stateHolder.name = actvProductName.getText().toString();
stateHolder.quantity = etProductQuantity.getText().toString();
}
In the onDismiss method I set the stateHolder back to null. When the dialog is created, it verifies if the stateHolder isn't null to recover the state or just initialize everything normally.

I solved this issue with answers of #ZsomborErdődy-Nagy and #AndyDennie . You must subclass this class and in you parent fragment call setRetainInstance(true), and dialogFragment.show(getFragmentManager(), "Dialog");
public class AbstractDialogFragment extends DialogFragment {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setRetainInstance(true);
}
#Override
public void onDestroyView() {
if (getDialog() != null && getRetainInstance())
getDialog().setDismissMessage(null);
super.onDestroyView();
}
}

I had a similar issue, however none of the above worked for me. In the end I needed to create the fragment in code instead of in the XML layout.
See: Replacing fragments and orientation change

I ran into this on my project and none of the above solutions helped.
If the exception looks something like
java.lang.RuntimeException: Unable to start activity ComponentInfo{
...
Caused by: java.lang.IllegalStateException: Fragment....
did not create a view.
It's caused by an issue with a fallback container Id that gets used after rotation. See this ticket for more details:
https://code.google.com/p/android/issues/detail?id=18529
Basically you can prevent the crash by making sure all of your xml fragments have a tag defined in the layout. This prevents the fallback condition from occurring if you rotate when a fragment is visible.
In my case I was able to apply this fix without having to override onDestroyView() or setRetainInstance(true), which is the common recommendation for this situation.

I encountered this problem and the onDestroyView() trick wasn't working. It turned out that it was because I was doing some rather intensive dialog creation in onCreate(). This included saving a reference to the AlertDialog, which I would then return in onCreateDialog().
When I moved all of this code to onCreateDialog() and stopped retaining a reference to the dialog, it started working again. I expect I was violating one of the invariants DialogFragment has about managing its dialog.

In onCreate() call setRetainInstance(true) and then include this:
#Override
public void onDestroyView() {
if (getDialog() != null && getRetainInstance()) {
getDialog().setOnDismissMessage(null);
}
super.onDestroyView();
}
When you call setRetainInstance(true) in onCreate(), onCreate() will no longer be called across orientation changes, but onCreateView() will still be called.
So you can still save the state to your bundle in onSaveInstanceState() and then retrieve it in onCreateView():
#Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putInt("myInt", myInt);
}
#Override
public View onCreateView(LayoutInflater inflater,
ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.my_layout, container);
if (savedInstanceState != null) {
myInt = savedInstanceState.getInt("myInt");
}
...
return view;
}