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Android: call adapter directly in viewpager or call fragment per page?

this question is related with this one that I asked before.
I create a viewpager in MainActivity.java like this:
final ViewPager viewPager = (ViewPager) findViewById(R.id.vp_horizontal_ntb);
viewPager.setAdapter(new PagerAdapter() {
#Override
public int getCount() {
return 5;
}
#Override
public boolean isViewFromObject(final View view, final Object object) {
return view.equals(object);
}
#Override
public void destroyItem(final ViewGroup container, final int position, final Object object) {
((ViewPager) container).removeView((View) object);
}
#Override
public Object instantiateItem(final ViewGroup container, final int position) {
if(position==0) {
// here is important!
} else if(position == 1) {
}
...
}
});
Now I want fill each page with some json RecyclerView data list.(get json from network).
each page has independent data list.
For first time, I create a fragment for each page like this:
if (position == 0) {
final View view = LayoutInflater.from(getActivity().getBaseContext()).inflate(R.layout.fragment_tab0, null, false);
tabFragment.MyAdapter adapter = new tabFragment.MyAdapter(getActivity().getSupportFragmentManager());
adapter.addFragment(new tab0Fragment(), getResources().getString(R.string.tab0));
container.addView(view);
return view;
}
(so for 5 page, I have 5 fragment.
DEMO
But My application run slow (laggy) when I swipe pages.(with tap buttom is normal)
So I tried write an Adapter class directly for each page like this:
if (position == 0) {
final View view = LayoutInflater.from(getBaseContext()).inflate(R.layout.item_vp_list, null, false));
final RecyclerView recyclerView = (RecyclerView) view.findViewById(R.id.rv);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(getBaseContext(), LinearLayoutManager.VERTICAL, false));
recyclerView.setAdapter(new Tab0RecycleAdapter());
container.addView(view);
return view;
}
with top code,my application run fast again with swap pages!
Is it important to create fragment per each page?
why I must use fragment?(because some programmer recommended it in viewpager)
my method (second method without fragment) is true or false for a real application?
(I am noob and this is my first app)

Now I want fill each page with some json RecyclerView data list.(get json from network).
If you perform this network task on the UI thread, it will block and could cause laggy performance. This could be the reason your pages load slowly. You should perform network tasks on a separate thread.
So I tried write an Adapter class directly for each page like this
You only need one adapter per recycler view. If you want to support multiple views within the same adapter, override getItemViewType(). Example here: https://stackoverflow.com/a/26245463/7395923
Is it important to create fragment per each page?
Why I must use fragment? (because some programmer recommended it in view pager)
It is possible to use a view pager without fragments. Base on your previous question (linked at the top), it does seem overkill to load an entire fragment just to inflate a view. Here is a link to an example of a view pager without fragments: https://stackoverflow.com/a/18710626/7395923
I hope this helps.

Add fragment into listview item

I want to have a fragment for each item in a listview, because I want to separate some logic out. I am using a view holder for each item. If the view doesn't exist, I create a new fragment and add it into the container.
holder.mMyFragment = new MyFragment(mActivity, this);
mActivity.getSupportFragmentManager().beginTransaction().add(R.id.my_container, holder.mMyFragment).commit();
Also for each item, I call holder.mMyFragment.setUi(dataSource, position) to set UI of the fragment based on the data source and position.
The problem I'm having is I initialize the UI elements of fragment in onCreateView method of the fragment class, but it's not called when I add the fragment to the item. So later when I call setUi() which uses some UI elements in fragment it complains a NullPointerException. Does anyone have a suggestion? Thanks!

"THERE IS A SOLUTION" for this.
The issue is, you cannot add fragment directly to the container(FrameLayout) with same "id" in listview as you have done in the above code.
The trick is, create listview(Recyclerview) of "LinearLayout". Then dynamically create FrameLayout in adapter and assign different id's for each. Inflate Fragment to FrameLayout and this FrameLayout to LinearLayout.
#Override
protected void onBindBasicItemView(RecyclerView.ViewHolder holder, int position) {
if (holder instanceof VideoHomeViewHolder) {
VideoHomeViewHolder videoHomeViewHolder = (VideoHomeViewHolder) holder;
FrameLayout frameLayout = new FrameLayout(mContext);
frameLayout.setId(position+1); //since id cannot be zero
FragmentHelper.popBackStackAndReplace(mFragmentManager, frameLayout.getId(),
new ShowLatestVideosFragment(mShowLatestVideosItems.get(position)));
videoHomeViewHolder.linearLayout.addView(frameLayout);
}
}

I want to have a fragment for each item in a listview, because I want to separate some logic out.
You can't use fragment as list item views because the API doesn't allow you - View and Fragment aren't even related so there's no way you can use it like that. Make custom views and use adapter getViewTypeCount and getView to use different list item behavior.
Fragment are managed by Activity's FragmentManager or by other Fragments child FragmentManager; while list item views are managed by ListView & ListAdapter. You can use ListViews in Fragments, but not the other way around.

A simple way.
One problem:You should store add restore fragment state.
holder.mMyFragment = new MyFragment(mActivity, this);
int id = View.generateViewId();
findViewByTag("abc").setId(id);
mActivity.getSupportFragmentManager().beginTransaction().add(id, holder.mMyFragment).commit();

Hi I was facing the same problem and I found the way to do it.
My problem was similar to you:
"I want to have a fragment for each item in a listview, because I want to separate some logic out"
In my app I have to give the option to display custom items in vertical (listView) and horizontal (ViewPager) mode. Additionally I had to deal with 18 custom items and each one with different logic, so the best approach was reusing the fragments that I was using for ViewPager in ListView.
I got it but not in the way you were trying, I mean, I used my fragments like "ViewHolders":
Define fragment's widget like variables of class in each fragment.
Create a custom ArrayAdapter and override: getViewTypeCount(), getItemViewType(int position), getCount(), getItem(int position) getView(int position, View convertView, ViewGroup parent)
In getView I checked what kind of layout I needed before "inflate" the respective XML, create a fragment, assign widget from XML to fragment (with rootView.findViewById) and set "tag" with the new fragment.
What you can see at this point is that fragments in ListView never got attached to Activity but you got what you wanted: logic distributed in several parts and all benefits of ListView (reuse of rows, scroll, etc).
If you need I can post part of my code but you have to deal with "spanglish" ;).
UPDATED
All the problem is because when you create a Fragment to be used with ViewPager, usually all "layout and "setup" code is inside onCreateView method, I mean:
Get the view object you are going to use (View rootView = inflater.inflate(R.layout.fragment_question_horizontal_container, container, false);)
Get the widgets from above layout, define behaviors, fonts, etc: (answer = (EditText)rootView.findViewById(R.id.answer_question_text);)
Until this point there is nothing weird.
If you are going to use a fragment with the behavior described above you have to "emulate" the call to onCreateView, fill the data and attach it to the listView.
Here is the trick: split the code in onCreateView in some methods that doesn't care about who's calling them. An example of my onCreateView:
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_pregunta_horizontal_container, container, false);
addAnswerLayout(rootView, R.layout.fragment_pregunta_texto, getActivity());
setUpComponents(rootView);
//those 2 methods are about my app logic so I'm not going to talk much about them
setUpQuestionState(savedInstanceState);
readSavedAnswer();
return rootView;
}
public void addAnswerLayout(View rootView, int optionId, Context context) {
mContext = context;
RelativeLayout relativeLayout = (RelativeLayout)rootView.findViewById(R.id.pregunta_container);
LayoutInflater inflater = ((Activity)mContext).getLayoutInflater();
View newView = inflater.inflate(optionId, relativeLayout, false);
relativeLayout.addView(newView);
}
public void setUpComponents(View rootView) {
//next line: some heritage that you can ignore
super.setUpComponents(rootView);
respuesta = (EditText)rootView.findViewById(R.id.pregunta_respuesta_texto);
respuesta.setTypeface(UiHelper.getInstance(getActivity()).typeface);
respuesta.setTextColor(mContext.getResources().getColor(R.color.drs_gris));
...
}
Now let's go to the CustomArrayAdapter for list view:
Define your customArrayAdapter something like this: PreguntasVerticalArrayAdapter extends ArrayAdapter<Pregunta> where "Pregunta" is a generic Fragment with the logic from above.
Override getViewTypeCount(), getItemViewType(int position), getCount(), getItem(int position) getView(int position, View convertView, ViewGroup parent).
The getView follow the same behavior: get the object for the given position in params, reuse a "viewholder" and fill the data. Here my getView:
#Override
public View getView(int position, View convertView, ViewGroup parent) {
View rowView = convertView;
Pregunta pregunta = mData.get(position);
if (rowView == null)
rowView = createQuestionUI(pregunta, parent, position);
fillDataInRow((PreguntaUI)rowView.getTag(), pregunta, position);
return rowView;
}
private View createPreguntaUI(Pregunta pregunta, ViewGroup parent, int position) {
View rootView = null;
LayoutInflater inflater = (mPreguntasVerticalFragment.getActivity()).getLayoutInflater();
//you can ignore this part of the code ralted to Bundle.
Bundle args = new Bundle();
args.putLong(PreguntaUI.PREGUNTAUI_ID, pregunta.getIdpregunta());
args.putInt(PreguntaUI.PREGUNTAUI_INDEX, position);
args.putInt(PreguntaUI.PREGUNTAUI_TOTAL_QUESTIONS, getCount());
//internal method of "pregunta" to know what kind of question it is.
String tipo = pregunta.getTipo();
if (tipo.equalsIgnoreCase(PreguntaType.TEXT.toString())) {
rootView = inflater.inflate(R.layout.fragment_pregunta_vertical_container, parent, false);
Pregunta_texto pregunta_texto = new Pregunta_texto();
pregunta_texto.setArguments(args);
//LOOK AT THIS POINT!!!: I'm calling the same methods that I called in onCreateView fragment's method.
pregunta_texto.addAnswerLayout(rootView, R.layout.fragment_pregunta_texto,
mPreguntasVerticalFragment.getActivity());
pregunta_texto.setUpComponents(rootView);
pregunta_texto.setUpQuestionState(null);
pregunta_texto.readSavedAnswer();
//I'm adding the fragment to reuse it when I can
rootView.setTag(pregunta_texto);
}
else if ...
return rootView;
}
That is all... at this point, if you have enough experience dealing with CustomArrayAdapters and Fragments you probably got it! :D

From the Android Documentation : "A Fragment represents a behavior or a portion of user interface in an Activity. You can combine multiple fragments in a single activity to build a multi-pane UI and reuse a fragment in multiple activities."
For your activity, do you want to add 2 fragments where the first one displays a listView (= ListFragment and the other one is in the right and is shown only when the user clicks on an item (from the first fragment or listView) ?

Instead of using ListFragment, you can use RecyclerView, Android has documentation on that:
https://developer.android.com/training/basics/fragments/creating.html#AddInLayout

Some confusion on the method instantiateItem(ViewGroup container, int position) of PagerAdapter

public Object instantiateItem(ViewGroup container, int position) {
ImageView view = new ImageView();
container.addView(view);
return view;
}
I read some example code of PagerAdapter, and they all write the addview method. This above is some simple code, And I know 'return view' is used for return the view for display, But what is the
container.addView(view)
do?

Adding the view to the container is actually what makes it appear on-screen. The object returned by instantiateItem is just a key/identifier; it just so happens that using the actual view for this purpose tends to be convenient if you aren't using something like a Fragment to manage the view for the page. (See the source for FragmentPagerAdapter for an example.)
The PagerAdapter method isViewFromObject helps the pager know which view belongs to which key. If you're just returning the view as the key object, you can implement this method trivially as:
public boolean isViewFromObject(View view, Object object) {
return view == object;
}

As per comments include in Source Code of PageAdapter
public abstract Object instantiateItem(View container, int position);
Create the page for the given position. The adapter is responsible
for adding the view to the container given here, although it only
must ensure this is done by the time it returns from
Container The containing View in which the page will be shown.
Position The page position to be instantiated.
Returns an Object representing the new page.This does not need to
be a View, but can be some other container of the page.

Can I set viewpager's item width?

I hope I can show 3 items in a page of viewpager, but now I only could set viewpager's padding value and margin value, so it only show one item in a page of viewpager. How can I set the item width? I think if I can set more little width of item, the viewpager will show more items in a page.

Quick Answer
What you want is overriding getPageWidth in the PagerAdapter implementation you made for that ViewPager.
For example setting it to 0.8f will make a single page cover only 80% of the viewpagers width so that part of the next and/or previous pages are visible.
#Override
public float getPageWidth(final int position) {
return 0.8f;
}
More information at https://developer.android.com/reference/android/support/v4/view/PagerAdapter.html#getPageWidth(int)
Other remarks
Also note that the negative margins will only cause the separate pages to overlap each other. The margin is used to define the space between each page.
If no alternative pageWidth is configured (there is no setter, only the override) it will cover 100% by default making no part of the other pages visible unless dragged.
Code example
A very nice overview of what is possible can be found here https://commonsware.com/blog/2012/08/20/multiple-view-viewpager-options.html
The view pager in your layout
<android.support.v4.view.ViewPager
android:id="#+id/viewpager"
android:layout_width="match_parent"
android:layout_height="match_parent">
</android.support.v4.view.ViewPager>
Example of an inline configured Adapter implementation, this would go in the onCreate or onViewCreated methods:
// get a reference to the viewpager in your layout
ViewPager mViewPager = (ViewPager) findViewById(R.id.viewpager);
// this margin defines the space between the pages in the viewpager mViewPager.setPageMargin(context.getResources().getDimensionPixelSize(R.dimen.margin_normal));
// setting the adapter on the viewpager, this could/should be a proper Adapter implementation in it's own class file instead
mViewPager.setAdapter(new PagerAdapter() {
// just example data to show, 3 pages
String[] titles = {"Eins", "Zwei", "Drei"};
int[] layouts = {R.layout.layout1, R.layout.layout2, R.layout.layout3};
#Override
public Object instantiateItem(ViewGroup container, int position) {
LayoutInflater inflater = LayoutInflater.from(MainActivity.this);
// here you can inflate your own view and dress up
ViewGroup layout = (ViewGroup) inflater.inflate(layouts[position], container, false);
container.addView(layout);
return layout;
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
container.removeView((View)object);
}
#Override
public float getPageWidth(final int position) {
return 0.8f;
}
#Override
public CharSequence getPageTitle(int position) {
return titles[position];
}
#Override
public int getCount() {
return layouts.length;
}
#Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}
});
Example code based on https://newfivefour.com/android-viewpager-simple-views.html

Have you tried setting the page margins to a negative value, see setPageMargin(int)? If I remember correctly, I read someone realizing something similar to what you're describing that way.
Alternatively, you could have a look at using a Gallery in stead, although I have to admit I'm not a big fan of them as they seem to be less flexible and more buggy.

Android: Viewpager and FragmentStatePageAdapter

I'm designing an app that allows users to flip between multiple pages in a ViewPager. I've been struggling trying to figure out how it is possible to remove a Fragment instance from a page when it is no longer visible on screen, cache it (to, say, a HashMap), and then restore it so that when the user flips back to that page, the views and everything else in it will be in the same state it was before removal. For example, my first page is a login screen that makes certain layout elements on that particular page visible/invisible on a successful login. When I flip forward enough pages then flip back to the first page, the layout is reset. This becomes more of a problem for another one of my pages which contains a huge, horizontal/vertical scrolling grid of data that I use a thread in the background to draw when it initializes. I use a progress dialog to notify the user of loading progress and that becomes really annoying everytime I have to load it.
So I did some research...
I browsed through the source code for FragmentStatePageAdapter and in the destroyItem() callback, the state of the Fragment instance being removed is saved to an ArrayList. When a new instance of the Fragment is being created in the instantiateItem() callback, if an instance of an item doesn't already exist (they keep track of this by using an ArrayList), a new Fragment instance is created and its saved state is initialized with the corresponding Fragment.SavedState data. Unfortunately, this data does not include the state that the Views were in although I noticed that for pages with a GridView/ListView, the state of the Views were somehow restored (if I scrolled to some random position, flipped a few pages and came back, it would not be reset).
According to the API:
The saved state can not contain dependencies on other fragments --
that is it can't use putFragment(Bundle, String, Fragment) to store a
fragment reference because that reference may not be valid when this
saved state is later used. Likewise the Fragment's target and result
code are not included in this state.
Being a noob to Android, I'm not quite sure I understand the last statement.
That being said, is there any way to cache View state? If not, I think I'll just go ahead and go with leaving all the fragment pages in memory.

I had the same problem problem and solved it by implementing these two functions
public void onSaveInstanceState (Bundle outState)
public void onActivityCreated (Bundle savedInstanceState)
on the fragments that I wanted to save. On the first function, you should save in the Bundle the date that you need to restore the views ( in my case I had a bunch of spinner so I used
an int array to save their positions). The second function, which is called when restoring your fragment, is where you implement the restoring process.
I hope this helps. I also made my adapter to inherit from FragmentStatePageAdapter but I am not sure that this is mandatory.

Listing of main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="fill_parent"
android:layout_height="fill_parent">
<TextView android:text="Page 1" android:id="#+id/textViewHeader"
android:layout_width="fill_parent" android:layout_height="wrap_content"
android:gravity="center" android:padding="10dip" android:textStyle="bold"></TextView>
<android.support.v4.view.ViewPager
android:layout_width="fill_parent" android:layout_height="fill_parent"
android:id="#+id/viewPager" />
</LinearLayout>
Setting up the ViewPager
ViewPager viewPager = (ViewPager) findViewById(R.id.viewPager);
MyPagerAdapter adapter = new MyPagerAdapter(this);
viewPager.setAdapter(adapter);
The PagerAdapter
#Override
public void destroyItem(View view, int arg1, Object object) {
((ViewPager) view).removeView((View)object);
}
#Override
public int getCount() {
return views.size();
}
#Override
public Object instantiateItem(View view, int position) {
View view = views.get(position);
((ViewPager) view).addView(view);
return view;
}
#Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}
look here for more details view pager example

Looking at the various documentation pieces, my best guess is that the views you are creating do not have an ID attached to them. Assuming that the fragment's saved state is created from Fragment.onSaveInstanceState, then the fragment will automatically save any view's state that has an id. You probably have a default id associated with your ListView/GridView if you created them from a layout file. You can also associate an id with the views by calling setId.
Also, for your custom filled fragment, you may also have to do something custom in onSaveInstanceState.

Here's an example of how I implemented caching in PagerAdapter. After filling the cache all future view requests are served from cache, only data is replaced.
public class TestPageAdapter extends PagerAdapter{
private int MAX_SIZE = 3;
private ArrayList<SoftReference<View>> pageCache = new ArrayList<SoftReference<View>>(3);
public TestPageAdapter(Context context){
// do some initialization
}
#Override
public int getCount() {
// number of pages
}
private void addToCache(View view){
if (pageCache.size() < MAX_SIZE){
pageCache.add(new SoftReference<View>(view));
} else {
for(int n = (pageCache.size()-1); n >= 0; n--) {
SoftReference<View> cachedView = pageCache.get(n);
if (cachedView.get() == null){
pageCache.set(n, new SoftReference<View>(view));
return;
}
}
}
}
private View fetchFromCache(){
for(int n = (pageCache.size()-1); n>= 0; n--) {
SoftReference<View> reference = pageCache.remove(n);
View view = reference.get();
if (view != null) {
return view;
}
}
return null;
}
#Override
public Object instantiateItem(View collection, int position) {
View view = fetchFromCache();
if (view == null) {
// not in cache, inflate manually
LayoutInflater inflater = (LayoutInflater) collection.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
view = inflater.inflate(R.layout.page, null);
}
setData(view, position);
((ViewPager) collection).addView(view, 0);
return view;
}
private void setData(View view, int position){
// set page data (images, text ....)
}
public void setPrimaryItem(ViewGroup container, int position, Object object) {
currentItem = (View)object;
}
public View getCurrentItem() {
return currentItem;
}
#Override
public boolean isViewFromObject(View view, Object object) {
return view == ((View) object);
}
#Override
public void destroyItem(View collection, int arg1, Object view) {
((ViewPager) collection).removeView((View) view);
addToCache((View) view);
}
}

I also ran into this problem when I was using PagerSlidingTabStrip and using and instance of FragmentPagerAdapter, switching to FragmentStatePagerAdapter definitely worked.
Then I use onSaveInstanceState() to save sate