Develop Reference

What is the best place to retrive ViewPager child's layout?

Good morning,
I have a Fragment which its layout has a ViewPager, I provide a custom PageAdapter to show two child layouts. One layout is to fill with personal data and another layout is to fill with Address data by the user. On my fragment I want to retrieve both layouts data and fill a object Pessoa(Person) with an attribute Endereco (Address). So far my ViewPager is working and both layout are displayed, however when I try to get the fields on both layouts, either on onCreateView or onResume fragment's method, using :
viewpager.getChildAt(0).findViewById(R.id.txt1)
I got an NullPointerException, but if I add an OnPageChangeListener this works, I not sure if it's the best approach. Is There a best place to retrieve a reference to the viewpager child's layout?
Ps. I don't want to use two other Fragments in order to display each of the layouts.
PageAdapter
public class ViewPagerCadastroPessoaAdapter extends PagerAdapter {
private Context context;
private int[] views = {R.layout.layout_cadastro_dados_pessoais,R.layout.layout_cadastro_endereco };
public ViewPagerCadastroPessoaAdapter(Context context) {
this.context = context;
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
LayoutInflater inflater = LayoutInflater.from(this.context);
View layout = inflater.inflate(views[position], container, false);
container.addView(layout, position);
return layout;
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
container.removeView((View) object);
}
#Override
public int getCount() {
return 2;
}
#Override
public CharSequence getPageTitle(int position) {
switch (position){
case 0:
return "Dados Pessoais";
case 1:
return "Endereço";
}
return super.getPageTitle(position);
}
#Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}}
ViewPager's holder Fragment
public class CadastroPessoaFragment extends Fragment {
private ViewPager viewPagerCadastroPessoa;
private TabLayout tabLayoutCadastroPessoa;
public CadastroPessoaFragment() {
}
public static CadastroPessoaFragment newInstance() {
return new CadastroPessoaFragment();
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View root = inflater.inflate(R.layout.fragment_cadastro_pessoa, container, false);
tabLayoutCadastroPessoa = root.findViewById(R.id.tabLayoutCadastroPessoa);
viewPagerCadastroPessoa = root.findViewById(R.id.viewPagerCadastroPessoa);
viewPagerCadastroPessoa.setOffscreenPageLimit(2);
viewPagerCadastroPessoa.setAdapter(new ViewPagerCadastroPessoaAdapter(getContext()));
tabLayoutCadastroPessoa.setupWithViewPager(viewPagerCadastroPessoa);
int cor = ContextCompat.getColor(getContext(), android.R.color.white);
tabLayoutCadastroPessoa.setTabTextColors(cor, cor);
//get a null pointer
viewPagerCadastroPessoa.getChildAt(0).findViewById(R.id.txt1);
viewPagerCadastroPessoa.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
#Override
public void onPageSelected(int position) {
//works fine
viewPagerCadastroPessoa.getChildAt(0).findViewById(R.id.txt1);
}
#Override
public void onPageScrollStateChanged(int state) {
}
});
return root;
}
#Override
public void onResume() {
super.onResume();
//get a null pointer
viewPagerCadastroPessoa.getChildAt(0).findViewById(R.id.txt1);
}
}
Thank you all in advance
UPDATE
According with
Anton Malyshev answer
The way Viewpager creates its pages is kind of "unsynchronized", so I used the following approach to solve my problem:
On my custom adapter I definied an interface with a single method onViewPagerReady(), as my Viewpager will always have only two pages, inside instantiateItem I check when position is 1 (once position starts with 0), if position == 1 I call the method onViewPagerReady that my fragment viewpager's holder implements, so inside this method I retrieve the layout of viewpager's children
public class ViewPagerCadastroPessoaAdapter extends PagerAdapter {
public interface ViewPagerObserver{
void onViewPagerReady();
}
private Context context;
private int[] views = {R.layout.layout_cadastro_dados_pessoais,R.layout.layout_cadastro_endereco };
private ViewPagerObserver observer;
public ViewPagerCadastroPessoaAdapter(Context context, ViewPagerObserver observer) {
this.context = context;
this.observer = observer;
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
LayoutInflater inflater = LayoutInflater.from(this.context);
View layout = inflater.inflate(views[position], container, false);
container.addView(layout, position);
if(position == 1){
observer.onViewPagerReady();
}
return layout;
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
container.removeView((View) object);
}
#Override
public int getCount() {
return 2;
}
#Override
public CharSequence getPageTitle(int position) {
switch (position){
case 0:
return "Dados Pessoais";
case 1:
return "Endereço";
}
return super.getPageTitle(position);
}
#Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}
}
Fragment Viewpager's Holder
#Override
public void onViewPagerReady() {
View rootCadastroDadosPessoais = viewPagerCadastroPessoa.getChildAt(0);
View rootCadastroEnderecos =viewPagerCadastroPessoa.getChildAt(1);
}
Thank you all.

Just wait until viewPagerCadastroPessoa.getChildCount() will be greater than 0. The pages in ViewPager are not created yet in onResume (they are created asynchronously).

android ViewPager starts at a wrong random location after reload

I am writing a simple view pager test app that loads a bunch of data from a website and creates pages to display them.
For the most part the displaying is pretty much all works. However, it falls apart when I load a new set of data to display. When I get a new set, it loads all the data perfectly well however, instead of starting from view 0 it starts at a random location. It could start at the end or somewhere in the middle.
I want all the data to load from page 1, like a book. If you load a new book the book should start from page 1 not a random page.
Reloading calls
I've tried using GotCampDetails() which sets the local variable in the class.
viewPager.setCurrentItem(0);
in my fragment but it doesn't work. Also called notifydatasetchanged() on my adapter, still didn't work.
What am I missing?
public class ViewPagerFragment extends Fragment implements WebReadResultsListener {
private ArrayList<HashMap<String, String>> campDetails;
CustomPagerAdapter adapter;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.camp_viewpager, container, false);
}
#Override
public void onViewCreated(View view, Bundle savedInstanceState) {
if (campDetails != null && ! campDetails.isEmpty()) {
ViewPager viewPager = (ViewPager) view.findViewById(R.id.viewpager);
adapter = new CustomPagerAdapter(getActivity(), campDetails, viewPager);
viewPager.setAdapter(adapter);
viewPager.setPageTransformer(true, new ZoomOutPageTransformer());
}
}
#Override
public boolean GotCampDetails(ArrayList<HashMap<String, String>> campDetails) {
this.campDetails = campDetails;
return true;
}
#Override
public boolean GotCampList(ArrayList<HashMap<String, String>> campDetails) {
return false;
}
#Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
getFragmentManager().putFragment(outState,"fragmentInstanceSaved",getFragmentManager().findFragmentById(R.id.content));
}
#Override
public void onConfigurationChanged(Configuration newConfig) {
super.onConfigurationChanged(newConfig);
// Handle orientation changes here
}
}
Adapter:
public class CustomPagerAdapter extends PagerAdapter implements ColorChangeListener {
private ArrayList<HashMap<String, String>> campDetails;
private ViewGroup collection;
private Context mContext;
private boolean isRunning = false;
private ColorChangeListener colorChangeListener;
private int color= pink;
private int currentposition;
private ViewPager viewPager;
public CustomPagerAdapter(Context context, final ArrayList<HashMap<String, String>> campDetails, ViewPager viewPager) {
this.campDetails=campDetails;
this.mContext = context;
this.viewPager = viewPager;
colorChangeListener = (ColorChangeListener) mContext;
viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
#Override
public void onPageSelected(int pos) {
currentposition = pos;
if (campDetails.get(currentposition).get("color").equals("green")) {
color = green;
} else {
color = pink;
}
ColorAppBar(color);
}
#Override
public void onPageScrolled(int arg0, float arg1, int arg2) {
}
#Override
public void onPageScrollStateChanged(int arg0) {
}
});
}
#Override
public Object instantiateItem(ViewGroup collection, final int position) {
LayoutInflater inflater = LayoutInflater.from(mContext);
ViewGroup layout = (ViewGroup) inflater.inflate(R.layout.child_item, collection, false);
if (campDetails.size() <= 0) {
Toast.makeText(mContext, "Error in getting camp details", Toast.LENGTH_SHORT).show();
return null;
}
if (campDetails.get(position).get("description").equals("RD") ) {
layout.setBackgroundColor(mContext.getResources().getColor(green));
} else {
layout.setBackgroundColor(mContext.getResources().getColor(pink));
}
collection.addView(layout);
this.collection = collection;
TextView eName = (TextView) layout.findViewById(R.id.en);
TextView nEName= (TextView) layout.findViewById(R.id.nen);
TextView textView6 = (TextView) layout.findViewById(R.id.textView6);
// ImageView nextImg = (ImageView) groupLayout.get(index).findViewById(R.id.nextImg);
eName.setText(campDetails.get(position).get("name"));
if (position+1 < campDetails.size()) {
nEName.setText(campDetails.get(position+1).get("name"));
textView6.setVisibility(View.VISIBLE);
} else {
nEName.setText("You are DONE!!");
textView6.setVisibility(View.INVISIBLE);
}
return layout;
}
#Override
public void destroyItem(ViewGroup collection, int position, Object view) {
collection.removeView((View) view);
}
#Override
public int getCount() {
return campDetails.size();
}
#Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}
#Override
public CharSequence getPageTitle(int position) {
return campDetails.get(position).get("name");
}
#Override
public void ColorAppBar(int color) {
colorChangeListener.ColorAppBar(color);
}
}

I finally managed to get it done.
I had to delay the function call setCurrentItem by a few milliseconds. Race condition? I don't know why this is the case but now it works perfectly.
Here is what I added in case someone else may find it useful:
pager.postDelayed(new Runnable() {
#Override
public void run() {
pager.setCurrentItem(pos);
}
}, 100);

I'm having trouble following the details well enough to pinpoint the problem, but this guy seems to have accomplished what you're trying to do: dynamically add and remove view to viewpager
hope it helps

OnPageChangeListener in ViewPager adapter?

I have a regular ViewPager with an adapter:
public class MyDialogFragment extends DialogFragment {
private ViewPager viewPager;
private MyViewPagerAdapter myViewPagerAdapter;
private City city;
public static MyDialogFragment newInstance() {
MyDialogFragment fragment = new MyDialogFragment();
return fragment;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_layout, container, false);
viewPager = (ViewPager) v.findViewById(R.id.viewPager);
city = Parcels.unwrap(getArguments().getParcelable("city"));
myViewPagerAdapter = new MyViewPagerAdapter(getContext());
viewPager.setAdapter(myViewPagerAdapter);
viewPager.addOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
#Override
public void onPageSelected(int position) {
// Page changed
}
});
return v;
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
public class MyViewPagerAdapter extends PagerAdapter {
private Context context;
private LayoutInflater layoutInflater;
public MyViewPagerAdapter(Context context) {
this.context = context;
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
layoutInflater = (LayoutInflater) getActivity().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View view = layoutInflater.inflate(R.layout.city_layout, container, false);
ImageView imageView = (ImageView) view.findViewById(R.id.cityImage);
Glide.with(context)
.load(city.getImage())
.into(imageView);
}
container.addView(view);
return view;
}
#Override
public int getCount() {
return city.size();
}
#Override
public boolean isViewFromObject(View view, Object obj) {
return view == ((View) obj);
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
container.removeView((View) object);
}
}
}
As you can see, I have a page change listener set on my ViewPager. But I need to be able to notify the adapter when the page has changed so that I can modify the adapter's ImageView. How can I do this?

Add a method to your adapter class
public class MyViewPagerAdapter extends PagerAdapter {
...
public void pageChanged(int position) {
// Do something
}
...
}
After that in your OnPageChangeListener use that method
#Override
public void onPageSelected(int position) {
myViewPagerAdapter.pageChanged(position);
}

One approach is to create a data structure in your adapter to map the pager view to its position. A SparseArray is most efficient:
private SparseArray<View> pageMap = new SparseArray<>();
Then in the adapter's instantiateItem() method, add the view to the SparseArray:
public Object instantiateItem(ViewGroup container, int position) {
...
pageMap.put(position, view);
...
}
Now in your OnPageChangeListener you can do the following:
#Override
public void onPageSelected(int position) {
View view = adapter.getView(pos);
if (view != null) {
ImageView iv = (ImageView) view.findViewById(R.id.your_image_view);
// You now have the image view
}
}
Make sure you remove views from the SparseArray in the adapter's destroyItem() method:
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
pageMap.remove(position);
...
}

You can use the constructor with imagelist to pass and that automatically called on next page..In your code will be modified like :::
ArrayList imageList=new ArrayList<>();
imageList.add("ImagePath here");
myViewPagerAdapter = new MyViewPagerAdapter(getContext(),imageList);
viewPager.setAdapter(myViewPagerAdapter);
Then your adapter will be like ::
public class MyViewPagerAdapter extends PagerAdapter {
private Context context;
private ArrayList<String> imageList
private LayoutInflater layoutInflater;
public MyViewPagerAdapter(Context context,ArrayList<String> imageList) {
this.context = context;
this.imageList = imageList;
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
layoutInflater = (LayoutInflater) getActivity().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View view = layoutInflater.inflate(R.layout.city_layout, container, false);
ImageView imageView = (ImageView) view.findViewById(R.id.cityImage);
Glide.with(context)
.load(imageList.get(position)) // This will be changes like
.into(imageView);
}
container.addView(view);
return view;
}
#Override
public int getCount() {
return city.size();
}
#Override
public boolean isViewFromObject(View view, Object obj) {
return view == ((View) obj);
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
container.removeView((View) object);
}
}
That done ..
After this, there are some suggestion that
- please use arraylist while using the viewpager ..
Now you just taking the parceble object from bundle..
you can do the same for the arraylist,
just receive the arraylist from the same bundle by passing the whole arraylist at once.
so you dont need to find the page change event..viewpager will automatically handle that..
Here's How to send & receiving the parceable arraylist
// while sending the list
Bundle bundle = new Bundle();
bundle.putParcelableArrayList("citylist", new ArrayList<City>());
// while receiving the list
ArrayList<City> citylist = getIntent().getParcelableArrayListExtra("citylist");
After this just get the all image and add in the imagelist array
for (int i = 0; i < citylist.size(); i++) {
imageList.add(citylist.get(i).getImage());
}
And pass this imageList in
myViewPagerAdapter = new MyViewPagerAdapter(getContext(),imageList);
viewPager.setAdapter(myViewPagerAdapter);
Tell me if needed more assitance.

Android ViewPager PagerAdapter contents without calling PagerAdapter#notifyDataSetChanged Exception

I have a ViewPager in my activity. The ViewPager shows different values on swiping the pager. But I get an IllegalStateException:
PagerAdapter changed the adapter's contents without calling PagerAdapter#notifyDataSetChanged!
Expected adapter item count: 0, found: 20
Pager id: com.exalt.vts:id/summarypager Pager class: class android.support.v4.view.ViewPager
Problematic adapter: class com.exalt.vts.DashBoard$MyPagerAdapter
This is my source code for PagerAdapter:
public class SamplePagerAdapter extends PagerAdapter{
List<View> pages = null;
public SamplePagerAdapter(List<View> pages){
this.pages = pages;
}
#Override
public Object instantiateItem(View collection, int position){
View v = pages.get(position);
((ViewPager) collection).addView(v, 0);
return v;
}
#Override
public void destroyItem(View collection, int position, Object view){
((ViewPager) collection).removeView((View) view);
}
#Override
public int getCount(){
return pages.size();
}
#Override
public boolean isViewFromObject(View view, Object object){
return view.equals(object);
}
#Override
public void finishUpdate(View arg0){
}
#Override
public void restoreState(Parcelable arg0, ClassLoader arg1){
}
#Override
public Parcelable saveState(){
return null;
}
#Override
public void startUpdate(View arg0){
}
}
This is the MainActivity:
public class MainActivity extends Activity {
ViewPager viewPager;
SamplePagerAdapter myPagerAdapter;
private TextView textView;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
List<View> pages = new ArrayList<View>();
viewPager = (ViewPager)findViewById(R.id.myviewpager);
myPagerAdapter = new SamplePagerAdapter(pages);
viewPager.setAdapter(myPagerAdapter);
viewPager.setCurrentItem(1);
LayoutInflater inflater = LayoutInflater.from(this);
View page = inflater.inflate(R.layout.mylayout, null);
for (int i = 0; i < 20; i++) {
page = inflater.inflate(R.layout.mylayout, null);
textView = (TextView) page.findViewById(R.id.text_view);
textView.setText("Страница "+i);
pages.add(page);
}
}
I try to add 20 views in my ViewPager but I get an exception.

You either need to move the following code from where it is currently to after your for loop, so that the adapter is set after your data set is setup
myPagerAdapter = new SamplePagerAdapter(pages);
viewPager.setAdapter(myPagerAdapter);
viewPager.setCurrentItem(1);
or alternatively, you can add the following after your for loop to notify the adapter that the data set has changed since you set it up
myPagerAdapter.notifyDataSetChanged();

How can i getCurrentView by position in a ViewPager?

I need getCurrentView by position in a ViewPager
This my ViewPagerAdapter
public class TutorialViewPagerAdapter extends ViewPagerAdapter {
private LayoutInflater mInflater;
private View view;
private List<Integer> views;
public TutorialViewPagerAdapter(Activity act, List<Integer> views) {
super(act, null);
this.views = views;
this.mInflater = LayoutInflater.from(this.activity);
}
#Override
public void destroyItem(View container, int arg1, Object view) {
((ViewPager) container).removeView((View) view);
}
#Override
public int getCount() {
return views.size();
}
#Override
public Object instantiateItem(ViewGroup collection, int position) {
int viewId = (Integer) views.get(position);
this.view = mInflater.inflate(viewId, null);
((ViewPager) collection).addView(view);
return view;
}
}
And this is my activity
public class Tutorial extends FragmentActivity implements
ViewPager.OnPageChangeListener {
private List<Integer> views;
private TutorialViewPagerAdapter viewPagerAdapter;
private ViewPager viewPager;
private CirclePageIndicator circlePageIndicator;
private int currentViewId;
private View currentView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.tutorial);
init();
}
private void init() {
views = new ArrayList<Integer>();
views.add(R.layout.tutorial_step_one);
views.add(R.layout.tutorial_step_two);
views.add(R.layout.tutorial_step_three);
views.add(R.layout.tutorial_step_four);
views.add(R.layout.tutorial_step_five);
viewPagerAdapter = new TutorialViewPagerAdapter(this, views);
viewPager = (ViewPager) findViewById(R.id.steps_view_pager);
circlePageIndicator = (CirclePageIndicator) findViewById(R.id.steps_indicator);
viewPager.setAdapter(viewPagerAdapter);
viewPager.setCurrentItem(0, false);
circlePageIndicator.setViewPager(viewPager);
circlePageIndicator.setCentered(true);
circlePageIndicator.setPadding(20, 20, 20, 20);
circlePageIndicator.notifyDataSetChanged();
circlePageIndicator.setCurrentItem(0);
viewPager.setOnPageChangeListener(this);
}
#Override
public void onPageScrollStateChanged(int state) {
int currentPosition = viewPager.getCurrentItem();
circlePageIndicator.setCurrentItem(currentPosition);
enableStep(currentPosition);
}
private void enableStep(int currentPosition) {
/*viewPagerAdapter.getItemPosition(object)
currentView = viewPager.getChildAt(viewPager.getRootView());
Log.d("DEBUG", currentView.toString() + " CURRENT VIEW");*/
}
#Override
public void onPageScrolled(int position, float positionOffset,
int positionOffsetPixels) {
}
#Override
public void onPageSelected(int position) {
}
}

You could add all your created views in instantiateItem to an ArrayList<View> and then make a public method for getting a view from the ArrayList with get(position). But be carefully, as soon the Activity is finished the views could be null

Instead of ViewPagerAdapter you can use FragmentPagerAdapter which will have getItem(int position) method by using which you can easily access view.
You can take a look at this post : Android Return back to same fragment after click on goto first fragment in view pager
Hope this help!!

It's moot point. What exactly You need? Current view or view by position. Imho it is different things.
Current view:
currentView = viewPager.getCurrentItem();
Or view by index (you pass wrong parameter - should be int):
currentView = viewPager.getChildAt(currentPosition);