This one is driving me nuts. Basically, I want to create a ViewPager and add a few Fragments to it. Then, all I want to do, it set a value in one of the Fragment's TextViews. I can add the Fragments fine, and they attach, but when I go to findViewById() for one of the TextViews in the first Fragment it throws a NullPointerException. I, for the life of me, can't figure out why.
Here's my code so far, let me know if more is needed please.
public class SheetActivity extends FragmentActivity {
// /////////////////////////////////////////////////////////////////////////
// Variable Declaration
// /////////////////////////////////////////////////////////////////////////
private ViewPager viewPager;
private PagerTitleStrip titleStrip;
private String type;
private FragmentPagerAdapter fragmentPager; //UPDATE
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_sheet);
viewPager = (ViewPager) findViewById(R.id.viewPager);
titleStrip = (PagerTitleStrip) findViewById(R.id.viewPagerTitleStrip);
// Determine which type of sheet to create
Intent intent = getIntent();
this.type = intent.getStringExtra("type");
FragmentManager manager = getSupportFragmentManager();
switch (type) {
case "1":
viewPager.setAdapter(new InstallAdapter(manager));
break;
case "2":
viewPager.setAdapter(new InstallAdapter(manager));
break;
}
fragmentPager = (FragmentPagerAdapter) viewPager.getAdapter(); //UPDATE
}
#Override
public void onResume() {
super.onResume();
fragmentPager.getItem(0).setText("something"); //UPDATE
}
class MyAdapter extends FragmentPagerAdapter {
private final String[] TITLES = { "Title1", "Title2" };
private final int PAGE_COUNT = TITLES.length;
private ArrayList<Fragment> FRAGMENTS = null;
public MyAdapter(FragmentManager fm) {
super(fm);
FRAGMENTS = new ArrayList<Fragment>();
FRAGMENTS.add(new FragmentA());
FRAGMENTS.add(new FragmentB());
}
#Override
public Fragment getItem(int pos) {
return FRAGMENTS.get(pos);
}
#Override
public int getCount() {
return PAGE_COUNT;
}
#Override
public CharSequence getPageTitle(int pos) {
return TITLES[pos];
}
}
}
All of Fragments I created only have the onCreateView() method overridden so I can display the proper XML layout. Other than that they are 'stock'. Why can't I interact with elements in any of the Fragments?
UPDATE:
So do something like this?
public class FragmentA extends Fragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle inState) {
return inflater.inflate(R.layout.fragment_a, container, false);
}
public void setText(String text) {
TextView t = (TextView) getView().findViewById(R.id.someTextView); //UPDATE
t.setText(text);
}
}
XML LAYOUT FOR FRAGMENT A
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >
<TextView
android:id="#+id/someTextView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:textSize="22sp" />
</LinearLayout>
The TextView is located in the fragments layout, not in the ViewPagers or the PagerAdapter, that is causing the NPE. Now, you have 2 options.
The first is the easiest, you should simple move your code for changing the text into the corresponding fragment's class, FragmentA in this case.
Secondly, you could make the TextView into FragmentA static, so it can be accessed by other classes. So your code would look something like this:
....
TextView myText;
#Override
public View onCreateView(....) {
myLayout = ....;
myText = myLayout.findViewById(yourID);
....
}
And then you would change the text from somewhere else (if it's really necessary):
FragmentA.myText.setText("new text");
Explaining method 2
Use the following in your Fragment.
public static void setText(String text) {
TextView t = (TextView) getView().findViewById(R.id.someTextView);
t.setText(text);
}
Then change the text like:
FragmentA.setText("Lulz");
Unless you are planning to change the value at runtime, you can pass the value into the fragment as a parameter. It is done my using a Bundle and passing it as args into a Fragment, which then retrieves it from it's args. More info here. If you implement this, your instantiation of new Fragments might look something like this:
public InstallAdapter(FragmentManager fm) {
super(fm);
FRAGMENTS = new ArrayList<Fragment>();
FRAGMENTS.add(FragmentA.newInstance("<text to set to the TextView>"));
FRAGMENTS.add(FragmentB.newInstance("<text to set to the TextView>"));
}
If, however, you are planning to update the value at runtime (it will change as user is running the app), then you want to use an Interface to channell communication between your fragment and your activity. Info here. This is what it might look like:
//Declare your values for activity;
ISetTextInFragment setText;
ISetTextInFragment setText2;
...
//Add interface
public interface ISetTextInFragment{
public abstract void showText(String testToShow);
}
...
//your new InstallAdapter
public InstallAdapter(FragmentManager fm) {
super(fm);
FRAGMENTS = new ArrayList<Fragment>();
Fragment fragA = new FragmentA();
setText= (ISetTextInFragment)fragA;
FRAGMENTS.add(fragA);
Fragment fragB = new FragmentB();
setText2= (ISetTextInFragment)fragB;
FRAGMENTS.add(fragB);
}
//then, you can do this from your activity:
...
setText.showText("text to show");
...
and it will update your text view in the fragment.
While it can be done "more easily", these methods are recomended because they reduce chances of bugs and make code a lot more readable and maintainable.
EDIT: this is what your Fragment should look like (modified your code):
public class FragmentA extends Fragment implements ISetTextInFragment {
TextView myTextView;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle inState) {
View v = inflater.inflate(R.layout.fragment_a, container, false);
myTextView = (TextView)v.findViewbyId(R.id.someTextView)
return v;
}
#Override
public void showText(String text) {
myTextView.setText(text);
}
}
If after that you are still getting a null pointer exception, your TextView is NOT located where it needs to me, namely in the R.layout.fragment_a filem, and it needs to be located there. Unless you are calling the interface method BEFORE the fragment finished loading, of course.
This line:
TextView t = (TextView) findViewById(R.id.someTextViewInFragmentA);
is looking for the view in your ParentActivity. Of course it wont find it and that's when you get your NPE.
Try something like this:
Add a "tag" to your fragments when you add them
Use someFragment = getSupportFragmentManager().findFragmentByTag("your_fragment_tag")
Get the view of the fragment
fragmentView = someFragment.getView();
And finally find your TextView and set the text
TextView t = (TextView) fragmentView.findViewById(R.id.someTextViewInFragmentA);
t.setText("some text");
How about to change this line
TextView t = (TextView) getView().findViewById(R.id.someTextView); //UPDATE
to
TextView t = (TextView) getActivity().findViewById(R.id.someTextView); //UPDATE
then you can try to update "t" with .setText("some_string") inside "SheetActivity".
Related
I have a tablayout (with 3 tabs) with viewpager and fragments.
I m trying to send the parsed Json data from MainActivity( When searchview data submitted ) to show in the textview of tabs fragments
See this Image link
The data is succesfully parsing but textview with data(in first tab) is not showing unless scrolled to 3rd tab
//Passing data from MainActivity
public String getMyData() {
return meaning;
}
//Setting value to textview from Fragment
#Override
public View onCreateView(#NonNull LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View v=inflater.inflate(R.layout.fragment_meaning, container, false);
MainActivity mainActivity= (MainActivity) getActivity();
assert mainActivity != null;
String data= mainActivity.getMyData();
TextView textView=v.findViewById(R.id.textVIew);
textView.setText(data);
return v;
}
Want to able to show data changes instantly as it is parsed, instead of scrolling to 3rd tab to see changes
Here are some steps that might help you.
On the ViewPager adaptor you have created, make the fragment objects. like below
FragmentOne fragOne; // this should be global
On the viewPager adaptor, do some thing like this,
fragOne = new FragmentOne() // whatever your implementation is.
Then after fetching the data from the server,
if ( fragOne != null ) {
fragOne.setValueOnView( " your data to be passed" );
}
and on the FragmentOne, create a function called setValueOnView
void setValueOnView(String yourString) {
v.findViewById(R.id.textVIew).setText(yourString);
}
And one more thing, while initializing the fragment onCreateView, create an object of View
View v; // global variable
#Override
public View onCreateView(#NonNull LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
v=inflater.inflate(R.layout.fragment_meaning, container, false);
Use this approach for other fragments as well
Inside getItem() method in ViewPager class use Fragment constructors with String parameter
#Override
public Fragment getItem(int position) {
switch (position) {
case 0:
FragmentOne tab1 = new FragmentOne("string parameter");
return tab1;
case 1:
FragmentTwo tab2 = new FragmentTwo("string parameter");
return tab2;
case 2:
FragmentThree tab3 = new FragmentThree("string parameter");
return tab3;
default:
return null;
}
}
Inside your Fragment:
public FragmentOne(String stringParameter) {
yourLocalVariable = stringParameter; // yourLocalVariable is declared inside Fragment class;
//now you can setText() for your TextView inside onViewCreated()
}
Of course you pass your String from MainActivity to ViewPager like you did earlier.
Use Observer
public class FragmentObserver extends Observable {
#Override
public void notifyObservers() {
setChanged(); // Set the changed flag to true, otherwise observers won't be notified.
super.notifyObservers();
}
}
Activity:
public class MyActivity extends Activity {
private MyAdapter mPagerAdapter;
#Override
public void onCreate(Bundle savedInstanceState) {
setContentView(R.layout.my_activity);
ViewPager pager = (ViewPager) findViewById(R.id.pager);
mPagerAdapter = new MyAdapter();
pager.setAdapter(mPagerAdapter);
}
private void updateFragments() {
mPagerAdapter.updateFragments();
}
}
Viewpager adapter
public class MyAdapter extends FragmentPagerAdapter {
private Observable mObservers = new FragmentObserver();
public MyAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
mObservers.deleteObservers(); // Clear existing observers.
Fragment fragment = new MyFragment();
if(fragment instanceof Observer)
mObservers.addObserver((Observer) fragment);
return fragment;
}
public void updateFragments() {
mObservers.notifyObservers();
}
}
Your Fragment
public class MyFragment extends Fragment implements Observer {
/* Fragment related stuff... */
#Override
public void update(Observable observable, Object data) {
View root = getView();
// Update your views here.
}
}
You will get data to update method even your fragment already loaded
I have a viewPager with say 4 pages. All 4 pages uses same Xml. When i do an event in 1st page somehow it always triggers in the last page.
Here is my PagerAdapter
#Override
public Object instantiateItem(ViewGroup container, int pos) {
View desktopView;
OnTouchListener tl = null;
desktopView = act.getLayoutInflater().inflate(
act.getViewPagerLayout(groupName), null);
RelativeLayout rr_appContainer, rr_dialogContainer;
ImageView rr_home_container = (ImageView) desktopView
.findViewById(R.id.imageView_forClick);
Button buttonChange = (Button)desktopView.findViewById(R.id.B1);
Button buttonDelete = (Button)desktopView.findViewById(R.id.B2);
rr_appContainer = (RelativeLayout) desktopView
.findViewById(R.id.rr_home_container);
rr_dialogContainer = (RelativeLayout) desktopView
.findViewById(R.id.rr_dialogView);
..........
buttonDelete.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
deletestuff();
}
buttonChange.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
changeColorOfStuff();
}
.....
return desktopView;
}
What is happening is, When i click on buttonChange from 1st page it supposed to change the color of text on 1st page, but actually it is changing color of the last page. Similarly buttonDelete is deleting color from last page.
Regardless of what page i am in, its reflecting those changes on last page.
Any help would be appreciated.
From the context given here, the deleteStuff() and changeColorOfStuff() can only be members of the Fragment/Activity that owns the adapter, or the adapter itself. So these methods can only act on members of those classes. ViewPager asks the adapter for the fragments it is going to display. However, the text in the fragment being shown by the ViewPager belong to the that fragment. To act on that text, you need a method that's a member of that fragment. The usual way to do this is to use a custom fragment. For example:
Custom Fragment (inner class):
public static class CustomFragment extends Fragment {
//members of the fragment
TextView yourTextView;
...
public static CustomFragment newInstance(int pos) {
CustomFragment fragment = new CustomFragment();
//get whatever info you need for this page
Bundle args = getInfoSomehow(pos);
fragment.setArguments(args)
return fragment;
}
#Override
public View onCreateView(Layout inflater, ViewGroup container, Bundle savedInstanceState) {
View root = inflater.inflate(....
yourTextView = root.findViewById(...) //this is the text view you want to change things in
//all the stuff you're currently doing in instantiateItem()
return root;
}
private void deleteStuff() {
//whatever you need to do. But notice that here it's acting on the TextView that belongs to this particular fragment
}
private void changeColorOfStuff() {...}
...
}
Then in your instantiateItem(...)
#Override
public Object instantiateItem(ViewGroup container, int pos) {
return CustomFragment.newInstance(pos);
}
I've been seeing some strange behavior with my ViewPager along with my own FragmentStatePagerAdapter.
My View hierarchy goes like this:
-> (1) Fragment root view (RelativeLayout)
-> (2) ViewPager
-> (3) ViewPager's current fragment view
When the Fragment that is responsible for the Fragment root view (1) gets hidden (using .hide() in a fragment transaction) and then shown (with .show()), the fragment view that was currently showing in the ViewPager (3) becomes null, although the fragment still exists. Basically, my ViewPager becomes completely blank/transparent.
The only way I have found to fix this is to call
int current = myViewPager.getCurrentItem();
myViewPager.setAdapter(myAdapter);
myViewPager.setCurrentItem(current);
after the parent fragment is shown. This somehow triggers the views to be recreated and appear on screen. Unfortunately, this occasionally causes exceptions dealing with the pager adapter calling unregisterDataSetObserver() twice on an old observer.
Is there a better way to do this? I guess what I am asking is:
Why are my fragment views inside my ViewPager getting destroyed when the parent fragment of the ViewPager is hidden?
Update: this also happens when the application is "minimized" and then "restored" (by pressing the home action key and then returning).
Per request, here's my pager adapter class:
public class MyInfoSlidePagerAdapter extends FragmentStatePagerAdapter {
private ArrayList<MyInfo> infos = new ArrayList<MyInfo>();
public MyInfoSlidePagerAdapter (FragmentManager fm) {
super(fm);
}
public MyInfoSlidePagerAdapter (FragmentManager fm, MyInfo[] newInfos) {
super(fm);
setInfos(newInfos);
}
#Override
public int getItemPosition(Object object) {
int position = infos.indexOf(((MyInfoDetailsFragment)object).getMyInfo());
return position > 0 ? position : POSITION_NONE;
}
#Override
public CharSequence getPageTitle(int position) {
return infos.get(position).getName();
}
#Override
public Fragment getItem(int i) {
return infos.size() > 0 ? MyInfoDetailsFragment.getNewInstance(infos.get(i)) : null;
}
#Override
public int getCount() {
return infos.size();
}
public Location getMyInfoAtPosition(int i) {
return infos.get(i);
}
public void setInfos(MyInfo[] newInfos) {
infos = new ArrayList<MyInfo>(Arrays.asList(newInfos));
}
public int getPositionOfMyInfo(MyInfo info) {
return infos.indexOf(info);
}
}
I've renamed some variables but other than that it is exactly what I have.
You're not providing enough info for your specific issue, so I built a sample project that tries to reproduce your issue: the app has an activity that holds a fragment (PagerFragment) within a relative layout and below this layout I have a button that hides & shows above PagerFragment. PagerFragment has a ViewPager and each fragment within pager adapter simply displays a label - this fragment is named DataFragment. The label list is created in parent activity and passed to PagerFragment and then through its adapter to each DataFragment. Changing the PagerFragment visibility is done with no issues and each time it's becoming visible again it shows the previous shown label.
The key of the issue:
Use Fragment#getChildFragmentManager() when you're creating the viewpager adapter and not getFragmentManager!
Maybe you can compare this simple project with what you have and check where are the differences. So here goes (top-down):
PagerActivity (the only activity in the project):
public class PagerActivity extends FragmentActivity {
private static final String PAGER_TAG = "PagerActivity.PAGER_TAG";
#Override
protected void onCreate(Bundle savedInstance) {
super.onCreate(savedInstance);
setContentView(R.layout.pager_activity);
if (savedInstance == null) {
PagerFragment frag = PagerFragment.newInstance(buildPagerData());
FragmentManager fm = getSupportFragmentManager();
fm.beginTransaction().add(R.id.layout_fragments, frag, PAGER_TAG).commit();
}
findViewById(R.id.btnFragments).setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
changeFragmentVisibility();
}
});
}
private List<String> buildPagerData() {
ArrayList<String> pagerData = new ArrayList<String>();
pagerData.add("Robert de Niro");
pagerData.add("John Smith");
pagerData.add("Valerie Irons");
pagerData.add("Metallica");
pagerData.add("Rammstein");
pagerData.add("Zinedine Zidane");
pagerData.add("Ronaldo da Lima");
return pagerData;
}
protected void changeFragmentVisibility() {
Fragment frag = getSupportFragmentManager().findFragmentByTag(PAGER_TAG);
if (frag == null) {
Toast.makeText(this, "No PAGER fragment found", Toast.LENGTH_SHORT).show();
return;
}
boolean visible = frag.isVisible();
Log.d("APSampler", "Pager fragment visibility: " + visible);
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
if (visible) {
ft.hide(frag);
} else {
ft.show(frag);
}
ft.commit();
getSupportFragmentManager().executePendingTransactions();
}
}
its layout file pager_activity.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="4dp" >
<Button
android:id="#+id/btnFragments"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:text="Hide/Show fragments" />
<RelativeLayout
android:id="#+id/layout_fragments"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_above="#+id/btnFragments"
android:layout_marginBottom="4dp" >
</RelativeLayout>
</RelativeLayout>
Observe that I am adding the PagerFragment when the activity is first shown - and the PagerFragment class:
public class PagerFragment extends Fragment {
private static final String DATA_ARGS_KEY = "PagerFragment.DATA_ARGS_KEY";
private List<String> data;
private ViewPager pagerData;
public static PagerFragment newInstance(List<String> data) {
PagerFragment pagerFragment = new PagerFragment();
Bundle args = new Bundle();
ArrayList<String> argsValue = new ArrayList<String>(data);
args.putStringArrayList(DATA_ARGS_KEY, argsValue);
pagerFragment.setArguments(args);
return pagerFragment;
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
data = getArguments().getStringArrayList(DATA_ARGS_KEY);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.pager_fragment, container, false);
}
#Override
public void onViewCreated(View view, Bundle savedInstanceState) {
pagerData = (ViewPager) view.findViewById(R.id.pager_data);
setupPagerData();
}
private void setupPagerData() {
PagerAdapter adapter = new LocalPagerAdapter(getChildFragmentManager(), data);
pagerData.setAdapter(adapter);
}
}
its layout (only the ViewPager that takes full size):
<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/pager_data"
android:layout_width="match_parent"
android:layout_height="match_parent" />
and its adapter:
public class LocalPagerAdapter extends FragmentStatePagerAdapter {
private List<String> pagerData;
public LocalPagerAdapter(FragmentManager fm, List<String> pagerData) {
super(fm);
this.pagerData = pagerData;
}
#Override
public Fragment getItem(int position) {
return DataFragment.newInstance(pagerData.get(position));
}
#Override
public int getCount() {
return pagerData.size();
}
}
This adapter creates a DataFragment for each page:
public class DataFragment extends Fragment {
private static final String DATA_ARG_KEY = "DataFragment.DATA_ARG_KEY";
private String localData;
public static DataFragment newInstance(String data) {
DataFragment df = new DataFragment();
Bundle args = new Bundle();
args.putString(DATA_ARG_KEY, data);
df.setArguments(args);
return df;
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
localData = getArguments().getString(DATA_ARG_KEY);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.data_fragment, container, false);
}
#Override
public void onViewCreated(View view, Bundle savedInstanceState) {
view.findViewById(R.id.btn_page_action).setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
Toast.makeText(getActivity(), localData, Toast.LENGTH_SHORT).show();
}
});
((TextView) view.findViewById(R.id.txt_label)).setText(localData);
}
}
and DataFragment's layout:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:padding="4dp" >
<Button
android:id="#+id/btn_page_action"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:text="Interogate" />
<TextView
android:id="#+id/txt_label"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:textAppearance="?android:attr/textAppearanceLarge" />
</RelativeLayout>
Enjoy coding!
maybe it will help mViewPager.setOffscreenPageLimit(5)
Set the number of pages that should be retained to either side of the
current page in the view hierarchy in an idle state. Pages beyond this
limit will be recreated from the adapter when needed.
This is offered as an optimization. If you know in advance the number
of pages you will need to support or have lazy-loading mechanisms in
place on your pages, tweaking this setting can have benefits in
perceived smoothness of paging animations and interaction. If you have
a small number of pages (3-4) that you can keep active all at once,
less time will be spent in layout for newly created view subtrees as
the user pages back and forth.
You should keep this limit low, especially if your pages have complex
layouts. This setting defaults to 1.
View Pager is pretty adamant in keeping keeping its Fragments fresh always and thus optimizing the performance by freeing up memory when a fragment is not used. Clearly that is a valid useful trait in a mobile system. But due to this persistent deallocation of resources the fragment is created everytime it gains focus.
mViewPager.setOffscreenPageLimit(NUMBEROFFRAGMENTSCREENS);
Here is the documentation.
this Old Post has an interesting Solution for your problem.. Please Refer
For me i changed to getChildFragmentManager() instead of getFragmentManager()
and works good.
Ex:
pagerAdapt = new PagerAdapt(getChildFragmentManager());
I had the same problem. My app (FragmentActivity) has a pager (ViewPager) with 3 framgents. While swiping between the fragments they are destroyed and recreated all the time. Actually it makes no problem in functionality (expect unclosed Cursors), but I was also wondering about this question.
I do not know if there is a workaround to change the behavior of the ViewPager, but I suggest to have a configuration object (maybe a static on) and before destroy save your myViewPager object at the config object.
public class App extends FragmentActivity {
static MyData data;
#Override
protected void onCreate(Bundle savedInstanceState) {
data = (MyData) getLastCustomNonConfigurationInstance();
if (data == null) {
data = new MyData();
data.savedViewPager = myViewPager;
} else {
myViewPager = data.savedViewPager;
}
}
#Override
public Object onRetainCustomNonConfigurationInstance() {
Log.d("onRetainCustomNonConfigurationInstance", "Configuration call");
return data;
}
}
public class MyData {
public ViewPager savedViewPager;
}
With this way, you can save the reference to the an object which won't be destroyed hence there is reference to it and you can reload all your crucial objects.
I hope you find my suggestion useful!
I'm kinda confused about the whole Fragment-way-of-thinking. I've followed a tutorial on how to create a ViewPager with Fragments like the Google Play app.
I have TabFragment class like this one:
public class SwipeyTabFragment extends SherlockFragment {
#Override
public void onCreate(Bundle b) {
super.onCreate(b);
Log.e("FRAGMENT: ", "Hello World!");
}
public static Fragment newInstance(String title) {
SwipeyTabFragment f = new SwipeyTabFragment();
Bundle args = new Bundle();
args.putString("title", title);
f.setArguments(args);
return f;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
ViewGroup root = (ViewGroup) inflater.inflate(R.layout.fragment_swipeytab, null);
final String title = getArguments().getString("title");
((TextView) root.findViewById(R.id.text)).setText(title);
return root;
}
}
I know that the onCreateView method initialize the layout and the controlls like Button, ListView and so on.
Over to my FragmentAdapter
private class SwipeyTabsPagerAdapter extends FragmentPagerAdapter implements SwipeyTabsAdapter {
private final Context mContext;
public SwipeyTabsPagerAdapter(Context context, FragmentManager fm) {
super(fm);
this.mContext = context;
}
#Override
public Fragment getItem(int position) {
return SwipeyTabFragment.newInstance(TITLES[position]);
}
#Override
public int getCount() {
return TITLES.length;
}
public TextView getTab(final int position, SwipeyTabs root) {
TextView view = (TextView) LayoutInflater.from(mContext).inflate(R.layout.swipey_tab_indicator, root, false);
view.setText(TITLES[position]);
view.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
mViewPager.setCurrentItem(position);
}
});
return view;
}
}
This will just construct a new Tab based on a String-Array, which will set the text and the header of the Fragment.
So this is where I get confused. Say for instance that I want several fragments with different layout, and different ways of interacting when the user presses on Button, Picture or whatever. How can I do so?
Thanks.
All the 'user presses button' stuff is handled in the fragments, you can call back to the Activity of course when you need to (see here).
You have to create different fragment classes for different layouts, logic. etc. and return them to the ViewPager in getItem. You could have a FirstPageFragment and a SecondPageFragment, then return them (depending on the index) in getView. This only makes sense if those fragments have different functionalities of course.
Hope it's clear what I mean ;)
EDIT: as to your comment:
I don't know what exactly you want to do, but you have your SwipeyTabFragment already defined in it's own file. Take this then, modify it, give it another layout and other functionality, then call it OtherFragment or whatever. Let's say you want to have 2 different 'pages' in your App - the getCount() method in your adapter defines the amount of 'pages' in your ViewPager, so let's let it return two.
In the getItem() method, if position is 0, let it return your SwipeyFragment, else (position is 1) let it return your new OtherFragment. Now you have a ViewPager with 2 different Fragments that can serve totally different purposes.
I'm new to Android developing and I would really appreciate some help here.
I'm using a fragment that contains a TextView and I'm using 5 instances of the same MyFragment class.
In the activity, i got a button and a ViewPager, and I need the button to update all the fragment instances content, whenever its clicked.
Here's the Activity
public class MainActivity extends FragmentActivity {
final static String[] CONTENT = {"a", "b"};
ViewPager pager;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
List<MyFragment> fragments = new Vector<MyFragment>();
for(int i = 0; i < 5; i++){
MyFragment fragment = new MyFragment(CONTENT);
fragments.add(fragment);
}
PagerAdapter adapter = new PagerAdapter(this.getSupportFragmentManager(), fragments);
pager = (ViewPager) findViewById(R.id.viewpager);
pager.setAdapter(adapter);
Button button = (Button) findViewById(R.id.button);
button.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
//method that isn't working
PagerAdapter adapter = (PagerAdapter)pager.getAdapter();
for(int i = 0; i < 5; i++){
MyFragment fragment = (MyFragment) adapter.getItem(i);
fragment.textView.setText(fragment.content[1]);
}
}
});
}
}
The Fragment
public class MyFragment extends Fragment{
String[] content;
TextView textView;
public MyFragment(String[] content) {
this.content = content;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_content, container, false);
textView = (TextView) view.findViewById(R.id.textView1);
textView.setText(content[0]);
return view;
}
}
And the FragmentPagerAdapter
public class PagerAdapter extends FragmentPagerAdapter{
List<MyFragment> fragments;
public PagerAdapter(FragmentManager fm, List<MyFragment> fragments) {
super(fm);
this.fragments = fragments;
}
#Override
public Fragment getItem(int arg0) {
return fragments.get(arg0);
}
#Override
public int getCount() {
return fragments.size();
}
}
The OnClick method gives me a NullPointerException whenever i try to access a fragment from the adapter which is less than adapter.getCurrentItem() - 1, or more than adapter.getCurrentItem() + 1.
Any idea on how to update all the fragments at the same time?
Thanks in advance.
The easiest way to update those fragments is to use your code and set the number of fragments that the ViewPager holds in memory to the number of total fragments - 1(so all fragments are valid no matter at what page you are). In your case:
pager.setOffscreenPageLimit(4); // you have 5 elements
You can still use the method from my comment with the method onPageScrollStateChanged(so the update will start the moment the user starts swiping) to see when the user is starting to swipe the pager and update the fragments to the left and right of the currently visible fragment, but this will be a bit difficult to get right so I recommend to go with the first option.
Some points regarding your code containing fragments:
If you nest the fragment class make it static so you don't tie it to the activity object.
Don't create a constructor for a Fragment besides the default one. If the framework needs to recreate the fragment it will call the default constructor and if it is not available it will throw an exception. For example, try to change the orientation of the phone/emulator and see what happens(this is one of the cases when Android will recreate the fragments). Last, use a custom name for the ViewPager's adapter, you use PagerAdapter which is the name of the super class of FragmentViewPager and it's very confusing for someone reading your code.
If you need to pass data to the Fragment you could use a creation method like the one below:
public static MyFragment newInstance(String text) {
MyFragment f = new MyFragment();
Bundle b = new Bundle();
b.putString("content", text);
f.setArguments(b);
return f;
}
The text will be available in MyFragment by using getArguments().getString("content");