Develop Reference

Android Fragment Null pointer exception

I am learning android developing(novice).I want to add a fragment to the mainActivity with a textview and change the text. This code works perfectly:
public class Fragment1 extends Fragment {
//#Nullable
//#Override
TextView textt;
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_fragment1, container, false);
((TextView)view.findViewById(R.id.textview)).setText("some text");
return view;
}
}
But this codes invokes null pointer exception:
public class Fragment1 extends Fragment {
//#Nullable
//#Override
TextView textt;
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_fragment1, container, false);
textt = (TextView)view.findViewById(R.id.textview);
return view;
}
public void updateText() {
textt.setText("some text");
}
}
and:
public class Fragment1 extends Fragment {
//#Nullable
//#Override
View view;
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
view = inflater.inflate(R.layout.fragment_fragment1, container, false);
return view;
}
public void updateText() {
((TextView)view.findViewById(R.id.textview)).setText("some text");
}
}
MainActivity:
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
Fragment1 frg1 = new Fragment1();
ft.replace(R.id.fragment_container, frg1);
ft.addToBackStack(null);
ft.commit();
frg1.updateText();
}
}
why these codes providing different outcome?
my project

frg1.updateText(); is called before the onCreateView lifecycle method of your fragment is called.. You should call the method after you set
textt = (TextView)view.findViewById(R.id.textview);
View view = inflater.inflate(R.layout.fragment_fragment1, container, false);
textt = (TextView)view.findViewById(R.id.textview);
this.updateText();//here
return view;
Check out fragment lifecycle docs regarding onCreateView
The system calls this when it's time for the fragment to draw its user interface for the first time.
This will happen when fragment is loaded not when it is created in your activity.

Here, the textview is not created when you call the updateText function.
Do such calls inside your fragment. Not on the activity which houses the fragment.

Using findViewById inside a Fragment

I am creating a new Tab interface and for every tab I have functionality like:
public class ClassViewFragment extends Fragment {
ListView classListView = null;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.class_view, container, false);
classListView = (ListView) findViewById(R.id.classList);
return rootView;
}
}
But I am getting cannot resolve method findViewById also at another place I am also unable to use runOnUiThread and getting Error:(88, 29) error: cannot find symbol method runOnUiThread(<anonymous Runnable>)
I understand these will work fine if my class was extended from Activity but it’s a tab fragment so how can I use this funcitons?

you need
classListView = (ListView) rootView.findViewById(R.id.classList);
as that is the view you are concerned with
to get runOnUiThred you need to do getActivity().runOnUiThread

You need to reference findViewById using the view,
public class ClassViewFragment extends Fragment {
ListView classListView = null;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.class_view, container, false);
classListView = (ListView) rootView .findViewById(R.id.classList);
return rootView;
}
}
For runOnUiThread is a possible duplicate of Modifying an Android view from a different thread
use its like,
activity.runOnUiThread(new Runnable());

Here is a shore explanation of findViewById method;
findViewById() method will work with the related object that your main layout is bound to. For example, In an activity, when you make a
setContentView(activity_main);
You imply that your Activity will retrieve its layouts from activity_main. So when you make a findViewById() in an activity, that actually means this.findViewById(), where this is your Activity.
So in your case, the layout class_view is bound to the rootView. But when you just write findViewById, it means that this.findViewById. And this is the scope you're in, which is the Fragment in your case. However, I don't think a Fragment has that capability. So you should refer to the rootView to retrieve your views.
rootView.findViewById()

Fragments don't have a findViewById() method like Activity, so you have to call the method of the root view of the fragment. Try doing rootView.findViewById(R.id.classList) instead.

#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_content_mediaplayer, container, false);
mSeekbar = (SeekBar) v.findViewById(R.id.seekBarMusic);
return v;

Use rootView.findViewById(R.id.classList) instead of findViewById(R.id.classList).
Try this:
public class ClassViewFragment extends Fragment {
ListView classListView = null;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.class_view, container, false);
classListView = (ListView) rootView.findViewById(R.id.classList);
return rootView;
}
}

findViewById must run inside onViewCreated() method
ListView classListView = null;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.class_view, container, false);
}
#Override
public void onViewCreated(View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
classListView = (ListView) view.findViewById(R.id.classList);
}
}`

Passing data from Fragment to Activity?

In my application,i have a Fragment class for Facebook login.I want to get this inflated layout from class in my Activity class so that i can display the facebook data in my SideMenu.How to get the layout in Activity class ?
This is my onCreate method
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
fa = super.getActivity();
ll = (LinearLayout) inflater.inflate(R.layout.login_notifications, container, false);
login();
return ll;
}

This is the code for showing layout in fragment:-
private static View rootView;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {
rootView = inflater.inflate(R.layout.location_layout, container,false);
return rootView;
}

Inflating a layout in a fragment

So I am finally learning Fragments after learning Activities. I am looking at a video tutorial. All of a sudden he changed the way a Fragment inflates a layout. Why does he have two different ways? The first way in FragmentA is:
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_a, container, false);
}
Then the other way in FragmentB is:
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_b, container, false);
if (savedInstanceState == null)
{
}
else {
savedInstanceState.getString("text");
TextView myText = (TextView) view.findViewById(R.id.textView);
myText.setText(data);
}
return view;
}
So why did it change from return inflater.inflate to View view = inflater.inflate
Sorry for dumb question, but I can't find this answer on Google.

It's basically the same,
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
has to return a View.
And
inflater.inflate(R.layout.fragment_b, container, false)
returns a View as well.
In the second example he assigns the return value of inflater.inflate() to a View object, as he needs to loads some data and set it on this View object... then he returns it.

public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// TODO Auto-generated method stub
View rootView = inflater.inflate(R.layout.lstindicators, container,
false);
And return your view thats all! :D
jejeje... and if you want to change your current fragment for another chechk this:
FragmentManager fragmentManager = getFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.content_frame, fragment).commit();

fragment and activity Android

In activity I can associate layout xml as following
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
how in the onCreate() of Fragment class load an Activity?
I have fragement class as in the following
public class TestFragment extends Fragment {
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle saved) {
}
}

If you want to inflate the xml layout inside the fragment you can do it easily with the LayoutInflater:
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.your_layout, container, false);
}
For further information read the offical Fragment Reference.