NullPointerException when accessing a Text Fragment texture in action
This seems to be a common problem, but after hours of trying random solutions provided as answers to similar questions, my code still throws a NullPointerException when I access the text element of a fragment from an Activity.
I can include (and view) my fragment when its textView has predefined text, or using setText()
in onCreateView()
the Fragment class, but not using the setter method (here set_message_success()
).
This is my Fragment class Fragment_Message
:
public class Fragment_Message extends Fragment {
TextView textview_message;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_messagebox, container, false);
textview_message = (TextView) view.findViewById(R.id.fragment_textview_message);
textview_message.setText("test");
return view;
}
public void set_message_success(String text) {
textview_message.setText(text);
}
}
And the corresponding lines from the Activity class:
FragmentManager frag_manager = getFragmentManager();
FragmentTransaction transaction = frag_manager.beginTransaction();
Fragment_Message fragment = new Fragment_Message();
fragment.set_message_success(message_green);
transaction.add(R.id.home_fragment_container, fragment, "Fragment");
transaction.commit();
home_fragment_container
is the RelativeLayout in my main_activity.xml, fragment_textview_message
is the textView in the fragment_messagebox.xml file, just so you know what it is.
A NullPointerException was thrown in set_message_success()
. Any ideas?
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You create a snippet, but the build loop fails. This line:
Fragment_Message fragment = new Fragment_Message();
DOES NOT automatically call onCreateView
, so your text view is not initialized (this null
) and when you try to set its text with the following line:
fragment.set_message_success(message_green);
you get an exception because the text viewer is not initialized to either initialize the text view in the constructor or define a snippet in the desired layout.
Look here for details
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The problem appears to be with the fragment lifecycle. When I add a fragment (done in action onCreate()
) and define its textView text in the fragment onCreateView()
, the fragment will display without issue. But accessing the fragment of the textView in the activity onCreate()
fails because - I guess the fragment hasn't been attached yet.
So, I added a fragment to the activities onCreate()
and changed the textView-text fragment in the activity onResume()
where (as I understand it) the fragment should be attached. It also helps to use executePendingTransactions()
. My working code:
Home.java
FragmentManager frag_manager;
FragmentTransaction transaction;
Fragment_Message fragment;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
frag_manager = getFragmentManager();
transaction = frag_manager.beginTransaction();
fragment = new Fragment_Message();
transaction.add(R.id.home_fragment_container, fragment, "Fragment_Messagebox");
transaction.commit();
}
@Override
protected void onResume() {
frag_manager.executePendingTransactions();
fragment.set_message_success("a message");
}
Fragment_Message.java
public class Fragment_Message extends Fragment {
TextView textview_message;
View view;
public Fragment_Message() {}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
view = inflater.inflate(R.layout.fragment_messagebox, container, false);
return view;
}
public void set_message_success(String text) {
textview_message = (TextView) view.findViewById(R.id.fragment_textview_message);
textview_message.setText(text);
}
}
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