I am trying to send data from one fragment to another, I am using bundle for that. But, whenever, I try to get any information from that bundle in the second fragment, I get an error message saying that I am trying to get a null object. I have set the arguments of the second fragment before I create it, and I have also add information to the bundle before sending it. I could not find out what is the problem. Here is the interface code in the main fragment which should open the details fragment,
public interface ListClickHandler {
public void onlistElementClicked ( Bundle args); //we'll have to override it in the parent activity.
}//end interface.
public void onAttach(Activity activity) {
super.onAttach(activity);
// This makes sure that the container activity has implemented
// the callback interface. If not, it throws an exception
try {
mCallback = (ListClickHandler) activity;
}//end try
catch (ClassCastException e) {
throw new ClassCastException(activity.toString()
+ " must implement ListClickHandler interface");
}//end catch
}
Also, I create the bundle in two places, once in the main fragment, which contains a list, if any item is clicked the bundle is created, info is added to the bundle, and that bundle is passed to the method inside the interface as the following,
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_todo_list, container, false);
mSimpleCursorAdapter=new SimpleCursorAdapter(getActivity(),R.layout.notes_row,null, from, to,0);
getLoaderManager().initLoader(LOADER_ID, null, this); //once this is done onCreateLoader will be called.
ListView listView = (ListView) rootView.findViewById(R.id.notes_list); //findViewById must be called using the rootView because we are inside a fragment.
listView.setAdapter(mSimpleCursorAdapter);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {
Cursor cursor = mSimpleCursorAdapter.getCursor();
if (cursor != null && cursor.moveToPosition(position)) {
String category= cursor.getString(1);
String summary= cursor.getString(2);
String description=cursor.getString(3);
long id= cursor.getLong(cursor.getColumnIndex(NotesContract.NotesTable._ID));
int locationId= cursor.getInt(cursor.getColumnIndex(NotesContract.NotesTable.COLUMN_LOCATION));
String [] retrievedData= {category, summary, description};
if (getActivity().findViewById (R.id.fragment_container)!=null){
//two pane layout:
Bundle args = new Bundle();
args.putStringArray("data",retrievedData);
/*args.putInt("update", 1);*/
args.putLong("id", id);
args.putInt("locationId", locationId);
mCallback.onlistElementClicked(args );/*this is available in the parent activity*/
}
else {
// one pane layout:
Intent intent = new Intent(getActivity(), NotesDetails.class);
intent.putExtra(Intent.EXTRA_TEXT, retrievedData);
/*intent.putExtra("update", 1); */ //to indicate that the query should be update not insert.
intent.putExtra("id", id);
intent.putExtra("locationId", locationId); //whether it is 0 or 1
startActivity(intent);
}
}//end outer cursor if.
}
});
return rootView;
}
The second place where I create and call the bundle is in the main activity (which contains the main fragment) when some items of the options menu are selected as the following,
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {//open the settings activity to enable the user to change the settings.
//open settings activity via intent here.
startActivity(new Intent (this, Settings.class));
return true;
}
if (id==R.id.text_note){ //open the details activity where the user can enter their notes and save it.
if (twoPane) {
args.putBoolean("location", false);
mCallBack.onlistElementClicked(args);
}
else {
Intent intent = new Intent(this, NotesDetails.class);
startActivity(intent);
return true; //this line is necessary
}
}//end if
if (id==R.id.location_note)
{
if (twoPane) {
args.putBoolean("location", true);
mCallBack.onlistElementClicked(args);
}
else {
//prepare intent here:
Intent intent = new Intent(this, NotesDetails.class);
intent.putExtra("location", true);
startActivity(intent);
}
}
return super.onOptionsItemSelected(item);
}
This is how I override onlistElementClicked in the main activity,
#Override
public void onlistElementClicked(Bundle args) {
DetailsFragment detailsFragment = new DetailsFragment();
detailsFragment.setArguments(args);
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.fragment_container, detailsFragment);
transaction.addToBackStack(null);
// Commit the transaction
transaction.commit();
}//end interface method.
And this is how I get the information inside the arguments of the details fragment (The fragment that should be opened from the main fragment).
Bundle args=this.getArguments();
After that I use args to get any information in the bundle, but I am getting the error which I mentioned previously.
Can any one please help me? I've checked several solutions on the web and nothing worked for me.
Thank you.
You should assign the value of Bundle like this:
public void onCreate(Bundle savedInstance){
super.onCreate(savedInstance);
youtBandGlobalMember = getArguments();
}
Bundle args=this.getArguments();
actually, I didn't call it in any method, it is called in the body of fragment class, and its value is assigned to a global variable. Is that wrong?
It's too early. Member variables are initialized when the object is constructed and that is before you can call setArguments() on the fragment object.
Postpone the getArguments() call to one of the on...() lifecycle callbacks in the fragment.
Related
I'm trying to implement PreferenceFragmentCompat and SharedPreferences.OnSharedPreferenceChangeListener.
My app consists of main activity and fragments. The home fragment has a list of URLs with a title, and I would like to add a setting to add a URL to this list. This is what I've tried so far:
Here's the SettingsFragment.java:
#Override
public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
Preference preference = findPreference(key);
if (preference instanceof EditTextPreference) {
EditTextPreference editTextPreference = (EditTextPreference) preference;
String value = editTextPreference.getText();
new HomeFragment().addLink(value);
} else {
assert preference != null;
preference.setSummary(sharedPreferences.getString(key, ""));
}
}
And the HomeFragment.java:
private ArrayList<LinkItem> urls = new ArrayList<>(Arrays.asList(
new LinkItem("LifeHacker RSS Feed", "https://lifehacker.com/rss"),
new LinkItem("Google News Feed", "https://news.google.com/news/rss");
private LinkItemAdapter itemAdapter;
private ListView listView;
#Override
public View onCreateView(#NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_home, container, false);
listView = view.findViewById(R.id.postListView);
itemAdapter = new LinkItemAdapter(getActivity(), R.layout.link_item, urls);
listView.setAdapter(itemAdapter);
listView.setOnItemClickListener(onItemClickListener);
itemAdapter.notifyDataSetChanged();
return view;
}
void addLink(String title) {
urls.add(new LinkItem(title, "https://google.com"));
itemAdapter.notifyDataSetChanged();
}
private AdapterView.OnItemClickListener onItemClickListener = new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
HomeFragmentDirections.ActionHomeFragmentToRssFragment action =
HomeFragmentDirections.actionHomeFragmentToRssFragment(urls.get(position).Link, urls.get(position).Title);
NavHostFragment.findNavController(HomeFragment.this).navigate(action);
}
};
If I try doing it like this, the itemAdapter will be null, crashing the app, so I am unsure of how to implement this. If I try recreating it in addLink like in the onCreate method of HomeFragment, the activity ends up being null. If I try passing the activity or the context from settings fragment, the same result occurs.
LinkItemAdapter adapts the following object:
public class LinkItem {
public String Title;
public String Link;
}
My results so far have always been the same: crash as soon as I click "OK" on the edit text field after changing it, due to a null pointer. Could anyone help me out with this, please? I am new to android.
Stack trace:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.myfragmentapp, PID: 5185
java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.myfragmentapp.adapters.LinkItemAdapter.notifyDataSetChanged()' on a null object reference
at com.example.myfragmentapp.screens.HomeFragment.addLink(HomeFragment.java:86)
at com.example.myfragmentapp.screens.SettingsFragment.onSharedPreferenceChanged(SettingsFragment.java:42)
at android.app.SharedPreferencesImpl$EditorImpl.notifyListeners(SharedPreferencesImpl.java:560)
at android.app.SharedPreferencesImpl$EditorImpl.apply(SharedPreferencesImpl.java:443)
at androidx.preference.Preference.tryCommit(Preference.java:1632)
at androidx.preference.Preference.persistString(Preference.java:1663)
at androidx.preference.EditTextPreference.setText(EditTextPreference.java:80)
at androidx.preference.EditTextPreferenceDialogFragmentCompat.onDialogClosed(EditTextPreferenceDialogFragmentCompat.java:99)
at androidx.preference.PreferenceDialogFragmentCompat.onDismiss(PreferenceDialogFragmentCompat.java:267)
at android.app.Dialog$ListenersHandler.handleMessage(Dialog.java:1377)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6709)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:769)
You should call addLink() after you've created the adapter:
public View onCreateView(#NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_home, container, false);
listView = view.findViewById(R.id.postListView);
itemAdapter = new LinkItemAdapter(getActivity(), R.layout.link_item, urls);
listView.setAdapter(itemAdapter);
listView.setOnItemClickListener(onItemClickListener);
addLnk();
return view;
}
If you're trying to set a value from one fragment to another you should either use callbacks or a ViewModel, the simpler of those being a callback:
Define a callback inteface:
interface OnSetPreferenceItem{
void setPrefItemInList(String item);
}
Inside SettingsFragment, define a variable:
private OnSetPreferenceItem callback;
In the same fragment, fill in the variable in onAttach:
public void onAttach(Context context) {
super.onAttach(context);
callback = (OnSetPreferenceItem )context;
}
Now instead of calling new HomeFragment().addLink(value);, call
callback.setPrefItemInList(value);
Let your parent activity implement that interface and implement the method suggested:
public void setPrefItemInList(String item){
homeFragment.addLink(item);
}
Modify your addLink method to protect it:
void addLink(String title) {
urls.add(new LinkItem(title, "https://google.com"));
if(itemAdapter!=null){
itemAdapter.notifyDataSetChanged();
}
}
I would suggest you using the lifecycle functions of the Fragment correctly. When you are modifying some data (i.e. adding a new URL in the list) from another fragment (i.e. SettingsFragment), you do not have to call the HomeFragment.addLink right away actually. Instead, you might consider having the onResume method implemented in your HomeFragment so that when you go back to your HomeFragment, the onResume function is called automatically and there you should update your list and consider calling notifyDataSetChanged on your adapter.
Hence I am trying to provide some pseudo code here. In your SettingsFragment do something like the following.
#Override
public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
Preference preference = findPreference(key);
if (preference instanceof EditTextPreference) {
EditTextPreference editTextPreference = (EditTextPreference) preference;
String value = editTextPreference.getText();
// new HomeFragment().addLink(value); // You do not call this here
saveTheNewURLInPrefrence(); // Just save the new value in your preference
} else {
assert preference != null;
preference.setSummary(sharedPreferences.getString(key, ""));
}
}
Now in your HomeFragment, implement the onResume function like the following.
#Override
protected void onResume() {
super.onResume();
urls = getAllItemsFromPreference();
if(itemAdapter != null) itemAdapter.notifyDataSetChanged();
else {
itemAdapter = new LinkItemAdapter(getActivity(), R.layout.link_item, urls);
listView.setAdapter(itemAdapter);
listView.setOnItemClickListener(onItemClickListener);
}
}
To understand more about fragment lifecycle, please check the documentation here. I hope you get the idea.
How can I add an Item Click Listener for my `RecyclerView.Adapter'
when the user clicks on the Card View item, Data sent to the PostContent Fragment?
Also, is it possible to send the data from this adapter to the new fragment using intent?
Please note my code:
public class PostDataAdapter extends RecyclerView.Adapter<PostDataAdapter.MyViewHolder> {
private List<PostData> PostDataList ;
public static class MyViewHolder extends RecyclerView.ViewHolder {
public TextView vPostContent, vPostDate, vPostAuthor, vPostTitr,VPostLikes,VPostViews;
public ImageView vPostPhoto;
public MyViewHolder(View v) {
super(v);
vPostContent = v.findViewById(R.id.PostContentTv);
vPostDate = v.findViewById(R.id.PostDateTv);
vPostAuthor = v.findViewById(R.id.PostAuthorTv);
vPostTitr = v.findViewById(R.id.PostTitrTv);
vPostPhoto = v.findViewById(R.id.PostPhoto);
VPostLikes=v.findViewById(R.id.PostLikeTv);
VPostViews=v.findViewById(R.id.PostViewTv);
}
}
public PostDataAdapter(List<PostData> postDataList) {
PostDataList = postDataList;
}
#Override
public PostDataAdapter.MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.row_posts, parent, false);
MyViewHolder vh = new MyViewHolder(v);
return vh;
}
#Override
public void onBindViewHolder(MyViewHolder holder, int position) {
holder.vPostDate.setText(PostDataList.get(position).getPostDate());
holder.vPostTitr.setText(PostDataList.get(position).getPostTitr());
holder.vPostContent.setText(PostDataList.get(position).getPostContent());
holder.vPostAuthor.setText(PostDataList.get(position).getPostAuthor());
holder.VPostViews.setText(PostDataList.get(position).getPostViews());
holder.VPostLikes.setText(PostDataList.get(position).getPostLikes());
new DownloadImageTask(holder.vPostPhoto).execute(PostDataList.get(position).getImgpost());
}
#Override
public int getItemCount() {
return PostDataList.size();
}
}
To add a ItemCLickListener for RecyclerView, you need to implement a custom Interface which the Fragment will implement. When the list item is clicked, then the callback function of the interface is called.
CustomItemClickListener.java:
public CustomItemClickListener {
void onItemClick(Object data);
}
Just add these to the PostDataAdapter:
PostDataAdapter.java:
private CustomItemClickListner clickListener;
public PostDataAdapter(CustomItemClickListner listener, List<PostData> postDataList) {
PostDataList = postDataList;
clickListener = listener
}
#Override
public void onBindViewHolder(MyViewHolder holder, int position) {
holder.vPostCardView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// Modify the parameters of the function according to what you want to send to the fragment
// As soon as this is called, the `onItemClick` function implemented in the Fragment gets called.
clickListener.onItemClick(Object data);
}
});
}
Fragment.java:
CustomFragment extends Fragment implements CustomItemClickListener {
public CustomFragment() {
}
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
View view;
PostDataAdapter adapter = new PostDataAdapter(this, new ArrayList<PostData>)
return view;
}
#Override
public void onItemClick(Object data) {
// Handle the data sent by the adapter on item click
}
}
Yu cand send data from Adapter to a Fragment with Intent:
Fragment fragment = new tasks();
FragmentManager fragmentManager = context.getSupportFragmentManager(); // this is the context of the Activity
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
Bundle bundle=new Bundle();
bundle.putString("name", "Osmar Cancino"); //key and value
//set Fragmentclass Arguments
fragment.setArguments(bundle);
fragmentTransaction.replace(R.id.content_frame, fragment);
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();
Although my suggestion is to manage the flow of screens from the parent activity, and manage the data through a Callback, even with a custom Interface
There are two ways you can do this.
Write recyclerview.onitem touchlistener(...). Then consume that event in your fragment. As you will get item position inside touchlistener callback, you can take out data from your list directly from the list you passed to your adapter (Assuming you have list reference outside in your fragment.)
Oobserver pattern.
Define a functional interface (one callback method with required parameters of the data you want to pass) implement inside your fragment. Send its reference with the constructor of adapter. Then Store reference in a interface type variable inside adapter. Write click listener on card. And on the card click, invoke method using interface type variable.
Intents can be used to send data to new activities but not fragments You'd have to use the Fragment Manager and attach a bundle to it to send data. You can refer to the documentation here on how to do so:
https://developer.android.com/training/basics/fragments/communicating#Deliver
To handle click on cards, you can create a listener when you create PostDataAdapter. Refer to the following link for a simple example:
https://stackoverflow.com/a/40584425/4260853
for adding click item for a Cardview, you can find the Cardview in MyViewHolder class by id and in onBindViewHolder set a click listerner for it like the following
#Override
public void onBindViewHolder(MyViewHolder holder, int position) {
holder.vPostCardView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
//write your codes here
}
});
}
if you have an intent that you want to send it's data to a fragment, you can get the intent data and send them with bundle to your fragment. for example do something like the following.
Bundle bundle = new Bundle();
bundle.putString("your_key",intent.getStringExtra("your_item_key_in_intent"));
and after that send bundle to your fragment with
fragment.setArguments(bundle);
I am trying to use Bundle to send data from an activity to a fragment. The activity is receiving the input from a dialogbox when the user clicks on the actionbar add icon. The button also opens the dialogbox but it sends the data straight to the fragment (I'm trying to learn the difference between activity and fragment and to interact with the dialogfragment). None of the solutions on the internet have worked for me, and I was hoping someone can help
I have provided a visualization to aid in my explanation of the issue. So initially, I click the action add icon that opens the dialogbox (2nd pic), when I enter an input, it doesn't alter the data on the fragment. Only when I press the action add icon for a second time, does the first input get updated (3rd pic). Also you may notice that it says "Bundle{[Dialog Input = First Input]}" where First Input is the user input. How do I change this to just, First Input. I tried clearing the textview before setting the value, but that doesn't work. Now lastly when I press the button, it opens the dialogbox and when I enter in data, the data from the action add icon (handled in activity then data sent to fragment) overlaps with the data from the button (data sent straight to fragment). Any help would be appreciated. Thanks in advance.
MainActivity:
public class MainActivity extends AppCompatActivity implements
MyCustomDialog.OnInputSelected{
public String dialogInput;
FragmentManager fragmentManager;
#Override
public void sendInput(String input) {
dialogInput = input;
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
fragmentManager = getSupportFragmentManager();
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
//Inflate the menu, this adds items to the action bar if it is present
getMenuInflater().inflate(R.menu.menu, menu);
return super.onCreateOptionsMenu(menu);
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
//Handle action bar clicks here. The action bar will automatically handle clicks on the home/up button
//so long as you specify a parent activity in AndroidManifest.xml
switch(item.getItemId()){
case R.id.action_add:
MyCustomDialog dialog = new MyCustomDialog();
dialog.show(getSupportFragmentManager(), "MyCustomDialog");
//Trying Bundle to pass data, dialog input between activity and fragment
Bundle bundle = new Bundle();
bundle.putString("Dialog Input", dialogInput);
//Set Fragment class arguments
MainFragment fragment = new MainFragment();
fragment.setArguments(bundle); //set argument bundle to fragment
fragmentManager.beginTransaction().replace(R.id.MainFragment,fragment).commit(); //now replace Mainfragment
Toast.makeText(this, "Action_Add Clicked Successfully", Toast.LENGTH_SHORT).show();
}
return super.onOptionsItemSelected(item);
}
}
MainFragment:
public class MainFragment extends Fragment implements MyCustomDialog.OnInputSelected{
TextView InputDisplay;
Button OpenDialog;
#Nullable
#Override
public View onCreateView(#NonNull LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_main, container, false);
InputDisplay = view.findViewById(R.id.InputDisplay);
OpenDialog = view.findViewById(R.id.Open_Dialog);
//Getting Main Activity dialog information with Bundle, that was received from toolbar add
Bundle bundle = getArguments();
if(bundle != null){
String dialogInput = bundle.toString();
//Clearing since Fragment call and activity call overlap each other.
InputDisplay.setText("");
InputDisplay.clearComposingText();
InputDisplay.setText(dialogInput);
}
//String dialogInput = this.getArguments().getString("Dialog Input");
OpenDialog.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Log.d("MainFragment", "onClick: opening dialog");
MyCustomDialog customDialog = new MyCustomDialog();
customDialog.setTargetFragment(MainFragment.this, 1);
customDialog.show(getFragmentManager(), "MyCustomDialog");
}
});
return view;
}
#Override
public void sendInput(String input) {
InputDisplay.setText("");
InputDisplay.setText(input);
}
}
My Custom Dialog:
public class MyCustomDialog extends DialogFragment {
private EditText Input;
private TextView ActionOK, ActionCANCEL;
private OnInputSelected onInputSelected;
public interface OnInputSelected{
void sendInput(String input);
}
#Override
public void onAttach(Context context) {
super.onAttach(context);
try{
Fragment onInputSelected_fragment = getTargetFragment();
Activity onInputSelected_activity = getActivity();
if(onInputSelected_fragment != null){
onInputSelected = (OnInputSelected) onInputSelected_fragment;
}else{
onInputSelected = (OnInputSelected) onInputSelected_activity;
}
//throw new RuntimeException("Custom Dialog onAttach Listener was NULL");
}catch(ClassCastException e){
Log.e("Custom Dialog", "onAttach: ClassCastException: " + e.getMessage());
}
}
#Nullable
#Override
public View onCreateView(#NonNull LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.dialog_my_custom, container, false);
Input = view.findViewById(R.id.Input);
ActionOK = view.findViewById(R.id.Action_OK);
ActionCANCEL = view.findViewById(R.id.Action_CANCEL);
ActionCANCEL.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
getDialog().dismiss();
}
});
ActionOK.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
onInputSelected.sendInput(Input.getText().toString());
getDialog().dismiss();
}
});
return view;
}
}
How do I change this to just, First Input.
your output is printed like this "Bundle{[Dialog Input = First Input]}" because you are directly doing bundle.toString(); instead of getting the value you have stored in the bundle.
change the above to this
String dialogInput = bundle.getString("Dialog Input")
InputDisplay.setText(dialogInput);
the data from the action add icon overlaps with the data from the button
Clear the existing text in the text view before setting the new value like this
String dialogInput = bundle.getString("Dialog Input")
InputDisplay.setText(");
InputDisplay.setText(dialogInput);
Also, I noticed that all the variable names that you have used are not following camel case I suggest you correct that as well.
I have an Activity A with a fragment frag2. Inside the fragment I have a RecyclerView and Adapter to show a list of custom class objects. Adding objects to the adapter is handled programmatically. I have a button inside TwoFragment that opens a FragmentDialog. I'd like to add an object to my Adapter by confirming this dialog, but it seems that the adapter is null when called from the FragmentDialog.
The same adapter is not null, and works if I call it from the fragment OnClick.
Moreover the adapter is null only after screen rotation, it works fine before rotating.
To communicate between the two Fragments I implement a communicator class in activity A.
Activity A
public void respond(String type) {
frag2.addSupport(type);
}
frag2
public RecyclerView rv;
public ArrayList<support> supports;
public myAdapter adapter;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
supports = new ArrayList<>();
adapter = new myAdapter(supports);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View layout = inflater.inflate( R.layout.fragment_two, container, false);
layout.setId(R.id.frag2);
if (savedInstanceState!=null)
{
supports = savedInstanceState.getParcelableArrayList("supports");
}
rv = (RecyclerView) layout.findViewById(R.id.rv);
adapter = new myAdapter(supports);
rv.setAdapter(myAdapter);
rv.setLayoutManager(new LinearLayoutManager(getActivity()));
rv.setItemAnimator(new DefaultItemAnimator());
#Override
public void onClick(View v) {
int id = v.getId();
switch (id){
case R.id.button1:
addSupport(type); // THIS WORKS ALWAYS, even after screen rotate
break;
case R.id.button2:
showDialog();
break;
}
}
public void showDialog(){
FragmentManager manager = getFragmentManager();
myDialog dialog = new myDialog();
dialog.show(manager, "dialog");
}
public void addSupport(String type){
adapter.addItem(new support(type)); // this line gives null pointer on adapter, but only if called after screen rotate and only if called from the dialog
}
dialog
communicator comm;
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.dialog, null);
comm = (myCommunicator) getActivity();
create = (Button) view.findViewById(R.id.button_ok);
create.setOnClickListener(this);
return view;
}
#Override
public void onClick(View v) {
if(v.getId()==R.id.button_ok)
{
// some controls to set type
comm.respond(type)
dismiss();
}
else {
dismiss();
}
myAdapter
public class myAdapter extends RecyclerView.Adapter<myAdapter.VH> {
private LayoutInflater inflater;
private ArrayList<support> data = new ArrayList<>();
// settings for viewholder
public myAdapter (ArrayList<support> data)
{
this.data=data;
}
public void addItem(support dataObj) {
data.add(dataObj);
notifyItemInserted(data.size());
}
}
logcat
FATAL EXCEPTION: main
java.lang.NullPointerException: Attempt to invoke virtual method 'myAdapter.addItem(myObject)' on a null object reference
I hope there are no mistakes, I shortened the code for better understanding. Keep in mind that everything works if I never rotate the screen.
I'm a beginner with android and I'm stuck with this for several days now. Please, help.
To understand the problem, it's as you say:
.. everything works if I never rotate the screen
So firstly to understand what happens on rotation, this is a quote from the Android Developer website:
Caution: Your activity will be destroyed and recreated each time the user rotates the screen. When the screen changes orientation, the system destroys and recreates the foreground activity because the screen configuration has changed and your activity might need to load alternative resources (such as the layout).
Ok, now to understand the error:
FATAL EXCEPTION: main
java.lang.NullPointerException: Attempt to invoke virtual method 'myAdapter.addItem(myObject)' on a null object reference
Essentially, in your dialog class, you have created a strong dependency by declaring :
comm = (myCommunicator) getActivity();
because comm references objects which would have been destroyed on rotation, hence the NullPointerException.
To further understand runtime changes, such as orientation changes, I'd recommend going through Handling Runtime Changes.
Update
Thank you for your answer, what would you recommend instead of comm = (myCommunicator) getActivity(); ?
The solution comes in 3 parts:
Make sure the onCreate of Activity A has the following:
#Override
public void onCreate(Bundle savedInstanceState) {
......
// find the retained fragment on activity restarts
FragmentManager fm = getFragmentManager();
frag2 = (Frag2) fm.findFragmentByTag(“frag2”);
// create frag2 only for the first time
if (frag2 == null) {
// add the fragment
frag2 = new Frag2();
fm.beginTransaction().add(frag2 , “frag2”).commit();
}
......
}
Add setRetainInstance(true) to the onCreate of frag2.
Remove the implicit referencing i.e. comm = (myCommunicator) getActivity();, and implement something more loosely coupled for dialog.
dialog
public interface Communicator {
void respond(String type);
}
Communicator comm;
....
public void addCommunicator(Communicator communicator) {
comm = communicator;
}
public void removeCommunicator() {
comm = null;
}
#Override
public void onClick(View v) {
if((v.getId()==R.id.button_ok) && (comm!=null))
{
// some controls to set type
comm.respond(type);
}
// Regardless of what button is pressed, the dialog will dismiss
dismiss();
}
This allows you do the following in frag2 (or any other class for that matter):
frag2
<pre><code>
public class Frag2 extends Fragment implements dialog.Communicator {
........
public void showDialog() {
FragmentManager manager = getFragmentManager();
myDialog dialog = new myDialog();
dialog.addCommunicator(this);
dialog.show(manager, "dialog");
}
#Override
public void respond(String type){
adapter.addItem(new support(type));
}
}
I'm using FragmentActivity for switching between Fragment. But I would like to have a Admin Button on a fragment, and when I click on it, a new fragment or activity appears like a child (with the back button in action bar).
How can I make it ?
Here is my code, that works, but the back button doesn't appear in action bar :
Fragment :
public class Reports extends Fragment {
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (container == null) {
return null;
}
public void onClick(View v) {
Intent intent = new Intent(getActivity(), LoginActivity.class);
getActivity().startActivity(intent);
}
});
}
}
Activity (for the moment... but maybe Fragment if we need ?) :
public class LoginActivity extends ActionBarActivity {
public static final String TAG = LoginActivity.class.getSimpleName();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.login);
Button loginButton = (Button) findViewById(R.id.loginButton);
loginButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
TextView emailText = (TextView) findViewById(R.id.emailText);
TextView passwordText = (TextView) findViewById(R.id.passwordText);
ParseUser.logInInBackground(emailText.getText().toString(), passwordText.getText().toString(), new LogInCallback() {
public void done(ParseUser user, ParseException e) {
if (user != null) {
Log.i(TAG, "Yeahhh Login OK");
finish();
} else {
runOnUiThread();
}
}
});
}
});
}
Maybe I have to change something in Manifest ?
All you need to do is enable it inside the activity you're currently at.
When inside a FragmentActivity: getActionBar().setHomeAsUpEnabled(boolean).
Otherwise, inside a Fragment: getActivity().getActionBar().setHomeAsUpEnabled(boolean).
U need to override the onCreateOptionsMenu and onOptionsItemSelected. In the onCreateOptionsMenu method do the following : Inflate the menu into the action bar. You can define the contents of the menu item under res/menu folder.
Next in the onOptionsItemSelected method, you can handle the clicks of the back button added in the action bar. Also keep in mind one thing. In the manifest please use a theme which has action bar in it.
Example : Under the application tag use
android:theme="#android:style/Theme.Light" and not anything like android:theme="#android:style/Theme.Light.NoTitleBar
Well if you are starting a new Activity you can enable the back button in it by writing shouldDisplayHomeUp(); in the onCreate() method and on back should take you to the previous activity in the back stack.
And in the other case of adding a new Fragment you can take a look on this answer for reference as it mentions that when you add a new Fragment you add it to the back stack like this
getSupportFragmentManager().beginTransaction()
.add(detailFragment, "detail")
// Add this transaction to the back stack
.addToBackStack()
.commit();
this will make the back button take you to your previous Fragment