I have a main activity class, and a private inner class within the main activity. The private inner class has methods that when called will display fragments. This inner class implements an interface defined in the Fragment's class, to be used as a sort of callback. It is probably easiest to show through code.
public class MainActivity extends FragmentActivity {
//on a button clicked
EditItemManger em = new EditItemManager();
em.begin();
private class EditItemManager implements on EditItemFragment.EditedItemClickedListener{
//consructor, other stuff. no onCreate method because this inner class does not (explicity??) extend activty
public void begin(){
EditItemFragment editItemFrag = new EditItemFragment();
FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.add(editItemFrag, EDIT_FRAG_TAG)
fragmentTransaction.commit();
}
#Override
public void onEditItemClicked() {
editFinish();
}
public void editFinish()
{
// other stuff
}
}
}
My EditItemFragment class, where the onAttach method always has a null activity parameter
public class EditItemFragment extends DialogFragment {
protected EditedItemClickedListener editedItemClickedListener;
protected ImageButton button;
public EditItemFragment(){}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
final Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.edit_name_fragment, container, false);
button = (ImageButton) view.findViewById(R.id.submit_new_item_button);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
editedItemClickedListener.onEditedItemButtonClicked();
}
});
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
try {
editedItemClickedListener= (EditedItemClickedListener) activity;
} catch (ClassCastException e) {
e.printStackTrace();
}
}
public interface OnEditNameButtonClickedListener {
public void onEditNameButtonClicked();
}
So because the parameter in onAttach() in my Fragment class is always null, it eventually causes a null pointer exception. I am wondering if it is because the fragment is called from a class that is not extending activity. The problem is that if this class extends activity, there will be an issue with trying to commit the Fragment Transaction
I guest your onAttach returns nullpointer exception. Its because your parent Activity the main activity doesnt implement your custom interface so it return null. See the code below let me know if it help you:
public class MainActivity extends FragmentActivity implements EditItemFragment.EditedItemClickedListener{
private DialogFragment editItemDialog;
//Do your code here
#Override
public void onEditItemClicked() {
editFinish();
}
public void showDialog(){
//this is for showing your custom dialog fragment
editItemDialog = EditItemFragment.newInstance();
editItemDialog.show(getSupportFragmentManager(),"editItemDialog");
}
}
this is for your EditItemFragment:
public class EditItemFragment extends DialogFragment{
//Do your code here
public static EditItemFragment newInstance(){
EditItemFragment editItemDialog = new EditItemFragment();
return editItemDialog;
}
}
Related
I find it very difficult to call the InsertSlider in the MainFragment from the BottomSheetDialog.
Any help and thanks
In the BottomSheet :
public class AdminBottomSheetMainSave extends BottomSheetDialogFragment
{
// One Method I don.t Know How To Work
//((MainFragment)getContext()).InsertSliders(new ImageSlider(0,Name,Image,Price,Description));
// Not Work Too
MainFragment fragment = new MainFragment();
fragment.InsertSliders(new ImageSlider(0,Name,Image,Price,Description));
}
In the Fragment :
public class MainFragment extends Fragment
{
public void InsertSliders(ImageSlider imageSlider)
{
imageSliderViewModel.insert(imageSlider);
Toast.makeText(getActivity(), "Done Insert"+imageSlider, Toast.LENGTH_SHORT).show();
}
What is the contact method how do I get to InsertSliders
you should use interface to communicate between two fragments and you need an activity to implement the interface.
define interface in your bottomsheetdialogfragment:
public class AdminBottomSheetMainSave extends BottomSheetDialogFragment
{
public Callback mCallback;
public interface Callback{
void insertSlider(ImageSlider slider);
}
#Override
public void onAttach(Activity activity){
super.onAttach(activity);
mCallback = (Callback) activity;
}
#Override
public void onViewCreated(#NonNull View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
//...
mCallback.insertSlider(new ImageSlider(0,Name,Image,Price,Description));
}
}
then in your activity in our case MainActivity implement Callback interface and override inserSlider method:
public class MainActivity extends AppCompatActivity implements Callback{
MainFragment mainFragment;
#Override
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//...
if(savedInstanceState == null){
mainFragment = MainFragment.newInstance(new Bundle()); // use real bundle here
getSupportFragmentManager()
.beginTransaction()
.add(R.id.fragment_holder, mainFragment, "FragMain").commit();
}
}
// Interface method
#Override
public void insertSlider(ImageSlider slider){
if(mainFragment != null){
mainFragment.insertSlider(slider);
}
}
now in your MainFragment:
public class MainFragment extends Fragment{
public static MainFragment newInstance(Bundle args){
MainFragment fragment = new MainFragment();
fragment.setArguments(args);
return fragment;
}
//... Class overrides here onCreateView etc..
// define insertSlider method
public void insertSlider(ImageSlider slider){
imageSliderViewModel.insert(slider);
Toast.makeText(getActivity(), "Done Insert"+slider, Toast.LENGTH_SHORT).show();
}
I have not found a clear solution anywhere on stack for this.
Here's my basic set up
public class Activity1 extends AppCompatActivity
{
private OnAttributesUpdatedListener onAttributesUpdatedListener;
public interface OnAttributesUpdatedListener
{
public void onAttributesUpdated();
}
public void setTargetFragment(Fragment fragment)
{
this.onAttributesUpdatedListener = (OnAttributesUpdatedListener) fragment;
}
private void whenFinishedSomethingCallback()
{
onAttributesUpdatedListener.onAttributesUpdated();
}
}
public class Fragment1 extends Fragment implements Activity1.OnAttributesUpdatedListener
{
button.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View view) {
if(rivalButtonClick == 0)
{
Activity1 activity1 = new Activity1();
activity1.setTargetFragment(Fragment1.this);
startActivity(new Intent(getActivity(), activity1.getClass()));
}
}
});
}
I get a null pointer exception and crashes on : onAttributesUpdatedListener.onAttributesUpdated(); because for some reason my listener never gets set properly. What's the proper way to do this?
You need to set the listener at start of the fragment onCreatView() or in onActivityCreated() only if the Desired Activity is a parent Activity of that particular fragment. Below is an example .
public class Activity1 extends AppCompatActivity {
private OnAttributesUpdatedListener onAttributesUpdatedListener;
public interface OnAttributesUpdatedListener {
public void onAttributesUpdated();
}
public void setListener(OnAttributesUpdatedListener onAttributesUpdatedListener) {
this.onAttributesUpdatedListener = onAttributesUpdatedListener;
}
private void whenFinishedSomethingCallback() {
if(onAttributesUpdatedListener!=null)
onAttributesUpdatedListener.onAttributesUpdated();
}
}
public class Fragment1 extends Fragment implements Activity1.OnAttributesUpdatedListener
{
#Override
public void onAttributesUpdated() {
// Do your stuff here
}
#Override
public void onActivityCreated(#Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
((Activity1)getActivity()).setListener(this);
}
}
Read about fragment Life cycle to make use of getActivity(). also remove the listener when fragment is destroyed .
Use LocalBroadcastManager for communicating between in case the Fragment exists in other Activity.
At first create an Interface like this:
public interface Listener{
void doSomething() }
Then implement this interface in your activity.
And also add
Listener listener
In your fragment
And in onAttach method in fragment use this
listener=(Listener)activity
Then call listener whenever you need .
I was able to create a single event callback from a fragment to the activity. However, I have problem with creating two event callbacks from the same fragment.
Basically, I have a button on the fragment1 layout, when click on it, it will execute something in mainactivity, and then, it changes hide the Button at fragment1 layout, and then I need to send a Boolean from the fragment to activity, then initiate fragment2.
How can I implement the 2nd callback interface in the mainacativity.
Here is my code:
at Fragment1:
public class Fragment1 extends Fragment{
private static final String TAG = "Fragment1";
Boolean in1, in2;
Button btn1;
ListenerA mListenerA;
public interface ListenerA{
public void methodA(Boolean in1);
};
ListenerB mListenerB;
public interface ListenerB{
public void methodB(Boolean in2);
};
#Override
public void onAttach(Context context) {
super.onAttach(context);
if(context instanceof ListenerA)
mListenerA = (ListenerA)context;
if(context instanceof ListenerB)
mListenerB = (ListenerB)context;
}
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
View myView = inflater.inflate(R.layout.fragment1, container, false);
btn1 = (Button) myView.findViewById(R.id.btn1_ID);
btn1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
mListenerA.methodA(true);
}
});
return myView;
}
public void showBtnMethod (Boolean showBtn){
if (showBtn==false) {
btn1.setVisibility(View.INVISIBLE);
mListenerB.methodB(true); //***** problematic line
}
}
}
and the code in the main activity is below. please note that on the first line I was able only to implement one method from the fragment.
public class MainActivity extends AppCompatActivity implements Fragment1.ListenerA {
private static final String TAG = "MainActivity";
public Fragment1 mFragment1;
public Fragment2 mFragment2;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
FragmentTransaction transaction1 = getSupportFragmentManager().beginTransaction();
mFragment1 = new Fragment1();
transaction1.replace(R.id.content_fragment_ID, mFragment1);
transaction1.commit();
}
}
// this gets called by ListenerA when click on the button
public void methodA(Boolean in){
if (in==true){
Toast.makeText(MainActivity.this, "mMethodA Executed", Toast.LENGTH_SHORT).show();
triggerShowMethod();
}
};
private void triggerShowMethod(){
mFragment1.showBtnMethod(false);
};
// Problematic section is below
public void methodB(Boolean in){
if (in==true){
FragmentTransaction transaction2 = getSupportFragmentManager().beginTransaction();
mFragment2 = new Fragment2();
transaction2.replace(R.id.content_fragment_ID, mFragment2);
transaction2.commit();
Toast.makeText(MainActivity.this, "mMethodB Executed", Toast.LENGTH_LONG).show();
}
};
}
You can simply consolidate both interfaces into one:
public interface Listener{
public void methodA(Boolean in1);
public void methodB(Boolean in2);
};
and in your MainActivity:
public class MainActivity extends AppCompatActivity implements Fragment1.Listener
Your activity doesn't implement ListenerB.
public class MainActivity extends AppCompatActivity implements Fragment1.ListenerA, Fragment1.ListenerB {
}
I have an Activity that starts a Fragment. Inside that fragment i have an EditText. And when i get the text that the user types there, i want to get that from my Activity with the help of an interface. I'm using this guide
On my MainActivity i'm implementing the commentListener interface and i've managed to get the result inside the onCommentEntered method. But on doneListener, which is triggered when the user presses a button finishing the activity, i'm getting null.
Obviously onCommentEntered runs after doneListener.
Any suggestions on how to get the result on doneListener?
class MainActivity implements fragment.commentListener{
static String comment;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.addtransaction);
done=(TextView)findViewById(R.id.done_button);
}
// called when user presses a button and MainActivity finishes.
public void doneListener(View v){
// Here i get NULL
System.out.println(comment);
finish();
}
#Override
public void onCommentEntered(String data) {
comment=data;
// Here i get what the user typed
System.out.println(comment);
}
}
My fragment
public class thefragment extends Fragment {
commentListener cListener;
static TextView note;
EditText comment;
public interface commentListener{
void onCommentEntered(String data);
}
public static thefragment newInstance(){
return new thefragment ();
}
public thefragment (){
}
#Override
public void onAttach(Context context) {
super.onAttach(context);
cListener=(commentListener) context;
}
#Override
public void onDetach() {
super.onDetach();
cListener=null;
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v;
v=inflater.inflate(R.layout.fragment, container, false);
comment=(EditText)v.findViewById(R.id.comment_picker);
comment.setOnFocusChangeListener(new View.OnFocusChangeListener() {
#Override
public void onFocusChange(View v, boolean hasFocus) {
if (!hasFocus) {
cListener.onCommentEntered(comment.getText().toString());
}
}
});
return v;
}
}
Create a new Interface, as well as implement the same in Fragment. create a method in the interface and override the same in Fragments. While calling the fragment from Activity create an Interface type fragment and call the interface method.
eg:
public class thefragment extends Fragment implement fragmentNofyInterface {
...
#Override
protected void notify(String txt){
mTvTxt.setText(txt);
}
.....
}
Interface Format
public interface fragmentNofyInterface {
protected void notify(String txt);
}
Activity format
class MainActivity implements fragment.commentListener{
.....
private fragmentNofyInterface mFragmentNotifier;
.........
thefragment mFragment = new thefragment();
mFragmentNotifier = (fragmentNofyInterface ) mFragment;
FragmentTransaction transaction = mFragmentMngr.beginTransaction().
add(R.id.rl_fragment_navigation_container,
mFragment);
transaction .commit();
......
//Notify the fragment when you required
mFragmentNotifier.notify("hello world");
}
Switching to addTextChangedListener and TextWatcher for my EditText, like this here,
seems to fix my problem.Now onCommentEntered method is called before doneListener and thus String commentgets whatever was typed in the EditText.Thanks everyone for helping.
I have this interface in my activity.
public interface LogoutUser {
void logout();
}
My fragment implements this interface, so in my fragment, I have this:
#Override
public void logout() {
// logout
}
In my activity I call
mLogoutUser.logout();
Where mLogoutUser is of the type LogoutUser interface.
My issue is the mLogoutUser object that is null. How can initialize it?
Thank you!
As I said in my comment, I resolved this issue using onAttach method in my fragment, but in this way you have to have the callback field (mLogoutUser in this case) declared in the fragment, and initialize it this way:
public class MyFragment extends ListFragment {
LogoutUser mLogoutUser;
// Container Activity must implement this interface
public interface LogoutUser {
public void logout();
}
#Override
public void onAttach(Context context) {
super.onAttach(context);
// This makes sure that the container activity has implemented
// the callback interface. If not, it throws an exception
try {
mLogoutUser = (LogoutUser) context;
} catch (ClassCastException e) {
throw new ClassCastException(context.toString()
+ " must implement LogoutUser");
}
}
...
}
More info in Communicating with Other Fragments.
But if your case is the field declared in the activity, you can use the onAttachFragment method from your activity to initialize your listener field this way:
#Override
public void onAttachFragment(Fragment fragment) {
super.onAttachFragment(fragment);
mLogoutUser = (LogoutUser) fragment;
}
Also, you can use an event bus to make this communication between fragments and activities. An option is the Otto library, from Square.
Sample for creating callback from Fragment to Activity
public interface CallBackListener {
void onCallBack();// pass any parameter in your onCallBack which you want to return
}
CallBackFragment.class
public class CallBackFragment extends Fragment {
private CallBackListener callBackListener;
public CallBackFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_call_back, container, false);
}
#Override
public void onActivityCreated(#Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
//getActivity() is fully created in onActivityCreated and instanceOf differentiate it between different Activities
if (getActivity() instanceof CallBackListener)
callBackListener = (CallBackListener) getActivity();
}
#Override
public void onViewCreated(View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
Button btn = (Button) view.findViewById(R.id.btn_click);
btn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if(callBackListener != null)
callBackListener.onCallBack();
}
});
}
}
CallbackHandlingActivity.class
public class CallbackHandlingActivity extends AppCompatActivity implements CallBackListener
{
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_all_user);
}
#Override
public void onCallBack() {
Toast.makeText(mContext,"onCallback Called",Toast.LENGTH_LONG).show();
}
}
Android Fragments - Communicating with Activity
You need to get a reference to your fragment with getFragmentById() or getFragmentByTag()
getFragmentManager().findFragmentById(R.id.example_fragment);
You can use kotlinx Channel to send data or callback between fragments and activity or vice versa
In your Mainactivity:
val loginPromptChannel = Channel<LoginPromptState>()
val loginStateFlow = loginPromptChannel.receiveAsFlow()
//onCreate
lifecycleScope.launchWhenStarted {
loginStateFlow.collect() { state ->
when (state) {
is LoginPromptState.Login -> {
//smooth scroll to login fragment
binding.viewpager.setCurrentItem(2, true)
}
}
}
}
//create sealed a class
sealed class LoginPromptState {
object Login : LoginPromptState()
}
In your fragment send callback like:
lifecycleScope.launch {
val channelLogin = (activity as MainActivity).loginPromptChannel
channelLogin.send(MainActivity.LoginPromptState.Login)
}