Develop Reference

how to change fragment views programmatically from the parent activity

I am having a fragment that contains for example one button, I want to allow the Activity containing the fragment to change this button view like for example color and title or src Image.
What's the best way to do that ?
Update : sorry If I wasn't clear enough but I want the activity to change the whole view as it's likes , like setting the padding, the color or anything.
It will create the view programmatically and the fragment should replace the old view by the new one and change the view's ID so that the fragment code isn't affected. And If i created methods in the fragment that takes these views when should the Main activity call them ? since the activity has to wait for the layout of the fragment to be created.

1. You must get you fragment from your activity
val fragment = supportFragmentManager.findFragmentByTag("tag")
or
val fragment = supportFragmentManager.findFragmentById(R.id.fragment)
2. Create a method that will do what you wants in you fragment and call this method from the activity
fragment.hideButton()
or you can use interface

Try this way according to your requirement
public abstract class BaseFragment extends Fragment {
BaseActivity yourActivity;
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
#Override
public void onAttach(Context context) {
super.onAttach(context);
yourActivity = (BaseActivity) context;
}
#Override
public void onDetach() {
yourActivity = null;
super.onDetach();
}
public void refreshview(){}
public void setDada(Data data){}
#override
publicn void onStart(){
yourActivity.setCurrentOpenedFragment(this);
}
}
Create the BaseActivity class
public abstract class BaseActivity extends AppCompatActivity{
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
public void setCurrentOpenedFragment(BaseFragment currentFragment){}
}
Extends the BaseFragment in your fragment i.e.
public class YourFragment extends BaseFragment{
View view;
Button button;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
view = inflater.inflate(R.layout.fragment, container, false);
button = (Button)view.findViewById(R.id.button);
return view;
}
#override
publicn void onStart(){
super.onStart();
//yourActivity.setCurrentOpenedFragment(this);
}
Data data;
#override
public void setDada(Data data){
this.data = data;
}
#Override
public void refreshview() {
button.setcolor(data.getcolor());
}
}
Write the below line of code in your Activity class
public class YourActivity extends BaseActivity{
public static final byte NONE = -1;
public static final byte HOME = 1;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.your_activity);
changeFragment(new YourFragment(), HOME);
initview();
}
public void initview(){
Button b = (Button)findViewById(R.id.button);
b.setOnClickListener(new OnClickListener(){
if(currentFragmentOnDrawer != null){
Data data = new Data();
data.setColor(getResource().getcolor(R.color.red));
currentFragmentOnDrawer.setDada(data);
currentFragmentOnDrawer.refreshview()
}
});
}
BaseFragment currentFragmentOnDrawer;
#Override
public void setCurrentOpenedFragment(BaseFragment currentFragment) {
super.setCurrentOpenedFragment(currentFragment);
this.currentFragmentOnDrawer = currentFragment;
}
public void changeFragment(Fragment targetFragment, byte state) {
FragmentTransaction ft = getSupportFragmentManager()
.beginTransaction();
ft.replace(R.id.main_fragment, targetFragment, "" + state);
ft.addToBackStack("" + state);
ft.commit();
}
}
Hope it will help for you

Creating Multiple event callbacks from fragment to the activity

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 {
}

onAttach() activity parameter null?

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;
}
}

Communication between Fragments in ViewPager

I'm trying to do this: http://android-er.blogspot.com/2012/06/communication-between-fragments-in.html
Except that I'm using a FragmentStatePagerAdapter
I have an Activity with two fragments(FragmentA & FragmentB)
FragmentA has an edittext and a button, FragmentB has a textview
Now all I want is that whenever I enter something in the edittext and click the button, that something will appear on my textview.
MainActivity:
public class MainActivity extends FragmentActivity {
ViewPager viewPager = null;
String TabFragmentB;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
viewPager = (ViewPager)findViewById(R.id.pager);
FragmentManager fragmentManager = getSupportFragmentManager();
viewPager.setAdapter(new MyAdapter(fragmentManager));
}
public class MyAdapter extends FragmentStatePagerAdapter {
public MyAdapter (FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int i) {
Fragment fragment = null;
if (i == 0)
{
fragment = new FragmentA();
}
if (i == 1)
{
fragment = new FragmentB();
}
return fragment;
}
#Override
public int getCount() {
return 2;
}
}
public void setTabFragmentB(String t) {
TabFragmentB = t;
}
public String getTabFragmentB() {
return TabFragmentB;
}
}
FragmentA:
public class FragmentA extends Fragment {
EditText et;
Button bt;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fraga, container, false);
et = (EditText)v.findViewById(R.id.edit1);
bt = (Button)v.findViewById(R.id.button1);
bt.setOnClickListener(Click);
return v;
}
OnClickListener Click = new OnClickListener(){
#Override
public void onClick(View v) {
String textPassToB = et.getText().toString();
String TabOfFragmentB = ((MainActivity)getActivity()).getTabFragmentB();
FragmentB fragmentB = (FragmentB)getActivity()
.getSupportFragmentManager()
.findFragmentByTag(TabOfFragmentB);
fragmentB.updateText(textPassToB);
}
};
}
FragmentB:
public class FragmentB extends Fragment {
TextView tv;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragb, container, false);
tv = (TextView)v.findViewById(R.id.text1);
String myTag = getTag();
((MainActivity)getActivity()).setTabFragmentB(myTag);
return v;
}
public void updateText(String t){
tv.setText(t);
}
}
LogCat:
FATAL EXCEPTION: main
java.lang.NullPointerException
at lmf.sample1.FragmentA$1.onClick(FragmentA.java:43)
at android.view.View.performClick(View.java:4212)
at android.view.View$PerformClick.run(View.java:17476)
at android.os.Handler.handleCallback(Handler.java:800)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5371)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
at dalvik.system.NativeStart.main(Native Method)
Whenever I click the button on my first fragment, my app crashes. What the hell is the problem?

You could use Intents (register broadcast receiver in fragment B and send broadcasts from fragment A.
Use EventBus: https://github.com/greenrobot/EventBus. It's my favorite approach. Very convinient to use, easy communications between any components (Activity & Services, for example).
Steps to do:
First, create some class to represent event when your text changes:
public class TextChangedEvent {
public String newText;
public TextChangedEvent(String newText) {
this.newText = newText;
}
}
Then, in fragment A:
//when text changes
EventBus bus = EventBus.getDefault();
bus.post(new TextChangedEvent(newText));
in fragment B:
EventBus bus = EventBus.getDefault();
//Register to EventBus
#Override
public void onCreate(SavedInstanceState savedState) {
bus.register(this);
}
//catch Event from fragment A
public void onEvent(TextChangedEvent event) {
yourTextView.setText(event.newText);
}

Fragments have access to there parent Activity.
Therefore the simplest approach is to register a callback in the parent Activity.
Update: Submit cache added to MainActivity.
public class MainActivity extends FragmentActivity {
private OnButtonClicked mOnButtonClicked;
private String mSubmitCache;
public interface OnButtonClicked {
void submit(final String s);
}
public void setOnButtonClicked(final OnButtonClicked c) {
mOnButtonClicked = c;
// deliver cached string, if any
if (TextUtils.isEmpty(mSubmitCache) == false) {
c.submit(mSubmitCache);
}
}
public void buttonClicked(final String s) {
if (mOnButtonClicked == null) {
// if FragmentB doesn't exist jet, cache value
mSubmitCache = s;
return;
}
mOnButtonClicked.submit(s);
}
}
public class FragmentA extends Fragment implements OnClickListener {
private MainActivity mMain;
private Button mButton;
#Override public onAttach(Activity a) {
mMain = (MainActivity) a;
}
#Override public void onClick(View v) {
mMain.buttonClicked("send this to FragmentB.");
}
}
public class FragmentB extends Fragment implements MainActivity.OnButtonClicked {
private MainActivity mMain;
private TextView mTextView;
// Called when the fragment's activity has been created
// and this fragment's view hierarchy instantiated
#Override public void onActivityCreated(Bundle savedState) {
mMain = (MainActivity) getActivity();
mMain.setOnButtonClicked(this);
}
#Override void submit(final String s) {
mTextView.setText(s);
}
}

I use Mr. Rodion's solution above. But in addition, Android Studio asked me to add #Subscribe annotation before onEvent method.
Like this:
#Subscribe
public void onEvent(TextChangedEvent event) {
textView.setText(event.newText);
}
According to EventBus’ API:
Subscribers implement event handling methods (also called “subscriber methods”) that will be called when an event is posted. These are defined with the #Subscribe annotation. Please note that with EventBus 3 the method name can be chosen freely (no naming conventions like in EventBus 2).

FragmentB is not even created until you switch to it so fragmentB.updateText(textPassToB); gives you NullPointerException.
You will need to store the text from the EditText in your activity and later when (if) the FragmentB is created you will need to read value from it.

How to make a callback between Activity and Fragment?

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)
}