Develop Reference

How to use Button to switch fragments in a ViewPager?

I have 3 main fragments inside viewpager and they have couple of buttons. I want each button to navigate to another fragment and back button to get back to main fragment. I tried to add fragment transaction but it does not work. What am I doing wrong here?
this is one of the main fragments
public class OneFragment extends Fragment implements View.OnClickListener{
public OneFragment() {
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_one, container, false);
}
#Override
public void onClick(View v) {
switch (v.getId()){
case R.id.aButton:
FragmentManager manager = getFragmentManager();
FragmentTransaction transaction = manager.beginTransaction();
transaction.replace(R.id.fragment_one, AFragment.newInstance());
transaction.commit();
break;
}
}
}
this is the fragment I want to navigate
public class AFragment extends Fragment{
public AFragment() {
}
public static AFragment newInstance() {
AFragment fragment = new AFragment();
return fragment;
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.a_fragment, container, false);
}
}

First, define a public method in your Activity to switch tabs in the ViewPager, and also define the onBackPressed() override, which will select the first index when the back button is pressed:
public void selectIndex(int newIndex) {
mViewPager.setCurrentItem(newIndex);
}
#Override
public void onBackPressed() {
int currentPosition = mViewPager.getCurrentItem();
if (currentPosition != 0) {
mViewPager.setCurrentItem(0);
} else {
super.onBackPressed();
}
}
Then, modify the click listener in the Fragment in order to call the selectIndex() method:
#Override
public void onClick(View v) {
switch (v.getId()){
case R.id.aButton:
//select the index of AFragment:
((MainActivity)getActivity()).selectIndex(1);
break;
}
}

How to switch between fragments using buttons

Fragment 1:
public class homePage extends Fragment {
private OnFragmentInteractionListener mListener;
private View view;
public homePage() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
view = inflater.inflate(R.layout.fragment_home_page, container, false);
Button btnLogin = (Button) view.findViewById(R.id.login);
Button btnRegister = (Button) view.findViewById(R.id.register);
btnLogin.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
loginView();
}
});
btnLogin.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
registerView();
}
});
return view;
}
public static homePage newInstance() {
homePage fragment = new homePage();
Bundle args = new Bundle();
return fragment;
}
public void registerView(){}
public void loginView(){}
public interface OnFragmentInteractionListener {
}
}
Acitivty :
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
homePage homepage = new homePage();
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, homepage)
.commit();
}
}
}
My fragment1 has two buttons with the id's "login" and "register". Whenever login is clicked, I want to go to my fragment_login.xml, and when register is clicked I want to go to my fragment_register.xml. Should I create these functions in my activity or in my fragment? And how should I do this? I'm fairly new to android and I'm trying to learn these basic things atm. Thanks for the help :(
Login context: "com.example.hoofdgebruiker.winkelskortrijk.login"
Register context: "com.example.hoofdgebruiker.winkelskortrijk.register"

You have to make a communication between Fragment objects via an Interface.
The Activity that make the switch between your fragments needs to implement that Interface.
So, in your case your classes must be defined as follows. This is your Interface, it helps you to tell your activity that a button has been clicked from within your Fragment:
public interface HomeClickListener {
void onLoginClick();
void onRegisterClick();
}
Your Activity needs to implement the above interface in order to be notified when a button has been clicked:
public class HomeActivity extends Activity implements HomeClickListener {
void onLoginClick() {
// Your activity code to replace your current Fragment with your Login fragment
}
void onRegisterClick() {
// Your activity code to replace your current Fragment with your Register fragment
}
}
Your fragment is hosted by an Activity, so you need to have a reference to it and notify it via an Interface:
public class LoginFragment extends Fragment {
final HomeClickListener homeClickListener
#Override
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 {
homeClickListener = (homeClickListener) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString() + " must implement OnHeadlineSelectedListener");
}
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
view = inflater.inflate(R.layout.fragment_home_page, container, false);
Button btnLogin = (Button) view.findViewById(R.id.login);
Button btnRegister = (Button) view.findViewById(R.id.register);
btnLogin.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
homeClickListener.onLoginClick();
}
});
btnLogin.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
homeClickListener.onRegisterClick();
}
});
return view;
}
}
More information here.

Android crashes on calling FragmentTransaction Replace method?

What I am trying to do is to use only one Activity as a host for many fragments such as the activity will host only one fragment at a time and the fragments should attached to the activity in a certain order.
My Fragment code:
public class FirstFragment extends Fragment{
//some code here to instantiate FirstFragment here.
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.main, container, false);
Button button = (Button) view.findViewById(R.id.button1);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
((MainActivity) getActivity()).onFirstFragmentFinished(position);
}
});
return view;
}
// Container Activity must implement this interface
public interface FirstFragmentListener {
public void onFirstFragmentFinished(int position);
}
}
Simply, in each fragment I have a button when pressed it will get the host activity and call the implemented method of FirstFragmentListener interface.
public class MainActivity extends AppCompatActivity implements FirstFragmentListener {
#Override
public void onCreateView(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTra = fragmentManager.beginTransaction();
fragmentTra .replace(R.id.main_layout, new FirstFragment());
fragmentTra.commit();
}
#Override
public void onFirstFragmentFinished(int position)
{
if(position == 1)
{
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTra = fragmentManager.beginTransaction();
fragmentTra .replace(R.id.main_layout, new SecondFragment());
fragmentTra.commit();
}
}
}
When the activity is created, always replace whatever inside this activity with FirstFragment layout.
When the FirstFragment finishes its work and the button on that fragment is pressed, it will call the implemented method of FirstFragment interface on this activity and then check the position for some value, if the condition is correct then go and replace FirstFragment with The SecondFragment instance.
The app is crashing when commit() method is called.

Use of your onFirstFragmentFinished is wrong. Look at official doc:
android-comunication-activity-ffragment
It is prefer to Override onAttach() method.

In Fragment you need View to bind with fragment like this :
public class FirstFragment extends Fragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.main, container, false);
Button button = (Button) view.findViewById(R.id.button1);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if(position == 1){
SecondFragment secondFrag= new SecondFragment();
getActivity().getFragmentManager().beginTransaction()
.replace(R.id.main_layout, secondFrag)
.addToBackStack(null)
.commit();
}
}
});
return view;
}
}

I look at my stack trace and I found this exception:
com.example.exchange.msbexchange E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.exchange.msbexchange, PID: 17975
java.lang.RuntimeException: com.example.exchange.msbexchange.MainActivity#1e7d93b must implement OnFragmentInteractionListener
at com.example.exchange.msbexchange.CurrencyFragment.onAttach(CurrencyFragment.java:83)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1030)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1259)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1624)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:517)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:6117)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
It is obviousely because my MainActivity does not implement the interface of the SecondFragment Class. I did not know this is mandatory for the fragments to work. I just need to implement the interface and now it is working.

you need implement your interface FirstFragmentListener in onAttach in fragment
FirstFragmentListener mCallback;
#Override
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 = (FirstFragmentListener) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString()
+ " must implement OnHeadlineSelectedListener");
}
}
then use it as you do on click or what ever you want

Where do you get position variable from? It seems that this variable does not have value...
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.main, container, false);
Button button = (Button) view.findViewById(R.id.button1);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
((MainActivity) getActivity()).onFirstFragmentFinished(position);
}
});
return view;
}

Issue with onClickListener for Button in Fragment

I have a button in a fragment class that I'd like to have trigger a method in the parent activity. I've implemented an interface for this.
My issue is that the View.onClickListener is giving me the following error:
Class 'Anonymous class derived from onClickListener' must either be declared abstract or implement abstract method 'onClick(View)' in 'onClickListener'
Which is odd, because I'm implementing onClick(View).
Here is the code in my Fragment:
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(com.zlaporta.chessgame.R.layout.gamedescfragment, container, false);
final Button make_move = (Button) v.findViewById(R.id.make_move);
make_move.setOnClickListener(new ***View.OnClickListener()*** {
public void OnClick(View v) {
makeMoveCallback.makeMoveMethod();
}
});
The stars indicate the portion of the code that Android Studio doesn't like.

Do it using Anonymous inner class in an object:
//declaring OnClickListener as an object
private OnClickListener btnClick = new OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
}
};
//passing listener object to button
make_move.setOnClickListener(btnClick);
Hope this will help :)

Just a typo: Replace the method name
OnClick
with
onClick

Could you try passing the OnClickListener from a method
e.g.,
private View.OnClickListener getButtonOnClickListener() {
return new View.OnClickListener() {
#Override
public void onClick(View v) {
// this is the code
}
};
}
and then using make_move.setOnClickListener(getButtonOnClickListener());

This is best way to using click event for button. using onClick listener implementing. use below code.
public class MyFragment extends Fragment implements OnClickListener {
Button mButton;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.main_layout, null);
mButton = (Button) view.findViewById(R.id.button1);
mButton.setOnClickListener(this);
return view;
}
#Override
public void onClick(View v) {
if (v == mButton) {
// Do something on click button
}
}
}
If using every click event separately it take more space. its better to use this code.

Add #Override above onClick method

Or you can use below method of button click Listener in OnActivityCreated() methos of Fragment.
make_move.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View view) {
makeMoveCallback.makeMoveMethod();
}
});

Call a fragmentMethod from another fragment, but can't refer to them in parentFragmentActivity's View pager

I m new to android and i m having trouble with fragment communication, reading about it discovered the standard method of creating an interface and implementing it from the parentActivity which doesn't work in my case which is as follows.
I have an Activity named as ActivityA which extends fragment activity,in which i have a view pager for i want to keep two fragments namely fragmentA and fragmentB which should be swipable fragments.
fragmentA has a button which onClicked should make a change in fragmentB, to be precise on click it should add a string in the listView in fragmentA.
Now i have created the both the fragments's layouts as well as added the viewPAger to my FragmentActivity, they work great on swiping, the function is executed onButtonClick of fragmentA and logic works perfectly, after this is i want the changes to be reflected in fragmentB.
Using the interface method i can't find the reference to my fragment by id as it is added by viewPager to ActivityA
How do i do this??
help me out.
Stackoverflow says don't ask questions with out code so
Here is the Sample code
Activity A which has a virewPAger, need help how to get my fragment's Reference from the viewPager
public class ActivityA extends FragmentActivity implements FragmentA.Communicator
{
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_A);
viewPager= (ViewPager) findViewById(R.id.pager);
fragmentManager=getSupportFragmentManager();
viewPager.setAdapter(new myAdapter(fragmentManager));
}
class myAdapter extends FragmentPagerAdapter{
public myAdapter(FragmentManager fragmentManager) {
super(fragmentManager);
}
#Override
public Fragment getItem(int i) {
Fragment fragment = null;
switch (i){
case 0: fragment = new listOfIDsScanned();
break;
case 1: fragment = new displayCounter();
break;
default: //something witch won't crush the app
break;
}
return fragment;
}
#Override
public int getCount() {
return 2;
}
}
This is fragmentA , actual fragment name is something else just for simple representation calling it fragmentA, which has an interface Communicator to communicate between fragments
public class fragmentA extends android.support.v4.app.Fragment implements View.OnClickListener
{
TextView counter;
Button scanStudentID;
int count=0;
String name=null,rollNo=null;
#Override
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
return inflater.inflate(R.layout.display_counter,container,false);
}
#Override
public void onActivityCreated(#Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
scanStudentID= (Button) getActivity().findViewById(R.id.startScanning);
scanStudentID.setOnClickListener(this);
}
#Override
public void onClick(View v)
{
switch(v.getId()){
case R.id.startScanning:
startScanning();
break;
}
}
public void startScanning()
{
startActivityForResult(new Intent(getActivity(),Barcode.class),1);
}
public interface Communicator
{
// necessary methods
}
}
now finally fragmentB, in which methodToBeCalled(parameters) has to be invoked on the button click in fragementA
public class fragementB extends android.support.v4.app.Fragment
{
ListView listView;
ArrayList<String> rollNo= new ArrayList<>();
ArrayList<String> studentName= new ArrayList<>();
#Override
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_list_of_ids_scanned,container,false);
}
#Override
public void onActivityCreated(#Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
listView= (ListView) getActivity().findViewById(R.id.listView);
}
public void methodToBeCalled(String rollNo,String studentName)
{
if(!alreadyScanned(rollNo))
{
}
else
{
}
}
boolean alreadyScanned(String rollNo)
{
return true;
}
}