I want to pass a data object to Fragment, here are two ways to do this:
public class MyFragment extends Fragment {
private Serializable way1;
private Serializable way2;
public void setDataWay1(Serializable way1) {
this.way1 = way1;
}
public void setDataWay2(Serializable way2) {
Bundle data = new Bundle();
data.putSerializable("data", way2);
setArguments(data);
}
}
So, what is the difference between the 2 ways? Sometimes, way1 may cause NullPointerException,why? If I want to pass a OnClickListener to Fragment, what should I do?
While both methods can set the appropriate data to your fragment for first time initialization. Note that fragments will be recreated and destroyed by the system (for example on screen rotation). When that happens the system will not really call the setter way (method 1) hence, it will be a giant FAIL. Therefore, it is recommended to use the setArguments() way.
Related
Hello fellow Android developers,
I wanna know how do you guys pass complex non serializable (& non parcelable) object to fragments. (such as Listener, Api client, ...)
Let me explain my use case:
The use case
I'm building an Android application composed of one "host" activity and 3 fragments.
Currently I'm passing the object using a custom constructor on the fragment (bad practice I know).
The fragments constructors looks like the following:
/**
* Do not remove ever or you'll face RuntimeException
*/
public FirstFragment() {
}
public FirstFragment(Session session,
ApiClient apiClient,
FirebaseAnalytics firebaseAnalytics) {
mSession = session;
mApiClient = apiClient;
mFirebaseAnalytics = firebaseAnalytics;
}
And I'm using them in the host activity like this
private FirstFragment getFirstFragment() {
if (mFirstFragment == null) {
mFirstFragment = new FirstFragment(mSession, mApiClient, mFirebaseAnalytics);
}
return mHomeFragment;
}
[...]
private void loadFragment(Fragment fragment, String tag) {
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.frame_container, fragment, tag);
transaction.commit();
}
[...]
private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
= new BottomNavigationView.OnNavigationItemSelectedListener() {
#Override
public boolean onNavigationItemSelected(#NonNull MenuItem item) {
switch (item.getItemId()) {
case FIRST_FRAGMENT_RES_ID:
toolbar.setTitle(R.string.first_fragment_title);
loadFragment(getFirstFragment(), "first_fragment");
return true;
[...]
}
return false;
}
};
This solution works well almost all the time. But sometimes (and I don't know when exactly) the default constructor is invoked and therefore all local members are null.
Possible solutions
To solve the problem I'm thinking about the following solutions:
Singletons, singletons everywhere
Most of the objects I'm passing are singletons therefore I can access them in the default constructor of the fragments:
public FirstFragment() {
mSession = Session.getInstance(getContext());
mApiClient = ApiClient.getInstance(getContext());
mFirebaseAnalytics = FirebaseAnalytics.getInstance(getContext());
}
Problems
However the above solution wouldn't work if I need to pass a callback or something. How can it be done like this then?
Access the objects using parent activity
I think it's one of the ugliest possible solutions because it will couple the Fragments to the parent activity. The idea is something like this
public FirstFragment() {
mSession = Session.getInstance(getContext());
mApiClient = ApiClient.getInstance(getContext());
mFirebaseAnalytics = FirebaseAnalytics.getInstance(getContext());
mListener = (Listener) getActivity(); // <- will works because parent activity implement the interface
}
Using broadcast & receiver
The idea is to keep passing singleton everywhere and use broadcast & receiver instead of listener.
How do you guys managed this scenario?
Thanks in advance !
You probably want to look into dependency injection (using a tool like Dagger or alternatives), especially for objects like an Api Client. Post the setup, you'd define, just once, how an Api Client instance could be constructed. And later you can use it pretty much everywhere with a one-line statement. The instance is guaranteed to be available upon the fragment instantiation. Further reading: https://dagger.dev/tutorial/
According to your use case, it might be easier to use a ViewModel and store your objects there. Your ViewModel will be shared across your fragments and your host
activity.
See https://developer.android.com/topic/libraries/architecture/viewmodel
Have you considered using "Shared" ViewModel?
Essentially, a sub-class of ViewModel (which is class designed to store and manage UI-related data in a lifecycle conscious way for activities and fragments) can be created like below,
class SharedViewModel : ViewModel()
Inside this class you can have your custom objects with their correct state
Next, in your 1st Fragment you can obtain a handle to this SharedViewmodel like below,
class MasterFragment : Fragment() {
private lateinit var model: SharedViewModel
And obtain the handle to it using below code,
model = activity?.run {
ViewModelProviders.of(this)[SharedViewModel::class.java]
}
You can write your own logic/method/flow inside SharedViewModel to manipulate any custom object's states.
And once all this is done, In your 2nd Fragment, you can create the handle to SharedViewModel similar to above code and using SharedViewModel object you can retrieve the "modified" custom object from same SharedViewModel
It's been several months and I have now come up with a different solution.
For the UI related data
For the UI related stuff I'm now using the androidx livedata
For the complex non serializable data
My use case was to pass complex object to the fragment, such as manager, parent activity (trough a listener), etc... The approach I have taken is by injecting these data manually from the parent activity.
The first things to do was to remove the objects from the fragment constructor and use the default constructor instead, so that I won't face any instantiation errors.
Then I have created an inject() method on the fragment classes that look like this:
public void inject(BillingManager billingManager, Listener listener) {
mBillingManager = billingManager;
mListener = listener;
}
Each fragment will have their own inject method width the objects that should be injected as parameters.
In the parent activity I have override the onAttachFragment() method to handle the fragment attach process:
#Override
public void onAttachFragment(#NonNull Fragment fragment) {
super.onAttachFragment(fragment);
if (fragment.getClass().equals(FirstFragment.class)) {
((FirstFragment) fragment).inject(mBillingManager, this);
} else if (fragment.getClass().equals(HomeFragment.class)) {
((HomeFragment) fragment).inject(this);
}
}
Simple, and now everything work great.
I have 5 fragments in ViewPager used to fill business object with several fields step by step, in each step some of those fields will be set. I've read many articles about communication between fragments but I'm not feeling comfortable the way others preferred, so after thinking about HOW should I do this in my case, finally I start thinking to use singleton model object which all fragments can easily access to its fields and fill them in specific steps.
As I'm new to android I want to hear from experts about using singleton instead of passing data between fragments such as implemented interface(It seems its so complicated and hard to maintenance). Any advice will be helpful.
While singleton approach seems easy to implement and understand it is way not to best way to achieve what you need. One reason is that your model object or as you call it business object lives outside of your activity's context which can create hard to find bugs. E.g. in case when more than one instance of your activity class is created by system and both keep reference to your singleton. See how you lose track of your objects?
What I would do is
Make my model object to implement Parcelable you will hate it at the beginning but once you get use to it it will become your model's best friend
Since your model is parcelable now you can easily pass it between fragments, activities, and even save it in shared preferences. One important thing to note here when you pass your parcelable between fragment or activity it is like pass by value, i.e. every time new instance is created.
Set your fragment's argument or if it is already instantiated then get arguments and add your model. here is an example:
if a fragment is not active yet:
Bundle args = new Bundle();
args.putParcable("businessObject", yourBusinessObjectThatIsParcable);
yourFragment.setArguments(args);
Otherwise:
yourFragment.getArguments().putParcelable("businessObject", yourBusinessObjectThatIsParcable);
In your fragment perhaps in onCreateView method get your model object like this MyParcableObject mpo = (MyParcableObject)getArguments().getParcelable("businessObject") and use it set whatever data you want.
When you finish editing your object on button click or in onPause method updated your fragment's arguments same way getArguments().putParcelable("businessObject", mpo);
in your last page or last fragment you can pass your object to your activity, here is how to do it
Even though it looks cumbersome but it is a practice that you need to get used to as an android developer. You get lot more control when your model implements parcelable.
Another way to do what you need is thru Delegation Pattern but it is mostly used for callbacks even though you can pass objects as well.
I wouldn't recommend a global singleton. There are two main reasons:
By definition, a singleton limits your app to a single instance of the main business object. If you (or a designer, or your boss's boss's boss) ever decide to have multiple of these ViewPagers at a time, you will have to change your architecture anyways.
The "Android way of thinking" is to expect that your user may put your app in the background and use other apps before returning to your app. If the system decides to kill your app in the background, then your singleton memory object will be destroyed, and your user will have lost all of their progress. The correct Android way to save state is by keeping the state in an Activity or Fragment, saving it appropriately in onSaveInstanceState(), and restoring it in onCreate().
All of the Fragments in the ViewPager can get a reference to the parent Activity via a call to getActivity(). Or if your ViewPager is within a Fragment, then all of the Fragments can access the parent Fragment via a call to getParentFragment(). You can then cast the result to the appropriate class (or better yet, interface) and make method calls to pass data back and forth. Keep track of your business data in the parent Activity/Fragment. This way, you don't need a global singleton
For example,
public class MyParentFragment extends Fragment {
private String mPageOneData;
private int mPageTwoData;
private List<Date> mPageThreeData;
public void setPageOneData(String data) {
mPageOneData = data;
}
...
}
public class PageOneFragment extends Fragment {
private void sendDataToParent(String data) {
Fragment f = getParentFragment();
if (f != null && f instanceof MyParentFragment) {
MyParentFragment parent = (MyParentFragment) f;
f.setPageOneData(data);
}
}
}
you can save your data in onSaveInstanceState() event of the activity in case your process will go into the background.
you can restore your data in onCreate() event by using Bundle and getExtras().
you can save your data in application class and the data will still be there in case your process will go into the background.
i prefer the first option because you don't want to make a mess in the application class with all the data from different activities and fragments.
I hope i could help :)
Have you checkout EventBus?
I'm not sure if it is the best approach, specially when your question is too broad, however it will be cool with just 5 fragments.
Hope it helps
I suppose in your MainActivity there is a ViewPager, and FragmentOne will be one of the fragments inside the view pager. Here the MainActivity is communicating to the FragmentOne to refreshhis adapter. Hope is clear.
In your MainActivity add this interface:
public interface Updateable {
public void update();
}
Implement this interface in a fragment that needs to be updated, and write the code to notify the adapter inside the update method:
public class FragmentOne extends Fragment implements MainActivity.Updateable {
...
#Override
public void update() {
// YOUR CODE TO UPDATE HERE, FOR EXAMPLE, HERE I'M UPDATING THE ADAPTER
if ( adapter != null ) {
adapter.notifyDataSetChanged();
} else {
Log.d("LOG_TAG", "null");
}
}
...
}
Call the update method from the MainActivity when the fragment loads first. You can do this overriding the getItemPosition method in your PagerAdapter, like this:
#Override
public int getItemPosition(Object object) {
if ( object != null && object instanceof FragmentOne ) {
FragmentOne f = (FragmentOne) object;
f.update();
}
return super.getItemPosition(object);
}
Finally, you have to call notifyDataSetChanged() of your viewPager adapter. This will force the adapter of your viewpager to call the getItemPosition method.
mViewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
int previousState;
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
#Override
public void onPageSelected(int position) {
}
#Override
public void onPageScrollStateChanged(int state) {
if (previousState == ViewPager.SCROLL_STATE_SETTLING && state == ViewPager.SCROLL_STATE_IDLE) {
if ( viewPagerAdapter.getItem(viewpager.getCurrentItem()) instanceof Pictures ) {
Log.d("LOG_TAG", "New Position=" + viewpager.getCurrentItem());
viewPagerAdapter.notifyDataSetChanged();
}
}
previousState = state;
}
});
Before choosing any option, keep in mind user can navigate or open any other app(s) so you lost your data.
You can use onSaveInstanceState but it will somehow difficult to maintain (as you said you are new in android). You can go with with singleton by using
Database - Use when you want to store maintain multiple records but you have to create a database getter/setter or use any ORM like RushOrm etc.
SharefPreference(preferably) - If you want to use single values.
In both cases you will create a singleton object and access its properties in your fragments.
make your objects parcelable and then pass it to other fragments using bundle. i.e bundle.putParcelable(obj) parcelable is very efficient and fast.
it should motivate you
http://www.developerphil.com/parcelable-vs-serializable/
I have multiple fragments in ViewPager. How can i get fragment first EditText Data to last Fragment?
I have set value in my first fragment like below -
txtConsAcNo.setText(account_no);
txtMeterSrMo.setText(mtr_serial_no);
Now i am getting this txtConsAcNo, txtMeterSrMo value on my last fragment like below-
ConDetFirstFragment f1 = new ConDetFirstFragment();
txtConsAcNo = f1.txtConsAcNo.getText().toString();
txtMeterSrMo = f1.txtMeterSrMo.getText().toString();
Now what i want that i am getting Null value and my app get unfortunately stopped. i want to get this data to my last fragment without bundle. how can i achieve this ?
Very Easy to Achieve this without Creating Interface, Bundle or intent -
I have declared all the variables in all the fragment "Public Static" like Below -
public static EditText txtConsAcNo, txtMeterSrMo;
After on any fragment i have declared variable to get data like below-
public static String txtConsAcNo,txtMeterSrMo;
Now i have created function to get value from first fragment in above variable below-
public static void getalldata(){
ConDetFirstFragment f1 = new ConDetFirstFragment();
txtConsAcNo = f1.txtConsAcNo.getText().toString();
txtMeterSrMo = f1.txtMeterSrMo.getText().toString();
}
Happy Coding...
There are a couple of problems here:
The first fragment may have been destroyed by the Android system to conserve memory.
Your fragments should not talk to each other directly
To achieve what you need, you need to jump through a few hoops.
Assuming that the source texts are EditText objects (ie. editable by the user), then add a TextWatcher to each of the EditText objects.
Create an Interface:
public interface TextPurveyor {
void setText1(String t);
String getText1();
void setText2(String t);
String getText1();
}
Implement this interface in the host Activity; and save the text values locally in the activity. Don't forget to save/restore them with the rest of the Activity state.
Make the TextWatcher objects call the appropriate setText(..) methods on the host activity:
((TextPurveyor)getActivity()).setText1(...);
Make each fragment check that the host activity implements this method.
When the second fragment wants a string, ask the activity for it:
((TextPurveyor)getActivity()).getText1();
To avoid coupling your project code tightly, try to use the design patterns that have been proven to work best like the Publisher/Subscriber as I will show you below:
There is a popular library I have always used in my projects called EventBus - just add the following to your build.gradle (module-level) file under dependencies :
compile 'org.greenrobot:eventbus:3.0.0'
Secondly, create a simple Plain Old Java Object (POJO) to represent your Event:
public class FragmentAToLastEvent{
private String txtConsAcNo;
private String txtMeterSrMo;
FragmentAToLastEvent(String acNo, String srMO){
this.txtConsAcNo = acNO;
this.txtMeterSrMo = srMO;
}
//getters and setters if needed
public String gettxtConsAcNo(){
return txtConsAcNo;
}
public String gettxtMeterSrMo(){
return txtMeterSrMo;
}
}
Next step is to actually use your Event class here:
So, in your fragment that you want to send text from EditText, simply do this:
String txtConsAcNo = f1.txtConsAcNo.getText().toString();
String txtMeterSrMo = f1.txtMeterSrMo.getText().toString();
EventBus.getDefault().post(new FragmentAToLastEvent(txtConsAcNo, txtMeterSrMo));
In your last fragment, simply do this to complete:
Inside onCreate or onAttach of your Fragment:
//register your event - making this class a subscriber
EventBus.getDefault().register(this)
//next, override a single method to receive the values you passed from above code (Fragment 1?)
public void onEvent(FragmentAToLastEvent event){
String txtConsAcNo = event.gettxtConsAcNo();
String txtMeterSrMo = event.gettxtMeterSrMo();
//now you can use your text here without problems!
}
Finally, remember to unregister inside onDestroy:
#Override
public void onDestroy(){
super.onDestroy();
EventBus.getDefault().unregister(this);
}
This is what I have always done and it is cleaner, without using interfaces that your fragments MUST implement and do all that!
I hope you find it helpful to you and good luck!
I have a list like fragment, and currently I am passing in info like so:
Fragment:
public void populate(Map<String, List<Book>> booksGroupedByType)
{
BookListAdapter bookListAdapter = new BookListAdapter(this.getActivity(), booksGroupedByType);
_lstBooks.setAdapter(bookListAdapter);
}
Activity:
private void populateBooksFragment()
{
Map<String, List<Book>> booksGroupedByType = _repository.getAllBooksGroupedByType();
BookListFragment bookListFragment = (BookListFragment) getFragment(R.id.fragBooks);
if (bookListFragment != null)
{
bookListFragment.populate(booksGroupedByType);
}
}
Then I felt it would be better if I could pass this information when creating the fragment, since we have no constructor available I looked up the method and found this:
public static DetailsFragment newInstance(int index) {
DetailsFragment f = new DetailsFragment();
// Supply index input as an argument.
Bundle args = new Bundle();
args.putInt("index", index);
f.setArguments(args);
return f;
}
I tried to implement, but found my Map was not serializable as it was and needed more work. So my question is, why go through this? is there a disadvantage to using my original approach (populate), which would even be faster than serializing?
I thought perhaps my fragment will lose its data when rotated, but no, when rotating (in emulator) the list was kept intact.
Let's say you have some data obtained in time/resource consuming way. If you don't want to download them each time configuration changes (and activity is destroyed), you have to somehow persist them.
First option is to put data into the bundle, so it will be available for the fragment even after it is autorecreated by the system. It may work for simple types, but for arbitrary object it's usually not an option because of performance reasons (serialization/parcelization).
Second option would be retaining the fragment, by setting a flag in fragment's onCreate():
setRetainInstanceState(true)
In that case fragment won't be destroyed after configuration change, but just detached from activity being destroyed, and attached to the new one. Any data you will pass e.g. via setters will be available too.
See also: Understanding Fragment's setRetainInstance(boolean)
I am working on an application using viewpagerindicator.
In my main activity that has the viewpagerindicator, I spin off a thread that does some computation and updates a an instance variable mString of the activity. I want to update a fragment in the viewpagerindicator with the mString. However, I can't seem to figure out the best way to reach the fragment.
Does anyone know of any good samples that do something similar to this?
Create a callback object in your Fragment, register it with your FragmentActivity. If mString is already set in FragmentActivity then you can return it immediately via the callback, otherwise, when the computation thread finishes, it can return the string via the callback. The callback method should do whatever the Fragment needs to do with the string, e.g. set the text of a TextView.
E.g. create an interface called DynamicDataResponseHandler as follows:
public interface DynamicDataResponseHandler {
public void onUpdate(Object data);
}
Then in your Fragment, implement that interface as follows:
private class MyStringDataResponseHandler implements DynamicDataResponseHandler {
#Override
public void onUpdate(Object object) {
mYourTextView.setText((String)object);
}
}
Your Fragment can then instantiate a MyStringDataResponseHandler object in its onCreate, pass that to the FragmentActivity via a method in the FragmentActivity like:
private MyStringDataResponseHandler mMyStringDataResponseHandler;
public void registerMyStringDataResponseHandler (DynamicDataResponseHandler callback) {
mMyStringDataResponseHandler = callback;
if(mString != null) {
mMyStringDataResponseHandler.onUpdate(mString);
}
}
And wherever in your Handler you obtain the value for mString, do something like this:
if(mMyStringDataResponseHandler != null) {
mMyStringDataResponseHandler.onUpdate(mString);
}
Do some reading on the concept of Callbacks to get a better understanding of what I'm doing above and other ways you can use them.
You want to update the UI of a Fragment in ViewPager after it is started, do i make it clear?
Ok, in this situation
You should add a public method in your custom Fragment.
Find the Fragment in your Activity.
Invoke the method after your calculation is done.
The question is same with this one.