What will be the implications if I passed an object to a fragment without using bundle? I just opened one of the old code and found it there and couldn't help asking this question as I have never tried it. Also I am not finding any memory leaks in it.
This is how it is implemented -
Activity class:
MyFragment fragment =
MyFragment.newInstance(getIntent().getStringExtra(DATA),
instance.getCallback(),
instance.getRequest());
getSupportFragmentManager().beginTransaction().replace(R.id.content, fragment).commit();
Fragment class:
public class MyFragment extends Fragment {
public MyFragment() {
/* Required empty public constructor */
}
public static MyFragment newInstance(String data, Callback callback,
Request request) {
MyFragment fragment = new MyFragment();
fragment.setCallback(callback);
fragment.setRequest(request);
fragment.setData(data);
return fragment;
}
private void setCallback(Callback callback) {
this.callback = callback;
}
private void setData(Data data) {
this.data = data;
}
private void setRequest(Request request) {
this.request = request;
}
}
Generally, what I have used till date is Fragment#setArguments(Bundle)
Please check out this answer: Why its not recommended to pass object to fragment with simple getter setter.
Long story short, you will lose your data on configuration changes.
There are mainly two ways of communicating with a fragment: via bundles or via an interface that you implement in your activity. Please see this link in order to see how to properly communicate with a fragment via an interface: https://developer.android.com/training/basics/fragments/communicating
I'm trying to make a ListFragment that will periodically be updated (Calls to update not shown here, but the update function is). Here's the log cat that I'm seeing:
04-05 11:05:44.252: V/QslLogFrag(2690): onCreate()
04-05 11:05:44.256: V/QslLogFrag(2690): onCreateView()
04-05 11:05:44.304: V/QslLogFrag(2690): onActivityCreate()
04-05 11:05:44.612: V/QslLogFrag(2690): null
04-05 11:05:44.736: V/QslLogFrag(2690): com.kd7uiy.qslmapper.QslLogAdapter#5282f55c
04-05 11:05:47.948: V/QslLogFrag(2690): null
The last 3 lines lines are all provided in the updateView class, which is called externally when there's new data to check. The first two are called essentially automatically, the third one is called by user input.
And the code:
public class QslLogFragment extends ListFragment {
private CursorAdapter mAdapter;
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
getListView().setFastScrollEnabled(true);
Cursor cursor = QslDatabase.getInstance(getActivity()).getTableQuery(
mFilters);
mAdapter= new QslLogAdapter(getActivity(), cursor, 0);
setListAdapter(mAdapter);
Log.v(TAG,"onActivityCreate()");
}
public void updateView() {
Cursor cursor = QslDatabase.getInstance(getActivity()).getTableQuery(
mFilters);
Log.v(TAG,""+getListAdapter());
if (getListAdapter() != null) {
((CursorAdapter) getListAdapter()).changeCursor(cursor);
}
}
Somehow it seems to me as if the adapter is getting set to null. Note I can still scroll through the ListView without problems, but I can't update it, with a new set of filters. Any ideas what's happening?
Note, QslAdapter extends CursorAdapter, and I'm using the Support Library CursorAdapter.
Here's a list of things I've tried:
I have tried just using setListAdapter and getListAdapter.
I have tried not using getListAdapter, but just keeping a reference to mAdapter.
I have verified that there is only one instance of this Fragment.
I am not calling setListAdapter anywhere.
I've verified that getListAdapter and mAdapter always report the same pointer, or null.
If #commonsware doesn't mind, I'll put this into an answer for prosperity. Although I'm sure if he has any further insights, he will create a much better answer.
I had the feeling you could be dealing with multiple copies of your QslLogFragment. I have faced similar problems previously.
In situations like this, it is a good idea to log your method calls, like you have done. Where it is "impossible" for the adapter to be different, that is the hint of having 2 fragments, hence the suggestion to log the fragment as well.
Place extra logs in ALL the Activity & Fragment lifecycle methods to track down the final piece of the puzzle. It may seem like overkill, but you could find some surprises.
In the case that I had, which you reminded me of, I had based my code on an Android SDK sample that actually created a new fragment each time I tried to access it. I had not cached any of the fragments that were previously created. So check the code that retrieves (or creates) your fragment.
Here is the code from my FragmentPagerAdapter that creates a new fragment each time. This is bad code, and I don't recommend it, but for now it serves its purpose in the demo it comes from.
public Fragment getItem(int position)
{
// TODO don't create a new fragment each time this is called
switch (position)
{
case 0:
{
return new WindFragment();
}
// more cases... etc...
default:
{
return new TemperatureFragment();
}
}
}
This is called every time the user flips to a new page, to show a different fragment. This code caused an issue very similar to yours.
My issue was very close to Richard's answer, but I'll post a better version of the code.
I have been using a function called TabsAdapter to manage my FragementPager. The default code is this:
#Override
public Fragment getItem(int position) {
TabInfo info = mTabs.get(position);
return Fragment.instantiate(mContext, info.clss.getName(), info.args);
}
I was setting a listener to the code by using the getItem function (My private listener), and thus was actually creating a new fragment!
The solution was to use a WeakHashMap to store previous instances of the fragment so I don't re-create them if I don't have to!
WeakHashMap<Integer,Fragment> mFragmentMap;
#Override
public Fragment getItem(int position) {
TabInfo info = mTabs.get(position);
if (mFragmentMap.get(position)==null){
mFragmentMap.put(position,Fragment.instantiate(mContext, info.clss.getName(), info.args));
}
return mFragmentMap.get(position);
}
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.
I've been working with lots of Fragments recently and have been using two distinct methods of passing in objects to the Fragments, but the only difference that I can see is that in the approach taken by FragmentOne below, the object you pass in must implement the Serializable interface (and everything associated with that).
Are there any benefits to using one over the other?
public class FragmentOne extends Fragment {
public static final String FRAGMENT_BUNDLE_KEY =
"com.example.FragmentOne.FRAGMENT_BUNDLE_KEY";
public static FragmentOne newInstance(SomeObject someObject) {
FragmentOne f = new FragmentOne();
Bundle args = new Bundle();
args.putSerializable(FRAGMENT_BUNDLE_KEY, someObject);
f.setArguments(args);
return f;
}
public SomeObject getSomeObject() {
return (SomeObject) getArguments().getSerializable(FRAGMENT_BUNDLE_KEY);
}
}
and
public class FragmentTwo extends Fragment {
SomeObject mSomeObject;
public static FragmentTwo newInstance(SomeObject someObject) {
FragmentTwo fragment = new FragmentTwo();
fragment.setSomeObject(someObject);
return fragment;
}
public void setSomeObject(SomeObject someObject) {
mSomeObject = someObject;
}
}
There are 3 ways to pass objects to a fragment
They are:
Passing the object through a setter is the fastest way, but state will not be restored automatically.
setArguments with Serializable objects is the slowest way (but okay for small objects, I think) and you have automatic state restoration.
Passing as Parcelable is a fast way (prefer it over 2nd one if you have collection of elements to pass), and you have automatic state restoration.
http://developer.android.com/reference/android/os/Parcelable.html
for Collection such as List :
I wanted to share my experience.
you need to implement Parcelable
Just use the putParcelableArrayList method.
ArrayList<LClass> localities = new ArrayList<LClass>;
...
Bundle bundle = new Bundle();
bundle.putParcelableArrayList(KEY_LClass_LIST, localities);
fragmentInstance.setArguments(bundle);
return fragmentInstance;
And retrieve it using...
localities = savedInstanceState.getParcelableArrayList(KEY_LCLass_LIST);
So, unless you need the custom ArrayList for some other reason, you can avoid doing any of that extra work and only implement Parcelable for your Locality class.
I have seen two general practices to instantiate a new Fragment in an application:
Fragment newFragment = new MyFragment();
and
Fragment newFragment = MyFragment.newInstance();
The second option makes use of a static method newInstance() and generally contains the following method.
public static Fragment newInstance()
{
MyFragment myFragment = new MyFragment();
return myFragment;
}
At first, I thought the main benefit was the fact that I could overload the newInstance() method to give flexibility when creating new instances of a Fragment - but I could also do this by creating an overloaded constructor for the Fragment.
Did I miss something?
What are the benefits of one approach over the other? Or is it just good practice?
If Android decides to recreate your Fragment later, it's going to call the no-argument constructor of your fragment. So overloading the constructor is not a solution.
With that being said, the way to pass stuff to your Fragment so that they are available after a Fragment is recreated by Android is to pass a bundle to the setArguments method.
So, for example, if we wanted to pass an integer to the fragment we would use something like:
public static MyFragment newInstance(int someInt) {
MyFragment myFragment = new MyFragment();
Bundle args = new Bundle();
args.putInt("someInt", someInt);
myFragment.setArguments(args);
return myFragment;
}
And later in the Fragment onCreate() you can access that integer by using:
getArguments().getInt("someInt", 0);
This Bundle will be available even if the Fragment is somehow recreated by Android.
Also note: setArguments can only be called before the Fragment is attached to the Activity.
This approach is also documented in the android developer reference: https://developer.android.com/reference/android/app/Fragment.html
The only benefit in using the newInstance() that I see are the following:
You will have a single place where all the arguments used by the fragment could be bundled up and you don't have to write the code below everytime you instantiate a fragment.
Bundle args = new Bundle();
args.putInt("someInt", someInt);
args.putString("someString", someString);
// Put any other arguments
myFragment.setArguments(args);
Its a good way to tell other classes what arguments it expects to work faithfully(though you should be able to handle cases if no arguments are bundled in the fragment instance).
So, my take is that using a static newInstance() to instantiate a fragment is a good practice.
There is also another way:
Fragment.instantiate(context, MyFragment.class.getName(), myBundle)
While #yydl gives a compelling reason on why the newInstance method is better:
If Android decides to recreate your Fragment later, it's going to call
the no-argument constructor of your fragment. So overloading the
constructor is not a solution.
it's still quite possible to use a constructor. To see why this is, first we need to see why the above workaround is used by Android.
Before a fragment can be used, an instance is needed. Android calls YourFragment() (the no arguments constructor) to construct an instance of the fragment. Here any overloaded constructor that you write will be ignored, as Android can't know which one to use.
In the lifetime of an Activity the fragment gets created as above and destroyed multiple times by Android. This means that if you put data in the fragment object itself, it will be lost once the fragment is destroyed.
To workaround, android asks that you store data using a Bundle (calling setArguments()), which can then be accessed from YourFragment. Argument bundles are protected by Android, and hence are guaranteed to be persistent.
One way to set this bundle is by using a static newInstance method:
public static YourFragment newInstance (int data) {
YourFragment yf = new YourFragment()
/* See this code gets executed immediately on your object construction */
Bundle args = new Bundle();
args.putInt("data", data);
yf.setArguments(args);
return yf;
}
However, a constructor:
public YourFragment(int data) {
Bundle args = new Bundle();
args.putInt("data", data);
setArguments(args);
}
can do exactly the same thing as the newInstance method.
Naturally, this would fail, and is one of the reasons Android wants you to use the newInstance method:
public YourFragment(int data) {
this.data = data; // Don't do this
}
As further explaination, here's Android's Fragment Class:
/**
* Supply the construction arguments for this fragment. This can only
* be called before the fragment has been attached to its activity; that
* is, you should call it immediately after constructing the fragment. The
* arguments supplied here will be retained across fragment destroy and
* creation.
*/
public void setArguments(Bundle args) {
if (mIndex >= 0) {
throw new IllegalStateException("Fragment already active");
}
mArguments = args;
}
Note that Android asks that the arguments be set only at construction, and guarantees that these will be retained.
EDIT: As pointed out in the comments by #JHH, if you are providing a custom constructor that requires some arguments, then Java won't provide your fragment with a no arg default constructor. So this would require you to define a no arg constructor, which is code that you could avoid with the newInstance factory method.
EDIT: Android doesn't allow using an overloaded constructor for fragments anymore. You must use the newInstance method.
Some kotlin code:
companion object {
fun newInstance(first: String, second: String) : SampleFragment {
return SampleFragment().apply {
arguments = Bundle().apply {
putString("firstString", first)
putString("secondString", second)
}
}
}
}
And you can get arguments with this:
val first: String by lazy { arguments?.getString("firstString") ?: "default"}
val second: String by lazy { arguments?.getString("secondString") ?: "default"}
I disagree with yydi answer saying:
If Android decides to recreate your Fragment later, it's going to call
the no-argument constructor of your fragment. So overloading the
constructor is not a solution.
I think it is a solution and a good one, this is exactly the reason it been developed by Java core language.
Its true that Android system can destroy and recreate your Fragment. So you can do this:
public MyFragment() {
// An empty constructor for Android System to use, otherwise exception may occur.
}
public MyFragment(int someInt) {
Bundle args = new Bundle();
args.putInt("someInt", someInt);
setArguments(args);
}
It will allow you to pull someInt from getArguments() latter on, even if the Fragment been recreated by the system. This is more elegant solution than static constructor.
For my opinion static constructors are useless and should not be used. Also they will limit you if in the future you would like to extend this Fragment and add more functionality to the constructor. With static constructor you can't do this.
Update:
Android added inspection that flag all non-default constructors with an error.
I recommend to disable it, for the reasons mentioned above.
I'm lately here. But somethings I just known that might help you a bit.
If you are using Java, there is nothing much to change. But for Kotlin developers, here is some following snippet I think that can make you a basement to run on:
Parent fragment:
inline fun <reified T : SampleFragment> newInstance(text: String): T {
return T::class.java.newInstance().apply {
arguments = Bundle().also { it.putString("key_text_arg", text) }
}
}
Normal call
val f: SampleFragment = SampleFragment.newInstance("ABC")
// or val f = SampleFragment.newInstance<SampleFragment>("ABC")
You can extend the parent init operation in child fragment class by:
fun newInstance(): ChildSampleFragment {
val child = UserProfileFragment.newInstance<ChildSampleFragment>("XYZ")
// Do anything with the current initialized args bundle here
// with child.arguments = ....
return child
}
Happy coding.
Best practice to instance fragments with arguments in android is to have static factory method in your fragment.
public static MyFragment newInstance(String name, int age) {
Bundle bundle = new Bundle();
bundle.putString("name", name);
bundle.putInt("age", age);
MyFragment fragment = new MyFragment();
fragment.setArguments(bundle);
return fragment;
}
You should avoid setting your fields with the instance of a fragment. Because whenever android system recreate your fragment, if it feels that the system needs more memory, than it will recreate your fragment by using constructor with no arguments.
You can find more info about best practice to instantiate fragments with arguments here.
Since the questions about best practice, I would add, that very often good idea to use hybrid approach for creating fragment when working with some REST web services
We can't pass complex objects, for example some User model, for case of displaying user fragment
But what we can do, is to check in onCreate that user!=null and if not - then bring him from data layer, otherwise - use existing.
This way we gain both ability to recreate by userId in case of fragment recreation by Android and snappiness for user actions, as well as ability to create fragments by holding to object itself or only it's id
Something likes this:
public class UserFragment extends Fragment {
public final static String USER_ID="user_id";
private User user;
private long userId;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
userId = getArguments().getLong(USER_ID);
if(user==null){
//
// Recreating here user from user id(i.e requesting from your data model,
// which could be services, direct request to rest, or data layer sitting
// on application model
//
user = bringUser();
}
}
public static UserFragment newInstance(User user, long user_id){
UserFragment userFragment = new UserFragment();
Bundle args = new Bundle();
args.putLong(USER_ID,user_id);
if(user!=null){
userFragment.user=user;
}
userFragment.setArguments(args);
return userFragment;
}
public static UserFragment newInstance(long user_id){
return newInstance(null,user_id);
}
public static UserFragment newInstance(User user){
return newInstance(user,user.id);
}
}
use this code 100% fix your problem
enter this code in firstFragment
public static yourNameParentFragment newInstance() {
Bundle args = new Bundle();
args.putBoolean("yourKey",yourValue);
YourFragment fragment = new YourFragment();
fragment.setArguments(args);
return fragment;
}
this sample send boolean data
and in SecendFragment
yourNameParentFragment name =yourNameParentFragment.newInstance();
Bundle bundle;
bundle=sellDiamondFragments2.getArguments();
boolean a= bundle.getBoolean("yourKey");
must value in first fragment is static
happy code
Ideally we shouldn't pass anything in the fragment constructor, fragment constructor should be empty or default.
Now the second question is, what if we want to pass interface variable or parameters-
We should use Bundle to pass data.
For Interface we can putParceble in bundle and make that interface implement parceble
If possible we can implement that interface in activity and in fragment we can initialize listener in OnAttach where we have context[ (context) Listener].
So that during configuration change (e.g. Font change) the Activity recreation listener won't go uninitialize and we can avoid a null pointer exception.
Best way to instantiate the fragment is use default Fragment.instantiate method or create factory method to instantiate the the fragment
Caution: always create one empty constructor in fragment other while restoring fragment memory will throw run-time exception.
You can use smth like this:
val fragment = supportFragmentManager.fragmentFactory.instantiate(classLoader, YourFragment::class.java.name)
because this answer now is Deprecated
Create an instance of the fragment using kotlin code.
Write in activity
val fragment = YourFragment.newInstance(str = "Hello",list = yourList)
Write in fragment
fun newInstance(str: String, list: ArrayList<String>): Fragment {
val fragment = YourFragment()
fragment.arguments = Bundle().apply {
putSerializable("KEY_STR", str)
putSerializable("KEY_LIST", list)
}
return fragment
}
Using the same fragment retrieve the data from bundle
val str = arguments?.getString("KEY_STR") as? String
val list = arguments?.getSerializable("KEY_LIST") as? ArrayList<String>
setArguments() is useless. It only brings a mess.
public class MyFragment extends Fragment {
public String mTitle;
public String mInitialTitle;
public static MyFragment newInstance(String param1) {
MyFragment f = new MyFragment();
f.mInitialTitle = param1;
f.mTitle = param1;
return f;
}
#Override
public void onSaveInstanceState(Bundle state) {
state.putString("mInitialTitle", mInitialTitle);
state.putString("mTitle", mTitle);
super.onSaveInstanceState(state);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle state) {
if (state != null) {
mInitialTitle = state.getString("mInitialTitle");
mTitle = state.getString("mTitle");
}
...
}
}
I believe I have a much simpeler solution for this.
public class MyFragment extends Fragment{
private String mTitle;
private List<MyObject> mObjects;
public static MyFragment newInstance(String title, List<MyObject> objects)
MyFragment myFrag = new MyFragment();
myFrag.mTitle = title;
myFrag.mObjects = objects;
return myFrag;
}