This question is mostly to solicit opinions on the best way to handle my app. I have three fragments being handled by one activity. Fragment A has one clickable element the photo and Fragment B has 4 clickable elements the buttons. The other fragment just displays details when the photo is clicked. I am using ActionBarSherlock.
The forward and back buttons need to change the photo to the next or previous poses, respectively. I could keep the photo and the buttons in the same fragment, but wanted to keep them separate in case I wanted to rearrange them in a tablet.
I need some advice - should I combine Fragments A and B? If not, I will need to figure out how to implement an interface for 3 clickable items.
I considered using Roboguice, but I am already extending using SherlockFragmentActivity so that's a no go. I saw mention of Otto, but I didn't see good tutorials on how to include in a project. What do you think best design practice should be?
I also need help figuring out how to communicate between a fragment and an activity. I'd like to keep some data "global" in the application, like the pose id. Is there some example code I can see besides the stock android developer's information? That is not all that helpful.
BTW, I'm already storing all the information about each pose in a SQLite database. That's the easy part.
The easiest way to communicate between your activity and fragments is using interfaces. The idea is basically to define an interface inside a given fragment A and let the activity implement that interface.
Once it has implemented that interface, you could do anything you want in the method it overrides.
The other important part of the interface is that you have to call the abstract method from your fragment and remember to cast it to your activity. It should catch a ClassCastException if not done correctly.
There is a good tutorial on Simple Developer Blog on how to do exactly this kind of thing.
I hope this was helpful to you!
The suggested method for communicating between fragments is to use callbacks\listeners that are managed by your main Activity.
I think the code on this page is pretty clear:
http://developer.android.com/training/basics/fragments/communicating.html
You can also reference the IO 2012 Schedule app, which is designed to be a de-facto reference app. It can be found here:
http://code.google.com/p/iosched/
Also, here is a SO question with good info:
How to pass data between fragments
It is implemented by a Callback interface:
First of all, we have to make an interface:
public interface UpdateFrag {
void updatefrag();
}
In the Activity do the following code:
UpdateFrag updatfrag ;
public void updateApi(UpdateFrag listener) {
updatfrag = listener;
}
from the event from where the callback has to fire in the Activity:
updatfrag.updatefrag();
In the Fragment implement the interface in CreateView do the
following code:
((Home)getActivity()).updateApi(new UpdateFrag() {
#Override
public void updatefrag() {
.....your stuff......
}
});
To communicate between an Activity and Fragments, there are several options, but after lots of reading and many experiences, I found out that it could be resumed this way:
Activity wants to communicate with child Fragment => Simply write public methods in your Fragment class, and let the Activity call them
Fragment wants to communicate with the parent Activity => This requires a bit more of work, as the official Android link https://developer.android.com/training/basics/fragments/communicating suggests, it would be a great idea to define an interface that will be implemented by the Activity, and which will establish a contract for any Activity that wants to communicate with that Fragment. For example, if you have FragmentA, which wants to communicate with any activity that includes it, then define the FragmentAInterface which will define what method can the FragmentA call for the activities that decide to use it.
A Fragment wants to communicate with other Fragment => This is the case where you get the most 'complicated' situation. Since you could potentially need to pass data from FragmentA to FragmentB and viceversa, that could lead us to defining 2 interfaces, FragmentAInterface which will be implemented by FragmentB and FragmentAInterface which will be implemented by FragmentA. That will start making things messy. And imagine if you have a few more Fragments on place, and even the parent activity wants to communicate with them. Well, this case is a perfect moment to establish a shared ViewModel for the activity and it's fragments. More info here https://developer.android.com/topic/libraries/architecture/viewmodel . Basically, you need to define a SharedViewModel class, that has all the data you want to share between the activity and the fragments that will be in need of communicating data among them.
The ViewModel case, makes things pretty simpler at the end, since you don't have to add extra logic that makes things dirty in the code and messy. Plus it will allow you to separate the gathering (through calls to an SQLite Database or an API) of data from the Controller (activities and fragments).
I made a annotation library that can do the cast for you. check this out.
https://github.com/zeroarst/callbackfragment/
#CallbackFragment
public class MyFragment extends Fragment {
#Callback
interface FragmentCallback {
void onClickButton(MyFragment fragment);
}
private FragmentCallback mCallback;
#Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.bt1
mCallback.onClickButton(this);
break;
case R.id.bt2
// Because we give mandatory = false so this might be null if not implemented by the host.
if (mCallbackNotForce != null)
mCallbackNotForce.onClickButton(this);
break;
}
}
}
It then generates a subclass of your fragment. And just add it to FragmentManager.
public class MainActivity extends AppCompatActivity implements MyFragment.FragmentCallback {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
getSupportFragmentManager().beginTransaction()
.add(R.id.lo_fragm_container, MyFragmentCallbackable.create(), "MY_FRAGM")
.commit();
}
Toast mToast;
#Override
public void onClickButton(MyFragment fragment) {
if (mToast != null)
mToast.cancel();
mToast = Toast.makeText(this, "Callback from " + fragment.getTag(), Toast.LENGTH_SHORT);
mToast.show();
}
}
Google Recommended Method
If you take a look at this page you can see that Google suggests you use the ViewModel to share data between Fragment and Activity.
Add this dependency:
implementation "androidx.activity:activity-ktx:$activity_version"
First, define the ViewModel you are going to use to pass data.
class ItemViewModel : ViewModel() {
private val mutableSelectedItem = MutableLiveData<Item>()
val selectedItem: LiveData<Item> get() = mutableSelectedItem
fun selectItem(item: Item) {
mutableSelectedItem.value = item
}
}
Second, instantiate the ViewModel inside the Activity.
class MainActivity : AppCompatActivity() {
// Using the viewModels() Kotlin property delegate from the activity-ktx
// artifact to retrieve the ViewModel in the activity scope
private val viewModel: ItemViewModel by viewModels()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
viewModel.selectedItem.observe(this, Observer { item ->
// Perform an action with the latest item data
})
}
}
Third, instantiate the ViewModel inside the Fragment.
class ListFragment : Fragment() {
// Using the activityViewModels() Kotlin property delegate from the
// fragment-ktx artifact to retrieve the ViewModel in the activity scope
private val viewModel: ItemViewModel by activityViewModels()
// Called when the item is clicked
fun onItemClicked(item: Item) {
// Set a new item
viewModel.selectItem(item)
}
}
You can now edit this code creating new observers or settings methods.
There are severals ways to communicate between activities, fragments, services etc. The obvious one is to communicate using interfaces. However, it is not a productive way to communicate. You have to implement the listeners etc.
My suggestion is to use an event bus. Event bus is a publish/subscribe pattern implementation.
You can subscribe to events in your activity and then you can post that events in your fragments etc.
Here on my blog post you can find more detail about this pattern and also an example project to show the usage.
I'm not sure I really understood what you want to do, but the suggested way to communicate between fragments is to use callbacks with the Activity, never directly between fragments. See here http://developer.android.com/training/basics/fragments/communicating.html
You can create declare a public interface with a function declaration in the fragment and implement the interface in the activity. Then you can call the function from the fragment.
I am using Intents to communicate actions back to the main activity. The main activity is listening to these by overriding onNewIntent(Intent intent). The main activity translates these actions to the corresponding fragments for example.
So you can do something like this:
public class MainActivity extends Activity {
public static final String INTENT_ACTION_SHOW_FOO = "show_foo";
public static final String INTENT_ACTION_SHOW_BAR = "show_bar";
#Override
protected void onNewIntent(Intent intent) {
routeIntent(intent);
}
private void routeIntent(Intent intent) {
String action = intent.getAction();
if (action != null) {
switch (action) {
case INTENT_ACTION_SHOW_FOO:
// for example show the corresponding fragment
loadFragment(FooFragment);
break;
case INTENT_ACTION_SHOW_BAR:
loadFragment(BarFragment);
break;
}
}
}
Then inside any fragment to show the foo fragment:
Intent intent = new Intent(context, MainActivity.class);
intent.setAction(INTENT_ACTION_SHOW_FOO);
// Prevent activity to be re-instantiated if it is already running.
// Instead, the onNewEvent() is triggered
intent.addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP | Intent.FLAG_ACTIVITY_CLEAR_TOP);
getContext().startActivity(intent);
There is the latest techniques to communicate fragment to activity without any interface follow the steps
Step 1- Add the dependency in gradle
implementation 'androidx.fragment:fragment:1.3.0-rc01'
I have been searching and haven't found the best way for nested fragments to communicate with parent fragment. The Android documentation states that:
All Fragment-to-Fragment communication is done through the associated Activity. Two Fragments should never communicate directly.
Suppose I have a Gallery app, there is a ViewPagerFragment (parent) and ImageFragment(child) that is used to show images full screen when they are clicked. I need to pass an ArrayList of Files from my parent fragment to the child fragment. What is a proper way to do it?
1) Create a getter for the ArrayList in parent fragment and use the getParentFragment() in a child fragment to access this method?
2) Implement an interface and go through the Activity, but how will I locate the child fragment from the Activity if it doesn't have an ID?
3) Or use this in parent fragment:
ChildFragment fragment =(ChildFragment)getChildFragmentManager().findFragmentById(R.id.child_fragment_id);
And just use a setter in child fragment.
But again how do I get the ID of the childFragment?
Thanks everyone in advance
If you want to communicate with your child Fragment to your parent Fragment you can use getParentFragment() method from your child fragment.
Example
public class ExampleParentFragment extends Fragment {
public int getCount() {
return 10;
}
}
public class ChildFragment extends Fragment {
void doAction() {
Fragment parentFragment = getParentFragment();
if(parentFragment instanceof ExampleParentFragment) {
int count = ((ExampleParentFragment) parentFragment).getCount();
}
}
}
I understand that the Fragment to Fragment communication through the activity is for sibling fragments which are coordinated by the same activity.
In this case the siblign fragments are coordinated by a parent fragment, so I would say that the communication should be managed by the parent fragment.
If you are working directly with the fragments then you do that using the ChildFragmentManager().
If you are working with a ViewPager you pass the ChildFragmentManager to the ViewPager insted of passing it the FragmentManager.
If you have to pass a List, I think the easiest is for the ChildFragment to request it when it is ready to receive it by calling a method on the ParentFragment. It can allways get its instace with getParentFragment().
I am not sure where is the safest place to call getParentFrament() to get the list but you can try in onCreateView() ,in onActivityCreated(), o in onResume().
To call the method that returns the list, you can cast the parent Fragment to the specific Fragment class you have extended, or else you can define an interface with the method that returns the List and make your extended parent Fragment implement it.
Then in the child Fragment, you refert to the parent by the interface to call the method and get the list.
Data should be passed to fragments using Bundle as arguments. So just pass the Arraylist(serialized or otherwise) to your child fragment when launching it
I want to get the context or instance of fragment in a activity.I tried following codeļ¼
In fragment:
public static XXFragment instance;
In the onCreate():
instance = this;
In activity:
Context context = XXFrangment.instance;
But it has NullPointerException error.Because I haven't invoked onCreate() of fragment.So how can I do to get the context or instance of Fragment?Hope somebody could help me!
I think there is some error in your way of thinking about Context :-)
First of all, Fragment does not have a Context until added to an Activity. After it is added, the Activity itself is it's Context, so there is no need to extract it from the Fragment. Just use this in Activity code :-)
As a side note, avoid static fields holding complex objects such as Fragments and Activities. In a real, production environment you will never do this, as it leads to so called memory leaks, a big problem in software.
It's good practice to use static method for fragment initializing. Implement this method in your fragment class:
public static YourFragment newInstance() {
Bundle args = new Bundle();
YourFragment fragment = new YourFragment();
fragment.setArguments(args);
return fragment;
}
As you can see, you are able to add parameters in a newInstance() method. These parameters are usually used for adding them as arguments of the fragment.
I'm just getting started with Android development and am trying to follow an example in a book and it's not compiling.
The book has me creating a Fragment in my application and then interacting with that fragment in my MainActivity; specifically the book says to call getFragmentManager().findFragmentByID(..) in the main activity, in order to access this fragment, but this is returning an error that the results of getFragmentManager can't be converted to the right type.
So I started poking around and noticed that by default, my installation of Android Studio is apparently using the v4 support library and so my Fragments are v4 Fragments and not the standard sdk Fragments (please correct me if I'm misinterpreting the situation).. and because of this, the call to getFragmentManager is apparently not the right way to get at a v4 Fragment.
Apparently I'm supposed to be calling getSupportFragmentManger instead, but Android Studio says that's not defined. I tried guessing what kind of import I might need in my main activity for it to be able to see getSupportFragmentManager, but I can't seem to figure that out either.
Any help at straightening this out would be very much appreciated.
I have looked at the v4 docs on google's site but honestly to a newbie it's not clear what calls go with what.
Michael
If you want to use support classes in your Activity, then it should also be an Activity from support library.
To accomplish that your Activity must extend AppCompatActivity.
public class MainActivity extends AppCompatActivity {
//Your code that calls getSupportFragmentManager()
}
You should choose some options here:
use android.support.v7.app.AppCompatActivity or android.support.v4.app.FragmentActivity as a parent of your activity
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
FragmentManager supportFragmentManager = getSupportFragmentManager();
}
}
Instead of android.support.v4.Fragment, use android.app.Fragment and simply use android.app.FragmentManger
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
android.app.FragmentManager fragmentManager = getFragmentManager();
}
}
In my code, I am properly using webview and handling onPageFinished and shouldOverrideUrlLoading events. Now I redefined it as DroidGap in order to handle its functions. I should then continue intercepting these events because if I override it, phonegap functions are not executed anymore (as I do on iOS)! how to embed it and handle described events? thank you
public class webPush extends Activity implements CordovaInterface{
You don't need to redefine it to DroidGap. You can use your own implementation using CordovaInterface and just copy the functions you need from DroidGap java class. That way you can edit existing code or add your own.
This is what the official PhoneGap documentation says:
Modify your activity so that it implements the CordovaInterface. It is recommended that you implement the methods that are included. You may wish to copy the methods from /framework/src/org/apache/cordova/DroidGap.java, or you may wish to implement your own methods
Embedding Cordova WebView on Android
Embedding Webview we can do like this way basically
public class CordovaViewTestActivity extends Activity implements CordovaInterface {
CordovaWebView cwv;
/* Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
cwv = (CordovaWebView) findViewById(R.id.tutorialView);
cwv.loadUrl("file:///android_asset/www/index.html");
}
If still you are getting the error ,kindly post your code along with logcat output,It will be easy to resolve the issue..