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'
This is likely an issue with me not properly understanding threading, however I often try and group code into a seperate class and become hindered by some it not being on the UI thread. I can't find anything that properly explains this however. As an example:
public class MyActivity extends Activity {
#Override
public void onCreate (Bundle bundle) {
HelperClass = new HelperClass(context);
}
}
public class HelperClass extends ContextWrapper {
someMethod () {
// Do stuff
}
}
When someMethod is called, if it's trying to do something thread dependant, I will get an error. I've had this with trying to keep some WebView logic in a seperate class as well as trying to access a realm database.
Using runnables seems very messy and I clearly don't understand exactly what's happening to beable to properly structure my code.
Can anyone explain why? and what the best soloution is?
I have a fragment class:
public class UploadFragmentOne extends Fragment {}
I have subclassed:
public interface Communicator {
void communicate(int position);
}
In the onCreateView:
((Communicator) getActivity()).communicate(1);
The hosting activity signature:
public class DetailsPager extends FragmentActivity implements UploadFragmentOne.Communicator {}
Member function in the above activity:
public void communicate(int position) {
Toast.makeText(DetailsPager.this, "Clicked " + position, Toast.LENGTH_LONG).show();
}
This works like a charm, but I dont understand HOW? Sorry this might be too dumb, but I want to know how the control flows in this?
You should have a look on the following link once.-
Now come to your query
(MyActivity)activity.some_method()
Now suppose you are going to attach the same fragment for another activity say MainActivity then you need to do like -
(MainActivity)activity.some_method()
Now suppose some other activity are implementing the same fragment then each time you need to use the instanceOf check and then call the method and also add it.
Again suppose a trivial case when you are going the create a library and you are going to offer some result delivery for the particular event then?
How will you get the instance type ?
interface as the name suggests offer a way to be communicated without the actual class instance. They only need to be implemented. You can have a look on the OnClickListener in the View class of android API sources.
I have to communicate between an Android Activity and another Java class. In a very, very stripped down version of what I want, I want the Java Class to run, and when it's done, set some information. To get a more specific idea of what I want to happen:
Activity {
CallJavaClass(); // Doesn't return anything, would be very bad form
GetInfoFromJavaClass() // Once the JavaClass has finished what needs to be done
}
What I could do:
Set a global variable in JavaClass that my Activity can access. I'd rather not do it this way, as I would have to implement some kind of OnChangedListener on that object in the JavaClass.
Use an Interface with Setters/ Getters. The problem with this is my JavaClass is a Singleton, and most of its methods are static, which is a no-go when working with an Interface.
Create a separate class that handles these variables. I would rather keep it simple and not have to use a bunch of different classes to do this, though.
So what do you think would be the best solution? If needed (and probably will be), I can provide more information about what exactly I want done. Thanks for your help in advance.
Sounds like something you could use AsyncTask for http://developer.android.com/reference/android/os/AsyncTask.html
then again, it depends on the specifics of what you're going for
AsyncTask should resolve your problem:
private class myTask extends AsyncTask<Void, Void, Boolean> {
protected void onPreExecute() {
super.onPreExecute();
// do something before starting the AsyncTask
}
#Override
protected Boolean doInBackground(Void... params) {
// do what you want to do
return false;
}
protected void onPostExecute(Boolean success)
{
super.onPostExecute(success);
// do something right after you finish the "doInBackground"
}
}
I'm managing the History in my project via Places.
What I do is this:
implement PlaceRequestHandler on top level (for example AppController),
register it -> eventBus.addHandler(PlaceRequestEvent.getType(), this);
implement method "onPlaceRequest" ,where i do project navigation.
I'm using GWT presenter and every presenter in my project overrides the onPlaceRequest method.
Why do I need this, when every request is handled from the top level "onPlaceRequest" method?
I will give an example:
public class AppController implements Presenter, PlaceRequestHandler
...........
public void bind()
{
eventBus.addHandler(PlaceRequestEvent.getType(), this);
...
}
public void onPlaceRequest(PlaceRequestEvent event)
{
// here is the project navigation tree
}
and let's take one presenter
public class SomePresenter extends Presenter<SomePresenter.Display>
{
... here some methods are overriden and
#Override
protected void onPlaceRequest(PlaceRequest request)
{
// what should I do here?
}
}
What is the idea, and how I'm supposed to use it?
Instead of making all of your presenters extend PlaceRequestHandler and managing those events yourself, you can attach a PlaceHistoryHandler and a PlaceController to your event bus. Together, they manage the browser's history and your places for you. When you ask your PlaceController to goTo() a different place, it will stop your current activity and use a mapping of places to activities (your presenters) to choose which one to start next.
To use this technique, you need to have your presenters extend AbstractActivity. Try following through Google's tutorial about it in GWT's documentation called GWT Development with Activities and Places.