I have an adapter what uses the activity context to register and unregister a listener.
Activity mActivity;
MyBroadcastReceiver mReceiver;
#Override
public void onAttachedToRecyclerView (RecyclerView recyclerView) {
super.onAttachedToRecyclerView(recyclerView);
mActivity.registerReceiver(mReceiver, ...);
}
#Override
public void onDetachedFromRecyclerView (RecyclerView recyclerView) {
super.onDetachedFromRecyclerView(recyclerView);
mActivity.unregisterReceiver(mReceiver);
mActivity = null;
}
Although the onAttachedToRecyclerView always gets called, the detach method never, so the adapter leaks a lot of memory even after closing the activity.(running is only noticeable in the Settings app)
What do I have to do?
To be safe, you could register the receiver in your Activity. You shouldn't hold on to an Activity reference anywhere really...
If you really want to register the receiver from your adapter use an interface.
public interface Registerer {
void register();
void unregister();
}
In Activity:
mRecyclerView.setAdapter(new RecyclerAdapter(someDataSet,
new Registerer() {
public void register() {
registerReceiver(mReceiver, ...);
}
public void unRegister() {
unregisterReceiver(mReceiver);
}
});
Then you can call the interface methods from your adapter. I don't really see the point of cramming this into your view adapter though.
Related
PlaylistFragment starts an adapter:
playlistsAdapter = new PlaylistRecyclerAdapter(playlistsListArray, addToPlaylist, mSong, getActivity(), this);
PlaylistRecyclerAdapter binds data to the PlaylistViewHolder, something like this:
((PlaylistViewHolder) viewHolder).bind(this, dataSet.get(position), addToPlaylist, mSong);
User clicks on an item in PlaylistViewHolder:
context.startActivity(PublicPlaylistActivity.createStartIntent(context, playlist));
Now here is the question, how can PublicPlaylistActivity talk back to the initial PlaylistFragment?
I suggest you'd better use Interface from fragment to adapter. So when user clicks anything in adapter, call function realization in fragment. If you need your activity to proceed some operation - ((YourActivity) getActivity()).someMethod() should be called from fragment.
Second trick is using broadcastreceiver to send events. A bit more complicated. You have to launch broadcast in view you need to recive message and send these messages from adapter. This approach is more complexible to debug and support if system is wide spread, so you'd better use interfaces.
There are several ways of doing that. The simplest way should be starting the PublicPlaylistActivity with startActivityForResult. In that way, then the activity finishes, you can set send some data to the caller fragment (which is PlaylistFragment in your case). Here is a nice tutorial about the implementation.
Another way of doing that is by using lifecycle methods. You might have a public static variable which can keep track of some status that you might observe in your onResume function of your PlaylistFragment when you are returning back from your PublicPlaylistActivity. You might consider a sample implementation as follows.
Define a public static variable in your PlaylistFragment. Then in your onResume function check the value of that variable and take actions accordingly.
public static boolean someIndicator = false; // Initialize with a default value
#Override
protected void onResume() {
super.onResume();
if(someIndicator == true) doSomething();
else doSomethingElse();
}
Now you can set the indicator variable from anywhere in your application actually which will have the effect on your PlaylistFragment. For example, from your PublicPlaylistActivity, you might consider doing something like this.
public void someFunctionInYourPublicPlaylistActivity() {
// ...
// Some code and then the following
PlaylistFragment.someIndicator = true;
}
Another way of achieving the same thing is by using a BroadcastReceiver. Here is a tutorial on how you can implement one.
It really depends on how you are structuring your whole activity-fragments communication. Hope that helps!
I would do a common "context" class (ComContext) with an interface. When you create your fragment, you also create this class. And from the activity you can check if it exists or not.
I assume that you already have a helper(AppHelper) class with static variables.
public class AppHelper {
public static ComContext comContext = null;
}
public class MainFragment {
#Override
public void onViewCreated(#NonNull View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
ConContext comContext = new ComContext();
comContext.listener = this;
AppHelper.comContext = comContext;
}
#Override
public void onDataChanged() {
}
#Override
public void onDestroyView() {
super.onDestroyView();
AppHelper.comContext = null;
}
}
public class MainActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (AppHelper.comContext != null) {
AppHelper.comContext.listener.onDataChanged();
}
}
}
public class ComContext {
public interface HelperListener {
void onDataChanged();
}
public HelperListener listener = null;
}
So first things first, here's the error that I'm getting:
java.lang.IllegalStateException: The application's PagerAdapter
changed the adapter's contents without calling
PagerAdapter#notifyDataSetChanged! Expected adapter item count: 18,
found: 28
I'm using a RecyclerView in my main activity and that has a List<Objects> as the dataset, that's all fine.
From that activity I call the second activity when a RecyclerView item is clicked that is basically a gallery implemented using a ViewPager using this code:
public void startSlideActivity(final int position) {
DataTransferer.get().storeItems(feed);
Intent i = new Intent(context, SlideActivity.class);
...
i.putExtra("POSITION", position);
context.startActivity(i);
}
My data is too large to transfer through an intent (using Parcelable or otherwise) so I'm using a singleton to hold and transfer my list, here's the code:
public class DataTransferer {
private static volatile DataTransferer singleton;
private List<Thing> items;
public static DataTransferer get(){
if (singleton == null) {
synchronized (DataTransferer.class) {
singleton = new DataTransferer();
}
}
return singleton;
}
private DataTransferer(){
}
public void storeItems(List<Thing> items){
this.items = items;
}
public List<Thing> getStoredItems(){
return items;
}
}
In the second activity I set the adapter and retrieve the list like so:
feed = DataTransferer.get().getStoredItems();
final int position = this.getIntent().getIntExtra("POSITION", 0);
adapter = new FeedPagerAdapter(SlideActivity.this, feed);
viewPager.setAdapter(adapter);
adapter.notifyDataSetChanged();
viewPager.setCurrentItem(position);
viewPager.setOffscreenPageLimit(4);
And finally here's in my PagerAdapter code:
public class FeedPagerAdapter extends PagerAdapter {
#BindView(R.id.item_image_view) ImageView image;
private final SlideActivity host;
private List<Thing> items;
public FeedPagerAdapter(SlideActivity host, List<Thing> items){
this.host = host;
this.items = items;
notifyDataSetChanged();
}
#Override
public Object instantiateItem(ViewGroup parent, int position) {
View view = LayoutInflater.from(host).inflate(R.layout.item, parent, false);
ButterKnife.bind(this, view);
...
parent.addView(view);
return view;
}
#Override
public int getCount() {
return items.size();
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
container.removeView((View)object);
}
#Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}
}
I've tried notifying the dataset in onResume and onPause and getItemCount in the adapter also, same problem.
Back to the main activity, this data is loaded over the network and adds items to the list when the load finishes. If I start my application and click on the item as soon they start to populate the RecyclerView, it opens the second activity and I get the crash. If I start the app and wait a second and click a RecyclerView item, it works as intended.
If anyone has any suggestions on how I can wait to make sure the list is stable when starting the second activity or a better way to implement a grid based RecyclerView gallery to open a viewpager type layout with the same dataset I would really appreciate it.
It's because you are using this line viewPager.setOffscreenPageLimit(4);, It's mean viewpager won't re-create the screen in all 4 pages. However, there is a function to detect if your screen has been visible completely, it's call setUserVisibleHint(). You just need to use like below:
//For the Fragment case
#Override
public void setUserVisibleHint(boolean isVisibleToUser) {
if (isVisibleToUser) {
//TODO notify your recyclerview data over here
}
}
EDIT:
For the Activity case: If targeting API level 14 or above, one can use
android.app.Application.ActivityLifecycleCallbacks
public class MyApplication extends Application implements ActivityLifecycleCallbacks {
private static boolean isInterestingActivityVisible;
#Override
public void onCreate() {
super.onCreate();
// Register to be notified of activity state changes
registerActivityLifecycleCallbacks(this);
....
}
public boolean isInterestingActivityVisible() {
return isInterestingActivityVisible;
}
#Override
public void onActivityResumed(Activity activity) {
if (activity instanceof MyInterestingActivity) {
isInterestingActivityVisible = true;
}
}
#Override
public void onActivityStopped(Activity activity) {
if (activity instanceof MyInterestingActivity) {
isInterestingActivityVisible = false;
}
}
// Other state change callback stubs
....
}
Register your application class in AndroidManifest.xml:
<application
android:name="your.app.package.MyApplication"
android:icon="#drawable/icon"
android:label="#string/app_name" >
Add onPause and onResume to every Activity in the project:
#Override
protected void onResume() {
super.onResume();
MyApplication.activityResumed();
}
#Override
protected void onPause() {
super.onPause();
MyApplication.activityPaused();
}
In your finish() method, you want to use isActivityVisible() to check if the activity is visible or not. There you can also check if the user has selected an option or not. Continue when both conditions are met.
I am implementing a login system. The user needs to be redirected to the login activity from any previous activity if the token is no longer valid. I can go to the login activity with this
new Intent(CurrentActivity.this, NextActivity.class);
But this needs the current activity. I just want to go to the login activity no matter where I am. I cannot know where I am because this is inside an entirely different package.
you should probably register in the Application class to ActivityLifecycleCallbacks and if the user is not registered send them to the correct Activity.
just be sure to not endlessly send them from the login page to itself
EDIT:
adding some code and explanation.
In order to figure out if an Activity that shouldn't be alive is going through lifecycle events you'll need to implement some sort of a gate keeper. Previously it used to be some sort of static state that is kept in the Application class and holds the current activity and sometime even the stack of current activities.
This was far from a complete solution and had issues due to different tasks and even isolated procesies.
In API 14 Android introduced the Activity lifecycle callbacks which can be passed into the method registerActivityLifecycleCallbacks int the Application class.
What you want to do basically is the following:
class ThepooshApplication extends Application {
private static sIsRegistered = false;
public static setIsRegistered(boolean isRegistered) { sIsRegistered = isRegistered; }
public void onCreate() {
registerActivityLifecycleCallbacks(new ActivityLifecycleCallbacks(){
#Override
void onActivityCreated(Activity activity, Bundle savedInstanceState){
if (!sIsRegistered && !(activity instanceof LoginActivity)) {
Intent loginIntent = new Intent(this, LoginActivity.class);
loginIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK
| Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(loginIntent);
}
}
#Override
void onActivityStarted(Activity activity) { /*empty method*/ }
#Override
void onActivityResumed(Activity activity) { /*empty method*/ }
#Override
void onActivityPaused(Activity activity) { /*empty method*/ }
#Override
void onActivityStopped(Activity activity) { /*empty method*/ }
#Override
void onActivitySaveInstanceState(Activity activity, Bundle outState) { /*empty method*/ }
#Override
void onActivityDestroyed(Activity activity) { /*empty method*/ }
});
}
}
You must add FLAG_ACTIVITY_NEW_TASK flag to your intent
myIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
Try some like this
Intent i = new Intent();
i.setClass(this,TestActivity.class);
i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(i);
Replace TestActivity.class for your target activity
I am confused about how communication with a Fragment and an Activity is made. For example, an interface was defined here (https://developer.android.com/training/basics/fragments/communicating.html).
public class HeadlinesFragment extends ListFragment {
OnHeadlineSelectedListener mCallback;
// Container Activity must implement this interface
public interface OnHeadlineSelectedListener {
public void onArticleSelected(int position);
}
...
#Override
public void onListItemClick(ListView l, View v, int position, long id) {
// The user clicked on a list item.
mCallback.onArticleSelected(position);
}
}
Eventually, the following method is called from the MainActivity.
public static class MainActivity extends Activity
implements HeadlinesFragment.OnHeadlineSelectedListener{
...
public void onArticleSelected(int position) {
// Do something
}
}
My questions are:
How does mCallback "know" which onArticleSelected method to call (as there might be other classes that have implemented OnHeadlineSelectedListener).
mCallback.onArticleSelected(position);
I wouldn't be confused if it went:
mCallback = new OnHeadSelectedListener() {
#Override
public void onArticleSelected(int position)
// Do something
}
and then mCallback is referred in some way in MainActivity to utilize the onArticleSelected method in some way. In the example code, however, the line intelligently sticks to "an" interface. How does that happen?
Also, I found that the Log I implemented onArticleSelected method from MainActivity is called previously to the one in onListItemClick method in HeadlineFragment. Is it expected?
Since you defined the OnHeadlineSelectedListener interface with only one method, and your activity implements it, there's no ambiguity in choosing the method when you use the activity as instance of this interface, 'cause all you know about activity while using it as instance of OnHeadlineSelectedListener interface is a presence of onArticleSelected(int) method in it.
It depends on when you call the logging function - before or after calling the callback method.
P.S. While this kind of communication between Activity and Fragment (or any other objects) is perfectly fine, personally I prefer the Event Bus approach, 'cause it gives us a possibility to organize code in a low coupled manner. Here are some nice implementations of Event Bus pattern:
https://github.com/greenrobot/EventBus
http://square.github.io/otto/
Take a look at them if you are interested in this approach.
Your mCallback is your activity, in the onAttach method of your fragment, you will set the activity as listener for your fragment. By this way, this is normal that the activity is notified when you call mCallback.onArticleSelected(position);
For your first part of question
You should have a look on onAttach and onDetach methods-
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
try {
mCallbacks = (OnHeadlineSelectedListener) activity;
} catch (ClassCastException e) {
throw new ClassCastException("Activity must implement OnHeadlineSelectedListener.");
}
}
#Override
public void onDetach() {
super.onDetach();
mCallbacks = null;
}
Second part-
The behavior is not expected.
You should not make your activity class static as well.
I'm relatively new to Android,
I have read related articles on detecting network connectivity changes and have implemented this BroadcastReceiver subclass, made the necessary additions to AndroidManifest.xml and I receive the requisite state change broadcasts as expected:
public class NetworkStateReceiver extends BroadcastReceiver {
#Override
public void onReceive(Context context, Intent intent) {
}
}
Question is: how can I receive or forward these notifications in/to my Activity subclasses? Apparently creating an instance of NetworkStateReceiver in my Activity subclass and overriding onReceive there doesn't do the trick.
Thanks in advance for any pointers...
Edit:
I ended up broadcasting an Intent from onReceive above like so:
Intent target = new Intent(CONNECTIVITY_EVENT);
target.putExtra(CONNECTIVITY_STATE, networkInfo.isConnected());
context.sendBroadcast(target);
And receiving that in my Activity like so:
#Override
protected String[] notifyStrings() {
return ArrayUtils.addAll(super.notifyStrings(), new String[] {NetworkStateReceiver.CONNECTIVITY_EVENT});
}
#Override
protected void notifyEvent(Intent intent, String action) {
super.notifyEvent(intent, action);
if (action != null) {
if (action.equalsIgnoreCase(NetworkStateReceiver.CONNECTIVITY_EVENT)) {
boolean isConnected = intent.getBooleanExtra(NetworkStateReceiver.CONNECTIVITY_STATE, true);
// Do something...
}
}
}
I would recommend using either
1) An interface approach. So declare an interface that has a networkChanged() method, and have the class which owns this BroadcastReceiver keep a list of classes who want to be notified of network changes with a local List<InterfaceName>
2) Skip the interface creating and use a subscription utility. My two favorites are
https://github.com/greenrobot/EventBus
and
https://gist.github.com/bclymer/6708819 (smaller, less used, also disclaimer: I wrote this)
With these you would create event classes with properties, and then subscribe and post instances of those classes.
In your activity
#Override
public void onCreate() {
...
EventBus.getInstance().subscribe(this, MyType.class);
}
#Override
public void onDestroy() {
...
EventBus.getInstance().unsubscribe(this, MyType.class);
}
#Override
public void newEvent(Object event) {
if (event instanceOf MyType) {
// do stuff
}
}
And then in your BroadcastReceiver
#Override
public void onReceive(Context context, Intent intent) {
EventBus.post(new MyType(true));
}
Example MyType
public class MyType {
public boolean networkEnabled;
public MyType(boolean networkEnabled) {
this.networkEnabled = networkEnabled;
}
}
This examples use the 2nd subscription utility (mine).