Develop Reference

How to attach a fragment onto a context (programmatically)?

Currently I'm coding an android project using Android Studio 3.1.2 and SDK 19.
When I refactored almost my whole code and replaced a lot of getContext() calls with requireContext() and getActivity() with requireActivity() i came across the problem, that the app crashes already at the launcher activity. I know that there are several posts related to the same problem of getting IllegalStateException: Fragment myFragment not attached to a contextbut they're all very project-specific so it doesn't actually show me the step i missed to do. So i hereby show you my example of code and pray for a merciful programmer that enlightens me, what I have to do, to solve this problem just in the suiting way.
This is my SplashActivity (the launcher activity):
public class SplashActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_splash);
Fragment fragmentToDisplay = null;
if (!(getIntent().getBooleanExtra("isLaunch", true))) {
fragmentToDisplay = new LoginFragment();
} else {
if (savedInstanceState == null) {
fragmentToDisplay = new SplashFragment();
}
}
if (fragmentToDisplay.isAdded()) {
getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container, fragmentToDisplay).commit();
}
}
}
This is the SplashFragment which gets loaded initially:
public class SplashFragment extends RequestingFragment {
private Handler delayHandler = new Handler();
#Override
public View onCreateView(#NonNull LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
View fragmentView = inflater.inflate(R.layout.fragment_splash, container, false);
requestQueue = Volley.newRequestQueue(this.requireContext());
requestParams.add(SessionHandler.getAppInstanceID(this.getContext()));
startRequest(RequestOperation.SESSION_CHECK);
onSuccess(new JSONObject(), "");
return fragmentView;
}
#Override
public void onDestroy() {
super.onDestroy();
delayHandler.removeCallbacksAndMessages(null);
}
#Override
public void onSuccess(final JSONObject json, String parsingKey) {
delayHandler.postDelayed(new Runnable() {
#Override
public void run() {
//parsing stuff
}
}, 2000);
}
#Override
public void onError() {
showErrorDialog();
}
private void showErrorDialog() {
//show a horrifying dialog
}
}
I would be very thankful, if someone could explain to me, what in particular is causing the exception and how do I do it correctly. Thanks in advance.

When to show a dropdown window in a fragment?

I'm getting the following error when trying to autocompleteTextView.showDropDown():
android.view.WindowManager$BadTokenException: Unable to add window -- token null is not valid; is your activity running?
I've tried to do this in various Fragment lifecycle methods. This error always pops up.
Where do I call methods that display additional windows in a fragment?
EDIT:
#BindView(R.id.acService) AutoCompleteTextView autocompleteSTextView;
#Override
public void onAttach(Context context)
{
super.onAttach(context);
this.context = context;
}
#Override
public void onDetach()
{
super.onDetach();
context = null;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState)
{
return inflater.inflate(R.layout.fragment_home, container, false);
}
#Override
public void onResume()
{
initialize();
loadSkillsData();
super.onResume();
}
private void initialize()
{
util = new Util(context);
requestService = new RequestService();
requestService.setServerUserId(getUser().getServerUserId());
geoDataClient = Places.getGeoDataClient(context);
autocompleteAdapter = new PlaceAutocompleteAdapter(context, geoDataClient, BOUNDS_WORLD, null);
autocompleteTextView.setAdapter(autocompleteAdapter);
mapFragment = (SupportMapFragment) getChildFragmentManager().findFragmentById(R.id.mapFragment);
mapFragment.getMapAsync(this);
autocompleteTextView.setOnFocusChangeListener(new View.OnFocusChangeListener()
{
#Override
public void onFocusChange(View view, boolean hasFocus)
{
if(hasFocus)
{
autocompleteService.showDropDown();
}
}
});
}
And here's how the fragment is loaded in the Activity. I'm using the MaterialNavigationDrawer:
private void replaceWithFragment(Fragment fragment)
{
getSupportFragmentManager().beginTransaction().replace(R.id.frame, fragment).commit();
navigationDrawer.closeDrawer();
}

onFocusChange() can be called before anything is actually visible.
Change
if(hasFocus)
{
autocompleteService.showDropDown();
}
to
if(hasFocus && isVisible())
{
autocompleteService.showDropDown();
}
This will make sure the fragment is actually showing and added to a Window before you try to show the dropdown.

Why does pressing back from detail activity after landscape-to-portrait-switch show an empty screen?

Below is the MainActivity class that I'm using. The code checks to see if the phone is in landscape or portrait. If it's in portrait, it will show the main fragment in the main activity only (the main fragment is a static fragment in the main_activity.xml file). Then if a "Recipe" is clicked it will open a detail activity with its own fragment. If the phone is in landscape mode, it will show the main fragment and the detail fragment side by side. Everything works perfectly fine however when I follow the procedure below I get a white screen instead of the main activity:
Procedure:
Switch to landscape
Switch back to portrait
Choose an item and wait for the detail activity to open
Press back
Here instead of the main activity window I get a white screen
If I don't switch to landscape and just start with the portrait mode everything is fine. It seems like switching to landscape does something that causes the problem and I can't figure out what. Any tip on what's going on or where to look would be much appreciated.
public class MainActivity extends AppCompatActivity implements RecipesFragment.OnRecipeClickListener {
private String RECIPE_PARCEL_KEY;
private boolean mTwoPane;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
RECIPE_PARCEL_KEY = getString(R.string.ParcelKey_RecipeParcel);
if (findViewById(R.id.linearLayoutTwoPane) != null) {
mTwoPane = true;
if (savedInstanceState == null) {
RecipeFragment recipeFragment = new RecipeFragment();
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction()
.add(R.id.recipeFrameForTwoPane, recipeFragment)
.commit();
}
} else {
mTwoPane = false;
}
}
#Override
public void OnRecipeClick(Recipe recipe) {
if (mTwoPane) {
RecipeFragment recipeFragment = new RecipeFragment();
recipeFragment.setRecipe(recipe);
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.recipeFrameForTwoPane, recipeFragment)
.commit();
} else {
Class destinationClass = DetailActivity.class;
Intent intentToStartDetailActivity = new Intent(this, destinationClass);
intentToStartDetailActivity.putExtra(RECIPE_PARCEL_KEY, recipe);
startActivity(intentToStartDetailActivity);
}
}
}
EDIT:
Adding RecipeFragment's code below:
public class RecipeFragment extends Fragment {
private Recipe mRecipe;
#BindView(R.id.tv_recipeName) TextView recipeNameTextView;
public RecipeFragment(){
}
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.recipe_fragment,container,false);
ButterKnife.bind(this,view);
if(mRecipe!=null) {
recipeNameTextView.setText(mRecipe.getName());
}else{
recipeNameTextView.setText(getString(R.string.messageSelectARecipe));
}
return view;
}
public void setRecipe(Recipe recipe){
mRecipe = recipe;
}
}
EDIT:
I followed #mt0s's advice and created different background colors for the fragments and activities and finally narrowed down the problem to a line in my recyclerview adapter code. My adapter code is below. Inside loadInBackground() on line URL url = new URL(getString(R.string.URL_RecipeJSON)); I get a Fragment RecipesFragment{96e9b6a} not attached to Activity exception. I don't understand why I'm getting this exception and what the best way to resolve this is. Have I placed the right code in the right fragment methods (ie OnCreate vs OnActivityCreated vs OnCreateView vs etc)?
public class RecipesFragment extends Fragment
implements RecipeAdapter.RecipeAdapterOnClickHandler,
LoaderManager.LoaderCallbacks<ArrayList<Recipe>> {
#BindView(R.id.rv_recipes) RecyclerView mRecyclerView;
private RecipeAdapter mRecipeAdapter;
private static final int LOADER_ID = 1000;
private static final String TAG = "RecipesFragment";
private OnRecipeClickListener mOnRecipeClickListener;
public RecipesFragment(){
}
public interface OnRecipeClickListener {
void OnRecipeClick(Recipe recipe);
}
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.recipes_fragment, container, false);
ButterKnife.bind(this, view);
LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity(), LinearLayoutManager.VERTICAL, false);
mRecyclerView.setLayoutManager(layoutManager);
mRecyclerView.setHasFixedSize(true);
mRecipeAdapter = new RecipeAdapter(this);
mRecyclerView.setAdapter(mRecipeAdapter);
return view;
}
#Override
public void onActivityCreated(#Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
}
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
getLoaderManager().initLoader(LOADER_ID, null, this);
}
#Override
public void onPause() {
super.onPause();
}
#Override
public void onResume() {
super.onResume();
}
#Override
public void OnClick(Recipe recipe) {
mOnRecipeClickListener.OnRecipeClick(recipe);
}
#Override
public void onAttach(Context context) {
super.onAttach(context);
try{
mOnRecipeClickListener = (OnRecipeClickListener) context;
} catch (ClassCastException e){
Log.e(TAG, "onAttach: Host activity class must implement OnRecipeClickListener.");
}
}
#Override
public Loader<ArrayList<Recipe>> onCreateLoader(int i, Bundle bundle) {
return new AsyncTaskLoader<ArrayList<Recipe>>(getActivity()) {
#Override
protected void onStartLoading() {
super.onStartLoading();
forceLoad();
}
#Override
public ArrayList<Recipe> loadInBackground() {
String response;
ArrayList<Recipe> recipes = null;
try {
URL url = new URL(getString(R.string.URL_RecipeJSON)); //***I get an exception here***
response = NetworkUtils.getResponseFromHttpUrl(url, getActivity());
recipes = RecipeJsonUtils.getRecipeFromJson(getActivity(), response);
} catch (Exception e) {
Log.e(TAG, "loadInBackground: " + e.getMessage());
}
return recipes;
}
};
}
#Override
public void onLoadFinished(Loader<ArrayList<Recipe>> loader, ArrayList<Recipe> recipes) {
mRecipeAdapter.setRecipeData(recipes);
}
#Override
public void onLoaderReset(Loader<ArrayList<Recipe>> loader) {
}
}

I finally figured out the problem and the solution. The problem is that onStartLoading() in the AsyncTaskLoader anonymous class in RecipesFragment class gets called every time the fragment is resumed whether the enclosing Loader is called or not. This causes the problem. I need to have control over when onStartLoading() is being called and I only want it to be called if and only if the enclosing Loader is being initialized or restarted. As such, I destroyed the loader in onPause() of the fragment and restarted it in onResume(). Hence, I added the following code to the RecipesFragment class:
#Override
public void onPause() {
super.onPause();
getLoaderManager().destroyLoader(LOADER_ID);
}
#Override
public void onResume() {
super.onResume();
getLoaderManager().restartLoader(LOADER_ID, null, this);
}
I also removed initLoader() from onCreate(). This way, every time the fragment is resumed (or created) onStartLoading() will be called. I tried this and it solves my problem.

When you switch from the landscape to portrait or the opposite the Android OS destroy your activity and recreate it again. this what probably trigger your problem

Android Fragment Webview Memory Leak

I could use some help identifying an issue in my code regarding fragments and webviews. I tried implementing some of the solutions in the other threads unsuccessfully. I've tested this same fragment being replaced without the webview being created inside and there is no leak. Any ideas? If not, can anyone pose an alternate solution?
Here's my webview fragment:
public class CustomWebViewFragment extends PageFragment
{
private LinearLayout mWebContainer;
private WebView mWebView;
/**
* public View onCreateView(LayoutInflater inflater, ViewGroup container,
* Bundle savedInstanceState)
*/
#SuppressLint("SetJavaScriptEnabled")
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
View v = inflater.inflate(R.layout.fragment_one, container, false);
//If I comment this line out, there is no memory leak
mWebView = new WebView(this.getActivity().getApplicationContext());
return v;
}
/**
* public void onDestroy()
*/
#Override
public void onDestroy()
{
super.onDestroy();
if (mWebView != null)
{
mWebView.loadUrl("about:blank");
mWebView.destroy();
mWebView = null;
}
}
}
Here's how I'm changing fragments:
#Override
public void onNavSelected(String page)
{
if (page != null && !page.equals(""))
{
System.gc();
if (page.equalsIgnoreCase(GlobalConstants.PAGE_1))
{
mCurrent = getFragment(); // Creates a new fragment
getSupportFragmentManager().beginTransaction()
.replace(R.id.main_fragment, mCurrent).commit();
}
}
}

Change
//If I comment this line out, there is no memory leak
mWebView = new WebView(this.getActivity().getApplicationContext());
&
#Override
public void onDestroy()
{
super.onDestroy();
if (mWebView != null)
{
mWebView.loadUrl("about:blank");
mWebView.destroy();
mWebView = null;
}
}
To
mWebView = new WebView(getActivity());
&
#Override
public void onDestroy()
{
// null out before the super call
if (mWebView != null)
{
mWebView.loadUrl("about:blank");
mWebView = null;
}
super.onDestroy();
}

Saving the state of fragments?

I have a fragment class. Here is it below:
public class FragmentA extends Fragment {
Button button;
WebView myWebView;
int mCurCheckPosition;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
#Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putInt("curChoice", mCurCheckPosition);
}
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
if (savedInstanceState != null) {
// Restore last state for checked position.
mCurCheckPosition = savedInstanceState.getInt("curChoice", 0);
}
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup group, Bundle saved)
{
View mainView = (View) inflater.inflate(R.layout.frag_a, group, false);
myWebView = (WebView) mainView.findViewById(R.id.webview);
myWebView.setWebViewClient(new MyWebViewClient());
myWebView.getSettings().setPluginsEnabled(true);
myWebView.getSettings().setBuiltInZoomControls(false);
myWebView.getSettings().setSupportZoom(false);
myWebView.getSettings().setJavaScriptCanOpenWindowsAutomatically(true);
myWebView.getSettings().setAllowFileAccess(true);
myWebView.getSettings().setDomStorageEnabled(true);
myWebView.loadUrl("http://www.bbc.co.uk");
return mainView;
}
public class MyWebViewClient extends WebViewClient {
/* (non-Java doc)
* #see android.webkit.WebViewClient#shouldOverrideUrlLoading(android.webkit.WebView, java.lang.String)
*/
#Override
public boolean shouldOverrideUrlLoading(WebView view, String url) {
if (url.endsWith(".mp4"))
{
Intent intent = new Intent(Intent.ACTION_VIEW);
intent.setDataAndType(Uri.parse(url), "video/*");
view.getContext().startActivity(intent);
return true;
}
else {
return super.shouldOverrideUrlLoading(view, url);
}
}
}
}
The problem is when I move to and from another fragment, the state of the original fragment (what web page it was on) is lost.
How can I prevent this? I want the state of the web page to remain switching to and from each fragment.
Thanks

You should use the WebView.saveState(Bundle state) method to in your onSaveInstanceState(Bundle outState) method and then restore the state using WebView.restoreState(Bundle state) in your onActivityCreated(Bundle savedInstanceState) method
#Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
mWebView.saveState(outState);
}
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
mWebView.restoreState(savedInstanceState);
}
Also keep in mind the Fragment Lifecycle. If your unsure where to restore the state (onCreate, onCreateView, onActivityCreated), take a look at the Fragment Lifecycle documentation to figure out the right place.
http://developer.android.com/guide/components/fragments.html
onCreate()
The system calls this when creating the fragment. Within your implementation, you should initialize essential components of the fragment that you want to retain when the fragment is paused or stopped, then resumed.
onCreateView()
The system calls this when it's time for the fragment to draw its user interface for the first time. To draw a UI for your fragment, you must return a View from this method that is the root of your fragment's layout. You can return null if the fragment does not provide a UI.
onActivityCreated()
Called when the fragment's activity has been created and this fragment's view hierarchy instantiated. It can be used to do final initialization once these pieces are in place, such as retrieving views or restoring state. It is also useful for fragments that use setRetainInstance(boolean) to retain their instance, as this callback tells the fragment when it is fully associated with the new activity instance. This is called after onCreateView(LayoutInflater, ViewGroup, Bundle) and before onStart().

I was having the same problem with webView content in a fragment. What worked for me was hiding the current fragment when loading a new one instead of replacing it. This causes the view to remain in the previous fragment and not be destroyed. View code below.
protected void showTableFragment( Fragment fragment, boolean allowBack, Asset table ) {
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction transaction = fragmentManager.beginTransaction();
if (table != null)
tableSection = (SectionTable) table;
Fragment lastFragment = fragmentManager.findFragmentByTag("first_frag" );
if ( lastFragment != null ) {
transaction.hide( lastFragment );
}
if ( fragment.isAdded() ) {
transaction.show( fragment );
}
else {
transaction.add( R.id.fragment, fragment, "second_frag" ).setBreadCrumbShortTitle( "second_frag" );
}
if ( allowBack ) {
transaction.addToBackStack( "second_frag" );
}
transaction.commit();
}