I have created an volley list in this i have problem to get data from adapter to activity and this activity to another activity. I have received error cannot cast activity.java to anotherActivity.java below is my code. Please help me anyone thanks.
My Interface itemclick in Adapter class
private OnItemClickGetPlaylist mListener;
public interface OnItemClickGetPlaylist{
public void OnPlaylistItemClick(String playlistName,int numOfItems,String imageViewForPlaylist);
}
public void setOnClickListenerOnPlaylist(OnItemClickGetPlaylist listener)
{
mListener = listener;
}
holder.itemView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
String id = playlist.getId_playlist_identify();
String PlaylistName = playlist.getTitile_of_playlist();
String imageOfPlaylist = playlist.getImage_of_playlist();
int numOfPlaylistSongs = getItemCount();
SendIdToDatabase(id);
if (mListener != null)
{
mListener.OnPlaylistItemClick(PlaylistName,numOfPlaylistSongs,imageOfPlaylist);
}
else {
Toast.makeText(context, "mListeren is null" + mListener, Toast.LENGTH_SHORT).show();
}
}
});
After get data handle OnPlaylistItemClick click in Activity below Codes
public void OnItemClickHandleInPlaylistActivity(String playlistName,int numOfItems,String imageViewForPlaylist)
{
//here is the adapter item click in activity now i want to send that data to another activity without any intent please help me.
// i have implement below code but it give me cannot cast activity to another activity error.
((anotherActivity) getApplicationContext()).OnItemClickInMusicActivity(playlistName,numOfItems,imageViewForPlaylist);
}
See the solution at https://stackoverflow.com/a/47637313/2413303
public class MyApplication extends Application {
private static MyApplication INSTANCE;
DataRepository dataRepository; // this is YOUR class
#Override
public void onCreate() {
super.onCreate();
INSTANCE = this;
dataRepository = new DataRepository();
}
public static MyApplication get() {
return INSTANCE;
}
}
The DataRepository should expose LiveData:
public class DataRepository {
private final MutableLiveData<MyData> data = new MutableLiveData<>();
public LiveData<MyData> getMyData() {
return data;
}
public void updateText(String text) {
MyData newData = data.getValue()
.toBuilder() // immutable new copy
.setText(text)
.build();
data.setValue(newData);
}
}
Where the Activity subscribes to this:
public class MyActivity extends AppCompatActivity {
DataRepository dataRepository;
TextView textView;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
MyApplication app = (MyApplication)getApplicationContext();
dataRepository = app.getDataRepository();
setContentView(R.layout.main_activity);
textView = findViewById(R.id.textview);
dataRepository.getMyData().observe(this, new Observer() {
#Override
public void onChange(MyObject myObject) {
textView.setText(myObject.getText());
}
}
}
So to update this text, you need to get the DataRepository class, and call updateText on it:
DataRepository dataRepository = MyApplication.get().dataRepository();
dataRepository.updateText("my new text");
Make sure that the data in DataRepository is properly persisted somewhere, or at least can be obtained again after process death. You might want to use a database for example (but not shared preferences).
If you don't want to use Intents, maybe you can use a publish/subscribe architecture. There is a library called eventbus (org.greenrobot:eventbus) very easy to use which could achieve what you want.
Use an Application Class instead.
public class MyApplicationClass extends Application{
#Override
public void onCreate() {
super.onCreate();
///do something on create
}
getterMethods(){...}
setterMethods(){...}
}
then add android:name=".MyApplicationClass" to manifest file
Now you can access the methods in class by
MyApplicationClass applicationClass = (MyApplicationClass)getApplicationContext();
int id = applicationClass .getterMethod().getID;
String playListName = applicationClass .getterMethod().getPlayListName();
and vice versa for Setter();
after that you can use it for data getting and setting Data throughout the application.
Hope it helps :)
References:
https://guides.codepath.com/android/Understanding-the-Android-Application-Class
I find the best to use callbacks.
in ClassA:
Create interface
MyCallback callback;
viod setCallback(MyCallback callback){
this.callback = callback;
}
viod onStop(){
callback = null;
}
interface MyCallback{
void doSomething(Params params);
}
in ClassB:
implement MyCallback
public class ClassB **implements ClassA.MyCallback**
set reference in onCreate
ClassA classA = new ClassA();
classA.setCallback(this);
// override method doSomething
#override
void doSomething(Params params){
//do your thing with the params…
}
when the job is done inside class A call:
callback.doSomething(params);
destroy reference inside class B in onStop()
classA.onStop();
Related
I created a very simple listener interface that looks like this:
public interface ReportDialogListener {
void shouldRemoveBlockedUser();
}
Now, in my ReportDialog class which is defined like this:
public class ReportDialog extends Dialog implements View.OnClickListener {}
I want to implement this listener and send callback for a certain action. However, when I do send callback after a certain action... my mDialogListener variable is null.
Where do I set the context?
This is what I tried:
private ReportDialogListener mDialogListener;
#Override
public void onAttachedToWindow() {
super.onAttachedToWindow();
try {
mDialogListener = (ReportDialogListener) getContext();
} catch (ClassCastException e) {
}
}
#Override
public void onDetachedFromWindow() {
super.onDetachedFromWindow();
mDialogListener = null;
}
But when I call mDialogListener.shouldRemoveBlockedUser();, mDialogListener is null...
Also- I made sure my main activity was implementing ReportDialogListener... thanks
Implement Listener in MainActivity
Public class MainActivity implements ReportDialogListener {
ReportDialogListener reportDialogListener ;
public void onCreate(Bundle saveInstanceState){
reportDialogListener =this;
}
#override
public void shouldRemoveBlockedUser(){
}
}
Pass reportDialogListener object to other class or activity and call the listener method reportDialogListener.shouldRemoveBlockedUser();
If this main activity implements the interface, do not use the activity context. Use this instead. mDialogListener = this;
Also i do not see where you implement the interface,only the View onClick interface you have actually implemented.
public class ReportDialog extends Dialog implements View.OnClickListener
to
public class ReportDialog extends Dialog implements View.OnClickListener,ReportDialogListener
To implement the interface in another, either you define it in the constructor of the calling program, or devise a method that does it.
Since my main activity was actually sending this when creating an instance of ReportDialog :
if (mReportDialog == null) {
mReportDialog = new ReportDialog(this);
}
I was able to assign it to a variable in the constructor of ReportDialog
public ReportDialog(Activity activity) {
super(activity);
mActivity = activity;
init();
}
Then, use it like this:
mDialogListener = (ReportDialogListener) mActivity;
Works perfectly.
public class MainActivity extends AppCompatActivity {
public ShareData SD = new ShareData();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
SD.set_numb(5);
}
// when button clicked
public void noviEkran(View view){
Intent i = new Intent(this,klasaB.class);
startActivity(i);
}
}
public class ShareData {
private int number;
public ShareData(){
this.number=0;
}
public void set_numb(int num){
number = num;
}
public int get_numb(){
return number;
}
}
public class klasaB extends Activity{
ShareData sd;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
int i =sd.get_numb();
System.out.println("Saved numb:" + i);
}
}
My question is, if i declare object in 1st class, and set its parameter number to 5, how to acces this number from other class because now my apk crashes when reading " int i =sd.get_numb(); " in class "klasaB".
Any suggestion how to make this work?
ps: i dont want to use static variables, or putExtra with Intents.
If data is simple/primitive then use Intent to pass data from one activity to another. That is what Intent is for.
If it is not (some sort of complex data structure or object), I would extend Application, by making a custom sub class. Application class (as the name implies) is accessible to all Activities, even when app transitions from one to another. Below is a very simple example, just to show you the idea. You can modify/adjust that to your needs.
public class MyApplication extends Application {
private X x;
public static void setX(X x) { ... }
public static X getX() { ... }
}
public class ActivityA extends Activity {
...
MyApplication.setX(x);
}
public class ActivityB extends Activity {
...
X x = MyApplication.getX();
}
You may have mixed up Activity/MainActivity/AppCombatActivity inheritance... I suspect that the reason you are seeing the error -- by the way, please look into "how to ask" and include a bit more information next time -- is that sd in klasaB is never initialized.
MainActivity.SD will hold that 5 after its onCreate(), whereas klasaB.sd is never set to anything.
You never reference or instantiate SD in class B. To get the data to ClassB you will need to set the data as an extra in the intent. Most classes cannot be sent in the intent, so for your case you should pass the primitive types of the object, then create the object.
// when button clicked
public void noviEkran(View view){
Intent i = new Intent(this,klasaB.class);
i.putExtra("TAG", SD.get_num());
startActivity(i);
And then in Class B
ShareData SD = new ShareData();
SD.set_num(getIntent.getIntExtra("TAG", 0);
You can access your class object either using implements Serializable or Parcelable
1.Implement serializable into your ShareData class
public class ShareData implements Serializable{
private int number;
public ShareData(){
this.number=0;
}
public void set_numb(int num){
number = num;
}
public int get_numb(){
return number;
}
}
2.create object of SharedData and share with intent to classB
public class MainActivity extends AppCompatActivity {
public ShareData SD = new ShareData();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
SD.set_numb(5);
}
// when button clicked
public void noviEkran(View view){
Intent i = new Intent(this,klasaB.class);
i.putExtras("key", SD)
startActivity(i);
}
}
3.Access in classB
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ShareData sd = (ShareData)getIntent().getSerializableExtra("key").
System.out.println("Saved numb:" + sd.get_num());
}
Use a singleton class
Declare an instance in ShareData class:
public class ShareData {
private static ShareData sdInstance = null;
...}
add this method in ShareData class:
public static ShareData getInstance(){
if(sdInstance == null){
sdInstance = new ShareData();
}
return sdInstance;
}
To get same object in other classes , use this
ShareData sd = ShareData.getInstance();
now you will receive same sd.get_numb()
this is My Situation:
I want to make two classes communicate with each other. So MainActivity is
making a new Object of SomeOtherstrangeClass.
public class MainActivity extends AppCompatActivity implements myEventListener {
private TextView txtHelloSet;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
txtHelloSet = (TextView) findViewById(R.id.txtHello);
SomeOtherStrangeClass someOtherStrangeClass = new SomeOtherStrangeClass();
}
#Override
public void someEvent(int e) {
Log.v("[Listener]", "SomeEvent triggered. Number: " + e);
txtHelloSet.setText("Event came in!");
}
}
#
public class SomeOtherStrangeClass {
public SomeOtherStrangeClass(){
EventThrower eventThrower = new EventThrower();
MainActivity mainActivity = new MainActivity();
eventThrower.addListener(mainActivity);
Log.v("[Listener]", "Throwing event");
eventThrower.someEvent(13);
}
}
interface myEventListener extends java.util.EventListener {
void someEvent(int e);
}
public class EventThrower {
private List<myEventListener> listeners = new ArrayList<myEventListener>();
public void addListener(myEventListener toAdd){
listeners.add(toAdd);
}
public void removeListener(myEventListener toRemove){
listeners.remove(toRemove);
}
public void someEvent(int e){
for(myEventListener el : listeners)
el.someEvent(e);
}
}
So this is how I'am doing it. But the Problem is, that when an event is thrown its like I'am still calling the Methode someEvent which is in MainActivity in SomeOtherStrangeClass. So I'am not able to modify any Objects in MainActivity. It's like they are not existing. I'am getting a NPE:
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
Why this is so?
Is there any solution for that?
MainActivity mainActivity = new MainActivity();
You are doing something wrong here. It is not supposed to create Activity objects like this. You should rethink about your application logic.
You need to reference the instance of MainActivity that is currently in foreground in order to recognize any callbacks in it.
Try changing the constructor for SomeOtherStrangeClass like this:
public SomeOtherStrangeClass(myEventListener listener) {
EventThrower eventThrower = new EventThrower();
eventThrower.addListener(listener);
Log.v("[Listener]", "Throwing event");
eventThrower.someEvent(13);
}
Then, in onCreate() of your activity,
SomeOtherStrangeClass someOtherStrangeClass = new SomeOtherStrangeClass(this);
I'm trying to pass variable data back to a Fragment's Containing Activity but it just doesn't seem to be working.
In the fragment I have:
public class MainActivityFragment extends Fragment {
public String profile_id;
OnPassIdListener onPassIdListener;
private FacebookCallback<LoginResult> mCallback = new FacebookCallback<LoginResult>() {
#Override
public void onSuccess(LoginResult loginResult) {
...
}
onPassIdListener.passId(profile_id);
}
public void onAttach(Context context) {
super.onAttach(context);
try {
onPassIdListener = (OnPassIdListener) context;
} catch (Exception ex) {
}
}
public interface OnPassIdListener {
void passId(String id);
}
In the container activity I have:
#Override
public void passId(String id) {
TextView textview = (TextView) findViewById(R.id.prof_id_test);
textview.setText(id);
}
However when the textview.setText is called, it is set to null... meaning that the variable is empty.
Additionally, I have checked that the variable actually contains data BEFORE it is passed to the activity and it does so it must be something to do with the way I am passing it over.
Any ideas? Thanks in advance for any tips.
You can get the attached activity calling it like
ContainerActivity activity = (ContainerActivity) getActivity();
Then just use their methods
activity.passId("");
I have an activity with multiple AsyncTask's, but when i press back button, the Activity is reloaded and the AsyncTask's are executed again. what should i do to Back to the previous activity and not reload the activity and asynctask ? please help.
public class LugarActivity extends SherlockActivity {
CargarDatos cargarDatos;
CargarComentarios cargarComentarios;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_lugar);
cargarDatos = new CargarDatos();
cargarCometarios = new CargarComentarios();
loadData();
}
public void loadData(){
cargarDatos.execute();
}
public void loadOtherData(){
cargarComentarios.execute();
}
public class CargarDatos extends AsyncTask<Integer, Integer, String>{
#Override
protected String doInBackground(Integer... params) {
// here download data
}
#Override
protected void onPostExecute(String html) {
loadOtherData();
}
}
public class CargarComentarios extends AsyncTask<Integer, Integer, String>{
#Override
protected String doInBackground(Integer... params) {
// here download data
}
}
}
FIXED!
i fixed the problem with Singleton class:
public class DataManager {
private static DataManager instance = null;
protected static boolean isShowingTheView = false;
protected DataManager() { }
public static synchronized DataManager getInstance() {
if (instance == null) {
instance = new DataManager();
}
return instance;
}
}
in the activity i add this code:
DataManager dataManager = new DataManager();
if(!dataManager.isShowingTheView){
loadData();
dataManager.isShowingTheView = true;
}else{
finish();
}
and finally i override the onDestroy() method
#Override
public void onDestroy(){
dataManager.isShowingTheView = false;
super.onDestroy();
}
Remove loadData() from onCreate and call somewhere else.
Use Fragments
http://www.androiddesignpatterns.com/2013/04/retaining-objects-across-config-changes.html
A fragment can stay in memory during a configuration change and therefore you can run your asynctask inside itself. You can then query the fragment for any state information you require from your tasks and update your Activity accordingly.
If your Activity is destroyed before the other activity starts, using the back button will call onCreate again, instead of onRestart or onResume.
See here for details.
As Kuffs already mentions, using Fragments is the way to go.
Uglier solution, you could also set a shared preference holding a boolean once your AsyncTask is launched (or on its onPostExecute) so that it won't launch again after checking for that preference on your Activity's onCreate.