Getting activity from context in android

Question

This one has me stumped   I need to call an activity method from within a custom layout class  The problem with this is that I don t know how to access the activity from within the layout   ProfileView  public class ProfileView extends LinearLayout       TextView profileTitleTextView      ImageView profileScreenImageButton      boolean isEmpty      ProfileData data      String name       public ProfileView Context context  AttributeSet attrs  String name  final ProfileData profileData                super context  attrs                                              Heres where things get complicated     public void onClick View v                  Need to get the parent activity and call its method          ProfileActivity x    ProfileActivity  context          x activityMethod              ProfileActivity  public class ProfileActivityActivity extends Activity         In here I am creating multiple ProfileViews and adding them to the activity dynamically       public void onCreate Bundle savedInstanceState                super onCreate savedInstanceState           setContentView R layout profile activity main              public void addProfilesToThisView                 ProfileData tempPd   new tempPd                Context actvitiyContext   this getApplicationContext              Profile view needs context  null  name and a profileData         ProfileView pv   new ProfileView actvitiyContext  null  temp  tempPd           profileLayout addView pv             As you can see above  I am instantiating the profileView programatically and passing in the activityContext with it  2 questions    Am i passing the correct context into the Profileview  How do I get the containing activity from the context

User · Answer

Context may be an Application  a Service  an Activity  and more   Normally the context of Views in an Activity is the Activity itself so you may think you can just cast this Context to Activity but actually you can t always do it  because the context can also be a ContextThemeWrapper in this case   ContextThemeWrapper is used heavily in the recent versions of AppCompat and Android  thanks to the android theme attribute in layouts  so I would personally never perform this cast   So short answer is  you can t reliably retrieve an Activity from a Context in a View  Pass the Activity to the view by calling a method on it which takes the Activity as parameter

User · Answer

how about some live data callback    class ProfileView      private val  profileViewClicked   MutableLiveData lt ProfileView gt        val profileViewClicked  LiveData lt ProfileView gt     profileViewClicked    class ProfileActivity     override fun onCreateView            profileViewClicked observe viewLifecycleOwner  Observer           activityMethod

User · Answer

an Activity is a specialization of Context so  if you have a Context you already know which activity you intend to use and can simply cast a into c  where a is an Activity and c is a Context   Activity a    Activity  c

User · Answer

If you like to call an activity method from within a custom layout class non-Activity Class  You should create a delegate using interface     It is untested and i coded it right   but i am conveying a way to achieve what you want   First of all create and Interface   interface TaskCompleteListener lt T gt       public void onProfileClicked T result        public class ProfileView extends LinearLayout       private TaskCompleteListener lt String gt  callback      TextView profileTitleTextView      ImageView profileScreenImageButton      boolean isEmpty      ProfileData data      String name       public ProfileView Context context  AttributeSet attrs  String name  final ProfileData profileData                super context  attrs                                           public setCallBack  TaskCompleteListener lt String gt  cb               this callback   cb              Heres where things get complicated     public void onClick View v                callback onProfileClicked  Pass your result or any type              And implement this to any Activity   and call it like  ProfileView pv   new ProfileView actvitiyContext  null  temp  tempPd   pv setCallBack new TaskCompleteListener                                     public void onProfileClicked String resultStringFromProfileView

User · Answer

And in Kotlin   tailrec fun Context activity    Activity    when     this is Activity - gt  this   else - gt   this as  ContextWrapper   baseContext  activity

User · Answer

This is something that I have used successfully to convert Context to Activity when operating within the UI in fragments or custom views  It will unpack ContextWrapper recursively or return null if it fails   public Activity getActivity Context context        if  context    null                return null            else if  context instanceof ContextWrapper                if  context instanceof Activity                        return  Activity  context                    else                       return getActivity   ContextWrapper  context  getBaseContext                          return null

User · Answer

This method should be helpful     public Activity getActivityByContext Context context    if context    null       return null         else if  context instanceof ContextWrapper   amp  amp   context instanceof Activity            return  Activity  context         else if context instanceof ContextWrapper           return getActivity   ContextWrapper  context  getBaseContext            return null           I hope this helps   Merry coding

User · Answer

No You can t   There are two different contexts in Android  One for your application  Let s call it the BIG one  and one for each view  let s call it the activity context    A linearLayout is a view  so you have to call the activity context  To call it from an activity  simply call  this   So easy isn t it   When you use  this getApplicationContext      You call the BIG context  the one that describes your application and cannot manage your view   A big problem with Android is that a context cannot call your activity  That s a big deal to avoid this when someone begins with the Android development  You have to find a better way to code your class  or replace  Context context  by  Activity activity  and cast it to  Context  when needed    Regards     Just to update my answer  The easiest way to get your Activity context is to define a static instance in your Activity  For example  public class DummyActivity extends Activity       public static DummyActivity instance   null        Override     public void onCreate Bundle savedInstanceState                super onCreate savedInstanceState               Do some operations here             Override     public void onResume                 super onResume            instance   this              Override     public void onPause                 super onPause            instance   null            And then  in your Task  Dialog  View  you could use that kind of code to get your Activity context   if  DummyActivity instance    null           Do your operations with DummyActivity instance

User · Answer

From your Activity  just pass in this as the Context for your layout   ProfileView pv   new ProfileView this  null  temp  tempPd     Afterwards you will have a Context in the layout  but you will know it is actually your Activity and you can cast it so that you have what you need   Activity activity    Activity  context

User · Answer

I used convert Activity  Activity activity    Activity  context

User · Answer

Never ever use getApplicationContext   with views   It should always be activity s context  as the view is attached to activity  Also  you may have a custom theme set  and when using  application s context  all theming will be lost  Read more about different versions of contexts here

[android] Getting activity from context in android

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