I don't really get the idea behind how this whole thing works really, so if I have some class A that need the context of a class B which extends Activity, how do i get that context?
I'm searching for a more efficient way than giving the context as a parameter to class A constructor. For example if class A is going to have millions of instances then we would end up having millions of redundant pointer to Context while we should be able somehow to have just one somewhere and a getter function...
This question is related to
android
android-context
You can use Application class(public class in android.application package),that is:
Base class for those who need to maintain global application state. You can provide your own implementation by specifying its name in your AndroidManifest.xml's tag, which will cause that class to be instantiated for you when the process for your application/package is created.
To use this class do:
public class App extends Application {
private static Context mContext;
public static Context getContext() {
return mContext;
}
public static void setContext(Context mContext) {
this.mContext = mContext;
}
...
}
In your manifest:
<application
android:icon="..."
android:label="..."
android:name="com.example.yourmainpackagename.App" >
class that extends Application ^^^
In Activity B:
public class B extends Activity {
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.sampleactivitylayout);
App.setContext(this);
...
}
...
}
In class A:
Context c = App.getContext();
Note:
There is normally no need to subclass Application. In most situation, static singletons can provide the same functionality in a more modular way. If your singleton needs a global context (for example to register broadcast receivers), the function to retrieve it can be given a Context which internally uses Context.getApplicationContext() when first constructing the singleton.
Ok, I will give a small example on how to do what you ask
public class ClassB extends Activity
{
ClassA A1 = new ClassA(this); // for activity context
ClassA A2 = new ClassA(getApplicationContext()); // for application context.
}
If you need the context of A in B, you need to pass it to B, and you can do that by passing the Activity A as parameter as others suggested. I do not see much the problem of having the many instances of A having their own pointers to B, not sure if that would even be that much of an overhead.
But if that is the problem, a possibility is to keep the pointer to A as a sort of global, avariable of the Application class, as @hasanghaforian suggested. In fact, depending on what do you need the context for, you could even use the context of the Application instead.
I'd suggest reading this article about context to better figure it out what context you need.
The best and easy way to get the activity context is putting .this after the name of the Activity. For example: If your Activity's name is SecondActivity, its context will be SecondActivity.this
You can create a constructor using parameter Context of class A then you can use this context.
Context c;
A(Context context){ this.c=context }
From B activity you create a object of class A using this constructor and passing getApplicationContext().
you pass the context to class B in it's constructor, and make sure you pass getApplicationContext() instead of a activityContext()
In Kotlin will be :
activity?.applicationContext?.let {
it//<- you context
}
Source: Stackoverflow.com