Needing Context in non-Activity classes

Question

I have some classes within my application that need to call Android functions that require the Context as a parameter. I don't have it as the class is not a subclass of the Activity class.

What is the correct way to tackle this problem?

1. Pass it as a parameter on each call?
2. Pass it at class instantiation and keep it?

Solution 1

It depends on the role of the class. But anyway pass ApplicationContext but not Activity one. If you pass Activity context gc can't remove it from the memory when after you don't need activity anymore. But application context is used while application was not finished by OS.Refer Avoid Memory Leaks

Solution 2

Pass it as a parameter. Or better yet, get the application context to avoid memory leaks.

public class Example {
    protected Context context;

    public Example(Context context){
        this.context = context.getApplicationContext();
    }
}

Solution 3

I'm pretty much always going with a constructor parameter approach. I pass it in the instantiation and keep a private reference in the instantiated class.

You have to think about one important thing. If the class you pass the Context will exist longer than the Activity instantiating it then you should use the application context. If that class is doing UI stuff you will need an activity context.

Make sure that the class you are passing an activity context to won't last longer than the Activity or you'll leak the entire activity.

If you don't do UI stuff then go with the application context.

Solution 4

I pass it as a parameter, i think its de best form to do it

Solution 5

Pass it at class instantiation and keep it.

One typical example is when you create a db helper. See this link

View more solutions

Comments

[theblitz]

On each call to the function?

[theblitz]

Perfect!Just what I was looking for

[Aracem]

Depends on the case. If u need only in a methop use a parameter. If u need in a class where it use many times, pass a parameter in the constructor and asing to a atribute: public class Example{ private Context mContext; public Example(Context context,int other, int other,int other){ this.context = context; [...] } public void method(){ Toast.makeText(mContext,"text",Toast.Toast.LENGTH_SHORT).sho‌​w(); } }

[theblitz]

It is a UI application so the instantiated class will disappear on exit.

[Octavian Damiean]

Well I know that it is an UI application as you were talking about an Activity but is the class needing that context doing UI stuff?

[theblitz]

:) Nope. But it is going to need to access SQLite so it needs the Context.

[theblitz]

Won't it disappear with the activity?

[Octavian Damiean]

Right then you should go for a non activity context.

[theblitz]

So - the Application Context?

[Maxim]

@theblitz If context object is used it is not be collected (as any other object)

[theblitz]

I meant that surely my instantiated class will disappear with the Activity itself when it closes.

[theblitz]

So just pass this.getApplicationContext to any class that need it. Right?

[Octavian Damiean]

Well in that particular case yes but keep in mind what I posted in my answer. With that type of context you won't always be able to do what you want.

[theblitz]

All my UI happens at the top level so it shouldn't be a problem.

[theblitz]

How come they pass "this" to NotesDbAdapter in the Notepad example? Isn't that the same thing?

[Maxim]

It is the same thing. So their example is not match to idea of their article I mentioned above. Same thing you can meet with convertView of CustomAdapter getView method that explained by Romain Guy on Google I/O. But convertView isn't used in some developer.android.com articles

[Adam Matan]

Link's dead - any new references?