Best practice to pass Context to non-activity classes?

Question

So, my first major application is almost coded and I'm doing optimizations on my code. The app works fine, but I'm not sure about my way of passing the context to other classes. I don't want to do it the wrong way. I stumbled upon articles and questions here in Stackoverflow about contexts and which is the right way to pass it to non-activity classes. I read the documentation as well, but being a Finn makes complicated tech speak even harder to understand.

So, a simple question. Is my way of passing my main activity's context to other (helper) classes correct? If not, where can I read more about better practice on these situations.

For example: MainActivity.java

public class MainActivity extends Activity {
    @Override
    protected void onCreate(Bundle sis){
        super(sis);
        new Helper(MyActivity.this).makeMyAppAwesome();
    }
}

Helper.java

public class Helper {
    Context context;
    Helper(Context ctx){
        this.context = ctx;
    }

    public void makeMyAppAwesome(){
        makeBaconAndEggsWithMeltedCheese(context);
    }
}

Is this OK? It would be nice if someone could provide an easy to read article with examples on this subject.

Answer 1

You can do that using ContextWrapper, as described here.

For example:

public class MyContextWrapper extends ContextWrapper {

    public MyContextWrapper(Context base) {
      super(base);
   }

    public void makeMyAppAwesome(){
        makeBaconAndEggsWithMeltedCheese(this);
    }
}

And call the non activity class like this from an Activity

new MyContextWrapper(this);

Answer 2

It is usually in your best interest to just pass the current context at the moment it is needed. Storing it in a member variable will likely lead to leaked memory, and start causing issues as you build out more Activities and Services in your app.

public void iNeedContext(Context context) {...

Also, in any class that has context, I'd recommend making a member variable for readability and searchability, rather than directly passing or (ClassName.)this. For example in MainActivity.java:

Context mContext = MainActivity.this;
Activity mActivity = MainActivity.this;

Answer 3

You could also create a static instance reference to your MainActivity initialized in the onCreate() method

public class MainActivity extends AppCompatActivity {

    public static MainActivity mMainActivity;

    @Override
    private onCreate(Bundle savedInstanceState){

    //...

    mMainActivity = this;

    }
}

and call the context like this:

MainActivity.mMainActivity;

or write a method getInstanceOf() if it's clearer and/or you prefer using an accessor

MainActivity.getInstanceOf();

This strategy might provide you with some flexibility if you decide later that you would like to call an instance method contained in your main activity like so:

MainActivity.mMainActivity.myInstanceMethod();

Just a suggestion. Criticism is welcome and encouraged.