Why use ContextWrapper directly in an Activity instead of implicit context from "this"

Question

Going through some supposedly "good" sources sources to learn the details and tricks of context handling in Android I have come across one pattern multiple time that I fail to understand.

What is the advantage of using a ContextWrapper when you could equally well use the implicit context?

For example why use the following in an activity method (defined directly in an Activity class)

...
ContextWrapper cw = new ContextWrapper(getApplicationContext())
File filesDir = cw.getFilesDir();
...

Instead of just

...
File filesDir = getFilesDir();
...

even though getFilesDir() is defined in the ContextWrapper class the Activity is anyway a subclass of ContextWrapper so you have direct access to the method anyway.

So what potential issue (that I fail to see) does this added complexity address?

Answer 1

I'd say (and I might be wrong) that in the scenario (and context) you presented might not make a difference. getApplicationContext().getFilesDir() could have been used just as easily.

However, I believe ContextWrapper might be useful in other scenarios. From what I understand, this is the adapter pattern. You may want to provide different behaviour only for certain methods while proxying all other to the original context reference you pass in.

Check out this piece of code from RemoteViews:

// RemoteViews may be built by an application installed in another
// user. So build a context that loads resources from that user but
// still returns the current users userId so settings like data / time formats
// are loaded without requiring cross user persmissions.
final Context contextForResources = getContextForResources(context);
Context inflationContext = new ContextWrapper(context) {
    @Override
    public Resources getResources() {
        return contextForResources.getResources();
    }
    @Override
    public Resources.Theme getTheme() {
        return contextForResources.getTheme();
    }
};