Activity Context in static classes

Often you will want to wrap some of Android’s classes in easier to use utility classes. Those utility classes often require a context to access the android OS or your apps’ resources. A common example of this is a wrapper for the SharedPreferences class. In order to access Androids shared preferences one must write:

context.getSharedPreferences(prefsName, mode);

And so one may be tempted to create the following class:

public class LeakySharedPrefsWrapper
{
    private static Context sContext;

    public static void init(Context context)
    {
        sContext = context;
    }

    public int getInt(String name,int defValue)
    {
        return sContext.getSharedPreferences("a name", Context.MODE_PRIVATE).getInt(name,defValue);
    }
}

now, if you call init() with your activity context, the LeakySharedPrefsWrapper will retain a reference to your activity, preventing it from being garbage collected.

How to avoid:

When calling static helper functions, you can send in the application context using context.getApplicationContext();

When creating static helper functions, you can extract the application context from the context you are given (Calling getApplicationContext() on the application context returns the application context). So the fix to our wrapper is simple:

public static void init(Context context)
{
    sContext = context.getApplicationContext();
}

If the application context is not appropriate for your use case, you can include a Context parameter in each utility function, you should avoid keeping references to these context parameters. In this case the solution would look like so:

public int getInt(Context context,String name,int defValue)
{
    // do not keep a reference of context to avoid potential leaks.
    return context.getSharedPreferences("a name", Context.MODE_PRIVATE).getInt(name,defValue);
}