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Activity Context in static classes

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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);
}
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Memory Leaks:
* Memory Leaks
* Avoid leaking Activities with AsyncTask
* Common memory leaks and how to fix them
* Detect memory leaks with the LeakCanary library
* Anonymous callback in activities
* Activity Context in static classes
* Avoid leaking Activities with Listeners
* Avoid memory leaks with Anonymous Class Handler Timer Task Thread
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164 Inter-app UI testing with UIAutomator
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234 Context
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258 Annotation Processor
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260 Singleton Class for Toast Message
261 Fastjson
262 Android Architecture Components
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264 Play Store
265 Loading Bitmaps Effectively
266 Getting system font names
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268 Convert vietnamese string to english
269 Contributors