[android] Static way to get 'Context' in Android?

Is there a way to get the current Context instance inside a static method?

I'm looking for that way because I hate saving the 'Context' instance each time it changes.

Here is an undocumented way to get an Application (which is a Context) from anywhere in the UI thread. It relies on the hidden static method ActivityThread.currentApplication(). It should work at least on Android 4.x.

try {
    final Class<?> activityThreadClass =
            Class.forName("android.app.ActivityThread");
    final Method method = activityThreadClass.getMethod("currentApplication");
    return (Application) method.invoke(null, (Object[]) null);
} catch (final ClassNotFoundException e) {
    // handle exception
} catch (final NoSuchMethodException e) {
    // handle exception
} catch (final IllegalArgumentException e) {
    // handle exception
} catch (final IllegalAccessException e) {
    // handle exception
} catch (final InvocationTargetException e) {
    // handle exception
}

Note that it is possible for this method to return null, e.g. when you call the method outside of the UI thread, or the application is not bound to the thread.

It is still better to use @RohitGhatol's solution if you can change the Application code.

Kotlin way:

Manifest:

<application android:name="MyApplication">

</application>

MyApplication.kt

class MyApplication: Application() {

    override fun onCreate() {
        super.onCreate()
        instance = this
    }

    companion object {
        lateinit var instance: MyApplication
            private set
    }
}

You can then access the property via MyApplication.instance

If you're open to using RoboGuice, you can have the context injected into any class you want. Here's a small sample of how to do it with RoboGuice 2.0 (beta 4 at time of this writing)

import android.content.Context;
import android.os.Build;
import roboguice.inject.ContextSingleton;

import javax.inject.Inject;

@ContextSingleton
public class DataManager {
    @Inject
    public DataManager(Context context) {
            Properties properties = new Properties();
            properties.load(context.getResources().getAssets().open("data.properties"));
        } catch (IOException e) {
        }
    }
}

Kotlin

open class MyApp : Application() {
    override fun onCreate() {
        super.onCreate()
        mInstance = this
    }

    companion object {
        lateinit var mInstance: MyApp
        fun getContext(): Context? {
            return mInstance.applicationContext
        }
    }
}

and get Context like

MyApp.mInstance

or

MyApp.getContext()

I use a variation of the Singleton design pattern to help me with this.

import android.app.Activity;
import android.content.Context;

public class ApplicationContextSingleton {
    private static Activity gContext;

    public static void setContext( Activity activity) {
        gContext = activity;
    }

    public static Activity getActivity() {
        return gContext;
    }

    public static Context getContext() {
        return gContext;
    }
}

I then call ApplicationContextSingleton.setContext( this ); in my activity.onCreate() and ApplicationContextSingleton.setContext( null ); in onDestroy();

No, I don't think there is. Unfortunately, you're stuck calling getApplicationContext() from Activity or one of the other subclasses of Context. Also, this question is somewhat related.

You can use the following:

MainActivity.this.getApplicationContext();

MainActivity.java:

...
public class MainActivity ... {
    static MainActivity ma;
...
    public void onCreate(Bundle b) {
         super...
         ma=this;
         ...

Any other class:

public ...
    public ANY_METHOD... {
         Context c = MainActivity.ma.getApplicationContext();

The majority of apps that want a convenient method to get the application context create their own class which extends android.app.Application.

GUIDE

You can accomplish this by first creating a class in your project like the following:

import android.app.Application;
import android.content.Context;

public class App extends Application {

    private static Application sApplication;

    public static Application getApplication() {
        return sApplication;
    }

    public static Context getContext() {
        return getApplication().getApplicationContext();
    }

    @Override
    public void onCreate() {
        super.onCreate();
        sApplication = this;
    }
}

Then, in your AndroidManifest you should specify the name of your class in the AndroidManifest.xml’s tag:

<application 
    ...
    android:name="com.example.App" >
    ...
</application>

You can then retrieve the application context in any static method using the following:

public static void someMethod() {
    Context context = App.getContext();
}

WARNING

Before adding something like the above to your project you should consider what the documentation says:

There is normally no need to subclass Application. In most situation, static singletons can provide the same functionality in a more modular way. If your singleton needs a global context (for example to register broadcast receivers), the function to retrieve it can be given a Context which internally uses Context.getApplicationContext() when first constructing the singleton.

REFLECTION

There is also another way to get the application context using reflection. Reflection is often looked down upon in Android and I personally think this should not be used in production.

To retrieve the application context we must invoke a method on a hidden class (ActivityThread) which has been available since API 1:

public static Application getApplicationUsingReflection() throws Exception {
    return (Application) Class.forName("android.app.ActivityThread")
            .getMethod("currentApplication").invoke(null, (Object[]) null);
}

There is one more hidden class (AppGlobals) which provides a way to get the application context in a static way. It gets the context using ActivityThread so there really is no difference between the following method and the one posted above:

public static Application getApplicationUsingReflection() throws Exception {
    return (Application) Class.forName("android.app.AppGlobals")
            .getMethod("getInitialApplication").invoke(null, (Object[]) null);
} 

Happy coding!

I've used this at some point:

ActivityThread at = ActivityThread.systemMain();
Context context = at.getSystemContext();

This is a valid context I used at getting system services and worked.

But, I used it only in framework/base modifications and did not try it in Android applications.

A warning that you must know: When registering for broadcast receivers with this context, it will not work and you will get:

java.lang.SecurityException: Given caller package android is not running in process ProcessRecord

Rohit's answer seems correct. However, be aware that AndroidStudio's "Instant Run" depends on not having static Context attributes in your code, as far as I know.

It depends on what you are using the context for. I can think of at least one disadvantage to that method:

If you are trying to create an AlertDialog with AlertDialog.Builder, the Application context won't work. I believe you need the context for the current Activity...

I just released a jQuery-inspired framework for Android called Vapor API that aims to make app development simpler.

The central $ facade class maintains a WeakReference (link to awesome Java blog post about this by Ethan Nicholas) to the current Activity context which you can retrieve by calling:

$.act()

A WeakReference maintains a reference without preventing the garbage collection reclaiming the original object, so you shouldn't have a problem with memory leaks.

The downside of course is that you run the risk that $.act() could return null. I have not come across this scenario yet though, so it's perhaps just a minimal risk, worth mentioning.

You can also set the context manually if you are not using VaporActivity as your Activity class:

$.act(Activity);

Also, much of the Vapor API framework uses this stored context inherently which might mean you needn't store it yourself at all if you decide to use the framework. Check out the site for more information and samples.

I hope that helps :)

If you for some reason want Application context in any class, not just those extending application/activity, maybe for some factory or helper classes. You can add the following singleton to your app.

public class GlobalAppContextSingleton {
    private static GlobalAppContextSingleton mInstance;
    private Context context;

    public static GlobalAppContextSingleton getInstance() {
        if (mInstance == null) mInstance = getSync();
        return mInstance;
    }

    private static synchronized GlobalAppContextSingleton getSync() {
        if (mInstance == null) mInstance = 
                new GlobalAppContextSingleton();
        return mInstance;
    }

    public void initialize(Context context) {
        this.context = context;
    }

    public Context getApplicationContext() {
        return context;
    }
}

then initialize it in your application class's onCreate with

GlobalAppContextSingleton.getInstance().initialize(this);

use it anywhere by calling

GlobalAppContextSingleton.getInstance().getApplicationContext()

I don't recommend this approach to anything but application context however. As it can cause memory leaks.

I think you need a body for the getAppContext() method:

public static Context getAppContext()
   return MyApplication.context; 

Assuming we're talking about getting the Application Context, I implemented it as suggested by @Rohit Ghatol extending Application. What happened then, it's that there's no guarantee that the context retrieved in such a way will always be non-null. At the time you need it, it's usually because you want to initialize an helper, or get a resource, that you cannot delay in time; handling the null case will not help you. So I understood I was basically fighting against the Android architecture, as stated in the docs

Note: There is normally no need to subclass Application. In most situations, static singletons can provide the same functionality in a more modular way. If your singleton needs a global context (for example to register broadcast receivers), include Context.getApplicationContext() as a Context argument when invoking your singleton's getInstance() method.

and explained by Dianne Hackborn

The only reason Application exists as something you can derive from is because during the pre-1.0 development one of our application developers was continually bugging me about needing to have a top-level application object they can derive from so they could have a more "normal" to them application model, and I eventually gave in. I will forever regret giving in on that one. :)

She is also suggesting the solution to this problem:

If what you want is some global state that can be shared across different parts of your app, use a singleton. [...] And this leads more naturally to how you should be managing these things -- initializing them on demand.

so what I did was getting rid of extending Application, and pass the context directly to the singleton helper's getInstance(), while saving a reference to the application context in the private constructor:

private static MyHelper instance;
private final Context mContext;    

private MyHelper(@NonNull Context context) {
    mContext = context.getApplicationContext();
}

public static MyHelper getInstance(@NonNull Context context) {
    synchronized(MyHelper.class) {
        if (instance == null) {
            instance = new MyHelper(context);
        }
        return instance;
    }
}

the caller will then pass a local context to the helper:

Helper.getInstance(myCtx).doSomething();

So, to answer this question properly: there are ways to access the Application Context statically, but they all should be discouraged, and you should prefer passing a local context to the singleton's getInstance().

For anyone interested, you can read a more detailed version at fwd blog

If you don't want to modify the manifest file, you can manually store the context in a static variable in your initial activity:

public class App {
    private static Context context;

    public static void setContext(Context cntxt) {
        context = cntxt;
    }

    public static Context getContext() {
        return context;
    }
}

And just set the context when your activity (or activities) start:

// MainActivity

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    // Set Context
    App.setContext(getApplicationContext());

    // Other stuff
}

Note: Like all other answers, this is a potential memory leak.

According to this source you can obtain your own Context by extending ContextWrapper

public class SomeClass extends ContextWrapper {

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

    public void someMethod() {
        // notice how I can use "this" for Context
        // this works because this class has it's own Context just like an Activity or Service
        startActivity(this, SomeRealActivity.class);

        //would require context too
        File cacheDir = getCacheDir();
    }
}

JavaDoc for ContextWrapper

Proxying implementation of Context that simply delegates all of its calls to another Context. Can be subclassed to modify behavior without changing the original Context.

in Kotlin, putting Context/App Context in companion object still produce warning Do not place Android context classes in static fields; this is a memory leak (and also breaks Instant Run)

or if you use something like this:

    companion object {
        lateinit var instance: MyApp
    }

It's simply fooling the lint to not discover the memory leak, the App instance still can produce memory leak, since Application class and its descendant is a Context.

Alternatively, you can use functional interface or Functional properties to help you get your app context.

Simply create an object class:

object CoreHelper {
    lateinit var contextGetter: () -> Context
}

or you could use it more safely using nullable type:

object CoreHelper {
    var contextGetter: (() -> Context)? = null
}

and in your App class add this line:

class MyApp: Application() {

    override fun onCreate() {
        super.onCreate()
        CoreHelper.contextGetter = {
            this
        }
    }
}

and in your manifest declare the app name to . MyApp

    <application
            android:name=".MyApp"

When you wanna get the context simply call:

CoreHelper.contextGetter()

// or if you use the nullable version
CoreHelper.contextGetter?.invoke()

Hope it will help.