Show dialog alert from a non-activity class in android

The problem is 'You can show AlertDialogs from Activity only'. This is not an issue of context.

Although this is not a good idea to show dialog from receiver (better is to use Notification), But if you want to do so you can create an Activity as dialog and show

call this method in activity class

public static void showAlert(Activity activity, String message) {

        TextView title = new TextView(activity);
        title.setText("Title");
        title.setPadding(10, 10, 10, 10);
        title.setGravity(Gravity.CENTER);
        title.setTextColor(Color.WHITE);
        title.setTextSize(20);

        AlertDialog.Builder builder = new AlertDialog.Builder(activity);
        // builder.setTitle("Title");
        builder.setCustomTitle(title);
        // builder.setIcon(R.drawable.alert_36);

        builder.setMessage(message);

        builder.setCancelable(false);
        builder.setNegativeButton("OK", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int id) {
                dialog.cancel();

            }

        });

        AlertDialog alert = builder.create();
        alert.show();
    }

If you always want to get the current activity from anywhere in the app you can register an ActivityLifecycleCallback on your Application instance.

Here's an untested implementation that might get you closer.

public class TestApp extends Application {

    private WeakReference<Activity> mActivity = null;

    @Override
    public void onCreate() {
        super.onCreate();
        registerActivityLifecycleCallbacks(new ActivityLifecycleCallbacks() {
            @Override
            public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
                mActivity = new WeakReference<Activity>(activity);
            }

            @Override
            public void onActivityDestroyed(Activity activity) {
                mActivity.clear();
            }

            /** Unused implementation **/
            @Override
            public void onActivityStarted(Activity activity) {}

            @Override
            public void onActivityResumed(Activity activity) {}
            @Override
            public void onActivityPaused(Activity activity) {}

            @Override
            public void onActivityStopped(Activity activity) {}

            @Override
            public void onActivitySaveInstanceState(Activity activity, Bundle outState) {}
        });
    }

    public Activity getCurrentActivity() {
        return mActivity.get();
    }

}

Then to use this throughout your app you would do some call like this ...

Activity activity = ((TestApp)getApplicationContext()).getCurrentActivity(); 

The advantages are you can always keep track of your current activity, however its a little too overkill for just handling Dialogs from within the Activity.

Just add this before your alertDialog.show();

alertDialog.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);

or try following if above didn't work:

alertDialog.getWindow().setType(WindowManager.LayoutParams.TYPE_APPLICATION_PANEL); 

and use this permission:

<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />