通过类名反射获取acitivity

public static ActivitygetActivity() {

Class activityThreadClass =null;

    try {

activityThreadClass = Class.forName("android.app.ActivityThread");

        Object activityThread = activityThreadClass.getMethod("currentActivityThread").invoke(null);

        Field activitiesField = activityThreadClass.getDeclaredField("mActivities");

        activitiesField.setAccessible(true);

        Map activities = (Map) activitiesField.get(activityThread);

        for (Object activityRecord : activities.values()) {

Class activityRecordClass = activityRecord.getClass();

            Field pausedField = activityRecordClass.getDeclaredField("paused");

            pausedField.setAccessible(true);

            if (!pausedField.getBoolean(activityRecord)) {

Field activityField = activityRecordClass.getDeclaredField("activity");

                activityField.setAccessible(true);

                Activity activity = (Activity) activityField.get(activityRecord);

                return activity;

            }

}

}catch (ClassNotFoundException e) {

e.printStackTrace();

    }catch (NoSuchMethodException e) {

e.printStackTrace();

    }catch (IllegalAccessException e) {

e.printStackTrace();

    }catch (InvocationTargetException e) {

e.printStackTrace();

    }catch (NoSuchFieldException e) {

e.printStackTrace();

    }

return null;

}