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Android ActivityGroup - NullPointerException

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耶瑟儿～
耶瑟儿～ 2021-01-16 20:27

I\'m trying to use activity groups - since I use tabs, and want to have the tabs when loading and activity after the list item was clicked,. but I\'m getting nullpointerexce

3条回答
  • 长情又很酷
    长情又很酷 (楼主)
    2021-01-16 20:40

    Came across the same issue and it seems that there is(or was) a bug with the LocalActivityManager that occurs when you're trying to (re)start an Activity with the same ID as a previously destroyed Activity. It will simply return null as Window, because of a bug inside the destroyActivity method. The workaround I'm using, uses reflection to properly destroy a activity (detailed explanation after the workaround) : 

    public boolean destroyActivityWorkAround(String id) {
    final LocalActivityManager activityManager = getLocalActivityManager();
    if(activityManager != null){
        activityManager.destroyActivity(id, false);             
        try {
            // Use reflection to get to the HashMaps with the records(which activities are started ect.)
            // to remove the records properly 
            // http://code.google.com/p/android/issues/detail?id=10083
            final Field mActivitiesField = LocalActivityManager.class.getDeclaredField("mActivities");
            if(mActivitiesField != null){
                mActivitiesField.setAccessible(true);
                @SuppressWarnings("unchecked")
                final Map mActivities = (Map)mActivitiesField.get(activityManager);
                if(mActivities != null){
                    mActivities.remove(id);
                }
                final Field mActivityArrayField = LocalActivityManager.class.getDeclaredField("mActivityArray");
                if(mActivityArrayField != null){
                    mActivityArrayField.setAccessible(true);
                    @SuppressWarnings("unchecked")
                    final ArrayList mActivityArray = (ArrayList)mActivityArrayField.get(activityManager);
                    if(mActivityArray != null){
                        for(Object record : mActivityArray){
                            final Field idField = record.getClass().getDeclaredField("id");
                            if(idField != null){
                                idField.setAccessible(true);
                                final String _id = (String)idField.get(record);
                                if(id.equals(_id)){
                                    mActivityArray.remove(record);
                                    break;
                                }
                            }
                        }
                    }
                }
            }
        } catch (Exception e) {
            Log.e(LOGTAG, this.getClass().getSimpleName() + ".destroyActivityWorkAround() removing activity using reflection failed with error:", e);
            //e.printStackTrace();
        }
        return true;
    }
    return false;
}



    This is a workaround because the LocalActivityManager.destroyActivity(...) contains a bug in several API-versions. The method doesn't remove  the Activity properly from its HashMap's (LocalActivityManager's source):
    


         public Window destroyActivity(String id, boolean finish) {
         LocalActivityRecord r = mActivities.get(id);   //<-- id's are the key's for the HashMap
         Window win = null;
         if (r != null) {
             win = performDestroy(r, finish);
             if (finish) {
                    mActivities.remove(r);  //--> This works on id's not the 'r object', this doesn't remove anything
             }
         }
         return win;
     } 

    


    the if(finish) statement should be as followed to remove the LocalActivityRecord of the activity being destroyed:
    


    if (finish) {
    mActivities.remove(id);    //--> mActivities should remove the id
    mActivityArray.remove(r);  //--> mActivitiesArray should remove the 'r object' (LocalActivityRecord)
}

    


    Although they say it's being fixed for Froyo but I still encountered it on a Samsung galaxy S2 running 2.3.3
    
    
    
             
    
                                                        
    
            
            
    
              
                
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