adapter.notifyDataSetChange（）在从另一个活动返回后不更新列表视图

Question

I have two Activities: 1. contains the listview (Activity1), 2. details of each row in the listview (Activity2).

When the user clicks on any row of the listview in Activity1, its respective details get displayed in Activity2 ie Activity2 is started. When the user edits some details in Activity2, all changes are saved to the server and when I return to Activity1 I am fetching the new(updated) list from the server and want to update the UI (listview) of Activity1. But this does not happen. I am doing the following to update the listview:

@Override
protected void onStart() {
    super.onStart();
    Toast.makeText(this, "onStart", Toast.LENGTH_LONG).show();
    PetService petService = FactoryMaker.getFactory(AppConstants.PET_SERVICE).getPetServiceImpl(AppConstants.PARSE_IMPL, this);
    //pets = petService.getPetList();
    //adapter = new PetListArrayAdapter(getApplicationContext(),R.layout.pet_list_item, pets);
    //petListView.setAdapter(adapter);

    pets = petService.getPetList();
    adapter.clear();
    adapter.addAll(pets);
    adapter.notifyDataSetChanged();

    if(pets.size()>0) {
        retrieve.setVisibility(View.INVISIBLE);
    }else{
        retrieve.setVisibility(View.VISIBLE);
    }
}

However if I set the adapter again(like the three lines I commented out), the listview gets updated as required but with notifyDataSetChanged(), its not working. I have followed all the questions for this problem but nothing seems to work. My adapter extends from ArrayAdapter. Please help!

My adapter implementation:

public class PetListArrayAdapter extends ArrayAdapter<Pet> {

     private final String TAG="PetListArrayAdapter";

     private List<Pet> pets = null;
     private Context applicationContext =null;

     public PetListArrayAdapter(Context context, int resource, List<Pet> petList) {
          super(context, resource, petList);
          pets = petList;
          applicationContext = context;
     }

     @Override
     public int getCount(){
          int size = 0;
          if(pets!=null) {
             size = pets.size();
          }
          return size+1;
     }

     @Override
     public int getItemViewType(int position) {
          return (position == 0) ? 0 : 1;
     }

     @Override
     public int getViewTypeCount() {
          return 2;
     }


     @Override
     public View getView(int position, View convertView, ViewGroup parent)  {
         Log.d(TAG, "getView for position" + position);
         int type = getItemViewType(position);
         LayoutInflater inflater = (LayoutInflater) getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
         if(convertView==null) {
              if(type==1) {
                  convertView = inflater.inflate(R.layout.pet_list_item, null);
                  TextView t = (TextView)convertView.findViewById(R.id.petName);
                  final Pet pet = pets.get(position-1);
                  Log.d(TAG, "pet:" + pet);
                  t.setText(pet.getName());

                  ImageView petImage =(ImageView)convertView.findViewById(R.id.petImage);

                  String imageUrl = pet.getThumbnailUrl();
                  //if(petImage.getDrawable()==null) {
                  if (imageUrl != null) {
                       Log.d(TAG, "Loading Image for position" + position);
                       new ImageDownloader(petImage).execute(imageUrl);
                  }
             /*}else{
             Log.d(TAG, "Image present for position" + position);
             }*/
          }else if (type==0){
               convertView = inflater.inflate(R.layout.add_pet, null);
          }
       }

       return convertView;
   }
}

Answer 1

Try

pets.clear();
pets.addAll(petService.getPetList());
adapter.notifyDataSetChanged();

I guess the adapter list looses its link to the actual list.

Answer 2

Add your fetching code in on resume

@Override
    protected void onResume() {
        super.onResume();

        pets = petService.getPetList();
        adapter.clear();
        adapter.addAll(pets);
        adapter.notifyDataSetChanged();

        if(pets.size()>0) {
            retrieve.setVisibility(View.INVISIBLE);
        }else{
            retrieve.setVisibility(View.VISIBLE);
        }
    }

Answer 3

1. First of, Start Activity2 using the startActivityForResult(intent,requesCode) instead of the startActivity(intent) method.

2. Override/implement the onActivityResult(int requestCode, int resultCode, Intent data) of Activity1 and execute these codes. This will ensure that onBackPressed your list gets updated

   pets.clear(); pets.addAll(petService.getPetList()); adapter.notifyDataSetChanged();

so your codes will look like

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    //...some codes

    pets.clear();
    pets.addAll(petService.getPetList());
    adapter.notifyDataSetChanged();

}

Answer 4

I tested with this adapter and it works on my side. However, I did not have images attached but it should be working fine.

public class CustomArrayAdapter extends ArrayAdapter<Pet> {
    private final String TAG = "PetListArrayAdapter";

    private List<Pet> pets = null;

    public CustomArrayAdapter(Context context, List<Pet> petList) {
         super(context, 0, petList);
         pets = petList;
    }

    @Override
    public int getCount() {
        int size = 0;
        if (pets != null) {
            size = pets.size() + 1;
        }
        return size;
    }

    @Override
    public int getItemViewType(int position) {
         return (position == 0) ? 0 : 1;
    }

    @Override
    public int getViewTypeCount() {
         return 2;
    }


    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
         Log.d(TAG, "getView for position" + position);
         ViewHolder holder;
         int type = getItemViewType(position);
         LayoutInflater inflater = LayoutInflater.from(getContext());
         if (convertView == null) {
             holder = new ViewHolder();
             if (type == 1) {
                 convertView = inflater.inflate(R.layout.list_item_layout, null);
                 holder.tvName = (TextView) convertView.findViewById(R.id.tv_name);
                 holder.tvDescription = (TextView) convertView.findViewById(R.id.tv_descriotion);
                 final Pet pet = pets.get(position - 1);
                 Log.d(TAG, "pet:" + pet);

                convertView.setTag(holder);
             } else if (type == 0) {
                  convertView = inflater.inflate(R.layout.list_add_layout, null);
                  holder.tvName = (TextView) convertView.findViewById(R.id.tv_add);
             }
        } else {
             holder = (ViewHolder) convertView.getTag();
        }
        if (holder != null) {
             if (type == 1) {
                 holder.tvName.setText(pets.get(position - 1).getName());
                 if (holder.tvDescription != null) {
                    holder.tvDescription.setText(pets.get(position - 1).getDescription());
                 }
             } else if (type == 0) {
                 holder.tvName.setText("Add new pet");
             }
         }

         return convertView;
     }
     static class ViewHolder {
         TextView tvName;
         TextView tvDescription;
     }
 }

I must add that you need to have a proper holder to handle the add pet layout and the layout for pets. What I added here it is just a starting point for you. I would create base holder containing one textview or nothing and use specific holders for specific types and you cast to the right holder whenever it is type 1 or 0.