Question

I’m trying to implement a simple android REST Client and i having some problems understanding how to pass data between my activities.

I have this ListActivity (I’m using the Spring REST Template) :

    public class MainActivity extends ListActivity
{
    protected static final String TAG = MainActivity.class.getSimpleName();
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //setContentView(R.layout.activity_main);
    }

    @Override
    protected void onListItemClick(ListView l, View v, int position, long id) {
        Toast.makeText(this, "You have selected" + position + id ,
                Toast.LENGTH_SHORT).show();
    }

    @Override
    protected void onStart() {

        super.onStart();
        new DownloadClientesTask().execute();
    }

    private void refreshClientes(List<Cliente> clientes) {
        if (clientes == null) {
            return;
        }

        ClientesListAdapter adapter = new ClientesListAdapter(this, clientes);
        setListAdapter(adapter);
    }

    private class DownloadClientesTask extends AsyncTask<Void, Void, List<Cliente>> {

        @Override
        protected List<Cliente> doInBackground(Void... params) {
            final String url = "http://192.168.1.119/~henry/api_slim/index.php/customers";

            try {
                // Set the Accept header for "application/json"
                HttpHeaders requestHeaders = new HttpHeaders();
                List<MediaType> acceptableMediaTypes = new ArrayList<MediaType>();
                acceptableMediaTypes.add(MediaType.APPLICATION_JSON);
                requestHeaders.setAccept(acceptableMediaTypes);

                // Populate the headers in an HttpEntity object to use for the request
                HttpEntity<?> requestEntity = new HttpEntity<Object>(requestHeaders);

                // Create a new RestTemplate instance
                RestTemplate restTemplate = new RestTemplate();
                restTemplate.getMessageConverters().add(new MappingJacksonHttpMessageConverter());

                // Perform the HTTP GET request
                ResponseEntity<Cliente[]> responseEntity = restTemplate.exchange(url, HttpMethod.GET, requestEntity,
                        Cliente[].class);

                // convert the array to a list and return it
                return Arrays.asList(responseEntity.getBody());
            } catch (Exception e) {
                // TODO Auto-generated catch block
                Log.e(TAG, e.getMessage(), e);
            }

            return null;

        }

        @Override
        protected void onPostExecute(List<Cliente> result) {

            refreshClientes(result);
        }

    } 

}

And this is My listAdapter :

public class ClientesListAdapter extends BaseAdapter{

    private List<Cliente> clientes;
    private final LayoutInflater layoutInflater;

    public ClientesListAdapter(Context context, List<Cliente> clientes) {
        this.clientes = clientes;
        this.layoutInflater = LayoutInflater.from(context);
    }

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return this.clientes != null ? clientes.size() : 0;
    }

    @Override
    public Cliente getItem(int position) {
        return this.clientes.get(position);
    }

    @Override
    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        if (convertView == null) {
            convertView = this.layoutInflater.inflate(R.layout.cliente_list_item, parent, false);
        }

        Cliente cliente = getItem(position);
        if (cliente != null) {
            TextView t = (TextView) convertView.findViewById(R.id.name);
            t.setText(cliente.getFirstname());
        }

        return convertView;
    }

}

This the POJO class of the data iḿ getting :

public class Cliente {
    private Integer id_customer; 
        private String firstname;
        public Integer getId_customer() {
        return id_customer;
    }
    public void setId_customer(Integer id_customer) {
        this.id_customer = id_customer;
    }
        public String getFirstname() {
        return firstname;
    }
    public void setFirstname(String firstname) {
        this.firstname = firstname;
    }
}

When i select an element from the listView i would like show details specific about this element on another activity or fragment, but i don’t know how to obtain the customer_id of this element from the list, do i have to save it when i procesing the response? do I need to use content provider or database provide this behavior? i’m really confused, thanks in advance for any help!

Answer 1

There are good examples on how to pass data from one activity to another here, pass objects between activities. You may want to take a look first to the solutions on those links.

Please see below an example that can put you on the right track.

List adapter class:

public class ClientesListAdapter extends BaseAdapter{

    //private members
    private List<Cliente> clientes;

    //adapter position - not used for this example
    public int adapterPosition;

    //context of app
    private Context mContext;

    //default constructor
    public ClientesListAdapter(Context context, List<Cliente> clientes) {

        //context pointer
        this.mContext = context;

        //alloc
        this.clientes = new ArrayList<Cliente>(clientes.size());
        this.clientes.addAll(clients);
    }

    //Holder for events and dates (memory management)
    public static class ViewHolder{
        TextView myTextView;//this is actually findViewById(R.id.name) @see getView() method
    }

    //generated method
    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return this.clientes != null ? clientes.size() : 0;
    }

    //generated method
    @Override
    public Cliente getItem(int position) {
        return this.clientes.get(position);
    }

    //generated method
    @Override
    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return position;
    }

    //get client's id
    public int getClienteId(int position){
        return this.clientes.get(position).getClienteId();
    }

    //get client's id without passing the position
    public int getClienteId(){
        return this.clientes.get(adapterPosition).getClienteId();
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        //row is actually convertView (the current view)
        View row = convertView;
        //holds our view elements
        ViewHolder holder;

        //if row is null 
        if(row == null){
            //inflate layout to get our view elements
            LayoutInflater inflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            row = inflater.inflate(com.yourapp.R.layout.my_layout, parent, false);//your layout here, modify code
            //set up the holder
            holder = new ViewHolder();
            holder.myTextView = (TextView) row.findViewById(com.yourapp.R.id.name);

            //give the row a tag (holder)
            row.setTag(holder);

        }else{
            //row is not null we can see it (no need to allocate memory)
            holder = (ViewHolder) row.getTag();
        }

        //get your cliente object
        Cliente cliente = this.clientes.get(position);
        if (cliente != null) {
            holder.myTextView.setText(cliente.getFirstname());
        }

        //copy position
        adapterPostion = position;

        return convertView;
    }

}

You see that we used a ViewHolder class for memory management. This is a good practice for holding view elements inside your list adapter. You can find more info about list views, explained by Romain Guy – The World of ListViews.

From your MainActivity allocate the adapter and get your item on click:

//---- code --- //
ListView myListView = (ListView)findViewById(R.id.mylistview);//or you may use ListActivity
ClientesListAdapter adapter = new ClientesListAdapter(this, clientes);//"this" or "getApplicationContext()"
myListView.setAdapter(adapter);
adapter.notifyDataSetChanged();//notify
// ---- code --- //
@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
    Toast.makeText(this, "You have selected" + position + id ,
            Toast.LENGTH_SHORT).show();

    Intent intent = new Intent(MyActivity.this, ActivityB.class);
    intent.putInt("cliente_id",adapter.getClienteId());
    startActivity(intent);
}

Another example is with implementing an interface in the adapter like this:

//--code//
//Interface method
private OnSaveEditsListener saveEditsListener = null;
public void setOnSaveEditsListener(OnSaveEditsListener l) {
    saveEditsListener = l;
}
//--code//

    @Override
    public View getView(final int position, View convertView, ViewGroup parent) {

        //--code--//

        //get clicked position of calendar (get clicked day)
        convertView.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                v.requestFocusFromTouch();
                currentAgendaPosition = position;
                try{
                    saveEditsListener.onSaveEdits();
                }catch(Exception ex){
                    ex.printStackTrace();
                }
            }
        });

        //returns current row
        return row;
    }
    //--code--//

And from your MainActivity start the second activity like this:

adapter.setOnSaveEditsListener(new OnSaveEditsListener() {

    @Override
    public void onSaveEdits() {
        //Start activity from here
        //--code--//
        startActivity(intent);
    }
});