不确定如何从列表的每个元素获取数据以从异步任务下载并显示其中的图像

Question

G'day guys!

I'm trying to work out a good approach to download pictures and update a user list with the picture once it has finished downloading.

So I'm trying to create a list of user profiles in an android app, where it displays their username and a little picture at the side of them. I've been watching tutorials for the last 2 weeks and slowly getting a feel for all thing android, and I have my app pulling data down from my SQL (via PHP) server without issue, BUT I'm having trouble working out how and where I can launch an asynchronous task to download a picture for each username.

I'm thinking something along the lines of flow like this

• User clicks refresh button to
• App talks to PHP on webserver and pulls down list of users (does this correctly so far)
• Parse all the data from the server that it got and turn it into a list (does this correctly so far)
• Data in the list contains URL for profile picture (does this correctly)
• Go through each list element one by one and begin async task to download picture (don't know how to go element by element to extract URL from list)
• Once picture is downloaded then display it (as above, don't know how to update each element)

The behavior is sort of inspired off the "Reddit is Fun" app, whereby all the articles are displayed and preview images are loaded and displayed as they are downloaded. You see a little spinning circle as a placeholder until the image is seen.

package com.example.administrator.hellopants;

import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.graphics.drawable.Drawable;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.Toast;

import org.apache.http.NameValuePair;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.InputStream;
import java.net.URL;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

public class UserlistActivity extends Activity{

    private ProgressDialog pDialog;
    JSONParser jParser = new JSONParser();
    ArrayList<HashMap<String, String>> allUserList;
    private static String url_all_users = "http://myurl.com/php/db_list_all_users.php";

    // JSON Node names
    private static final String TAG_SUCCESS = "success";
    private static final String TAG_USERLIST = "userlist";
    private static final String TAG_ID = "id";
    private static final String TAG_USERNAME = "username";

    JSONArray userlist = null;


    Button buttonRefresh;

    @Override
    public void onCreate(Bundle saveInstanceState) {
        super.onCreate(saveInstanceState);
        setContentView(R.layout.activity_userlist);

        allUserList = new ArrayList<HashMap<String,String>>();

        buttonRefresh = (Button) findViewById(R.id.button_refresh);
        buttonRefresh.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View view) {
                new PopulateUserList().execute();

            }
        });
    }

    class PopulateUserList extends AsyncTask<String, String, String> {

        ListView lvItems = (ListView) findViewById(R.id.listview_usernames);

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog = new ProgressDialog(UserlistActivity.this);
            pDialog.setMessage("Loading users details. Please wait...");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(true);
            pDialog.show();
        }

        protected String doInBackground(String... args) {

            List<NameValuePair> params = new ArrayList<NameValuePair>();
            JSONObject json = jParser.makeHttpRequest(url_all_users, "GET", params);
            Log.d("All Usernames JSON Output: ", json.toString());

            try {
                // Checking for SUCCESS TAG
                int success = json.getInt(TAG_SUCCESS);

                if (success == 1) {
                    // products found
                    // Getting Array of Products
                    userlist = json.getJSONArray(TAG_USERLIST);

                    // looping through All Products
                    for (int i = 0; i < userlist.length(); i++) {
                        JSONObject c = userlist.getJSONObject(i);

                        // Storing each json item in variable
                        String id = c.getString(TAG_ID);
                        String name = c.getString(TAG_USERNAME);

                        // creating new HashMap
                        HashMap<String, String> map = new HashMap<String, String>();

                        // adding each child node to HashMap key => value
                        map.put(TAG_ID, id);
                        map.put(TAG_USERNAME, name);

                        // adding HashList to ArrayList
                        allUserList.add(map);
                    }
                } else {
                    // no products found
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }


            return null;
        }

        protected void onPostExecute(String file_url) {
            pDialog.dismiss();

            runOnUiThread(new Runnable() {
                public void run() {
                    ListAdapter adapter = new SimpleAdapter(
                            UserlistActivity.this, allUserList,
                            R.layout.list_userliststyle, new String[] { TAG_ID,
                            TAG_USERNAME},
                            new int[] { R.id.list_userliststyle_id, R.id.list_userliststyle_username });
                    // updating listview
                    lvItems.setAdapter(adapter);
                }
            });



        }
    }

    public class DownloadImageBackground extends AsyncTask<String, Void, Drawable> {

        ImageView imageView;
        String myURL = null;

        @Override
        protected Drawable doInBackground(String...strings) {
            this.myURL = strings[0];
            Log.i("doInBackground", "Loading image from: "+ myURL.toString());
            //TODO: Pass the correct URL to download_image
            return download_Image(myURL);
        }

        @Override
        protected void onPostExecute(Drawable result) {
            imageView.setImageDrawable(result);
        }

        private Drawable download_Image(String url) {
            try {
                InputStream is = (InputStream) new URL(url).getContent();
                Drawable d = Drawable.createFromStream(is, url);
                return d;
            } catch (Exception e) {
                Log.e("download_Image", "Caught exception: "+e.getMessage());
                return null;
            }
        }
    }
}

Answer 1

Okie thanks to Nasch, that seemed to help prod me in the right direction

        String username = allUserList.get(0).get(TAG_USERNAME);
        Log.d("And the winner is", username);

And thus the username string is printed out. To do that with a URL is probably similar, but my main problem was trying to work out how to pull data out from the list and that seems to have been solved now :D (finally after 3 days, phew )

Had a feeling it would be something simple that I couldn't figure out.