异步从互联网/数据库下载图像到Android ListView

Question

我试图在列表中设置drawable。我的列表不包含图像。 我使用几个TextViews和一个ImageView从list_item.xml中填充它。

如果我的图像存储在Res android文件夹中，我没有任何问题，但是我在这里从数据库加载此图像。

现在，我用这个方法王的：

SimpleAdapter adapter = new SimpleAdapter(this.getBaseContext(), list, 
R.layout.xml_leaderboard_item, keys, views); 

有没有办法在我的列表中添加该绘制/位图？或者可能以编程方式将该图像放在Res文件夹中，以便我可以使用它？

Answer 1

我终于能够做到我想要的。下面是结果：

我从我的数据库异步下载这些图片。我无法将其添加到ListView中... 以下是我可能感兴趣的代码。

public class LeaderboardScreen extends ListActivity implements View.OnClickListener 
{ 
    private UserAdapter    adapter; 
    private ArrayList<User>   users; 
    private UserPictureDownloader user_picture_cache; 
    ... 

    protected void onCreate(Bundle saved_instance_state) 
    { 
     ... 
     users = new ArrayList<User>(); 
     adapter = new UserAdapter(this, R.layout.xml_leaderboard_item, users); 
     user_picture_cache = new UserPictureDownloader(); 
     setListAdapter(adapter);  
     ... 
    }  


    private class UserAdapter extends ArrayAdapter<User> 
    { 
     private ArrayList<User>  users; 

     public UserAdapter(Context context, int text_view_res_id, ArrayList<User> users) 
     { 
      super(context, text_view_res_id, users); 
      this.users = users; 
     } 

     public View   getView(int position, View view, ViewGroup parent) 
     { 
      LayoutInflater layout = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
      view = layout.inflate(R.layout.xml_leaderboard_item, null); 


      ImageView iv_pic = (ImageView)view.findViewById(R.id.lead_pic); 
      TextView et_position = (TextView)view.findViewById(R.id.lead_position); 
      TextView et_user = (TextView)view.findViewById(R.id.lead_user); 
      TextView et_score = (TextView)view.findViewById(R.id.lead_s_value); 
      TextView et_reput = (TextView)view.findViewById(R.id.lead_r_value); 
      TextView et_contrib = (TextView)view.findViewById(R.id.lead_c_value); 
      TextView et_bronze = (TextView)view.findViewById(R.id.lead_bronze_value); 
      TextView et_silver = (TextView)view.findViewById(R.id.lead_silver_value); 
      TextView et_gold = (TextView)view.findViewById(R.id.lead_gold_value); 

      User current_user = users.get(position); 
      if (current_user != null) 
      {    
       // Set available informations right away. 
       et_position.setText(String.valueOf(position + 1)); 
       et_user.setText(current_user.GetLogin()); 
      et_score.setText(String.valueOf(current_user.GetScore())); 
      et_reput.setText(String.valueOf(current_user.GetReputation())); 
      et_contrib.setText(String.valueOf(current_user.GetNumberOfQuestionPost())); 
      et_bronze.setText(String.valueOf(current_user.GetBadgeBronze())); 
      et_silver.setText(String.valueOf(current_user.GetBadgeSilver())); 
      et_gold.setText(String.valueOf(current_user.GetBadgeGold())); 

      // Fetch user image asynchronously. 
      final int pos = position; 
      final String user_login = current_user.GetLogin(); 
      final ImageView _iv_pic = iv_pic; 

      final Handler handler = new Handler() 
       { 
       @Override 
       public void   handleMessage(Message message) 
       { 
        _iv_pic.setImageDrawable((Drawable)message.obj); 
       } 
      }; 

      Thread thread = new Thread() 
      { 
       @Override 
       public void   run() 
       { 
        try 
        { 
         Drawable dwb = (Drawable)user_picture_cache.GetCachedObject(user_login, handler); 
         handler.sendMessage(handler.obtainMessage(0, dwb)); 
        } 
        catch (Exception e) { Log.e(TAG, e.getMessage()); } 
       } 
      }; 
      thread.start(); 
     } 
     return view; 
    } 
} 

的DownloadCache类：

public class DownloadCache 
{ 
    private final String TAG = "DownloadCache"; 

    private ConcurrentHashMap<String, CountDownLatch> queued_downloads; 
    private ConcurrentHashMap<String, Object>   cache; 

    public DownloadCache() 
    { 
     queued_downloads = new ConcurrentHashMap<String, CountDownLatch>(); 
     cache = new ConcurrentHashMap<String, Object>(); 
    } 


    public Object GetCachedObject(String url, Handler handler) throws InterruptedException 
    { 
     // Check for a running download, if found wait for its result. 
     CountDownLatch complete_event = queued_downloads.get(url); 
     if (complete_event != null) 
     complete_event.await(); 

     // Check for cached object. 
     Object obj = cache.get(url); 
     if (obj != null) 
      return obj; 

     obj = StartDownload(url, handler); 
     return obj; 
    } 

private Object StartDownload(String url, Handler handler) 
    { 
     CountDownLatch complete_event = new CountDownLatch(1); 
     queued_downloads.put(url, complete_event); 

     Object obj = DoDownloadWork(url, handler); 
     cache.put(url, obj); 

     queued_downloads.remove(url); 

     complete_event.countDown(); 
     return obj; 
    } 

    public Object DoDownloadWork(String url, Handler handler) 
    { 
     return null; 
    } 
} 

希望这有助于。

Answer 2

使用BitmapFactory类对数据库中的图像字节数据进行解码。然后在您的ImageView上使用setImageBitmap或setImageDrawable方法。

byte[] imageData = ...;  
Bitmap bitmap = BitmapFactory.decodeByteArray(imageData, 0, imageData.length); 
imageView.setImageBitmap(bitmap);