Question

我使用 AsyncTask 加载图片，为了更新ListView，我正在使用 notifyDataSetChanged（）方法。

但 notifyDataSetChanged（）不会更改ListView onProgressUpdate（）中的任何内容。我不想使用 cursor.requery ，因为它是不推荐使用的方法。

为什么 notifyDataSetChanged（）对我不起作用？

public class News extends BasicActivity implements OnItemClickListener{
private SQLiteDatabase db = null;
private ListView lvNews;
private TaskImgSm taskImgSm = null;
private NewsListAdapter adapter;
private Cursor cur;
boolean pause = false;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.news);

    db = SQLiteDatabase.openDatabase(((MyApp) getApplication()).getDbPath(), null, SQLiteDatabase.OPEN_READWRITE);
    lvNews = (ListView) findViewById(R.id.list_news);
    lvNews.setOnItemClickListener(this);
    listFilling();

    if (taskImgSm != null && taskImgSm.getStatus() != AsyncTask.Status.FINISHED) taskImgSm.cancel(true);
    taskImgSm = new TaskImgSm();
    taskImgSm.execute();        
}

private void listFilling() {
    cur = db.query("news", new String[] { "_id", "id_news", "title", "date", "img_url", "img_sm" }, null, null, null, null, null);
    startManagingCursor(cur);
    adapter = new NewsListAdapter(this, cur, db);
    lvNews.setAdapter(adapter);
    adapter.notifyDataSetChanged();
}

class TaskImgSm extends AsyncTask<Void, String, Void> {
    Cursor curs;
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        curs = db.query("news", new String[] { "_id", "id_news", "img_url", "img_sm" }, null, null, null, null, null);
        startManagingCursor(curs);
    }

    @Override
    protected Void doInBackground(Void... unused) {
        curs.moveToFirst();
        while (curs.isAfterLast() == false) {
            if (curs.getBlob(curs.getColumnIndex("img_sm")) == null) {
                String imgUrl = curs.getString(curs.getColumnIndex("img_url"));
                String idNews = curs.getString(curs.getColumnIndex("id_news"));
                updateImg(imgUrl, idNews, "img_sm");
                publishProgress();
            }
            curs.moveToNext();
        }           
        return (null);
    }

    private void updateImg(String img_URL, String whereId, String imgColumn) {
        try {
            DefaultHttpClient mHttpClient = new DefaultHttpClient();
            HttpGet mHttpGet = new HttpGet();
            mHttpGet.setURI(new URI(img_URL));
            HttpResponse mHttpResponse = mHttpClient.execute(mHttpGet);
            if (mHttpResponse.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
                HttpEntity entity = mHttpResponse.getEntity();
                if (entity != null) {
                    // insert to database
                    ContentValues values = new ContentValues();
                    values.put(imgColumn, EntityUtils.toByteArray(entity));
                    db.update("news", values, "id_news=" + whereId, null);
                }
            }
        } catch (URISyntaxException e) {e.printStackTrace();
        } catch (ClientProtocolException e) {e.printStackTrace();
        } catch (IOException e) {e.printStackTrace();}
    }

    @Override
    protected void onProgressUpdate(String... item) {
        if (pause == false) {
            adapter.notifyDataSetChanged();
        }
    }

    @Override
    protected void onPostExecute(Void unused) {}
}

@Override
protected void onPause() {
    pause = true;
    super.onPause();
}

@Override
protected void onResume() {
    pause = false;
    adapter.notifyDataSetChanged();
    super.onResume();
}

@Override
protected void onDestroy() {
    if (taskImgSm != null && taskImgSm.getStatus() != AsyncTask.Status.FINISHED) taskImgSm.cancel(true);
    super.onDestroy();
}
}

Answer 1

它不起作用的原因是因为notifyDataSetChanged()仅告诉ListView适配器中的数据已更改。由于该数据未更改（因为您尚未再次查询数据库），因此ListView不会显示任何更新。您需要再次执行查询并更新适配器中的数据，然后调用notifyDatasetChanged()。

Answer 2

为什么不使用ContentProvider。

使用ContentProvider，您可以使用notifyChange（uri）方法

更新表

此处的教程http://thinkandroid.wordpress.com/2010/01/13/writing-your-own-contentprovider/

Answer 3

我认为您可能希望更新ImageView方法中ListView中的onPostExecute()。这就是我完成类似于你正在做的事情的方式：Multithreading For Performance

如何从AsyncTask更新ListView？

3 个答案: