运行两个ASyncTasks Android Studio

Question

任何人都可以帮助我解决我的代码？

显然问题是我不能在我的主线程上运行多个ASyncTask。任何人都可以给我一些建议，如何我可以修复我的代码？ 谢谢！

对于不评论我的代码，我表示歉意。我可以解释一下，如果你们在阅读时感到困惑。

public class MainActivity extends AppCompatActivity { 

    ListView listView; 
    private SQLiteDatabase myDatabase; 
    private Cursor cursor; 
    boolean finished = false; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 

     listView = (ListView) findViewById(R.id.listView); 
     myDatabase = this.openOrCreateDatabase("HackerNews", MODE_PRIVATE, null); 

     Cursor cursor = myDatabase.rawQuery("SELECT * FROM ids", null); 
     int index = cursor.getColumnIndex("urlID"); 
     cursor.moveToFirst(); 

     DownloadContent content = new DownloadContent(); 

     while(cursor != null){ 
       String newUrl = "https://hacker-news.firebaseio.com/v0/item/" + cursor.getString(index) + ".json?print=pretty"; 
       content.execute(newUrl); 
       cursor.moveToNext(); 
     } 
    } 

    public class DownloadIDs extends AsyncTask<String, Void, String> { 

     @Override 
     protected String doInBackground(String... params) { 

      String result = ""; 
      URL url; 
      HttpURLConnection urlConnection = null; 
      try { 
       url = new URL(params[0]); 
       urlConnection = (HttpURLConnection) url.openConnection(); 
       InputStream inputStream = urlConnection.getInputStream(); 
       InputStreamReader reader = new InputStreamReader(inputStream); 
       int data = reader.read(); 

       while (data >= 0) { 
        char current = (char) data; 
        result += current; 
        data = reader.read(); 
       } 

       return result; 

      } catch (Exception e) { 
       e.printStackTrace(); 
       return "Fail"; 
      } 
     } 

     @Override 
     protected void onPostExecute(String s) { 
      super.onPostExecute(s); 

      myDatabase.execSQL("CREATE TABLE IF NOT EXISTS ids (id INTEGER PRIMARY KEY, urlID VARCHAR)"); 
      cursor = myDatabase.rawQuery("SELECT COUNT(*) FROM ids", null); 
      cursor.moveToFirst(); 
      int count = cursor.getInt(0); 

      if (!(count > 0)) { 

       try { 
        JSONArray ids = new JSONArray(s); 
        for (int i = 0; i < ids.length(); i++) { 
         myDatabase.execSQL("INSERT INTO ids (urlID) VALUES ('" + ids.getString(i) + "')"); 
        } 

       } catch (JSONException e) { 
        e.printStackTrace(); 
       } 
      } else { 
       Log.i("message", "TABLE1 IS NOT EMPTY"); 
      } 
     } 
    } 

    public class DownloadContent extends AsyncTask<String, Void, String> { 

     @Override 
     protected String doInBackground(String... params) { 
      String result = ""; 
      URL url; 
      HttpURLConnection urlConnection = null; 
      try { 
       url = new URL(params[0]); 
       urlConnection = (HttpURLConnection) url.openConnection(); 
       InputStream inputStream = urlConnection.getInputStream(); 
       InputStreamReader reader = new InputStreamReader(inputStream); 
       int data = reader.read(); 

       while (data >= 0) { 
        char current = (char) data; 
        result += current; 
        data = reader.read(); 
       } 

       return result; 

      } catch (Exception e) { 
       e.printStackTrace(); 
       return null; 
      } 
     } 

     @Override 
     protected void onPostExecute(String s) { 
      super.onPostExecute(s); 

      myDatabase.execSQL("CREATE TABLE IF NOT EXISTS content(id INTEGER PRIMARY KEY, title VARCHAR, url VARCHAR)"); 
      cursor = myDatabase.rawQuery("SELECT COUNT(*) FROM content", null); 
      cursor.moveToFirst(); 
      int count = cursor.getInt(0); 

      if (!(count > 0)) { 

       try { 
        JSONObject jsonObject = new JSONObject(s); 
        String title = jsonObject.getString("title"); 
        String url = jsonObject.getString("url"); 

        myDatabase.execSQL("INSERT INTO content (title, url) VALUES('" + title +"','" + url + "')"); 

       } catch (JSONException e) { 
        e.printStackTrace(); 
       } 
      } else { 
       Log.i("mess2", "table 2 is NOT EMPTY"); 
      } 
     } 
    } 
} 

Answer 1

每个AsyncTask实例只能运行一次。解决这个问题最简单的方法就是在需要运行时创建一个新实例。

while(cursor != null) { 
    String newUrl = "https://hacker-news.firebaseio.com/v0/item/" + cursor.getString(index) + ".json?print=pretty"; 
    new DownloadContent().execute(newUrl); 
    cursor.moveToNext(); 
}