當填充ArrayList的asynctasks完成時，我想要使用ArrayList

Question

當然，我的代碼中刪除了一些不重要的部分。這裏是擴展AsyncTask的3類。 LoadAllProducts執行三個DownloadTask，每個DownloadTask執行ParserTask和ParserTask填充ArrayList。畢竟完成後，我想用arrayList去做。

public class MapActivity extends FragmentActivity { 
     private ProgressDialog pDialog; 
     DownloadTask downloadTask; 

     @Override 
     public void onCreate(Bundle savedInstanceState) { 
      super.onCreate(savedInstanceState); 
      setContentView(R.layout.map_layout); 
      dists = new ArrayList<String>(); 
      // Loading products in Background Thread 
      new LoadAllProducts().execute(); 
    } 

....在這裏我想與填充後的ArrayList dists中工作.....

// Fetches data from url passed 
    private class DownloadTask extends AsyncTask<String, Void, String> 
    { 
     // Downloading data in non-ui thread 
     @Override 
     protected String doInBackground(String... url){} 

     // Executes in UI thread, after the execution of doInBackground() 
     @Override 
     protected void onPostExecute(String result){ 
      super.onPostExecute(result); 
      parserTask.execute(result); 
     } 
    } 

    /** A class to parse the Google Places in JSON format */ 
    private class ParserTask extends AsyncTask<String, Integer, List<List<HashMap<String, String>>>>{ 
     // Parsing the data in non-ui thread 
     @Override 
     protected List<List<HashMap<String, String>>> doInBackground(String... jsonData){ 
     } 

     // Executes in UI thread, after the parsing process 
     @Override 
     protected void onPostExecute(List<List<HashMap<String, String>>> result){ 
      //here is arrayList filled 
      dists.add(result); 
     } 
    } 
    /** 
    * Background Async Task to Load all product by making HTTP Request 
    * */ 
    class LoadAllProducts extends AsyncTask<String, String, String> { 

     /** 
     * Before starting background thread Show Progress Dialog 
     * */ 
     @Override 
     protected void onPreExecute() { 
      super.onPreExecute(); 
      pDialog = new ProgressDialog(MapActivity.this); 
      pDialog.setMessage("....."); 
      pDialog.setIndeterminate(false); 
      pDialog.setCancelable(false); 
      pDialog.show(); 
     } 

     /** 
     * getting All products from url 
     * */ 
     protected String doInBackground(String... args) { 
      return null; 
     } 
     /** 
     * After completing background task Dismiss the progress dialog 
     * **/ 
     protected void onPostExecute(String result) { 
      for(int i; i < 3; i++){ 
       downloadTask = new DownloadTask(); 
       downloadTask.execute(result); 
      } 
     } 
    } 
} 

Answer 1

爲什麼不直接在最後一個asyncTask的onPostExecute中調用您的活動方法來運行。

public class MapActivity extends FragmentActivity { 


    boolean areTasksComplete = false; 
    //call this when last task is complete 
    public void afterAllTasksComplete(List<List<HashMap<String, String>>> result) { 
     areTasksComplete = true; 
     dists.add(result); 

    } 

    private class DownloadTask extends AsyncTask<String, Void, String> 
    { 
     // Downloading data in non-ui thread 
     @Override 
     protected String doInBackground(String... url){} 

     // Executes in UI thread, after the execution of doInBackground() 
     @Override 
     protected void onPostExecute(String result){ 
      super.onPostExecute(result); 
      parserTask.execute(result); 
     } 
    } 

    /** A class to parse the Google Places in JSON format */ 
    private class ParserTask extends AsyncTask<String, Integer, List<List<HashMap<String, String>>>>{ 
     // Parsing the data in non-ui thread 
     @Override 
     protected List<List<HashMap<String, String>>> doInBackground(String... jsonData){ 
     } 

     // Executes in UI thread, after the parsing process 
     @Override 
     protected void onPostExecute(List<List<HashMap<String, String>>> result){ 

      afterAllTasksComplete(result); 
     } 
    } 
    /** 
    * Background Async Task to Load all product by making HTTP Request 
    * */ 
    class LoadAllProducts extends AsyncTask<String, String, String> { 

     //.....// 

     /** 
     * After completing background task Dismiss the progress dialog 
     * **/ 
     protected void onPostExecute(String result) { 
      for(int i; i < 3; i++){ 
       downloadTask = new DownloadTask(); 
       downloadTask.execute(result); 
      } 
     } 
    } 

} 

此外，還有一個名爲BoltsFramework的庫，它使鏈接異步工作更容易。 https://github.com/BoltsFramework/Bolts-Android

Answer 2

你應該嘗試使用onPostExecute。

從技術上講，沒有內建機制來檢查所有任務是否完成，因此如果一個任務完成，如果完成，檢查另一個等等，您可以嘗試每隔一段時間檢查一次，而重置機制，如果他們中的任何一個沒有完成。

用簡單的話說 - 每隔一段時間檢查一次，直到一切完成。