Question

我的代码当然会删除一些不重要的部分。这里有3个类，扩展了AsyncTask。 LoadAllProducts执行三个DownloadTask，每个DownloadTask执行ParserTask和ParserTask填充ArrayList。毕竟我想要使用arrayList。

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();
     }

....在这里我希望在填充后使用arrayList dists .....

    // 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

您应该尝试使用onPostExecute。

从技术上讲，没有内置机制来检查所有任务是否都已完成，所以你可以尝试每一个任务完成，如果一个任务完成，如果完成，检查另一个等等，同时重置机制如果其中任何一个没有完成。

用简单的话说 - 经常检查，直到一切都完成。

Answer 2

为什么不在最后一个asyncTask的onPostExecute中调用您的活动方法来运行。

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，还有一个名为BoltsFramework的库，它使链接异步工作更容易。 https://github.com/BoltsFramework/Bolts-Android

当填充ArrayList的asynctasks完成后，我想使用ArrayList

2 个答案: