android - 在 AsyncTask 中传递 ArrayList>

Question

我犯了一些错误，我不知道如何走出去。最初，代码是这样的，它可以工作:

public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        ArrayList<HashMap<String, String>> menuItems = new ArrayList<HashMap<String, String>>();

        XMLParser parser = new XMLParser();
        String xml = parser.getXmlFromUrl(URL); // getting XML
        Document doc = parser.getDomElement(xml); // getting DOM element

        NodeList nl = doc.getElementsByTagName(KEY_ITEM);
        // looping through all item nodes <item>
        for (int i = 0; i < nl.getLength(); i++) {
            // creating new HashMap
            HashMap<String, String> map = new HashMap<String, String>();
            Element e = (Element) nl.item(i);
            // adding each child node to HashMap key => value
            map.put(KEY_ID, parser.getValue(e, KEY_ID));
            map.put(KEY_NAME, parser.getValue(e, KEY_NAME));
            map.put(KEY_COST, parser.getValue(e, KEY_COST));

            // adding HashList to ArrayList
            menuItems.add(map);
        }

        // Adding menuItems to ListView
        ListAdapter adapter = new SimpleAdapter(this, menuItems,
                R.layout.list_item,
                new String[] { KEY_NAME, KEY_COST }, new int[] {
                        R.id.name, R.id.cost });

        setListAdapter(adapter);


    }

既然我投入了另一个 Activity ，我应该是错误的。研究了一下我发现你需要使用任务同步但不知道如何结束。这是代码:

public class TaskAsincrono  extends AsyncTask<ArrayList<String>, Void, ArrayList<String>> {
        @Override
        protected void onPreExecute(){
        }

        @Override
        protected void onProgressUpdate(Void[] values) {

        };

        @Override
        protected ArrayList<String> doInBackground(ArrayList<String>... params) {
            ArrayList<HashMap<String, String>> menuItems = new ArrayList<HashMap<String, String>>();

            XMLParser parser = new XMLParser();
            String xml = parser.getXmlFromUrl(URL); // getting XML
            Document doc = parser.getDomElement(xml); // getting DOM element

            NodeList nl = doc.getElementsByTagName(KEY_ITEM);
            // looping through all item nodes <item>
            for (int i = 0; i < nl.getLength(); i++) {
                // creating new HashMap
                HashMap<String, String> map = new HashMap<String, String>();
                Element e = (Element) nl.item(i);
                // adding each child node to HashMap key => value
                map.put(KEY_ID, parser.getValue(e, KEY_ID));
                map.put(KEY_NAME, parser.getValue(e, KEY_NAME));
                map.put(KEY_COST, parser.getValue(e, KEY_COST));

                // adding HashList to ArrayList
                menuItems.add(map);

            }

            return menuItems;
        }

        @Override
        protected void onPostExecute(ArrayList<String> success) {
            //se l'alert è visibile viene rimosso
            if(dialog.isShowing()) dialog.dismiss();

            ListAdapter adapter = new SimpleAdapter(this, menuItems,
                    R.layout.list_item,
                    new String[] { KEY_NAME, KEY_COST }, new int[] {
                            R.id.name, R.id.cost });

            setListAdapter(adapter);

        }

        @Override
        protected void onCancelled() {
            mAuthTask = null;
        }
    }

我该怎么办？

非常感谢

Answer 1

只需遵循 Raghunandan 的建议即可。

如果你的返回类型是 ArrayList < HashMap < String,String > 那你为什么要返回 ArrayList < Sting >。

改成这样:

public class TaskAsincrono  extends AsyncTask<ArrayList<String>, Void, ArrayList<String>>

到

public class TaskAsincrono  extends AsyncTask<String, Void, ArrayList<HashMap<String,String>>>

还有:

 @Override
 protected ArrayList<String> doInBackground(ArrayList<String>... params)

到

    @Override
    protected ArrayList<HashMap<String,String>> doInBackground(String... params)

我认为您的程序中的 doInBackground() 需要 url 作为其参数，因此您可以将其从 ArrayList < String > 更改为简单的 String [] ..

你的 AsyncTask 骨架是这样的:

    public class TaskAsincrono  extends AsyncTask<String, Void, ArrayList<HashMap<String, String>>> {

    @Override, 
    protected void onPreExecute(){
       //what you want to do before AsyncTask execution(runs on UI thread)
      ......................
    }

    @Override
    protected void onProgressUpdate(Void[] values) {
       //About updates.......... 
    };

    @Override
    protected ArrayList<HashMap<String, String>> doInBackground(String... params) {
        ArrayList<HashMap<String, String>> menuItems = new ArrayList<HashMap<String, String>>();

         for (String extraUrl : params) {
           //do all stuffs here 
           //like parse xml stuffs 
           //put them to hashmap then add the hashmap to arraylist(menuitems).... 
           }
           return menuItems;
       }
 }

现在您可以像这样从 AsyncTask 外部获取 ArrayList(如按钮 onclick 或从 onCreate() )。

 TaskAsincrono  task = new TaskAsincrono  ();
    try {
        ArrayList<HashMap<String, String>> arr = new ArrayList<HashMap<String, String>>();
        arr = task.execute(URL).get();

同时也关注Developer Link For AsyncTask了解更多。

一切顺利