Question

我目前在android上做一个项目，当我测试函数doInBackground，并将值返回到字符串时，程序执行成功。

但是，在我的项目中，我想从服务器获取多个东西。所以我想用HashMap来帮助我实现这个目标。但它会引发错误。谁能告诉我为什么？另外，当我将String转换为HashMap时，onPostExecute方法的覆盖也有错误[Method不会覆盖其超类中的方法。

有人知道发生了什么吗？我的代码如下所示。

class retrieveData extends AsyncTask<String,String,String> {
    @Override
    protected void onPreExecute(){
        super.onPreExecute();
        pDialog = new ProgressDialog(MainActivity.this);
        pDialog.setMessage("Please Wait...");
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(true);
        pDialog.show();
    }

    @Override
    protected HashMap<String, String> doInBackground(String... args){
        // new retrieveData().execute();
        List<NameValuePair> params = new ArrayList<NameValuePair>();

        // getting JSON string from URL
        jsonObject = jsonParser.getJSONFromUrl(REG_URL, params);

        try {
            a = jsonObject.getString("key");
            b = jsonObject.getString("name");
            c = jsonObject.getString("gender");

            // creating new HashMap
            map = new HashMap<String, String>();

            // adding each child node to HashMap key => value
            map.put("key", a);
            map.put("name", b);
            map.put("gender", c);

        } catch (JSONException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return map;
    }

    // SuperClass does not have HashMap imposed...
    @Override
    protected void onPostExecute(HashMap<String, String> map){
        pDialog.dismiss();
        String aReceived = map.get("key");
        String bReceived = map.get("name");
        String cReceived = map.get("gender");
        tv.setText(aReceived + '\n' + bReceived + '\n' + cReceived);
    }
}

Answer 1

就像，

一样简单

    class A extends AsyncTask<String, String, HashMap<String, String>>
    {

        @Override
        protected void onPreExecute()
        {
            super.onPreExecute();
            // TODO Auto-generated method stub
        }

        @Override
        protected HashMap<String, String> doInBackground(String... params)
        {
            // TODO Auto-generated method stub
            return null;
        }

        @Override
        protected void onPostExecute(HashMap<String, String> result)
        {
            super.onPostExecute(result);
            // TODO Auto-generated method stub
        }
    }

Answer 2

试试这个让我知道

class Loaddata extends AsyncTask<HashMap, HashMap, HashMap> {
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }

    protected HashMap<String, String> doInBackground(HashMap... args) {
        // Building Parameters
        HashMap<String, String> map = new HashMap<String, String>();
        try {

             List<NameValuePair> params = new ArrayList<NameValuePair>();

            // getting JSON string from URL
            jsonObject = jsonParser.getJSONFromUrl(REG_URL, params);

    try {
        a = jsonObject.getString("key");
        b = jsonObject.getString("name");
        c = jsonObject.getString("gender");

        // creating new HashMap
        map = new HashMap<String, String>();

        // adding each child node to HashMap key => value
        map.put("key", a);
        map.put("name", b);
        map.put("gender", c);

    } catch (JSONException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

        } catch (Exception e) {

        }

        return map;
    }

     @Override
protected void onPostExecute(HashMap map){
    pDialog.dismiss();
    String aReceived = map.get("key");
    String bReceived = map.get("name");
    String cReceived = map.get("gender");
    tv.setText(aReceived + '\n' + bReceived + '\n' + cReceived);
}
}

AsyncTask：如何从doInBackground返回HashMap？

2 个答案: