使用 AsyncTask 填充 ListView

Question

这可能不是很优雅，但我想做的是连接到 Web 服务，获取 JSON，解析它，从中创建一个对象，将该对象添加到 ArrayList，然后使用该 ArrayList填充我的 ListView。

我正在尝试使用 AsyncTask 完成所有这些工作。

总结：doInBackgroud 接受一个 url 的字符串，用它来连接一个 web 服务。我将 JSON 数据作为字符串获取，对其进行解析，从数据中构造一个新对象，然后将其添加到 ArrayList。然后在onPostExecute 中，我尝试使用利用我的ArrayList 的ArrayAdapter 设置listadapter。

这是我所拥有的：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.StringWriter;
import java.io.Writer;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.Arrays;

import org.json.JSONArray;
import org.json.JSONObject;

import oauth.signpost.OAuthConsumer;
import oauth.signpost.basic.DefaultOAuthConsumer;
import android.app.ListActivity;
import android.app.ProgressDialog;
import android.os.AsyncTask;
import android.os.Bundle;
import android.widget.ArrayAdapter;

public class AllOffersListActivity extends ListActivity {

    private static final String CONSUMER_KEY = "bla";
    private static final String CONSUMER_SECRET = "bla";


    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);



        new CreateArrayListTask().execute("http://example.com/sample.json");




    }

    private class CreateArrayListTask extends AsyncTask<String, Void, ArrayList<Offer>> {
        private final ProgressDialog dialog = new ProgressDialog(AllOffersListActivity.this);

        @Override
        protected void onPreExecute() {
            this.dialog.setMessage("Fetching offers...");
            this.dialog.show();

        }
        @Override
        protected ArrayList<Offer> doInBackGround(String...urls) {
            ArrayList<Offer> offerList = new ArrayList<Offer>();

            for(String url: urls) {
                OAuthConsumer consumer = new DefaultOAuthConsumer(CONSUMER_KEY, CONSUMER_SECRET);
                consumer.setTokenWithSecret("", "");

                try {

                    URL url1 = new URL(url);
                    HttpURLConnection request = (HttpURLConnection) url1.openConnection();

                    // sign the request
                    consumer.sign(request);

                    // send the request
                    request.connect();


                    String JSONString = convertStreamToString(request.getInputStream());

                    JSONObject jObject = new JSONObject(JSONString);

                    JSONObject offerObject = jObject.getJSONObject("offer");

                    String titleValue = offerObject.getString("title");
                    //System.out.println(titleValue);

                    String descriptionValue = offerObject.getString("description");
                    //System.out.println(attributeValue);
                    JSONObject businessObject = offerObject.getJSONObject("business");
                    String nameValue = businessObject.getString("name");

                    Offer myOffer = new Offer(titleValue, descriptionValue, nameValue);

                    offerList.add(myOffer);

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

                } 
            }
            return offerList; 

        }

        @Override
        protected void onPostExecute(ArrayList<Offer> offerList) {
            if(this.dialog.isShowing())
                this.dialog.dismiss();
            setListAdapter(new ArrayAdapter<Offer>(AllOffersListActivity.this, android.R.layout.simple_list_item_1, offerList));        
        }
    }

    private String convertStreamToString(InputStream inputStream) throws IOException {
        if(inputStream != null) {
            Writer writer = new StringWriter();

            char[] buffer = new char[1024];

            try {

                Reader reader = new BufferedReader( new InputStreamReader(inputStream, "UTF-8"));

                int n;
                while((n = reader.read(buffer)) != -1) {
                    writer.write(buffer, 0, n);

                }
            } finally {
                inputStream.close();
            }
            return writer.toString();
        } else {
            return "";
        }

    }

}

我看到两个错误。一个在我的私人异步课程上："The type AllOffersListActivity.CreateArrayListTask must implement the inherited abstract method AsyncTask<String,Void,ArrayList<Offer>>.doInBackground(String...)"

其次，在我的doInBackGround Override 上，我得到：The method doInBackGround(String...) of type AllOffersListActivity.CreateArrayListTask must override or implement a supertype method

我在这里错过了什么？

Answer 1

这只是一个小错字；应该是doInBackground 而不是doInBackGround。

Answer 2

@LuxuryMode 你在doInBackGround上犯了错误

正确的拼写是doInBackground

asynctask 必须实现doInBackground 方法，因此它无法识别此方法，因为方法名称错误，因此它会给您错误

 The method doInBackGround(String...) of type AllOffersListActivity.CreateArrayListTask must 
override or implement a supertype method