java.lanCannot execute task:任务已经执行(一个任务只能执行一次)

Question

当我在搜索编辑框中输入数据并单击数据时，它会给出json数据，第一次给出结果，但第二次单击搜索编辑框时，它显示AsyncTask错误。。请帮忙解决这个问题。。提前感谢

import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
import android.widget.ListView;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.HashMap;

public class MainActivity extends AppCompatActivity {
    JSONObject jsonobject;
    ListView listview;
    ListViewAdapter adapter;
    EditText search;
    ArrayList<HashMap<String, String>> arraylist;
    static String name = "name";
    static String temp = "temp";
    static String pressure = "pressure";
    DownloadJSON Asynctask= new DownloadJSON();
    CityJson cityJson=new CityJson();
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        search= (EditText) findViewById(R.id.search);
        search.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v)
            {
                String zipcode = search.getText().toString();
                final String []params=
                {"http://api.openweathermap.org/data/2.5/weather?q="+zipcode+",in&appid=2de143494c0b295cca9337e1e96b00e0"};

               cityJson.execute(params);

            }
        });
        Asynctask.execute();
    }
    private class CityJson extends AsyncTask<String,Void,Void>
    {
        @Override
        protected Void doInBackground(String... params)
        {
    try
    {
        arraylist = new ArrayList<HashMap<String, String>>();
            jsonobject = CityAsyncTask
                    .getJSONfromURL(params[0]);
        HashMap<String, String> map = new HashMap<String, String>();
        map.put("name", jsonobject.getString("name"));
        JSONObject mainobJsonObject = jsonobject.getJSONObject("main");
        map.put("temp", mainobJsonObject.getString("temp"));
        map.put("pressure", mainobJsonObject.getString("pressure"));
        arraylist.add(map);
    } catch (JSONException e) {
        Log.e("Error", e.getMessage());
        e.printStackTrace();
    }
    return null;
    }
    @Override
    protected void onPostExecute(Void args)
        {
        // Locate the listview in listview_main.xml
        listview = (ListView) findViewById(R.id.listview);
        // Pass the results into ListViewAdapter.java
        adapter = new ListViewAdapter(MainActivity.this, arraylist);
        // Set the adapter to the ListView
        listview.setAdapter(adapter);
        // Close the progressdialog
        }
    }
    private class DownloadJSON extends AsyncTask<Void, Void, Void>
    {
        @Override
        protected Void doInBackground(Void...params) {
            arraylist = new ArrayList<HashMap<String, String>>();
            // Retrieve JSON Objects from the given URL address
         try {
                String [] weatherurl={"http://api.openweathermap.org/data/2.5/weather?zip=560086,in&appid=2de143494c0b295cca9337e1e96b00e0",
                       "http://api.openweathermap.org/data/2.5/weather?q=chennai,in&appid=2de143494c0b295cca9337e1e96b00e0",
                        "http://api.openweathermap.org/data/2.5/weather?q=delhi,in&appid=2de143494c0b295cca9337e1e96b00e0",
                       "http://api.openweathermap.org/data/2.5/weather?q=mumbai,in&appid=2de143494c0b295cca9337e1e96b00e0",
                        "http://api.openweathermap.org/data/2.5/weather?q=kolkata,in&appid=2de143494c0b295cca9337e1e96b00e0"};
                for (int i = 0; i < weatherurl.length; i++) {
                    jsonobject = CityAsyncTask
                            .getJSONfromURL(weatherurl[i]);
                    HashMap<String, String> map = new HashMap<String, String>();
                    map.put("name", jsonobject.getString("name"));
                    JSONObject mainobJsonObject = jsonobject.getJSONObject("main");
                    map.put("temp", mainobJsonObject.getString("temp"));
                    map.put("pressure", mainobJsonObject.getString("pressure"));
                    arraylist.add(map);
                }
            } catch (JSONException e) {
                Log.e("Error", e.getMessage());
                e.printStackTrace();
            }
            return null;
        }
        @Override
        protected void onPostExecute(Void args) {
            // Locate the listview in listview_main.xml
            listview = (ListView) findViewById(R.id.listview);
            // Pass the results into ListViewAdapter.java
            adapter = new ListViewAdapter(MainActivity.this, arraylist);
            // Set the adapter to the ListView
            listview.setAdapter(adapter);
            // Close the progressdialog
        }
    }
}

Answer 1

您只能执行一次特定的异步任务。您需要创建一个新的异步任务实例才能再次执行。

有关详细信息，请阅读AsyncTask | Android Developers中的线程规则。

search.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v)
        {
            String zipcode = search.getText().toString();
            final String []params=
            {"http://api.openweathermap.org/data/2.5/weather?q="+zipcode+",in&appid=2de143494c0b295cca9337e1e96b00e0"};

           //cityJson.execute(params);
           //Replace above line with following line
           cityJson = new CityJson();
           cityJson.execute(params);

        }
    });