Android RuntimeException：无法实例化活动

Question

I created this application to get the wether details to my app.

I have a GetWeather Class in my Android App in which I have a constructor that I pass my current city and state.

GetWeather weather = new GetWeather(city_send,state_code);

The constructor then pings an API URL with required city, state and API credentials to receive a weather data json as response. But when i run the app it stops saying Unable to instantiate activity.

Main Activity

    protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);


            Button b1 = (Button) findViewById(R.id.showData);

            b1.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View v) {

                Intent nextScreen = new Intent(MainActivity.this, GetWeather.class);
                GetWeather  gw = new GetWeather("CA","Anuradhapura");

                    startActivity(nextScreen);
                }
            });
        }

GetWeather class


import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
...
...

import android.util.Log;  


public class GetWeather {


    private static String WEATHER_URL = "http://api.wunderground.com/api/key/conditions/q/";

    public String weather;
    public String temperature_string;
    public Bitmap weather_icon;

    public GetWeather() {

    }
    public  GetWeather(String city, String state){

        city = city.replaceAll(" ", "_");
        //construct post URL
        final String GET_WEATHER_URL = WEATHER_URL + state + "/" + city + ".json";  
        new Thread(new Runnable()
        {
            public void run()
            {
                String request = GET_WEATHER_URL;
                HttpResponse rp = null;
                JSONObject jObject = null;
                try {
                    rp = (new DefaultHttpClient()).execute(new HttpPost(request));
                } catch (ClientProtocolException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                if (rp != null && rp.getStatusLine().getStatusCode() == HttpStatus.SC_OK){
                    Log.i("Get Weather", "Success");
                    HttpEntity entity = rp.getEntity();
                    InputStream is = null;
                    try {
                        is = entity.getContent();
                    } catch (IllegalStateException e2) {
                        e2.printStackTrace();
                    } catch (IOException e2) {
                        e2.printStackTrace();
                    } catch (NullPointerException n1){
                        n1.printStackTrace();
                    }
                    final char[] buffer = new char[0x10000];
                    StringBuilder out = new StringBuilder();
                    Reader in = null;
                    String json_string_response = null;
                    try {
                        in = new InputStreamReader(is, "UTF-8");
                    } catch (UnsupportedEncodingException e) {
                        e.printStackTrace();
                    } catch (NullPointerException n1){
                        n1.printStackTrace();
                    }
                    int read = 0;
                    do {
                        try {
                            read = in.read(buffer, 0, buffer.length);
                        } catch (IOException e) {
                            e.printStackTrace();
                        } catch (NullPointerException n1){
                            n1.printStackTrace();
                        }
                        if (read>0) {
                            out.append(buffer, 0, read);
                        }
                    } while (read>=0);

                    try {
                        is.close();
                        json_string_response = out.toString();
                    } catch (IOException e1) {
                        e1.printStackTrace();
                    }
                    try {
                        jObject = new JSONObject(json_string_response);
                    } catch (JSONException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    } 
                    try {



                         JSONObject current_observation = jObject.getJSONObject("current_observation");
                         weather = current_observation.getString("weather"); 
                         temperature_string = current_observation.getString("temperature_string");
                         String icon_url = current_observation.getString("icon_url");
                         weather_icon = get_weather_icon(icon_url);


                    } catch (JSONException e4) {
                        // TODO Auto-generated catch block
                        e4.printStackTrace();
                    }
                }else{
                        String response = rp.toString().toString();
                        Log.e("Get Weather", response);
                }

            }
        }).start();     
    }

    public static Bitmap get_weather_icon(String url){
        Bitmap bitmap = null;
        InputStream in = null;
        BufferedOutputStream out = null;

        try {

            bitmap = BitmapFactory.decodeStream((InputStream)new URL(url).getContent());

        } catch (MalformedURLException e) {
              e.printStackTrace();
        } catch (IOException e) {
          e.printStackTrace();
        }

        return bitmap;

    }

}

LogCat view

03-20 04:48:01.544: D/AndroidRuntime(1074): Shutting down VM
03-20 04:48:01.554: W/dalvikvm(1074): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
03-20 04:48:01.644: E/AndroidRuntime(1074): FATAL EXCEPTION: main
03-20 04:48:01.644: E/AndroidRuntime(1074): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.jsonapp/com.example.jsonapp.GetWeather}: java.lang.ClassCastException: com.example.jsonapp.GetWeather cannot be cast to android.app.Activity
03-20 04:48:01.644: E/AndroidRuntime(1074):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2106)
03-20 04:48:01.644: E/AndroidRuntime(1074):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
03-20 04:48:01.644: E/AndroidRuntime(1074):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
03-20 04:48:01.644: E/AndroidRuntime(1074):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
03-20 04:48:01.644: E/AndroidRuntime(1074):     at android.os.Handler.dispatchMessage(Handler.java:99)
03-20 04:48:01.644: E/AndroidRuntime(1074):     at android.os.Looper.loop(Looper.java:137)
03-20 04:48:01.644: E/AndroidRuntime(1074):     at android.app.ActivityThread.main(ActivityThread.java:5041)
03-20 04:48:01.644: E/AndroidRuntime(1074):     at java.lang.reflect.Method.invokeNative(Native Method

Edit:

  {
  "response": {
  "version":"0.1",
  "termsofService":"http://www.wunderground.com/weather/api/d/terms.html",
  "features": {
  "conditions": 1
  }
    }
  , "current_observation": {
        "image": {
        "url":"http://icons-ak.wxug.com/graphics/wu2/logo_130x80.png",
        "title":"Weather Underground",
        "link":"http://www.wunderground.com"
        },
        "display_location": {
        "full":"Anuradhapura, Sri Lanka",
        "city":"Anuradhapura",
        "state":"",
        "state_name":"Sri Lanka",
        "country":"SB",
        "country_iso3166":"LK",
        "zip":"00000",
        "magic":"1",
        "wmo":"43421",
        "latitude":"8.32999992",
        "longitude":"80.41999817",
        "elevation":"89.00000000"
        },
        "observation_location": {
        "full":"Anuradhapura, ",
        "city":"Anuradhapura",
        "state":"",
        "country":"Sri Lanka",
        "country_iso3166":"LK",
        "latitude":"8.33333302",
        "longitude":"80.41666412",
        "elevation":"322 ft"
        },
        "estimated": {
        },
        "station_id":"43421",
        "observation_time":"Last Updated on March 20, 8:30 AM IST",
        "observation_time_rfc822":"Thu, 20 Mar 2014 08:30:00 +0530",
        "observation_epoch":"1395284400",
        "local_time_rfc822":"Thu, 20 Mar 2014 11:08:59 +0530",
        "local_epoch":"1395293939",
        "local_tz_short":"IST",
        "local_tz_long":"Asia/Colombo",
        "local_tz_offset":"+0530",
        "weather":"Scattered Clouds",
        "temperature_string":"83 F (28 C)",
        "temp_f":83,
        "temp_c":28,
        "relative_humidity":"73%",
        "wind_string":"Calm",
        "wind_dir":"",
        "wind_degrees":0,
        "wind_mph":0,
        "wind_gust_mph":0,
        "wind_kph":0,
        "wind_gust_kph":0,
        "pressure_mb":"1012",
        "pressure_in":"29.89",
        "pressure_trend":"",
        "dewpoint_string":"76 F (24 C)",
        "dewpoint_f":76,
        "dewpoint_c":24,
        "heat_index_string":"NA",
        "heat_index_f":"NA",
        "heat_index_c":"NA",
        "windchill_string":"NA",
        "windchill_f":"NA",
        "windchill_c":"NA",
        "feelslike_string":"83 F (28 C)",
        "feelslike_f":"83",
        "feelslike_c":"28",
        "visibility_mi":"12.0",
        "visibility_km":"20.0",
        "solarradiation":"--",
        "UV":"-1","precip_1hr_string":" in ( mm)",
        "precip_1hr_in":"",
        "precip_1hr_metric":"--",
        "precip_today_string":" in ( mm)",
        "precip_today_in":"",
        "precip_today_metric":"--",
        "icon":"partlycloudy",
        "icon_url":"http://icons-ak.wxug.com/i/c/k/partlycloudy.gif",
        "forecast_url":"http://www.wunderground.com/global/stations/43421.html",
        "history_url":"http://www.wunderground.com/history/airport/43421/2014/3/20/DailyHistory.html",
        "ob_url":"http://www.wunderground.com/cgi-bin/findweather/getForecast?query=8.33333302,80.41666412"
    }
}

Answer 1

java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.jsonapp/com.example.jsonapp.GetWeather}: java.lang.ClassCastException: com.example.jsonapp.GetWeather cannot be cast to android.app.Activity

public class GetWeather {

GetWeather is not a Activity class

You have

Intent nextScreen = new Intent(MainActivity.this, GetWeather.class);
GetWeather  gw = new GetWeather("CA","Anuradhapura");
startActivity(nextScreen); 

You only need

GetWeather  gw = new GetWeather("CA","Anuradhapura");

and remove the other 2 lines

Edit:

public class GetWeather { 


private static String WEATHER_URL = "http://api.wunderground.com/api/706d22f330042323/conditions/q/"; 

public String weather; 
public String temperature_string; 
public Bitmap weather_icon; 

public GetWeather() { 

} 
public GetWeather(String city, String state){ 

city = city.replaceAll(" ", "_"); 
//construct post URL 
final String GET_WEATHER_URL = WEATHER_URL + state + "/" + city + ".json"; 
new Thread(new Runnable() 
{ 
public void run() 
{ 
String request = GET_WEATHER_URL; 
HttpResponse rp = null; 
JSONObject jObject = null; 
try 
{ 
HttpClient httpclient = new DefaultHttpClient(); 
httpclient.getParams().setParameter(CoreProtocolPNames.PROTOCOL_VERSION, HttpVersion.HTTP_1_1); 
HttpGet request1 = new HttpGet("http://api.wunderground.com/api/706d22f330042323/conditions/q/CA/Anuradhapura.json"); 
HttpResponse response = httpclient.execute(request1); 
HttpEntity resEntity = response.getEntity(); 
String _response=EntityUtils.toString(resEntity); 
jObject = new JSONObject(_response); 
JSONObject current_observation = jObject.getJSONObject("current_observation"); 
weather = current_observation.getString("weather"); 
Log.i("..............",""+weather); 
temperature_string = current_observation.getString("temperature_string"); 
String icon_url = current_observation.getString("icon_url"); 
weather_icon = get_weather_icon(icon_url); 

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


} 
}).start(); 
} 

public static Bitmap get_weather_icon(String url){ 
Bitmap bitmap = null; 
InputStream in = null; 
BufferedOutputStream out = null; 

try { 

bitmap = BitmapFactory.decodeStream((InputStream)new URL(url).getContent()); 

} catch (MalformedURLException e) { 
e.printStackTrace(); 
} catch (IOException e) { 
e.printStackTrace(); 
} 

return bitmap; 

} 

}

The log:

03-20 02:16:46.273: I/..............(1358): Mostly Cloudy

Answer 2

you have this:

Intent nextScreen = new Intent(MainActivity.this, GetWeather.class);

GetWeather is not an activity class hence you cannot pass this to the method of Intent. Change it to Activity class by extending GetWeahter to activity.

Answer 3

public class GetWeather {
}

Since your not extending Activity in GetWeather class you cant state that class has a activity.

You must extend the Activity class to GetWeather class as shown below.

public class GetWeather extends Activity {
}

I would rather suggest you to use AsyncTask