在Android应用程序中获取JSON

我正在尝试解析我的应用程序中的一些JSON。我有一个活动，用户在他们的位置键入，然后按下按钮打开另一个活动。问题是，当打开第二个活动时，应用程序崩溃。我使用了一个教程来找出如何获取JSON数据，但无法找出我做错了什么。我是Android开发的新手，因此非常感谢您的任何想法或帮助

这是我的密码：

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.View;
import android.view.inputmethod.EditorInfo;
import android.view.inputmethod.InputMethodManager;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.TextView.OnEditorActionListener;

public class WeatherLocation extends Activity
{
    EditText locationText;
    TextView label;
    Button getWeather;
    String enteredText;
    String url = "http://api.worldweatheronline.com/free/v1/weather.ashx?q=%s&format=json&num_of_days=5&key=37a5fj42xpyptvjgkhrx5rwu";
    String newURL;

    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.weatherlocation);

        locationText = (EditText) findViewById(R.id.locationText);
        label = (TextView) findViewById(R.id.label);
        getWeather = (Button) findViewById(R.id.showWeather);

        locationText.setText("Current Location");

        locationText.setOnEditorActionListener(new OnEditorActionListener()
        {
             @Override
            public boolean onEditorAction(TextView v, int actionId, KeyEvent event) 
            {
                 boolean handled = false;
                 if (actionId == EditorInfo.IME_ACTION_DONE)
                 {
                     enteredText = locationText.getText().toString();
                     System.out.println(enteredText);

                    // hide the virtual keyboard
                    InputMethodManager imm = (InputMethodManager)getSystemService(Context.INPUT_METHOD_SERVICE);
                    imm.hideSoftInputFromWindow(getCurrentFocus().getWindowToken(), 
                                              InputMethodManager.RESULT_UNCHANGED_SHOWN);

                    newURL = String.format(url, enteredText);
                    System.out.println("Formatted URL: " + newURL);
                     handled = true;
                 }

                 return handled;
            }
        });

        getWeather.setOnClickListener(new View.OnClickListener()
        {
            public void onClick(View v)
            {
                Intent weather = new Intent(WeatherLocation.this, Weather.class);
                startActivity(weather);
            }
        });
    }
}

天气信息类：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;

public class Weather extends WeatherLocation 
{
    TextView currentTemp;

    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.weather);

        currentTemp = (TextView) findViewById(R.id.currentTemp);     

        // Create instance of JSONParser
        JSONParser jParser = new JSONParser();

        // getting JSON string from URL
        System.out.println(newURL);
        JSONObject json = jParser.getJSONFromUrl(newURL);

        try
        {
            JSONObject data = new JSONObject(json.getString("data"));
            JSONArray currentConditions = data.getJSONArray("current_condition");
            JSONArray weather = data.getJSONArray("weather");

            JSONObject temp = currentConditions.getJSONObject(0);
            String fahr = temp.getString("temp_F");
            currentTemp.setText(fahr);
        }
        catch(Exception e)
        {
            e.getMessage().toString();
        }
    }

    public static class JSONParser
    {
        static InputStream is = null;
        static JSONObject jObj = null;
        static String json = "";

        // constructor
        public JSONParser()
        {

        }

        public JSONObject getJSONFromUrl(String url)
        {
            // Making HTTP request
            try
            {
                // defaultHttpClient
                DefaultHttpClient httpClient = new DefaultHttpClient();
                HttpPost httpPost = new HttpPost(url);

                HttpResponse httpResponse = httpClient.execute(httpPost);
                HttpEntity httpEntity = httpResponse.getEntity();
                is = httpEntity.getContent();
            }
            catch (UnsupportedEncodingException e)
            {
                e.printStackTrace();
            }
            catch (ClientProtocolException e)
            {
                e.printStackTrace();
            }
            catch (IOException e)
            {
                e.printStackTrace();
            }

            try
            {
                BufferedReader reader = new BufferedReader(new InputStreamReader(is, "iso-8859-1"), 8);
                StringBuilder sb = new StringBuilder();
                String line = null;
                while ((line = reader.readLine()) != null)
                {
                    sb.append(line + "\n");
                }
                is.close();
                json = sb.toString();
            }
            catch (Exception e)
            {
                Log.e("Buffer Error", "Error converting result " + e.toString());
            }

            // try to parse the string to a JSON object
            try
            {
                jObj = new JSONObject(json);
            }
            catch (JSONException e)
            {
                Log.e("JSON Parser", "Error parsing data " + e.toString());
            }

            // return JSON String
            return jObj;
        }
    }
}

错误：

10-14 13:11:28.523: E/AndroidRuntime(6583): FATAL EXCEPTION: main
10-14 13:11:28.523: E/AndroidRuntime(6583): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.kentuckyfarmbureau.kyfb/com.kentuckyfarmbureau.kyfb.Weather}: java.lang.NullPointerException
10-14 13:11:28.523: E/AndroidRuntime(6583):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
10-14 13:11:28.523: E/AndroidRuntime(6583):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
10-14 13:11:28.523: E/AndroidRuntime(6583):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
10-14 13:11:28.523: E/AndroidRuntime(6583):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
10-14 13:11:28.523: E/AndroidRuntime(6583):     at android.os.Handler.dispatchMessage(Handler.java:99)
10-14 13:11:28.523: E/AndroidRuntime(6583):     at android.os.Looper.loop(Looper.java:137)
10-14 13:11:28.523: E/AndroidRuntime(6583):     at android.app.ActivityThread.main(ActivityThread.java:5103)
10-14 13:11:28.523: E/AndroidRuntime(6583):     at java.lang.reflect.Method.invokeNative(Native Method)
10-14 13:11:28.523: E/AndroidRuntime(6583):     at java.lang.reflect.Method.invoke(Method.java:525)
10-14 13:11:28.523: E/AndroidRuntime(6583):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
10-14 13:11:28.523: E/AndroidRuntime(6583):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-14 13:11:28.523: E/AndroidRuntime(6583):     at dalvik.system.NativeStart.main(Native Method)
10-14 13:11:28.523: E/AndroidRuntime(6583): Caused by: java.lang.NullPointerException
10-14 13:11:28.523: E/AndroidRuntime(6583):     at com.android.internal.os.LoggingPrintStream.println(LoggingPrintStream.java:298)
10-14 13:11:28.523: E/AndroidRuntime(6583):     at com.kentuckyfarmbureau.kyfb.Weather.onCreate(Weather.java:42)
10-14 13:11:28.523: E/AndroidRuntime(6583):     at android.app.Activity.performCreate(Activity.java:5133)
10-14 13:11:28.523: E/AndroidRuntime(6583):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
10-14 13:11:28.523: E/AndroidRuntime(6583):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
10-14 13:11:28.523: E/AndroidRuntime(6583):     ... 11 more

编辑： 我在Weather.java（第二个活动）中编辑了代码，其中包括：

Intent intent = getIntent();
        String url = intent.getStringExtra("INTENT_KEY_URL");

System.out.println(url);
        JSONObject json = jParser.getJSONFromUrl(url);

---

您正在ui线程上运行与网络相关的操作

JSONObject json = jParser.getJSONFromUrl(newURL);

在JsonParser中，您有

HttpResponse httpResponse = httpClient.execute(httpPost);

使用

线程

或

异步任务

class TheTask extends AsyncTask<Void,Void,Void>
  {

    @Override
    protected void onPostExecute(Void result) {
        // TODO Auto-generated method stub
        super.onPostExecute(result);



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

    }

    @Override
    protected Void doInBackground(Void... params) {
            // get json from url here
            getJSONFromUrl(String url);
        return null;
    }

  }

class任务扩展异步任务
{
@凌驾
受保护的void onPostExecute（void结果）{
//TODO自动生成的方法存根
super.onPostExecute（结果）；
@凌驾
受保护的void onPreExecute（）{
//TODO自动生成的方法存根
super.onPreExecute（）；
}
@凌驾
受保护的Void doInBackground（Void…参数）{
//从这里的url获取json
getJSONFromUrl（字符串url）；
返回null；
}
}

调用

new任务（）.execute（）

---

首先，您必须将您的“url”发送到第二个活动。为此，您可以使用带有额外参数的Intent

像下面

    Intent weather = new Intent(WeatherLocation.this, Weather.class);
    weather .putExtra("INTENT_KEY_URL",newURL );
    startActivity(weather);

    Intent intent =getIntent();
    String url =intent.getStringExtra("INTENT_KEY_URL");

在第二个活动中，您可以将URL放入onCreate方法中，如下所示

    Intent weather = new Intent(WeatherLocation.this, Weather.class);
    weather .putExtra("INTENT_KEY_URL",newURL );
    startActivity(weather);

    Intent intent =getIntent();
    String url =intent.getStringExtra("INTENT_KEY_URL");

然后您可以使用它来查询json数据

---

如果您可以发布此错误的堆栈跟踪信息，这将非常有帮助。

将堆栈跟踪信息发布到此处错误已添加。第42行Weather.javaSystem.out.println（newURL）；您没有在

Weather.java

中初始化

newURL

。您需要有打印语句的url，并使用

Log

而不是

System.out.println（newURL）

来获得NPE