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I am parsing JSON weather api in Android from a url. I am successfully getting all the values that i am parsing in the application. But after displaying the values on emulator the app is crashing and i am getting runtime exception.

Here is the logcat errors that i am getting :

10-20 09:34:26.040: E/AndroidRuntime(748): FATAL EXCEPTION: main
10-20 09:34:26.040: E/AndroidRuntime(748): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.work/com.example.work.SingleItemView}: java.lang.NullPointerException
10-20 09:34:26.040: E/AndroidRuntime(748):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2137)
10-20 09:34:26.040: E/AndroidRuntime(748):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
10-20 09:34:26.040: E/AndroidRuntime(748):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
10-20 09:34:26.040: E/AndroidRuntime(748):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
10-20 09:34:26.040: E/AndroidRuntime(748):  at android.os.Handler.dispatchMessage(Handler.java:99)
10-20 09:34:26.040: E/AndroidRuntime(748):  at android.os.Looper.loop(Looper.java:137)
10-20 09:34:26.040: E/AndroidRuntime(748):  at android.app.ActivityThread.main(ActivityThread.java:5103)
10-20 09:34:26.040: E/AndroidRuntime(748):  at java.lang.reflect.Method.invokeNative(Native Method)
10-20 09:34:26.040: E/AndroidRuntime(748):  at java.lang.reflect.Method.invoke(Method.java:525)
10-20 09:34:26.040: E/AndroidRuntime(748):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
10-20 09:34:26.040: E/AndroidRuntime(748):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-20 09:34:26.040: E/AndroidRuntime(748):  at dalvik.system.NativeStart.main(Native Method)
10-20 09:34:26.040: E/AndroidRuntime(748): Caused by: java.lang.NullPointerException
10-20 09:34:26.040: E/AndroidRuntime(748):  at com.example.work.SingleItemView.<init>(SingleItemView.java:5)
10-20 09:34:26.040: E/AndroidRuntime(748):  at java.lang.Class.newInstanceImpl(Native Method)
10-20 09:34:26.040: E/AndroidRuntime(748):  at java.lang.Class.newInstance(Class.java:1130)
10-20 09:34:26.040: E/AndroidRuntime(748):  at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
10-20 09:34:26.040: E/AndroidRuntime(748):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2128)
10-20 09:34:26.040: E/AndroidRuntime(748):  ... 11 more

Here is my code.

MainActivity.java :

public class MainActivity extends Activity {
    // Declare Variables
    JSONObject jsonobject;
    JSONArray jsonarray;
    ListView listview;
    ListViewAdapter adapter;
    ProgressDialog mProgressDialog;
    ArrayList<HashMap<String, String>> arraylist;
    static String NAME = "id";
    static String TYPE = "description";
    static String child = "country";
    static String child1 = "temp";
    static String child2 = "temp_min";
    static String child3 = "temp_max";
    static String child4 = "pressure";
    static String child5 = "humidity";






    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // Get the view from listview_main.xml
        setContentView(R.layout.activity_main);
        // Execute DownloadJSON AsyncTask
        new DownloadJSON().execute();
    }

    // DownloadJSON AsyncTask
    private class DownloadJSON extends AsyncTask<Void, Void, Void> {

        @Override
        protected void onPreExecute() {
          super.onPreExecute();
            // Create a progressdialog
            mProgressDialog = new ProgressDialog(MainActivity.this);

            // Set progressdialog message
            mProgressDialog.setMessage("Loading...");
            mProgressDialog.setIndeterminate(false);
            // Show progressdialog
            mProgressDialog.show();
        }
        @Override
        protected Void doInBackground(Void...arg0) {
            // Create an array
            arraylist = new ArrayList<HashMap<String, String>>();
            // Retrieve JSON Objects from the given URL address
            jsonobject = JSONParser
                    .getJSONfromURL("http://api.openweathermap.org/data/2.5/weather?q=Germany");


            try {

                JSONObject child=jsonobject.getJSONObject("sys");
                HashMap<String, String> map1 = new HashMap<String, String>();

                map1.put(MainActivity.child, "Country - " +child.getString("country"));
                arraylist.add(map1);
                JSONObject child1=jsonobject.getJSONObject("main");

                 HashMap<String, String> map2 = new HashMap<String, String>();

                map1.put(MainActivity.child1, "Temperature - " +child1.getString("temp"));
                map1.put(MainActivity.child2, "Minimum Temperature - " +child1.getString("temp_min"));
                map1.put(MainActivity.child3, "Maximum Temperature - " +child1.getString("temp_max"));
                map1.put(MainActivity.child4, "Pressure - " +child1.getString("pressure"));
                map1.put(MainActivity.child5, "Humidity - " +child1.getString("humidity"));
                arraylist.add(map2);

                // Locate the array name in JSON
                JSONArray jsonarray=jsonobject.getJSONArray("weather");
                for (int i = 0; i < jsonarray.length(); i++) {
                    HashMap<String, String> map = new HashMap<String, String>();
                    jsonobject = jsonarray.getJSONObject(i);

                    // Retrieve JSON Objects

                   map.put(MainActivity.NAME, "Id : "+jsonobject.getString("id"));
                   map.put(MainActivity.TYPE, "Description : "+jsonobject.getString("description"));

                    // Set the JSON Objects into the array
                    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
            mProgressDialog.dismiss();
        }
    }
}

SingleItemView.java :

package com.example.work;
import android.content.Intent;
public class SingleItemView {
    Intent intent = getIntent();
    String id = intent.getStringExtra("name");
    String name = intent.getStringExtra("type");
    String child = intent.getStringExtra("child");
    String child1 = intent.getStringExtra("child1");
    String child2 = intent.getStringExtra("child2");
    String child3 = intent.getStringExtra("child3");
    String child4 = intent.getStringExtra("child4");
    String child5 = intent.getStringExtra("child5");

    private Intent getIntent() {
        // TODO Auto-generated method stub
        return null;
    }

}

ListViewAdapter.java :

public class ListViewAdapter extends BaseAdapter {

    // Declare Variables
    Context context;
    LayoutInflater inflater;
    ArrayList<HashMap<String, String>> data;
    HashMap<String, String> resultp = new HashMap<String, String>();

    public ListViewAdapter(Context context,
            ArrayList<HashMap<String, String>> arraylist) {
        this.context = context;
        data = arraylist;

    }

    @Override
    public int getCount() {
        return data.size();
    }

    @Override
    public Object getItem(int position) {
        return null;
    }

    @Override
    public long getItemId(int position) {
        return 0;
    }

    public View getView(final int position, View convertView, ViewGroup parent) {
        // Declare Variables
        TextView id;
        TextView description;
        TextView country;
        TextView temp;
        TextView temp_min;
        TextView temp_max;
        TextView pressure;
        TextView humidity;
        //ImageView flag;

        inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        View itemView = inflater.inflate(R.layout.listview_item, parent, false);
        // Get the position
        resultp = data.get(position);

        // Locate the TextViews in listview_item.xml
        id = (TextView) itemView.findViewById(R.id.id);
        description = (TextView) itemView.findViewById(R.id.description);
        country = (TextView) itemView.findViewById(R.id.country);
        temp = (TextView) itemView.findViewById(R.id.temp);
        temp_min = (TextView) itemView.findViewById(R.id.temp_min);
        temp_max = (TextView) itemView.findViewById(R.id.temp_max);
        pressure = (TextView) itemView.findViewById(R.id.pressure);
        humidity = (TextView) itemView.findViewById(R.id.humidity);

        // Capture position and set results to the TextViews
        id.setText(resultp.get(MainActivity.NAME));
        description.setText(resultp.get(MainActivity.TYPE));
        country.setText(resultp.get(MainActivity.child));
        temp.setText(resultp.get(MainActivity.child1));
        temp_min.setText(resultp.get(MainActivity.child2));
        temp_max.setText(resultp.get(MainActivity.child3));
        pressure.setText(resultp.get(MainActivity.child4));
        humidity.setText(resultp.get(MainActivity.child5));
        // Capture ListView item click
        itemView.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // Get the position
                resultp = data.get(position);
                Intent intent = new Intent(context, SingleItemView.class);
                // Pass all id data
                intent.putExtra("name", resultp.get(MainActivity.NAME));
                // Pass all main data
                intent.putExtra("type", resultp.get(MainActivity.TYPE));

                intent.putExtra("child", resultp.get(MainActivity.child));

                // Start SingleItemView Class
                context.startActivity(intent);

            }
        });
        return itemView;
    }
}

AndroidManifest.xml :

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.work"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="18" />
    <uses-permission android:name="android.permission.INTERNET" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.work.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name="com.example.work.SingleItemView"
            android:label="@string/app_name" >
        </activity>
    </application>

</manifest>

I am getting all the values that i am parsing in my application but i am not getting why is it crashing.

4

2 回答 2

1

从官方文档：

要与 Context.startActivity() 一起使用，所有活动类都必须在其包的 AndroidManifest.xml 中具有相应的声明。

你得到了一些正确的部分：

<activity
    android:name="com.example.work.SingleItemView"
    android:label="@string/app_name" >
</activity>

但这是（是）问题：

  • SingleItemView不是类的子类/内部Activity类；
  • 您定义getIntent了返回null. 这就是为什么你得到一个NullPointerException;
  • 您的所有属性SingleItemView都使用以下模式进行设置：property = intent.getStringExtra("keyName");并将Intent intent = getIntent();确保intent是null. NullPointerException因此，当您在 null 对象上调用方法时，会增加一些s。
  • 你所有的String对象都将是null因为你没有在你的intent. 你首先要做的就是intent.putExtra("key", stringObject)之前intent.getStringExtra("key")。因此，还有一些NullPointerExceptions。

对于初学者，SingleItemView类：

public class SingleItemView extends Activity{

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.your_activity_layout);

        Intent intent = getIntent();
        String id = intent.getStringExtra("name");
        String name = intent.getStringExtra("type");
        String child = intent.getStringExtra("child");
        String child1 = intent.getStringExtra("child1");
        String child2 = intent.getStringExtra("child2");
        String child3 = intent.getStringExtra("child3");
        String child4 = intent.getStringExtra("child4");
        String child5 = intent.getStringExtra("child5");
   }
}

我绝对肯定您的代码需要进行更多修复才能使其正常工作。

于 2013-10-20T14:14:31.560 回答
0

它显然会崩溃，因为你写了下面的行

Intent intent = getIntent();

你还说 getIntent() 返回null。你想达到什么目的？

无论如何，崩溃的原因是我上面解释的。

于 2013-10-20T14:03:43.953 回答