在Android应用程序中，我使用JSON来获取MySQL对象。在活动中，我在列表中显示对象。选择其中一个对象后，应该打开一个新活动，但是有一个我无法找到的错误。
这是应该打开第二个活动的第一个活动的代码的一部分：
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_categorias);
contactList = new ArrayList<HashMap<String, String>>();
ListView lv = getListView();
// Listview on item click listener
lv.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// getting values from selected ListItem
String name = ((TextView) view.findViewById(R.id.name))
.getText().toString();
String cost = ((TextView) view.findViewById(R.id.email))
.getText().toString();
//Starting single contact activity
Intent in = new Intent(getApplicationContext(),
ofertas_list.class);
in.putExtra(TAG_NAME, name);
in.putExtra(TAG_ID, cost);
startActivity(in);
}
});
// Calling async task to get json
new GetContacts().execute();
}
这里是第二个活动中未打开的部分代码，会引发错误。
// JSON node keys
private static final String TAG_NAME = "nombreCategoria";
private static final String TAG_ID = "idCategoria";
// getting intent data
Intent in = getIntent();
// Get JSON values from previous intent
String name = in.getStringExtra(TAG_NAME);
String email = in.getStringExtra(TAG_ID);
这是错误日志
04-08 13:24:04.053: E/AndroidRuntime(1321): FATAL EXCEPTION: main
04-08 13:24:04.053: E/AndroidRuntime(1321): Process: com.example.vivegrancanaria2014_001, PID: 1321
04-08 13:24:04.053: E/AndroidRuntime(1321): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.vivegrancanaria2014_001/com.example.vivegrancanaria2014_001.ofertas_list}: java.lang.NullPointerException
04-08 13:24:04.053: E/AndroidRuntime(1321): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2121)
04-08 13:24:04.053: E/AndroidRuntime(1321): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
04-08 13:24:04.053: E/AndroidRuntime(1321): at android.app.ActivityThread.access$800(ActivityThread.java:135)
04-08 13:24:04.053: E/AndroidRuntime(1321): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
04-08 13:24:04.053: E/AndroidRuntime(1321): at android.os.Handler.dispatchMessage(Handler.java:102)
04-08 13:24:04.053: E/AndroidRuntime(1321): at android.os.Looper.loop(Looper.java:136)
04-08 13:24:04.053: E/AndroidRuntime(1321): at android.app.ActivityThread.main(ActivityThread.java:5017)
04-08 13:24:04.053: E/AndroidRuntime(1321): at java.lang.reflect.Method.invokeNative(Native Method)
04-08 13:24:04.053: E/AndroidRuntime(1321): at java.lang.reflect.Method.invoke(Method.java:515)
04-08 13:24:04.053: E/AndroidRuntime(1321): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
04-08 13:24:04.053: E/AndroidRuntime(1321): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
04-08 13:24:04.053: E/AndroidRuntime(1321): at dalvik.system.NativeStart.main(Native Method)
04-08 13:24:04.053: E/AndroidRuntime(1321): Caused by: java.lang.NullPointerException
04-08 13:24:04.053: E/AndroidRuntime(1321): at com.example.vivegrancanaria2014_001.ofertas_list.<init>(ofertas_list.java:35)
04-08 13:24:04.053: E/AndroidRuntime(1321): at java.lang.Class.newInstanceImpl(Native Method)
04-08 13:24:04.053: E/AndroidRuntime(1321): at java.lang.Class.newInstance(Class.java:1208)
04-08 13:24:04.053: E/AndroidRuntime(1321): at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
04-08 13:24:04.053: E/AndroidRuntime(1321): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2112)
04-08 13:24:04.053: E/AndroidRuntime(1321): ... 11 more
我需要你的帮助来解释错误日志，我无法找到崩溃原因。
谢谢
修改
以下是第二项活动的代码：
import java.util.ArrayList;
import java.util.HashMap;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.ListActivity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.TextView;
public class ofertas_list extends ListActivity {
private ProgressDialog pDialog;
// JSON node keys
private static final String TAG_NAME = "nombreCategoria";
private static final String TAG_ID = "idCategoria";
// getting intent data
Intent in = getIntent();
// Get JSON values from previous intent
String name = in.getStringExtra(TAG_NAME);
String email = in.getStringExtra(TAG_ID);
// JSON node keys
private static final String TAG_CATEGORIAS = "Categorias";//valor del nodo principal
// Get JSON values from previous intent
// URL to get contacts JSON
private static String url = "http://xxxxxxxxx";//not shown for security reasond
// JSON Node names
private static final String TAG_NOMBREEMPRESA = "nombreEmpresa";
private static final String TAG_IDEMPRESA = "idEmpresa";
private static final String TAG_DESCRIPCIONEMPRESA = "descripcionEmpresa";
private static final String TAG_STRIMAGEN = "strImagen";
private static final String TAG_DIRECCIONEMPRESA = "direccionEmpresa";
private static final String TAG_TELEFONOEMPRESA = "telefonoEmpresa";
private static final String TAG_FACEBOOKEMPRESA = "facebookEmpresa";
private static final String TAG_EMAILEMPRESA = "emailEmpresa";
private static final String TAG_TEXTOOFERTA = "textoOferta";
private static final String TAG_HORARIOEMPRESA = "horarioEmpresa";
private static final String TAG_CATEGORIAEMPRESA = "categoriaEmpresa";
private static final String TAG_LATITUDEMPRESA = "latitudEmpresa";
private static final String TAG_LONGITUDEMPRESA = "longitudEmpresa";
private static final String TAG_VALORACIONEMPRESA = "valoracionEmpresa";
// contacts JSONArray
JSONArray contacts = null;
// Hashmap for ListView
ArrayList<HashMap<String, String>> contactList;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_categorias);
contactList = new ArrayList<HashMap<String, String>>();
ListView lv = getListView();
// Listview on item click listener
lv.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// getting values from selected ListItem
//cambiar por los nuevos campos
String name = ((TextView) view.findViewById(R.id.name))
.getText().toString();
String cost = ((TextView) view.findViewById(R.id.email))
.getText().toString();
//Starting single contact activity
//cambiar por los nuevos campos
Intent in = new Intent(getApplicationContext(),
SingleContactActivity.class);
in.putExtra(TAG_NAME, name);
in.putExtra(TAG_ID, cost);
startActivity(in);
}
});
// Calling async task to get json
new GetContacts().execute();
}
/**
* Async task class to get json by making HTTP call
* */
private class GetContacts extends AsyncTask<Void, Void, Void> {
@Override
protected void onPreExecute() {
super.onPreExecute();
// Showing progress dialog
pDialog = new ProgressDialog(ofertas_list.this);
pDialog.setMessage("Cargando datos...");
pDialog.setCancelable(false);
pDialog.show();
}
@Override
protected Void doInBackground(Void... arg0) {
// Creating service handler class instance
ServiceHandler sh = new ServiceHandler();
// Making a request to url and getting response
String jsonStr = sh.makeServiceCall(url, ServiceHandler.GET);
Log.d("Response: ", "> " + jsonStr);
if (jsonStr != null) {
try {
JSONObject jsonObj = new JSONObject(jsonStr);
// Getting JSON Array node
contacts = jsonObj.getJSONArray(TAG_CATEGORIAS);
// looping through All Contacts
for (int i = 0; i < contacts.length(); i++) {
JSONObject c = contacts.getJSONObject(i);
String nombreEmpresa = c.getString(TAG_NOMBREEMPRESA);
String descripcionEmpresa = c.getString(TAG_DESCRIPCIONEMPRESA);
String strImagen = c.getString(TAG_STRIMAGEN);
String direccionEmpresa = c.getString(TAG_DIRECCIONEMPRESA);
String telefonoEmpresa = c.getString(TAG_TELEFONOEMPRESA);
String facebookEmpresa = c.getString(TAG_FACEBOOKEMPRESA);
String emailEmpresa = c.getString(TAG_EMAILEMPRESA);
String textoOferta = c.getString(TAG_TEXTOOFERTA);
String horarioEmpresa = c.getString(TAG_HORARIOEMPRESA);
String categoriaEmpresa = c.getString(TAG_CATEGORIAEMPRESA);
String valoracionEmpresa = c.getString(TAG_VALORACIONEMPRESA);
String latitudEmpresa = c.getString(TAG_LATITUDEMPRESA);
String longitudEmpresa = c.getString(TAG_LONGITUDEMPRESA);
String idEmpresa = c.getString(TAG_IDEMPRESA);
// Phone node is JSON Object
// tmp hashmap for single contact
HashMap<String, String> contact = new HashMap<String, String>();
// adding each child node to HashMap key => value
contact.put(TAG_IDEMPRESA, idEmpresa);
contact.put(TAG_NOMBREEMPRESA, nombreEmpresa);
contact.put(TAG_DESCRIPCIONEMPRESA,descripcionEmpresa);
contact.put(TAG_STRIMAGEN,strImagen);
contact.put(TAG_DIRECCIONEMPRESA,direccionEmpresa);
contact.put(TAG_TELEFONOEMPRESA,telefonoEmpresa);
contact.put(TAG_FACEBOOKEMPRESA,facebookEmpresa);
contact.put(TAG_EMAILEMPRESA,emailEmpresa);
contact.put(TAG_TEXTOOFERTA,textoOferta);
contact.put(TAG_HORARIOEMPRESA,horarioEmpresa);
contact.put(TAG_CATEGORIAEMPRESA,categoriaEmpresa);
contact.put(TAG_VALORACIONEMPRESA,valoracionEmpresa);
contact.put(TAG_LATITUDEMPRESA,latitudEmpresa);
contact.put(TAG_LONGITUDEMPRESA,longitudEmpresa);
// adding contact to contact list
contactList.add(contact);
}
} catch (JSONException e) {
e.printStackTrace();
}
} else {
Log.e("ServiceHandler", "Couldn't get any data from the url");
}
return null;
}
@Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
// Dismiss the progress dialog
if (pDialog.isShowing())
pDialog.dismiss();
/**
* Updating parsed JSON data into ListView
* */
ListAdapter adapter = new SimpleAdapter(
ofertas_list.this, contactList,
R.layout.list_item_ofertas, new String[] { TAG_NOMBREEMPRESA, TAG_DIRECCIONEMPRESA}, new int[] { R.id.name,
R.id.email });
setListAdapter(adapter);
}
}
}
答案 0 :(得分：5)
在onCreate之前不要初始化变量，你只需声明变量并在onCreate方法中初始化它们。这将解决你的问题
答案 1 :(得分：1)
//Starting single contact activity
Intent in = new Intent(getApplicationContext(),
ofertas_list.class);
而不是getApplicationContext（）使用CurrentActivity.this或只是＆＃34;这＆＃34;。
另外，请你完整地发布ofertas_list.class。因为看起来可能是问题所在。
答案 2 :(得分：-2)
java.lang.NullPointerException意味着你的一个变量是null，只需将点放在行列中并尝试调试......你会找到空指针所在的位置＆amp;解决你的问题。 试试这个＆＃39;而不是getApplicationContext（）。