发生java.lang.NullPointerException Log-cat表示尝试在空对象引用上调用虚方法'java.lang.String org.json.JSONObject.toString（）'
这是我的代码： 我正在尝试从服务器（MySql）数据库获取jSon数据，然后将其显示在列表中。
public class AllProducts extends ListActivity {
private ProgressDialog pDialog;
JSONParser jParser=new JSONParser();
ArrayList<HashMap<String,String>> productsList;
private static String url_all_products = "http://server:host.../view.php";
private static final String TAG_SUCCESS="success";
private static final String TAG_PRODUCTS = "products";
private static final String TAG_PID = "pid";
private static final String TAG_NAME = "name";
JSONArray products=null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.all_products);
productsList=new ArrayList<HashMap<String, String>>();
new LoadAllProducts().execute();
new LoadAllProducts().execute();
ListView lv = getListView();
}
class LoadAllProducts extends AsyncTask<String,String,String>
Java.lang.NullPointerException尝试在空对象引用上调用虚方法'java.lang.String org.json.JSONObject.toString（）'
发生在class LoadAllProducts extends AsyncTask<String,String,String>
{
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog= new ProgressDialog(AllProducts.this);
pDialog.setMessage("Loading Products....Wait..");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
pDialog.show();的例外情况
}
@Override
protected String doInBackground(String... params) {
ContentValues param=new ContentValues();
JSONObject json= jParser.makeHttpRequest(url_all_products,"GET",param);
Log.d("All Products: ", json.toString());
在Log.d("All Products: ", json.toString());
try{
int success=json.getInt(TAG_SUCCESS);
if(success==1)
{
products = json.getJSONArray(TAG_PRODUCTS);
for(int j=0; j<products.length() ; j++ )
{
JSONObject c = products.getJSONObject(j);
String id=c.getString(TAG_PID);
String name=c.getString(TAG_NAME);
HashMap<String,String> map=new HashMap<String,String>();
map.put(TAG_PID,id);
map.put(TAG_NAME,name);
productsList.add(map);
}
}
else {
Intent i=new Intent(getApplicationContext(),NewProduct.class);
i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(i);
}
}catch(JSONException e)
{
e.printStackTrace();
}
return null;
}
}
}
我的UI中有一个按钮，用于从服务器获取数据并将其显示在列表中，当我点击按钮，pDialog显示然后应用程序“无响应”并发生这些异常
这是LogCat
09-03 16:10:40.500 27696-31923/com.example.vashisht.myapplication W/System.err﹕ at libcore.io.IoBridge.connectErrno(IoBridge.java:137)
09-03 16:10:40.500 27696-31923/com.example.vashisht.myapplication W/System.err﹕ at libcore.io.IoBridge.connect(IoBridge.java:122)
09-03 16:10:40.500 27696-31923/com.example.vashisht.myapplication W/System.err﹕ ... 19 more
09-03 16:10:40.500 27696-31923/com.example.vashisht.myapplication E/Buffer Error﹕ Error converting result java.lang.NullPointerException: lock == null
09-03 16:10:40.500 27696-31923/com.example.vashisht.myapplication E/JSON Parser﹕ Error parsing data org.json.JSONException: End of input at character 0 of
09-03 16:10:40.510 27696-31923/com.example.vashisht.myapplication E/AndroidRuntime﹕ FATAL EXCEPTION: AsyncTask #1
Process: com.example.vashisht.myapplication, PID: 27696
java.lang.RuntimeException: An error occured while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:300)
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
at java.util.concurrent.FutureTask.run(FutureTask.java:242)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
at java.lang.Thread.run(Thread.java:818)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String org.json.JSONObject.toString()' on a null object reference
at com.example.vashisht.myapplication.AllProducts$LoadAllProducts.doInBackground(AllProducts.java:76)
at com.example.vashisht.myapplication.AllProducts$LoadAllProducts.doInBackground(AllProducts.java:57)
at android.os.AsyncTask$2.call(AsyncTask.java:288)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
at java.lang.Thread.run(Thread.java:818)
09-03 16:10:40.980 27696-27696/com.example.vashisht.myapplication E/WindowManager﹕ android.view.WindowLeaked: Activity com.example.vashisht.myapplication.AllProducts has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView{10a4b377 V.E..... R......D 0,0-1026,348} that was originally added here
at android.view.ViewRootImpl.<init>(ViewRootImpl.java:382)
at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:261)
at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:69)
at android.app.Dialog.show(Dialog.java:298)
at com.example.vashisht.myapplication.AllProducts$LoadAllProducts.onPreExecute(AllProducts.java:67)
at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:587)
at android.os.AsyncTask.execute(AsyncTask.java:535)
at com.example.vashisht.myapplication.AllProducts.onCreate(AllProducts.java:50)
at android.app.Activity.performCreate(Activity.java:5958)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1129)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2364)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2474)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1359)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:155)
at android.app.ActivityThread.main(ActivityThread.java:5696)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1029)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:824)
09-03 16:10:44.250 27696-31923/com.example.vashisht.myapplication D/Process﹕ killProcess, pid=27696
09-03 16:10:44.260 27696-31923/com.example.vashisht.myapplication D/Process﹕ com.android.internal.os.RuntimeInit$UncaughtHandler.uncaughtException:138 java.lang.ThreadGroup.uncaughtException:693 java.lang.ThreadGroup.uncaughtException:690
答案 0 :(得分：0)
这意味着JSONObject json == null。您可以在调用JSONObject上的方法之前在代码中进行检查。我猜你在调用httprequest时实际上并没有得到数据。