Java Android AsyncTask-doInBackground未运行

我试图使用AsyncTask发出HTTP请求并获取一些JSON，但由于某种原因，我的Async任务的doInBackground方法从未运行过。 对于这个问题，我已经在SO上看到了一些解决方案，但似乎没有任何解决方案-我也尝试使用常规线程而不是异步任务，但它似乎有类似的问题

包含AsyncTask类的My fragment类：

public class ChallengeListFragment extends ListFragment {

    ...

    private ArrayList<Challenge> mChallenges;

    // Creating JSON Parser object
    JSONParser jParser = new JSONParser();

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        getActivity().setTitle(R.string.challenges_list_fragment_title);
        mChallenges = new ArrayList<Challenge>();


        new JSONRetriever().execute("URL_HERE");

        ...
    }


    // Async Task class to perform HTTP requests in a separate thread:
    private class JSONRetriever extends AsyncTask<String, Void, JSONObject>{

        JSONArray challengesJsonArray;
        JSONObject challengesJsonObject;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            Log.i(LOG_TAG, "onPreExecute()!!!");
        }

        @Override
        protected JSONObject doInBackground(String... url) {
            challengesJsonObject = jParser.getJSONFromUrl(url[0]);
            return challengesJsonObject;
        }

        @Override
        protected void onPostExecute(JSONObject jsonObject) {
           super.onPostExecute(jsonObject);
           Log.i(LOG_TAG, jsonObject.toString());
        }
    }
}

我已经对该程序进行了多次检查，在运行preExecute（）时，doInBackground（）从未运行过。发生这种情况或类似情况时，我没有运行任何其他异步任务

非常感谢您的建议，谢谢

更新： 按照注释中的建议，我尝试删除doInBackground（）中的代码，并在其中放入一个log语句，它似乎实际上正在运行，尽管在我逐步执行程序时，该方法似乎从未被输入

发生这种情况时的完整日志是：

850-850/com.ethanml.proveit I/PROVEIT﹕ onPreExecute()!!!
12-08 19:01:45.952      850-850/com.ethanml.proveit D/AndroidRuntime﹕ Shutting down VM
12-08 19:01:45.952      850-878/com.ethanml.proveit D/PROVEIT﹕ DO IN BACKGROUND
12-08 19:01:45.962      850-850/com.ethanml.proveit W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x41465700)
12-08 19:01:45.992      850-850/com.ethanml.proveit E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.ethanml.proveit/com.ethanml.proveit.ChallengeListActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
            at android.app.ActivityThread.access$600(ActivityThread.java:141)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5103)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.ethanml.proveit.ChallengeListFragment.onCreate(ChallengeListFragment.java:55)
            at android.app.Fragment.performCreate(Fragment.java:1673)
            at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:854)
            at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1057)
            at android.app.BackStackRecord.run(BackStackRecord.java:682)
            at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1435)
            at android.app.Activity.performStart(Activity.java:5142)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
            at android.app.ActivityThread.access$600(ActivityThread.java:141)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5103)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
            at dalvik.system.NativeStart.main(Native Method)

---

日志中提到的第55行ChallengeListFragment上的NPE引用了一个for循环，我正在使用该循环逐步遍历JSON数组，该数组应该在异步任务的onPostExecute中填充-因为这似乎永远不会执行，所以JSONArray为空，程序崩溃。

确定它没有运行吗？返回前是否尝试调用

Log.e（）

内部

doInBackground（）

？你确定没有

异常被
getJSONFromUrl（）
抛出吗？正如Emmanuel告诉你的，你需要删除doInBackground（）中的代码，只需使用Log.d，然后在运行应用程序时检查日志消息是否打印。OK看起来你是对的，调试日志实际上是有效的…但是当我在它没有进入方法之前手动调试并逐步执行它时：S这意味着你们知道这可能是什么吗？这里是onPreExecute和doInBackground（）之间的LogCat日志：12-08 19:07:45.832 945-945/com.ethanml.proveit D/debug﹕ onPreExecute（）！！！12-08 19:07:45.852945-945/com.ethanml.proveit D/AndroidRuntime﹕ 关闭VM 12-08 19:07:45.852 945-945/com.ethanml.proveit W/dalvikvm﹕ threadid=1:线程以未捕获异常退出（组=0x41465700）12-08 19:07:45.872 945-968/com.ethanml.proveit D/DEBUG﹕ !!! 在后台做。。。然后是一个NullPointerException，它引用代码中的for循环，在上面的代码中，for循环通过（未分配的）JSONArray。现在您知道doInBackground正在调用geting，请尝试将日志放入get getJSONFromUrl函数中，并确定请求是否成功发送
850-850/com.ethanml.proveit I/PROVEIT﹕ onPreExecute()!!!
12-08 19:01:45.952      850-850/com.ethanml.proveit D/AndroidRuntime﹕ Shutting down VM
12-08 19:01:45.952      850-878/com.ethanml.proveit D/PROVEIT﹕ DO IN BACKGROUND
12-08 19:01:45.962      850-850/com.ethanml.proveit W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x41465700)
12-08 19:01:45.992      850-850/com.ethanml.proveit E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.ethanml.proveit/com.ethanml.proveit.ChallengeListActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
            at android.app.ActivityThread.access$600(ActivityThread.java:141)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5103)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.ethanml.proveit.ChallengeListFragment.onCreate(ChallengeListFragment.java:55)
            at android.app.Fragment.performCreate(Fragment.java:1673)
            at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:854)
            at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1057)
            at android.app.BackStackRecord.run(BackStackRecord.java:682)
            at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1435)
            at android.app.Activity.performStart(Activity.java:5142)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
            at android.app.ActivityThread.access$600(ActivityThread.java:141)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5103)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
            at dalvik.system.NativeStart.main(Native Method)