getActivity從片段返回null

對於學校我正在製作一個android應用程序。對於這個應用程序，我有一個片段，它顯示了一個數據庫中只有字符串的gridview。爲此，我需要一個片段。當我調用getActivity（）時，它返回null。 onAttach方法，建議here在應用程序崩潰之前不會被調用。我應該如何解決這個問題？
weekFragmetn.xml：getActivity從片段返回null

package nl.siebeh.schoolmate; 

import java.util.ArrayList; 

import android.app.Activity; 
import android.content.Context; 
import android.os.Bundle; 
import android.support.v4.app.Fragment; 
import android.util.Log; 
import android.view.ContextMenu; 
import android.view.ContextMenu.ContextMenuInfo; 
import android.view.LayoutInflater; 
import android.view.MenuItem; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.GridView; 

public class weekFragment extends Fragment { 
    dbLayer db; 
    Context mContext; 

    @Override 
    public void onAttach(Activity activity) { 
     mContext = getActivity(); 
     Log.i("Schoolmate","onAttach called"); 
     super.onAttach(activity); 
    } 

    public weekFragment newInstance(String title) { 
     Log.i("Schoolmate","newInstance called"); 
     db = new dbLayer(mContext); 
     weekFragment fragment = new weekFragment(); 
     ArrayList<ArrayList<Object>> result = null; 

     if(title == "leraren"){ 
      result = db.getAllRowsAsArrays("weekTeacher", null); 
     }else if(title == "locatie"){ 
      result = db.getAllRowsAsArrays("weekLocation", null); 
     }else if(title == "vakken"){ 
      result = db.getAllRowsAsArrays("weekSubjects", null); 
     } 

     String[] array = new String[60]; 

     for(int i = 0; i < 60; i++){ 
      array[i] = ""; 
     } 

     array[1] = getResources().getStringArray(R.array.days)[0]; 
     array[2] = getResources().getStringArray(R.array.days)[1]; 
     array[3] = getResources().getStringArray(R.array.days)[2]; 
     array[4] = getResources().getStringArray(R.array.days)[3]; 
     array[5] = getResources().getStringArray(R.array.days)[4]; 

     for(int i = 1; i < 10; i++){ 
      array[i] = Integer.toString(i); 
     } 

     for(int position = 0; position < result.size(); position++){ 
      ArrayList<Object> row = result.get(position); 
      int hour = Integer.valueOf(row.get(1).toString()).intValue(); 
      int day = Integer.valueOf(row.get(0).toString()).intValue(); 
      int pos = 6 * hour + day; 
      array[pos] = row.get(position).toString(); 
     } 
     fragment.mContent = array; 

     return fragment; 
    } 

    private String[] mContent = {""}; 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
     if (container == null) { 
      return null; 
     } 
     View v = inflater.inflate(R.layout.week_fragment, container, false); 
     GridView gridview = (GridView) v.findViewById(R.id.gridview); 
     gridview.setAdapter(new weekAdapter(mContext, mContent)); 
     return gridview; 
    } 

    @Override 
    public boolean onContextItemSelected(MenuItem item) { 
     return super.onContextItemSelected(item); 
    } 

    @Override 
    public void onCreateContextMenu(ContextMenu menu, View v, ContextMenuInfo menuInfo) { 
     super.onCreateContextMenu(menu, v, menuInfo); 
    } 



}

logcat的：（因爲點擊該項目啓動活動，其中片段開始/嵌入在列表中的項目）

09-29 19:10:56.611: INFO/ActivityManager(70): Starting: Intent { cmp=nl.siebeh.schoolmate/.overviewWeek } from pid 536 
09-29 19:10:56.970: INFO/Schoolmate(536): newInstance called 
09-29 19:11:06.631: WARN/ActivityManager(70): Launch timeout has expired, giving up wake lock! 
09-29 19:11:06.671: WARN/ActivityManager(70): Activity idle timeout for HistoryRecord{40770188 nl.siebeh.schoolmate/.overviewWeek} 
09-29 19:12:20.661: DEBUG/SntpClient(70): request time failed: java.net.SocketException: Address family not supported by protocol 
09-29 19:14:11.811: DEBUG/dalvikvm(536): Debugger has detached; object registry had 413 entries 
09-29 19:14:11.811: ERROR/SchoolMate(536): java.lang.NullPointerException 
09-29 19:14:11.811: INFO/SchoolMate(536): Context is null 
09-29 19:14:11.820: WARN/System.err(536): java.lang.NullPointerException 
09-29 19:14:11.820: WARN/System.err(536):  at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:118) 
09-29 19:14:11.820: WARN/System.err(536):  at nl.siebeh.schoolmate.dbLayer.<init>(dbLayer.java:50) 
09-29 19:14:11.820: WARN/System.err(536):  at nl.siebeh.schoolmate.weekFragment.newInstance(weekFragment.java:31) 
09-29 19:14:11.820: WARN/System.err(536):  at nl.siebeh.schoolmate.fragmentAdapter.getItem(fragmentAdaptar.java:21) 
09-29 19:14:11.820: WARN/System.err(536):  at nl.siebeh.schoolmate.titleFragmentAdapter.getItem(titleFragmentAdapter.java:1) 
09-29 19:14:11.820: WARN/System.err(536):  at android.support.v4.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:62) 
09-29 19:14:11.820: WARN/System.err(536):  at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:321) 
09-29 19:14:11.820: WARN/System.err(536):  at android.support.v4.view.ViewPager.populate(ViewPager.java:441) 
09-29 19:14:11.820: WARN/System.err(536):  at android.support.v4.view.ViewPager.onAttachedToWindow(ViewPager.java:563) 
09-29 19:14:11.820: WARN/System.err(536):  at android.view.View.dispatchAttachedToWindow(View.java:6156) 
09-29 19:14:11.820: WARN/System.err(536):  at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:1122) 
09-29 19:14:11.820: WARN/System.err(536):  at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:1127) 
09-29 19:14:11.820: WARN/System.err(536):  at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:1127) 
09-29 19:14:11.820: WARN/System.err(536):  at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:1127) 
09-29 19:14:11.820: WARN/System.err(536):  at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:1127) 
09-29 19:14:11.820: WARN/System.err(536):  at android.view.ViewRoot.performTraversals(ViewRoot.java:765) 
09-29 19:14:11.830: WARN/System.err(536):  at android.view.ViewRoot.handleMessage(ViewRoot.java:1859) 
09-29 19:14:11.840: WARN/System.err(536):  at android.os.Handler.dispatchMessage(Handler.java:99) 
09-29 19:14:11.840: WARN/System.err(536):  at android.os.Looper.loop(Looper.java:123) 
09-29 19:14:11.840: WARN/System.err(536):  at android.app.ActivityThread.main(ActivityThread.java:3683) 
09-29 19:14:11.840: WARN/System.err(536):  at java.lang.reflect.Method.invokeNative(Native Method) 
09-29 19:14:11.840: WARN/System.err(536):  at java.lang.reflect.Method.invoke(Method.java:507) 
09-29 19:14:11.850: WARN/System.err(536):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
09-29 19:14:11.850: WARN/System.err(536):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
09-29 19:14:11.850: WARN/System.err(536):  at dalvik.system.NativeStart.main(Native Method) 
09-29 19:14:11.850: DEBUG/AndroidRuntime(536): Shutting down VM 
09-29 19:14:11.850: WARN/dalvikvm(536): threadid=1: thread exiting with uncaught exception (group=0x40015560) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536): FATAL EXCEPTION: main 
09-29 19:14:11.870: ERROR/AndroidRuntime(536): java.lang.NullPointerException 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at nl.siebeh.schoolmate.weekFragment.newInstance(weekFragment.java:49) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at nl.siebeh.schoolmate.fragmentAdapter.getItem(fragmentAdaptar.java:21) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at nl.siebeh.schoolmate.titleFragmentAdapter.getItem(titleFragmentAdapter.java:1) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at android.support.v4.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:62) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:321) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at android.support.v4.view.ViewPager.populate(ViewPager.java:441) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at android.support.v4.view.ViewPager.onAttachedToWindow(ViewPager.java:563) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at android.view.View.dispatchAttachedToWindow(View.java:6156) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:1122) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:1127) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:1127) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:1127) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:1127) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at android.view.ViewRoot.performTraversals(ViewRoot.java:765) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at android.view.ViewRoot.handleMessage(ViewRoot.java:1859) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at android.os.Handler.dispatchMessage(Handler.java:99) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at android.os.Looper.loop(Looper.java:123) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at android.app.ActivityThread.main(ActivityThread.java:3683) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at java.lang.reflect.Method.invokeNative(Native Method) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at java.lang.reflect.Method.invoke(Method.java:507) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
09-29 19:14:11.870: ERROR/AndroidRuntime(536):  at dalvik.system.NativeStart.main(Native Method) 
09-29 19:14:11.890: WARN/ActivityManager(70): Force finishing activity nl.siebeh.schoolmate/.overviewWeek 
09-29 19:14:12.413: WARN/ActivityManager(70): Activity pause timeout for HistoryRecord{40770188 nl.siebeh.schoolmate/.overviewWeek} 
09-29 19:14:21.910: WARN/ActivityManager(70): Launch timeout has expired, giving up wake lock! 
09-29 19:14:22.441: WARN/ActivityManager(70): Activity idle timeout for HistoryRecord{4070c7a0 nl.siebeh.schoolmate/.schoolmate} 
09-29 19:14:32.451: WARN/ActivityManager(70): Activity destroy timeout for HistoryRecord{40770188 nl.siebeh.schoolmate/.overviewWeek}

來源

2011-09-29 Siebe

你不有 a getActivity()調用，這使得很難回答這個問題。

您正在獲得NullPointerException，因爲mContext是null。我的猜測是mContext是null，因爲在fragmentAdapter的代碼中，你打電話給new weekFragment()，然後打電話給newInstance()就可以了。您大概以爲您正在遵循Fragment JavaDoc中概述的某些模式，但在那裏，newInstance()是static方法，而不是您在此處使用的實例方法。

取出newInstance()中的所有代碼，並將其移至onActivityCreated()或某段時間片段附加到活動中，以便getActivity()起作用。一路上，刪除您的onAttach()實施和mContext數據成員，這兩者都不需要（並且mContext以非常可怕的方式填充）。

來源

2011-09-29 20:27:26 CommonsWare

感謝您的快速響應。在onAttach中應該將mContext設置爲getActivity（），現在它是我在另一個站點上找到的東西。我會立即嘗試。 – Siebe

@Swilzard：「在onAttach中應該將mContext設置爲getActivity（）」 - 否，當需要「Activity」時調用'getActivity（）'。 – CommonsWare

@CommonsWare：在我的情況下，我點擊按鈕啓動片段..因此，這裏假設活動已經創建。但現在在這裏如果調用getActivity（）。finish（）from fragment..it的給予NULL POINTER ...任何建議。 – CoDe

getActivity從片段返回null

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