对于学校我正在制作一个Android应用程序。对于这个应用程序，我有一个片段，它从数据库中显示一个只有字符串的gridview。为此，我需要一个片段。当我调用getActivity（）时，它返回null。在应用程序崩溃之前，不会调用onAttach方法，如建议的here。我该怎么解决这个问题？ weekFragmetn.xml：
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 :(因为点击列表中的项目开始活动，片段在哪里开始/嵌入）
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}
答案 0 :(得分：8)
您没有 getActivity()来电，这使得回答问题变得很困难。
您获得了NullPointerException，因为mContext是null。我的猜测mContext是null，因为在fragmentAdapter的代码中，您正在调用new weekFragment()，然后在其上调用newInstance()。您可能认为您正在遵循Fragment JavaDocs中概述的某些模式，但在那里，newInstance()是static方法，而不是您在此处拥有的实例方法。
从newInstance()中获取所有代码，并将其移至onActivityCreated()或将片段附加到活动，以便getActivity()正常工作。在此过程中，请删除您的onAttach()实施和mContext数据成员，这些成员都不需要（并且mContext以非常可怕的方式填充）。