错误：尝试在空对象引用上调用虚方法’java.lang.Object android.content.Context.getSystemService（java.lang.String）’
public class AlarmTask implements Runnable{ // The date selected for the alarm private final Calendar date; // The android system alarm manager private final AlarmManager am; // Your context to retrieve the alarm manager from private final Context context; public AlarmTask(Context context, Calendar date) { this.context = context; this.am = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE); //error for this line this.date = date; } 有类似的问题，但在敲打我的头后，我无法解决问题。 我收到以下这些错误！ 是因为碎片吗？
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference at android.content.ContextWrapper.getSystemService(ContextWrapper.java:562) at lol.com.epl.AlarmTask.(AlarmTask.java:24) at lol.com.epl.ScheduleService.setAlarm(ScheduleService.java:47) at lol.com.epl.ScheduleClient.setAlarmForNotification(ScheduleClient.java:58) at lol.com.epl.FixFragment.onCreateView(FixFragment.java:88) at android.support.v4.app.Fragment.performCreateView(Fragment.java:1962) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1026) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1207) at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738) at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1572) at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:493) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5257) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
这就是我打电话给class级的方式
public void setAlarm(Calendar c) { // This starts a new thread to set the alarm // You want to push off your tasks onto a new thread to free up the UI to carry on responding new AlarmTask(this, c).run(); }
这是我调用setAlarm函数的地方
public void setAlarmForNotification(Calendar c){ ScheduleService mBoundService = new ScheduleService(); mBoundService.setAlarm(c); }
在你的代码中
this.am = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);
context为null 。
检查你的stacktrace你正在初始化AlarmTask
at lol.com.epl.FixFragment.onCreateView(FixFragment.java:88)
在onActivityCreated方法中移动此调用。
如果你在一个不同的片段中返回一个片段，并在返回到片段时执行一个导致该片段的方法
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference
将该方法包装在一个
if (getActivity() != null) { // Code goes here. }
问题将得到解决。
您可以使用getActivity() ，它返回与片段关联的活动。 所以你的代码将成为：
public AlarmTask(Calendar date) { this.am = (AlarmManager)getActivity().getSystemService(Context.ALARM_SERVICE); //error for this line this.date = date; }