错误：尝试在空对象引用上调用虚拟方法“java.lang.Object android.content.Context.getSystemService(java.lang.String)”
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error:Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference
提问by
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;
}
There are similar questions, but after banging my head I couldn't sort out the problem. I am getting these following errors! Is it due to fragments?
有类似的问题，但敲了敲脑袋后，我无法解决问题。我收到以下错误！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.<init>(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.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)
This is how I am calling the class
这就是我打电话给班级的方式
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();
}
This is where I call the setAlarm function
这是我调用 setAlarm 函数的地方
public void setAlarmForNotification(Calendar c){
ScheduleService mBoundService = new ScheduleService();
mBoundService.setAlarm(c);
}
采纳答案by Gabriele Mariotti
In your code the
在您的代码中
this.am = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);
the contextis null.
的context是null。
Checking your stacktrace your are initializing the AlarmTaskin
检查你的堆栈跟踪你的初始化AlarmTask中
at lol.com.epl.FixFragment.onCreateView(FixFragment.java:88)
Move this call in the onActivityCreatedmethod.
在onActivityCreated方法中移动这个调用。
回答by Zain Zafar
You can use getActivity(), which returns the activity associated with a fragment.
So your code will become:
您可以使用getActivity()，它返回与片段关联的活动。所以你的代码将变成：
public AlarmTask(Calendar date) {
this.am = (AlarmManager)getActivity().getSystemService(Context.ALARM_SERVICE); //error for this line
this.date = date;
}
回答by Udit Kapahi
If you are returning to a fragment while being inside a different fragment, and upon returning to the fragment you execute a method which is causing the
如果您在不同片段内返回片段，并且在返回片段时执行导致
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference
Wrapped that method in a
将该方法包装在一个
if (getActivity() != null) {
// Code goes here.
}
and problem will be solved.
问题将得到解决。
