我有一个奇怪的问题。我采取相同的code在两个地方(无论是在 ListFragments
),但一工程和其他抛出一个 NullPointerException异常
。
下面是我的code(ListFragment的一个子类的一部分):
公共静态类DeleteDialogFragment扩展DialogFragment {
静态DeleteDialogFragment的newInstance(INT ARG){
返回新DeleteDialogFragment();
}
@覆盖
公共对话onCreateDialog(包savedInstanceState){
返回新AlertDialog.Builder(getActivity())
.setTitle(R.string.confirm_delete)
.setMessage(R.string.teacher_confirm_delete_message)
.setPositiveButton(R.string.yes,新DialogInterface.OnClickListener(){
公共无效的onClick(DialogInterface对话,诠释它){
((TeachersFragment)getTargetFragment())deleteTeacher()。
}
})
.setNegativeButton(R.string.no,空)
。创建();
}
}
公共无效deleteTeacher(){
DbUtils.deleteTeacher(背景下,将selectedItem);
}
我在另一个ListFragment同样的事情(除了我投它一对 AssignmentListFragment
代替 TeachersFragment
),以及一个完美的作品。在这两种情况下, DeleteDialogFragment
类是ListFragment下直接嵌套。
该错误消息我得到如下:
E / AndroidRuntime(15282):致命异常:主要
E / AndroidRuntime(15282):显示java.lang.NullPointerException
E / AndroidRuntime(15282):在com.acedit.assignamo.setup.TeachersFragment.access $ 6(TeachersFragment.java:145)
E / AndroidRuntime(15282):在com.acedit.assignamo.setup.TeachersFragment$DeleteDialogFragment$1.onClick(TeachersFragment.java:137)
E / AndroidRuntime(15282):在com.android.internal.app.AlertController $ ButtonHandler.handleMessage(AlertController.java:166)
E / AndroidRuntime(15282):在android.os.Handler.dispatchMessage(Handler.java:99)
E / AndroidRuntime(15282):在android.os.Looper.loop(Looper.java:137)
E / AndroidRuntime(15282):在android.app.ActivityThread.main(ActivityThread.java:4575)
E / AndroidRuntime(15282):在java.lang.reflect.Method.invokeNative(本机方法)
E / AndroidRuntime(15282):在java.lang.reflect.Method.invoke(Method.java:511)
E / AndroidRuntime(15282):在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:786)
E / AndroidRuntime(15282):在com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
E / AndroidRuntime(15282):在dalvik.system.NativeStart.main(本机方法)
由于 getTargetFragment()
返回null(我检查在调试模式下通过指定的返回值给一个临时变量,它是零),这似乎有些奇怪,它使它的 deleteTeacher()
方法崩溃之前(公共无效deleteTeacher(){
是行145)。
任何想法到底是什么问题?如果您需要更多code,只是让我知道。
编辑:这里是code,我称之为 setTargetFragment
(在此code我能我的其他实例使用这
,而不是 getTargetFragment
,所以我认为这是问题所在。
私有类CustomOnClickListener实现OnClickListener {
公共无效的onClick(视图v){
Toast.makeText(背景下,巴顿pressed,Toast.LENGTH_SHORT).show();
如果(V == viewHolder.editButton)
startActivity(新意图(背景下,getEditClass())putExtra(Values.KEY_ROWID,(长)v.getTag()));
其他{//删除它
将selectedItem =(长)v.getTag();
DeleteDialogFragment FRAG =新DeleteDialogFragment();
frag.setTargetFragment(getTargetFragment(),0);
frag.show(getFragmentManager(),confirmDelete);
}
}
}
解决方案
现在的问题是,你没有一个参考TeacherFragment,因为 getTargetFragment()
是空
,但你可以获取片段等方式尝试使用FragmentManager的 getFragmentById()
或 getFragmentByTag()
的方法。
I am having an odd problem. I am implementing the same code in two places (both in ListFragments
), but one works and the other throws a NullPointerException
.
Here's my code (all part of a subclass of ListFragment):
public static class DeleteDialogFragment extends DialogFragment {
static DeleteDialogFragment newInstance(int arg) {
return new DeleteDialogFragment();
}
@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
return new AlertDialog.Builder(getActivity())
.setTitle(R.string.confirm_delete)
.setMessage(R.string.teacher_confirm_delete_message)
.setPositiveButton(R.string.yes, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
((TeachersFragment)getTargetFragment()).deleteTeacher();
}
})
.setNegativeButton(R.string.no, null)
.create();
}
}
public void deleteTeacher() {
DbUtils.deleteTeacher(context, selectedItem);
}
I have exactly the same thing in another ListFragment (except I'm casting it to an AssignmentListFragment
instead of a TeachersFragment
), and that one works flawlessly. In both cases the DeleteDialogFragment
class is nested directly under the ListFragment.
The error message I'm getting is as follows:
E/AndroidRuntime(15282): FATAL EXCEPTION: main
E/AndroidRuntime(15282): java.lang.NullPointerException
E/AndroidRuntime(15282): at com.acedit.assignamo.setup.TeachersFragment.access$6(TeachersFragment.java:145)
E/AndroidRuntime(15282): at com.acedit.assignamo.setup.TeachersFragment$DeleteDialogFragment$1.onClick(TeachersFragment.java:137)
E/AndroidRuntime(15282): at com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:166)
E/AndroidRuntime(15282): at android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime(15282): at android.os.Looper.loop(Looper.java:137)
E/AndroidRuntime(15282): at android.app.ActivityThread.main(ActivityThread.java:4575)
E/AndroidRuntime(15282): at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime(15282): at java.lang.reflect.Method.invoke(Method.java:511)
E/AndroidRuntime(15282): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
E/AndroidRuntime(15282): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
E/AndroidRuntime(15282): at dalvik.system.NativeStart.main(Native Method)
Given that getTargetFragment()
returns null (I checked in debug mode by assigning the return value to a temporary variable and it is null), it seems odd that it makes it to the deleteTeacher()
method before crashing (public void deleteTeacher() {
is line 145).
Any ideas what the heck is wrong? If you need more code, just let me know.
EDIT: Here is the code where I call setTargetFragment
(in my other instance of this code I was able to use this
instead of getTargetFragment
, so I think that is where the problem lies.
private class CustomOnClickListener implements OnClickListener {
public void onClick(View v) {
Toast.makeText(context, "Button pressed", Toast.LENGTH_SHORT).show();
if (v == viewHolder.editButton)
startActivity(new Intent(context, getEditClass()).putExtra(Values.KEY_ROWID, (Long)v.getTag()));
else { // Delete it
selectedItem = (Long) v.getTag();
DeleteDialogFragment frag = new DeleteDialogFragment();
frag.setTargetFragment(getTargetFragment(), 0);
frag.show(getFragmentManager(), "confirmDelete");
}
}
}
解决方案
The problem is you don't have a reference to the TeacherFragment since getTargetFragment()
is null
, but you can fetch the Fragment other ways try using the FragmentManager's getFragmentById()
or getFragmentByTag()
methods.
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