我有一个活动及其带有LinearLayout
的子片段,我在其中生成了按钮。创建片段后,一切运行正常。但是,当父活动下载新项目时,我在片段中调用用于生成按钮并将其添加到视图的方法,但是LinearLayout
返回null,我不知道为什么。我或者需要修复它,或者找到一种方法来“重新显示”我的片段。这是相关代码:
SongFragment:
LinearLayout linearLayout;
DatabaseHelper databaseHelper;
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_song, container, false);
linearLayout = rootView.findViewById(R.id.songFragmentMainLayout);
databaseHelper = new DatabaseHelper(getActivity());
return rootView;
}
@Override
public void onResume() {
super.onResume();
RefreshButtons();
}
public void RefreshButtons(){
linearLayout.removeAllViews(); //this line is where the NullPointerException is called
...
}
MainActivity:
//refresh fragment view
SongFragment fragment = (SongFragment) sectionsPagerAdapter.getItem(0);
if(downloadQueue.size() == 0){
fragment.RefreshButtons();
Toast.makeText(context, "New songs downloaded", Toast.LENGTH_SHORT).show();
}
...
public class SectionsPagerAdapter extends FragmentPagerAdapter {
public SectionsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
Fragment fragment = null;
switch (position) {
case 0:
fragment = new SongFragment();
break;
case 1:
fragment = new PlaceholderFragment();
break;
}
return fragment;
}
@Override
public int getCount() {
return 2;
}
@Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return "Songs";
case 1:
return "Playlists";
}
return null;
}
}
感谢您的帮助。
方法fragment.RefreshButtons();
返回一个NPE,因为如果您按应有的方式实现了SectionsPagerAdapter
,则getItem()
返回该片段的一个新实例,该实例尚未附加到片段管理器,因此导致[C0 ]。
所以您应该做的是得到一个当前活动的片段实例,如下所示:
Nullpointer exception
[ Fragment frag = (Fragment) mViewPager.getAdapter().instantiateItem(mViewPager, 0);
是片段的位置,因此,例如,如果您有3个片段,0
将返回第一个片段实例,等等...