可见时刷新片段中的适配器
refresh adapter in fragment when it is visible
我有两个片段..我想在我的第一个片段中的 setUserVisibleHint 方法中刷新我的列表视图适配器 adapter.notifyDataSetChanged()
:
@Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
if(isVisibleToUser){
adapter.notifyDataSetChanged();
}
}
但我得到这个异常:
java.lang.NullPointerException
at com.androidbelieve.drawerwithswipetabs.FirstFragment.setUserVisibleHint(FirstFragment.java:247)
at android.support.v4.app.FragmentPagerAdapter.setPrimaryItem(FragmentPagerAdapter.java:130)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1175)
不好意思我对Fragments有点了解,这是什么"setPrimaryItem"!?
这是我的标签片段:
public class TabFragment extends Fragment {
View x;
public static TabLayout tabLayout;
public static ViewPager viewPager;
public static int int_items = 2 ;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
x = inflater.inflate(R.layout.tab_layout,null);
tabLayout = (TabLayout) x.findViewById(R.id.tabs);
viewPager = (ViewPager) x.findViewById(R.id.viewpager);
viewPager.setOffscreenPageLimit(2);
viewPager.setAdapter(new MyAdapter(getChildFragmentManager()));
viewPager.getCurrentItem();
viewPager.addOnPageChangeListener(new OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
}
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
@Override
public void onPageScrollStateChanged(int state) {
}
});
tabLayout.post(new Runnable() {
@Override
public void run() {
tabLayout.setupWithViewPager(viewPager);
}
});
return x;
}
class MyAdapter extends FragmentPagerAdapter{
public MyAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position)
{
switch (position){
case 0 : return new FirstFragment();
case 1 : return new ZZZFavorites();
}
return null;
}
@Override
public int getCount() {
return int_items;
}
@Override
public CharSequence getPageTitle(int position) {
switch (position){
case 0 :
return "Online";
case 1 :
return "Favorites";
}
return null;
}
}
}
你的 adapter
是 null
。在访问它之前执行null-check
。
if (isVisibleToUser && adapter != null) {
adapter.notifyDataSetChanged();
}
我有两个片段..我想在我的第一个片段中的 setUserVisibleHint 方法中刷新我的列表视图适配器 adapter.notifyDataSetChanged()
:
@Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
if(isVisibleToUser){
adapter.notifyDataSetChanged();
}
}
但我得到这个异常:
java.lang.NullPointerException at com.androidbelieve.drawerwithswipetabs.FirstFragment.setUserVisibleHint(FirstFragment.java:247) at android.support.v4.app.FragmentPagerAdapter.setPrimaryItem(FragmentPagerAdapter.java:130) at android.support.v4.view.ViewPager.populate(ViewPager.java:1175)
不好意思我对Fragments有点了解,这是什么"setPrimaryItem"!?
这是我的标签片段:
public class TabFragment extends Fragment {
View x;
public static TabLayout tabLayout;
public static ViewPager viewPager;
public static int int_items = 2 ;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
x = inflater.inflate(R.layout.tab_layout,null);
tabLayout = (TabLayout) x.findViewById(R.id.tabs);
viewPager = (ViewPager) x.findViewById(R.id.viewpager);
viewPager.setOffscreenPageLimit(2);
viewPager.setAdapter(new MyAdapter(getChildFragmentManager()));
viewPager.getCurrentItem();
viewPager.addOnPageChangeListener(new OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
}
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
@Override
public void onPageScrollStateChanged(int state) {
}
});
tabLayout.post(new Runnable() {
@Override
public void run() {
tabLayout.setupWithViewPager(viewPager);
}
});
return x;
}
class MyAdapter extends FragmentPagerAdapter{
public MyAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position)
{
switch (position){
case 0 : return new FirstFragment();
case 1 : return new ZZZFavorites();
}
return null;
}
@Override
public int getCount() {
return int_items;
}
@Override
public CharSequence getPageTitle(int position) {
switch (position){
case 0 :
return "Online";
case 1 :
return "Favorites";
}
return null;
}
}
}
你的 adapter
是 null
。在访问它之前执行null-check
。
if (isVisibleToUser && adapter != null) {
adapter.notifyDataSetChanged();
}