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In my child Fragment, I have a Recyclerview, and I haved an Appbar layout in my parent Fragment. When the Recyclerview's first item is visible, I need to update the appbar layout in my parent fragment
My interface
public interface OnListFirstItemVisibleListener {
public void sendDataToFragmentOnFirstItemVisible(boolean data, int dy);
}
in Child Fragment class
public class MyChildFragment extends Fragment{
private OnListFirstItemVisibleListener mListFirstItemVisibleListener;
.............
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
mListFirstItemVisibleListener=(OnListFirstItemVisibleListener) new ParentFragment();
return view;
}
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
if(mLinearLayoutManager.findFirstCompletelyVisibleItemPosition()==0&&mListFirstItemVisibleListener != null){
mListFirstItemVisibleListener.sendDataToFragmentOnFirstItemVisible(true,dy);
}else{
mListFirstItemVisibleListener.sendDataToFragmentOnFirstItemVisible(false,dy);
}
}
In Parent Fragment class
I implemented the interface
public class MyParentFragment extends Fragment implements OnListFirstItemVisibleListener{
............
@Override
public void sendDataToFragmentOnFirstItemVisible(boolean data, int dy) {
if (dy < 0&&data==true)
mAppBarLayout.setExpanded(true);
}
}
But I get Appbar layout as null
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.design.widget.AppBarLayout.setExpanded(boolean)' on a null object
Where am I going wrong?
592
To keep fragments self-contained, you should not have fragments communicate directly with other fragments or with its host activity. The Fragment library provides two options for communication: a shared ViewModel and the Fragment Result API. The recommended option depends on the use case.
To allow a Fragment to communicate up to its Activity , you can define an interface in the Fragment class and implement it within the Activity . The Fragment captures the interface implementation during its onAttach() lifecycle method and can then call the Interface methods in order to communicate with the Activity .
To pass data between fragments in the same fragment manager, the listener should be added to the destination fragment with requestKey in order to receive the result produces from another fragment with the same key.
You have to use the ChildFragmentManager. You Parent should look like this:
public class ParentFragment extends Fragment {
private TextView mActionBar;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_parent, container, false);
mActionBar = (TextView) view.findViewById(R.id.actionBar);
return view;
}
@Override
public void onResume() {
super.onResume();
getChildFragmentManager().beginTransaction().add(R.id.childHolder, new ChildFragment()).commit();
}
public void setActionBarHidden(boolean isHidden) {
mActionBar.setVisibility(isHidden ? GONE : VISIBLE);
}
}
And your child like this:
public class ChildFragment extends Fragment {
public ChildFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_child, container, false);
mRecyclerView = (RecyclerView) view.findViewById(R.id.recyclerView);
mLinearLayoutManager = new LinearLayoutManager(getActivity());
mRecyclerView.setLayoutManager(mLinearLayoutManager);
mRecyclerView.setAdapter(new MyAdapter(mDataSet));
return view;
}
@Override
public void onResume() {
super.onResume();
mParentFragment = (ParentFragment) getParentFragment();
mRecyclerView.setOnScrollListener(new RecyclerView.OnScrollListener() {
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
if (mLinearLayoutManager.findFirstCompletelyVisibleItemPosition() == 0 && mParentFragment != null) {
mParentFragment.setActionBarHidden(true);
} else {
mParentFragment.setActionBarHidden(false);
}
}
});
}
}
ParentFragment parentFrag = ((ParentFragment)ChildFragment.this.getParentFragment());
parentFrag.YourParentFragmentMethod();
this is worked for me...
40
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