子片段到父片段的通信 [英] Child Fragment to Parent Fragment communication
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问题描述
在我的孩子Fragment中,我有一个Recyclerview,并且在我的父Fragment中有一个Appbar布局.当Recyclerview的第一项可见时,我需要更新父片段中的appbar布局
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
我的界面
public interface OnListFirstItemVisibleListener {
public void sendDataToFragmentOnFirstItemVisible(boolean data, int dy);
}
在儿童片段"类中
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);
}
}
在父片段"类中
我实现了界面
public class MyParentFragment extends Fragment implements OnListFirstItemVisibleListener{
............
@Override
public void sendDataToFragmentOnFirstItemVisible(boolean data, int dy) {
if (dy < 0&&data==true)
mAppBarLayout.setExpanded(true);
}
}
但是我得到的Appbar布局为空
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
我要去哪里错了?
推荐答案
您必须使用ChildFragmentManager.您的父母应该看起来像这样:
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);
}
}
您的孩子是这样的
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);
}
}
});
}
}
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