对主持人的要求：这不是重复的问题，请阅读以下信息。
在问这个问题之前，我已经尝试了几乎所有可用的SO解决方案，但是没有一个对我有用，有的导致崩溃而有的根本不起作用（我是初学者，有可能我在我的代码中做错了什么，我不怪任何人在SO上无法得到的答案都无法解决我的问题）。下面是我的代码，请看一下：
fragment_tab1.xml（包含recyclerview）：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:layout_height="match_parent"
android:layout_width="match_parent"
android:background="#333333"
android:orientation="vertical"
xmlns:android="http://schemas.android.com/apk/res/android">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginTop="96dp">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="42dp"
android:background="@color/colorPrimaryDark"
android:id="@+id/sort1"
android:orientation="horizontal">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/sort"
android:layout_marginLeft="10dp"
android:fontFamily="@font/quicksand"
android:textStyle="bold"
android:text="Sort by:"
android:textColor="#ffffff"/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="10dp"
style="@style/Widget.AppCompat.Button.Colored"
android:text="Oldest first"/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
style="@style/Widget.AppCompat.Button.Colored"
android:text="Newest first"/>
</LinearLayout>
<android.support.v7.widget.RecyclerView
android:id="@+id/recycler_view"
android:layout_below="@id/sort1"
android:clipToPadding="false"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginBottom="10dp"
android:padding="5dp" />
</RelativeLayout>
</LinearLayout>
Fragmenttab1.java
public class tab1 extends Fragment {
RecyclerView mRecyclerView;
FirebaseDatabase mFirebaseDatabase;
DatabaseReference mRef;
LinearLayoutManager manager;
private static final String TAG = "tab1";
ProgressDialog progressDialog;
View rootView;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
//Returning the layout file after inflating
//Change R.layout.tab1 in you classes
rootView = inflater.inflate(R.layout.fragment_tab1, container, false);
return rootView;
}
@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
mRecyclerView = (RecyclerView) rootView.findViewById(R.id.recycler_view);
manager = new LinearLayoutManager(getActivity());
mRecyclerView.setLayoutManager(manager);
mRecyclerView.setItemViewCacheSize(20);
mRecyclerView.setDrawingCacheEnabled(true);
mFirebaseDatabase = FirebaseDatabase.getInstance();
mRef = mFirebaseDatabase.getReference("memes");
mFirebaseDatabase.getInstance().getReference().keepSynced(true);
progressDialog = new ProgressDialog(getActivity());
progressDialog.setMessage("Please Wait");
progressDialog.show();
}
public void onStart() {
super.onStart();
FirebaseRecyclerAdapter<Model, ViewHolder> firebaseRecyclerAdapter =
new FirebaseRecyclerAdapter<Model, ViewHolder>(
Model.class,
R.layout.row2,
ViewHolder.class,
mRef
) {
@Override
protected void populateViewHolder(ViewHolder viewHolder, Model model, int position) {
viewHolder.setDetails(getActivity(), model.getTitle(), model.getDesc(), model.getImage());
progressDialog.cancel();
}
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
ViewHolder viewHolder = super.onCreateViewHolder(parent, viewType);
viewHolder.setOnClickListener(new ViewHolder.ClickListener(){
@Override
public void onItemClick(View view, int position){
//get data from firebase here
String mTitle = getItem(position).getTitle();
String mDesc= getItem(position).getDesc();
String mImage = getItem(position).getImage();
//pass this data to new activity
Intent intent = new Intent(view.getContext(), ArticleDetail.class);
intent.putExtra("title", mTitle);// put title
intent.putExtra("desc", mDesc);// put description
intent.putExtra("image", mImage); //put image urls
startActivity(intent);
}
@Override
public void onItemLongClick(View view, int position){
//TODO your own implementation on long item click
}
});
return viewHolder;
}
};
mRecyclerView.setAdapter(firebaseRecyclerAdapter);
}
@Override
public void onPause() {
super.onPause();
SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getActivity());
View firstChild = mRecyclerView.getChildAt(0);
int firstVisiblePosition = mRecyclerView.getChildAdapterPosition(firstChild);
int offset = firstChild.getTop();
Log.d(TAG, "Postition: " + firstVisiblePosition);
Log.d(TAG, "Offset: " + offset);
preferences.edit()
.putInt("position", firstVisiblePosition)
.putInt("offset", offset)
.apply();
}
@Override
public void onResume(){
super.onResume();
}
@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
}
@Override
public void onViewStateRestored(@Nullable Bundle savedInstanceState) {
super.onViewStateRestored(savedInstanceState);
}
}
答案 0 :(得分：0)
您应该使用此方法返回可见的第一项：
int findFirstVisibleItemPosition();
然后必须将该索引保存在onPause（）上，当用户返回检索时，将其设置在onResume（）上：
void scrollToPosition (int position)
答案 1 :(得分：0)
花了这么多天，尝试了许多解决方案之后，终于有了https://stackoverflow.com/a/42563804/2128364
为我的问题找到了可行的解决方案我已将工作解决方案移至另一种方法以使其在片段中起作用。
也许这可以节省某人的生活，这是它的工作原理：
您必须使用onPause方法保存状态：
mBundleRecyclerViewState = new Bundle();
mListState = mRecyclerView.getLayoutManager().onSaveInstanceState();
mBundleRecyclerViewState.putParcelable(KEY_RECYCLER_STATE, mListState);
然后使用onResume方法还原它：
if (mBundleRecyclerViewState != null) {
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
mListState = mBundleRecyclerViewState.getParcelable(KEY_RECYCLER_STATE);
mRecyclerView.getLayoutManager().onRestoreInstanceState(mListState);
}
}, 50);
}
mRecyclerView.setLayoutManager(staggeredGridLayoutManager);
答案 2 :(得分：0)
如果还没有，请在您的recyclerView中添加build.gradle依赖项
implementation "androidx.recyclerview:recyclerview:1.2.0-alpha05"
比在初始化列表适配器之后才设置stateRestorationPolicy。
listAdapter = ListAdapter()
// Set scroll restore policy
listdapter.stateRestorationPolicy =
RecyclerView.Adapter.StateRestorationPolicy.PREVENT_WHEN_EMPTY
有关stateRestorationPolicy和不同类型的策略visit this article
答案 3 :(得分：-1)
尝试使用MVVM体系结构。使用ViewModel，因此保存的数据不依赖于生命周期。同时查看LiveData以对ViewModel的变化做出反应。