Android 如何保存和恢复片段中的recyclerview位置

您好，我想在从一个片段导航到另一个片段时保存回收器视图的位置，然后在返回片段时恢复滚动位置

注

到现在为止我没有尝试过任何方法，因为我不知道我到底在哪里 必须在my Home_Fragmen.java或PostAdapter_Home.java中实现它

现在，我如何在代码中实现这一点

Home\u Fragment.java

 public class Home_Fragment extends Fragment {
    private final DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference("uploads");
    public List<Upload> mUploads;
    PostAdapter_Home postsAdapter;
    RecyclerView postRecyclerView;
    ShimmerFrameLayout shimmerFrameLayout;

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_home, container, false);
        requireActivity().setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
        postRecyclerView = view.findViewById(R.id.recyclerViewHome);
        shimmerFrameLayout = view.findViewById(R.id.shimmerEffect);
        SnapHelper snapHelper = new PagerSnapHelper();
        snapHelper.attachToRecyclerView(postRecyclerView);
        postRecyclerView.setLayoutManager(
                new StaggeredGridLayoutManager(1, StaggeredGridLayoutManager.VERTICAL)
        );

        getData();
        shimmerFrameLayout.startShimmer();
        mUploads = new ArrayList<>();
        postsAdapter = new PostAdapter_Home(getContext(), mUploads);
        postRecyclerView.setAdapter(postsAdapter);
        return view;
    }

    private void getData() {
        databaseReference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                if (snapshot.exists()) {

                    postRecyclerView.setVisibility(View.VISIBLE);
                    shimmerFrameLayout.stopShimmer();
                    shimmerFrameLayout.setVisibility(View.GONE);
                    mUploads.clear();
                    for (DataSnapshot dataSnapshot : snapshot.getChildren()) {
                        Upload upload = dataSnapshot.getValue(Upload.class);
                        assert upload != null;
                        upload.setmKey(dataSnapshot.getKey());
                        mUploads.add(upload);


                    }

                }

                //notify the adapter
                postsAdapter.notifyDataSetChanged();
            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {
            }
        });
    }
}

public class PostAdapter_Home extends RecyclerView.Adapter<PostAdapter_Home.PostViewHolder> {
    public static List<Upload> mUploads;
    public Context mcontext;
    //    ShimmerFrameLayout shimmerFrameLayout;


    public PostAdapter_Home(Context context, List<Upload> uploads) {
        mUploads = uploads;
        mcontext = context;
    }


    @NonNull
    @Override
    public PostViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view;
        view = LayoutInflater.from(mcontext).inflate(R.layout.post_item_container_home, parent, false);
        return new PostViewHolder(view);

    }

    @Override
    public void onBindViewHolder(@NonNull PostViewHolder holder, int position) {
        Upload uploadCurrent = mUploads.get(position);
        Shimmer shimmer = new Shimmer.ColorHighlightBuilder()
                .setBaseColor(Color.parseColor("#F3F3F3"))
                .setBaseAlpha(1)
                .setHighlightColor(Color.parseColor("#E7E7E7"))
                .setHighlightAlpha(1)
                .setDropoff(50)
                .build();
        ShimmerDrawable shimmerDrawable = new ShimmerDrawable();
        shimmerDrawable.setShimmer(shimmer);
        Glide.with(mcontext)
                .load(uploadCurrent.getmImageUrl())
                .diskCacheStrategy(DiskCacheStrategy.DATA)
                .placeholder(shimmerDrawable)
                .into(holder.imageView);


    }

    @Override
    public int getItemCount() {
        return mUploads.size();
    }

    public static class PostViewHolder extends RecyclerView.ViewHolder {
        ShapeableImageView imageView;

        public PostViewHolder(@NonNull View itemView) {
            super(itemView);
            imageView = itemView.findViewById(R.id.imagePostHome);
        }


        public void setOnItemClickListener(PostAdapter.OnItemClickListener listener) {

        }
    }
}

public class Home\u片段扩展了片段{
private final DatabaseReference DatabaseReference=FirebaseDatabase.getInstance（）.getReference（“上载”）；
公共列表多路广播；
后适应者之家后适应者；
回收视图后回收视图；
摆振框架布局摆振框架布局；
@可空
@凌驾
创建视图时的公共视图（@NonNull LayoutInflater inflater、@Nullable ViewGroup container、@Nullable Bundle savedInstanceState）{
视图=充气机。充气（R.layout.fragment\u home，container，false）；
requireActivity（）.setRequestedOrientation（ActivityInfo.SCREEN\u ORIENTATION\u Graphic）；
postRecyclerView=view.findViewById（R.id.RecyclerViewWhome）；
shimmerFrameLayout=view.findViewById（R.id.shimmerEffect）；
SnapHelper SnapHelper=新页面SnapHelper（）；
snapHelper.attachToRecyclerView（postRecyclerView）；
postRecyclerView.setLayoutManager(
新的StaggedGridLayoutManager（1，StaggedGridLayoutManager.VERTICAL）
);
getData（）；
shimmerFrameLayout.startShimmer（）；
mUploads=newarraylist（）；
postsAdapter=新的PostAdapter_Home（getContext（），mUploads）；
postRecyclerView.setAdapter（postsAdapter）；
返回视图；
}
私有void getData（）{
databaseReference.addValueEventListener（新的ValueEventListener（）{
@凌驾
public void onDataChange（@NonNull DataSnapshot snapshot snapshot）{
if（snapshot.exists（））{
postRecyclerView.setVisibility（View.VISIBLE）；
shimmerFrameLayout.stopShimmer（）；
shimmerFrameLayout.setVisibility（View.GONE）；
mUploads.clear（）；
对于（DataSnapshot DataSnapshot:snapshot.getChildren（））{
Upload Upload=dataSnapshot.getValue（Upload.class）；
断言上传！=null；
upload.setmKey（dataSnapshot.getKey（））；
添加（上传）；
}
}
//通知适配器
postsAdapter.notifyDataSetChanged（）；
}
@凌驾
已取消公共void（@NonNull DatabaseError）{
}
});
}
}

PostAdapter_Home.java

 public class Home_Fragment extends Fragment {
    private final DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference("uploads");
    public List<Upload> mUploads;
    PostAdapter_Home postsAdapter;
    RecyclerView postRecyclerView;
    ShimmerFrameLayout shimmerFrameLayout;

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_home, container, false);
        requireActivity().setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
        postRecyclerView = view.findViewById(R.id.recyclerViewHome);
        shimmerFrameLayout = view.findViewById(R.id.shimmerEffect);
        SnapHelper snapHelper = new PagerSnapHelper();
        snapHelper.attachToRecyclerView(postRecyclerView);
        postRecyclerView.setLayoutManager(
                new StaggeredGridLayoutManager(1, StaggeredGridLayoutManager.VERTICAL)
        );

        getData();
        shimmerFrameLayout.startShimmer();
        mUploads = new ArrayList<>();
        postsAdapter = new PostAdapter_Home(getContext(), mUploads);
        postRecyclerView.setAdapter(postsAdapter);
        return view;
    }

    private void getData() {
        databaseReference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                if (snapshot.exists()) {

                    postRecyclerView.setVisibility(View.VISIBLE);
                    shimmerFrameLayout.stopShimmer();
                    shimmerFrameLayout.setVisibility(View.GONE);
                    mUploads.clear();
                    for (DataSnapshot dataSnapshot : snapshot.getChildren()) {
                        Upload upload = dataSnapshot.getValue(Upload.class);
                        assert upload != null;
                        upload.setmKey(dataSnapshot.getKey());
                        mUploads.add(upload);


                    }

                }

                //notify the adapter
                postsAdapter.notifyDataSetChanged();
            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {
            }
        });
    }
}

public class PostAdapter_Home extends RecyclerView.Adapter<PostAdapter_Home.PostViewHolder> {
    public static List<Upload> mUploads;
    public Context mcontext;
    //    ShimmerFrameLayout shimmerFrameLayout;


    public PostAdapter_Home(Context context, List<Upload> uploads) {
        mUploads = uploads;
        mcontext = context;
    }


    @NonNull
    @Override
    public PostViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view;
        view = LayoutInflater.from(mcontext).inflate(R.layout.post_item_container_home, parent, false);
        return new PostViewHolder(view);

    }

    @Override
    public void onBindViewHolder(@NonNull PostViewHolder holder, int position) {
        Upload uploadCurrent = mUploads.get(position);
        Shimmer shimmer = new Shimmer.ColorHighlightBuilder()
                .setBaseColor(Color.parseColor("#F3F3F3"))
                .setBaseAlpha(1)
                .setHighlightColor(Color.parseColor("#E7E7E7"))
                .setHighlightAlpha(1)
                .setDropoff(50)
                .build();
        ShimmerDrawable shimmerDrawable = new ShimmerDrawable();
        shimmerDrawable.setShimmer(shimmer);
        Glide.with(mcontext)
                .load(uploadCurrent.getmImageUrl())
                .diskCacheStrategy(DiskCacheStrategy.DATA)
                .placeholder(shimmerDrawable)
                .into(holder.imageView);


    }

    @Override
    public int getItemCount() {
        return mUploads.size();
    }

    public static class PostViewHolder extends RecyclerView.ViewHolder {
        ShapeableImageView imageView;

        public PostViewHolder(@NonNull View itemView) {
            super(itemView);
            imageView = itemView.findViewById(R.id.imagePostHome);
        }


        public void setOnItemClickListener(PostAdapter.OnItemClickListener listener) {

        }
    }
}

公共类PostAdapter\u Home扩展了RecyclerView.Adapter{
公共静态列表多路复用器；
公共语境；
//摆振框架布局摆振框架布局；
公共PostAdapter_主页（上下文、列表上载）{
mUploads=上传；
mcontext=上下文；
}
@非空
@凌驾
public PostViewHolder onCreateViewHolder（@NonNull ViewGroup父级，int viewType）{
视图；
view=LayoutFlater.from（mcontext）.充气（R.layout.post\u item\u container\u home，parent，false）；
返回新的PostViewHolder（视图）；
}
@凌驾
public void onBindViewHolder（@NonNull PostViewHolder，int位置）{
Upload uploadCurrent=mUploads.get（位置）；
Shimmer Shimmer=新的Shimmer.ColorHighlightBuilder（）
.setBaseColor（Color.parseColor（“#f3”））
.a（1）
.setHighlightColor（Color.parseColor（#E7E7E7”））
.setHighlightAlpha（1）
.设置衰减（50）
.build（）；
ShimmerDrawable ShimmerDrawable=新的ShimmerDrawable（）；
微光可绘制。设置嵌合体（微光）；
使用（mcontext）滑动
.load（uploadCurrent.getmImageUrl（））
.diskCacheStrategy（diskCacheStrategy.DATA）
.占位符（可微光绘制）
.插入（支架.图像视图）；
}
@凌驾
public int getItemCount（）{
返回mUploads.size（）；
}
公共静态类PostViewHolder扩展了RecyclerView.ViewHolder{
ShapeableImageView图像视图；
公共PostViewHolder（@NonNull View itemView）{
超级（项目视图）；
imageView=itemView.findViewById（R.id.imagePostHome）；
}
public void setOnItemClickListener（PostAdapter.OnItemClickListener侦听器）{
}
}
}

一个简单的解决方案是使用静态变量

将以下内容作为属性添加到类中：

public static int saved_position=0

（

0

值必须是recyclerView position的默认值）

每当recyclerView值更改时，添加

Home\u Fragment.saved\u position=…

，以保存变量中的实际位置。这行代码可以毫无问题地在任何文件上运行，因为静态变量是公共的

创建片段时，请将recyclerView位置设置为保存在

主页\u片段中的位置。保存的\u位置

，这就是为什么必须将默认值设置为初始值的原因

如果由于某种原因，recyclerView中的元素数量发生变化，请记住将

Home\u Fragment.saved\u position

的值更改为默认值

---

只要应用程序未完全关闭，就会存储该值。如果应用程序放在后台，值将被存储，直到其他应用程序占用变量使用的RAM内存…兄弟，我了解一点，但如果你告诉我确切的代码是什么，我应该在我的代码中在哪里实现它，这将非常有帮助，顺便说一句，谢谢你的回答。确切的代码取决于你