java - ServerValue.TIMESTAMP 在 Firebase 中保存和检索时间戳

Question

我的代码没有从 Firebase 返回 timestamp，我不知道为什么。此外，在 if else 语句的 private void setupWidgets 方法中 timestamp 显示为红色，我不知道为什么——我把** 在它旁边...有谁知道为什么我在上面声明了它？为什么我没有在 TextView 中获取 timestamp？

我已将这两页用作引用 How to save the current date/time when I add new value to Firebase Realtime Database & Convert ServerValue.TIMESTAMP To date除了我看过的所有视频，但它仍然无法正常播放。

PostAdapter.java

    public class ViewHolder extends RecyclerView.ViewHolder {

            public ImageView image_profile, post_image, like, comment, attend_event, save_event, more_options;
            public TextView username, number_of_likes, description, number_of_comments, text_event, text_location, text_date_time,
                    number_of_people_attending_event, timestamp;

            public ViewHolder(@NonNull View itemView) {
                super(itemView);

                image_profile = itemView.findViewById(R.id.image_profile);
                post_image = itemView.findViewById(R.id.post_image);
                like = itemView.findViewById(R.id.like);
                comment = itemView.findViewById(R.id.comment);
                username = itemView.findViewById(R.id.username);
                number_of_likes = itemView.findViewById(R.id.number_of_likes);
                description = itemView.findViewById(R.id.description);
                number_of_comments = itemView.findViewById(R.id.number_of_comments);
                timestamp = itemView.findViewById(R.id.timestamp);

            }
        }

    private void saveTimestamp() {
            DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
            Map map = new HashMap();
            map.put("timestamp", ServerValue.TIMESTAMP);
            reference.child("Posts").updateChildren(map);
        }

        private void setupWidgets() {
            String timestampDifference = getTimestampDifference();
            if (!timestampDifference.equals("0")) {
                **timestamp.setText(timestampDifference + " days ago");
            } else {
                **timestamp.setText("Today");
            }
        }

        //Timestamp
        private String getTimestampDifference() {
            String difference = "";
            Calendar calendar = Calendar.getInstance();
            SimpleDateFormat simpleDateFormat = new SimpleDateFormat("dd-MMM-yyyy HH:mm:ss");
            Date today = calendar.getTime();
            simpleDateFormat.format(today);
            Date timestamp;
            final String dateTime = simpleDateFormat.format(calendar.getTime());
            try {
                timestamp = simpleDateFormat.parse(dateTime);
                difference = String.valueOf(Math.round(((today.getTime() - timestamp.getTime()) / 1000 / 60 / 60 / 24)));
            } catch (ParseException e) {
                difference = "0";
            }
            return difference;

        }

post_item.xml

<TextView
                android:id="@+id/timestamp"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_below="@+id/description"
                android:layout_marginStart="10dp"
                android:layout_marginBottom="10dp"
                android:text="Have to add a Timestamp" />

PostAdapter.java

    package com.e.events.Adapter;

    public class PostAdapter extends RecyclerView.Adapter<PostAdapter.ViewHolder> {

        public Context mContext;
        public List<Post> mPost;

        private FirebaseUser firebaseUser;

        public PostAdapter(Context mContext, List<Post> mPost) {
            this.mContext = mContext;
            this.mPost = mPost;
        }

        @NonNull
        @Override
        public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
            View view = LayoutInflater.from(mContext).inflate(R.layout.post_item, parent, false);
            return new PostAdapter.ViewHolder(view);
        }

        @Override
        public void onBindViewHolder(@NonNull final ViewHolder holder, int position) {

            firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
            final Post post = mPost.get(position);

            Glide.with(mContext).load(post.getPostimage())
                    .apply(new RequestOptions().placeholder(R.drawable.placeholderimg))
                    .into(holder.post_image);

            if ("".equals(post.getDescription())) {
                holder.description.setVisibility(View.GONE);
            } else {
                holder.description.setVisibility(View.VISIBLE);
                holder.description.setText(post.getDescription());
            }

            if ("".equals(post.getText_event())) {
                holder.text_event.setVisibility(View.GONE);
            } else {
                holder.text_event.setVisibility(View.VISIBLE);
                holder.text_event.setText(post.getText_event());
            }

            if ("".equals(post.getText_location())) {
                holder.text_location.setVisibility(View.GONE);
            } else {
                holder.text_location.setVisibility(View.VISIBLE);
                holder.text_location.setText(post.getText_location());
            }

            if ("".equals(post.getText_date_time())) {
                holder.text_date_time.setVisibility(View.GONE);
            } else {
                holder.text_date_time.setVisibility(View.VISIBLE);
                holder.text_date_time.setText(post.getText_date_time());
            }
            publisherInfo(holder.image_profile, holder.username, post.getPublisher());
            eventLiked(post.getPostid(), holder.like);
            number_of_likes(holder.number_of_likes, post.getPostid());

            holder.like.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    if (holder.like.getTag().equals("like")) {
                        FirebaseDatabase.getInstance().getReference().child("Likes").child(post.getPostid())
                                .child(firebaseUser.getUid()).setValue(true);
                        addNotification(post.getPublisher(), post.getPostid());
                    } else {
                        FirebaseDatabase.getInstance().getReference().child("Likes").child(post.getPostid())
                                .child(firebaseUser.getUid()).removeValue();
                    }
                }
            });

            publisherInfo(holder.image_profile, holder.username, post.getPublisher());
            attending_event(post.getPostid(), holder.attend_event);
            number_of_people_attending_event(holder.number_of_people_attending_event, post.getPostid());
            getComments(post.getPostid(), holder.number_of_comments);
            isSaved(post.getPostid(), holder.save_event);

            holder.attend_event.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    if (holder.attend_event.getTag().equals("attend_event")) {
                        FirebaseDatabase.getInstance().getReference().child("Attending Event").child(firebaseUser.getUid())
                                .child(post.getPostid()).setValue(true);
                    } else {
                        FirebaseDatabase.getInstance().getReference().child("Attending Event").child(firebaseUser.getUid())
                                .child(post.getPostid()).removeValue();
                    }
                }
            });

            holder.image_profile.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    SharedPreferences.Editor editor = mContext.getSharedPreferences("PREFS", Context.MODE_PRIVATE).edit();
                    editor.putString("profileid", post.getPublisher());
                    editor.apply();

                    ((FragmentActivity) mContext).getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,
                            new ProfileFragment()).commit();
                }
            });

            holder.username.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    SharedPreferences.Editor editor = mContext.getSharedPreferences("PREFS", Context.MODE_PRIVATE).edit();
                    editor.putString("profileid", post.getPublisher());
                    editor.apply();

                    ((FragmentActivity) mContext).getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,
                            new ProfileFragment()).commit();
                }
            });

            holder.post_image.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    SharedPreferences.Editor editor = mContext.getSharedPreferences("PREFS", Context.MODE_PRIVATE).edit();
                    editor.putString("postid", post.getPostid());
                    editor.apply();

                    ((FragmentActivity) mContext).getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,
                            new PostDetailFragment()).commit();
                }
            });

            holder.save_event.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    if (holder.save_event.getTag().equals("save")) {
                        FirebaseDatabase.getInstance().getReference().child("Saves").child(firebaseUser.getUid())
                                .child(post.getPostid()).setValue(true);
                    } else {
                        FirebaseDatabase.getInstance().getReference().child("Saves").child(firebaseUser.getUid())
                                .child(post.getPostid()).removeValue();
                    }
                }
            });

            holder.attend_event.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    if (holder.attend_event.getTag().equals("attend event")) {
                        FirebaseDatabase.getInstance().getReference().child("Attending Event").child(post.getPostid())
                                .child(firebaseUser.getUid()).setValue(true);
                    } else {
                        FirebaseDatabase.getInstance().getReference().child("Attending Event").child(post.getPostid())
                                .child(firebaseUser.getUid()).removeValue();
                    }
                }
            });

            holder.comment.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Intent intent = new Intent(mContext, CommentsActivity.class);
                    intent.putExtra("postid", post.getPostid());
                    intent.putExtra("publisherid", post.getPublisher());
                    mContext.startActivity(intent);
                }
            });

            holder.number_of_comments.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Intent intent = new Intent(mContext, CommentsActivity.class);
                    intent.putExtra("postid", post.getPostid());
                    intent.putExtra("publisherid", post.getPublisher());
                    mContext.startActivity(intent);
                }
            });

            holder.number_of_likes.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Intent intent = new Intent(mContext, FollowersActivity.class);
                    intent.putExtra("id", post.getPostid());
                    intent.putExtra("title", "likes");
                    mContext.startActivity(intent);
                }
            });

            holder.more_options.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    PopupMenu popupMenu = new PopupMenu(mContext, v);
                    popupMenu.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() {
                        @Override
                        public boolean onMenuItemClick(MenuItem item) {
                            switch (item.getItemId()) {
                                case R.id.edit_event:
                                    editPost(post.getPostid());
                                    return true;
                                case R.id.delete_event:
                                    FirebaseDatabase.getInstance().getReference("Posts").child(post.getPostid()).removeValue()
                                            .addOnCompleteListener(new OnCompleteListener<Void>() {
                                                @Override
                                                public void onComplete(@NonNull Task<Void> task) {
                                                    if (task.isSuccessful()) {
                                                        Toast.makeText(mContext, "Event deleted", Toast.LENGTH_SHORT).show();
                                                    }
                                                }
                                            });
                                    return true;
                                case R.id.report_event:
                                    Toast.makeText(mContext, "Event has been reported", Toast.LENGTH_SHORT).show();
                                    return true;
                                default:
                                    return false;
                            }
                        }
                    });
                    popupMenu.inflate(R.menu.event_menu);
                    if (!post.getPublisher().equals(firebaseUser.getUid())) {
                        popupMenu.getMenu().findItem(R.id.edit_event).setVisible(false);
                        popupMenu.getMenu().findItem(R.id.delete_event).setVisible(false);
                    }
                    popupMenu.show();
                }
            });

        }

        @Override
        public int getItemCount() {
            if (mPost != null) {
                return mPost.size();
            } else {
                return 0;
            }

        }

        public class ViewHolder extends RecyclerView.ViewHolder {

            public ImageView image_profile, post_image, like, comment, attend_event, save_event, more_options;
            public TextView username, number_of_likes, description, number_of_comments, text_event, text_location, text_date_time,
                    number_of_people_attending_event, timestamp;

            public ViewHolder(@NonNull View itemView) {
                super(itemView);

                image_profile = itemView.findViewById(R.id.image_profile);
                post_image = itemView.findViewById(R.id.post_image);
                like = itemView.findViewById(R.id.like);
                comment = itemView.findViewById(R.id.comment);
                username = itemView.findViewById(R.id.username);
                number_of_likes = itemView.findViewById(R.id.number_of_likes);
                description = itemView.findViewById(R.id.description);
                number_of_comments = itemView.findViewById(R.id.number_of_comments);
                text_event = itemView.findViewById(R.id.text_event);
                text_location = itemView.findViewById(R.id.text_location);
                text_date_time = itemView.findViewById(R.id.text_date_time);
                attend_event = itemView.findViewById(R.id.attend_event);
                number_of_people_attending_event = itemView.findViewById(R.id.number_of_people_attending_event);
                save_event = itemView.findViewById(R.id.save_event);
                more_options = itemView.findViewById(R.id.more_options);
                timestamp = itemView.findViewById(R.id.timestamp);

            }
        }

        private void saveTimestamp() {
            DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
            Map map = new HashMap();
            map.put("timestamp", ServerValue.TIMESTAMP);
            reference.child("Posts").updateChildren(map);
        }

        //Set words for the timestamp "Today" or "___ days ago"
        private void setupWidgets() {
            String timestampDifference = getTimestampDifference();
            if (!timestampDifference.equals("0")) {
                timestamp.setText(timestampDifference + " days ago");
            } else {
                timestamp.setText("Today");
            }
        }

        //Timestamp
        private String getTimestampDifference() {
            Log.d(TAG, "getTimestampDifference: getting timestamp difference");

            String difference = "";
            Calendar calendar = Calendar.getInstance();
            SimpleDateFormat simpleDateFormat = new SimpleDateFormat("dd-MMM-yyyy HH:mm:ss", Locale.US);
            simpleDateFormat.setTimeZone(TimeZone.getTimeZone("America/Chicago"));
            Date today = calendar.getTime();
            simpleDateFormat.format(today);
            Date timestamp;
            final String dateTime = simpleDateFormat.format(calendar.getTime());
            try {
                timestamp = simpleDateFormat.parse(dateTime);
                difference = String.valueOf(Math.round(((today.getTime() - timestamp.getTime()) / 1000 / 60 / 60 / 24)));
            } catch (ParseException e) {
                difference = "0";
            }
            return difference;

        }

        private void getComments(String postid, final TextView comments) {
            DatabaseReference reference = FirebaseDatabase.getInstance().getReference().child("Comments").child(postid);

            reference.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                    comments.setText(dataSnapshot.getChildrenCount() + "");
                }

                @Override
                public void onCancelled(@NonNull DatabaseError databaseError) {

                }
            });
        }

        private void eventLiked(String postid, final ImageView imageView) {

            final FirebaseUser firebaseUser = FirebaseAuth.getInstance().getCurrentUser();

            DatabaseReference reference = FirebaseDatabase.getInstance().getReference().child("Likes").child(postid);

            reference.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                    if (dataSnapshot.child(firebaseUser.getUid()).exists()) {
                        imageView.setImageResource(R.drawable.ic_event_liked_aqua_fill);
                        imageView.setTag("liked");
                    } else {
                        imageView.setImageResource(R.drawable.ic_favorite_heart_hollow);
                        imageView.setTag("like");
                    }
                }

                @Override
                public void onCancelled(@NonNull DatabaseError databaseError) {

                }
            });
        }

        private void addNotification(final String userid, final String postid) {
            DatabaseReference reference = FirebaseDatabase.getInstance().getReference("Notifications").child(userid);

            HashMap<String, Object> hashMap = new HashMap<>();

            hashMap.put("userid", firebaseUser.getUid());
            hashMap.put("comment", "liked your Event");
            hashMap.put("postid", postid);
            hashMap.put("ispost", true);

            reference.push().setValue(hashMap);
        }

        private void number_of_likes(final TextView likes, String postid) {
            DatabaseReference reference = FirebaseDatabase.getInstance().getReference().child("Likes").child(postid);

            reference.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                    likes.setText(dataSnapshot.getChildrenCount() + "");
                }

                @Override
                public void onCancelled(@NonNull DatabaseError databaseError) {

                }
            });
        }

        private void attending_event(String postid, final ImageView imageView) {

            final FirebaseUser firebaseUser = FirebaseAuth.getInstance().getCurrentUser();

            DatabaseReference reference = FirebaseDatabase.getInstance().getReference().child("Attending Event").child(postid);

            reference.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                    if (dataSnapshot.child(firebaseUser.getUid()).exists()) {
                        imageView.setImageResource(R.drawable.ic_person_attending_event_light_green);
                        imageView.setTag("attending event");
                    } else {
                        imageView.setImageResource(R.drawable.ic_person_plus_black_attend_event);
                        imageView.setTag("attend event");
                    }
                }

                @Override
                public void onCancelled(@NonNull DatabaseError databaseError) {

                }
            });
        }

        private void number_of_people_attending_event(final TextView number_of_people, String postid) {
            DatabaseReference reference = FirebaseDatabase.getInstance().getReference().child("Attending Event").child(postid);

            reference.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                    number_of_people.setText(dataSnapshot.getChildrenCount() + "");
                }

                @Override
                public void onCancelled(@NonNull DatabaseError databaseError) {

                }
            });
        }

        private void publisherInfo(final ImageView image_profile, final TextView username, String userid) {
            DatabaseReference reference = FirebaseDatabase.getInstance().getReference("Users").child(userid);

            reference.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                    User user = dataSnapshot.getValue(User.class);
                    Glide.with(mContext).load(user.getImageurl()).into(image_profile);
                    username.setText(user.getUsername());

                }

                @Override
                public void onCancelled(@NonNull DatabaseError databaseError) {

                }
            });
        }

        private void isSaved(final String postid, final ImageView imageView) {
            FirebaseUser firebaseUser = FirebaseAuth.getInstance().getCurrentUser();

            DatabaseReference reference = FirebaseDatabase.getInstance().getReference().child("Saves").child(firebaseUser.getUid());
            reference.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                    if (dataSnapshot.child(postid).exists()) {
                        imageView.setImageResource(R.drawable.ic_bookmark_darker_version);
                        imageView.setTag("saved");
                    } else {
                        imageView.setImageResource(R.drawable.ic_save_hollow);
                        imageView.setTag("save");
                    }
                }

                @Override
                public void onCancelled(@NonNull DatabaseError databaseError) {

                }
            });
        }

        //Editing Event
        private void editPost(final String postid) {
            AlertDialog.Builder alertDialog = new AlertDialog.Builder(mContext);
            alertDialog.setTitle("Edit Event");

            final EditText editText = new EditText(mContext);
            LinearLayout.LayoutParams linearLayoutParams = new LinearLayout.LayoutParams(
                    LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.MATCH_PARENT);

            editText.setLayoutParams(linearLayoutParams);
            alertDialog.setView(editText);

            getText(postid, editText);

            alertDialog.setPositiveButton("Edit",
                    new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int which) {

                            HashMap<String, Object> hashMap = new HashMap<>();
                            hashMap.put("description", editText.getText().toString());

                            FirebaseDatabase.getInstance().getReference("Posts")
                                    .child(postid).updateChildren(hashMap);
                        }
                    });
            alertDialog.setNegativeButton("Cancel",
                    new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int which) {
                            dialog.dismiss();
                        }
                    });
            alertDialog.show();
        }

        private void getText(String postid, final EditText editText) {
            DatabaseReference reference = FirebaseDatabase.getInstance().getReference("Posts").child(postid);
            reference.addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                    editText.setText(dataSnapshot.getValue(Post.class).getDescription());
                }

                @Override
                public void onCancelled(@NonNull DatabaseError databaseError) {

                }
            });
        }
    }


[![screenshot_timestamp][1]][1]


  [1]: /image/TZfI7.png

Answer 1

您收到该错误是因为您尝试使用在 setupWidgets() 方法中不可见的变量。您的 timestamp 变量在您的 ViewHolder 类中仅可见。那是它的范围。看，您只能在不能在类外使用的构造函数中使用该变量。要解决这个问题，您可以将这些方法移动到您的 ViewHolder 类中，或者在调用它们时将其作为参数传递。