Question

我能够生成一个时间戳并将其存储在Firebase Realtime Database中。但是无法弄清楚应该如何检索它并在textview中显示它。我知道它是作为一个长值检索并存储为Map 我还在模型类中创建了以下内容，但不知道下一步该怎么做。

private Map<String, String> timestamp;

发送消息的代码

    private void sendMessage(String sender, final String receiver, String message) {

        if (sender.equals(receiver)){
            Toast.makeText(MessageActivity.this,"Message Can't be sent",Toast.LENGTH_SHORT).show();
        }
        else {

            HashMap<String, Object> hashMap = new HashMap<>();
            hashMap.put("sender", sender);
            hashMap.put("receiver", receiver);
            hashMap.put("message", message);
            hashMap.put("timestamp", ServerValue.TIMESTAMP);
            hashMap.put("isseen", false);


            DatabaseReference Chatreference = FirebaseDatabase.getInstance().getReference("Chats");

            Key = Chatreference.child(ChatKey).push().getKey();
            Chatreference.child(ChatKey).child(Key).setValue(hashMap);
}

阅读邮件的代码

private void readMessages(String myid, String userid, String imageurl) {

    mChat = new ArrayList<>();

    Chatreference = FirebaseDatabase.getInstance().getReference("Chats").child(ChatKey);


    Chatreference.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
            Chat chat = dataSnapshot.getValue(Chat.class);
            if (chat.getReceiver().equals(myid) && chat.getSender().equals(userid) ||
                    chat.getReceiver().equals(userid) && chat.getSender().equals(myid)) {
                chat.setMessageId(dataSnapshot.getKey());
                mChat.add(chat);
                Log.d(TAG, "Child_Event_Listener_Called");
                Log.d(TAG, "msg " + chat.getMessage());
            }

            messageAdapter = new MessageAdapter(MessageActivity.this, mChat, imageurl);
            recyclerView.setAdapter(messageAdapter);
            messageAdapter.notifyDataSetChanged();


        }


        @Override
        public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {


        }

        @Override
        public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {

            Chat chat = dataSnapshot.getValue(Chat.class);
            chat.setMessageId(dataSnapshot.getKey());

            mChat.remove(chat);
            messageAdapter.notifyDataSetChanged();


        }

        @Override
        public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

        }

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

        }

    });

}

更新模型类

    public class Chat {
    private String sender;
    private String receiver;
    private  String message;
    private boolean isseen;
    private Map<String, String> timestamp;
    String MessageId;


    public Chat(String sender, String receiver, String message, boolean isseen, Map<String, String> timestamp) {
        this.sender = sender;
        this.receiver = receiver;
        this.message = message;
        this.isseen = isseen;
        this.timestamp = timestamp;
    }

    public Chat() {
    }

    public String getSender() {
        return sender;
    }

    public void setSender(String sender) {
        this.sender = sender;
    }

    public String getReceiver() {
        return receiver;
    }

    public void setReceiver(String receiver) {
        this.receiver = receiver;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    public String getMessageId() {
        return MessageId;
    }

    public void setMessageId(String messageId) {
        MessageId = messageId;
    }

    public boolean isIsseen() {
        return isseen;
    }

    public void setIsseen(boolean isseen) {
        this.isseen = isseen;
    }

    public Map<String, String> getTimestamp() {
        return timestamp;
    }

    public void setTimestamp(Map<String, String> timestamp) {
        this.timestamp = timestamp;
    }

    @Override
    public boolean equals(@Nullable Object obj) {
        if(obj instanceof Chat){
            Chat chat=(Chat) obj;
            return this.MessageId.equals(chat.getMessageId());}
        else
            return false;
    }
}

Answer 1

您要读取的是child中的FirebaseDatabase。以下是有关如何通过snapshot读取子元素的示例，您将从firebase获得该元素。这里的模型有所不同，因为您的数据库中将具有不同的NoSql结构。

var userId = firebase.auth().currentUser.uid;
return firebase.database().ref('/users/' + userId).once('value').then(function(snapshot) {
  var username = (snapshot.val() && snapshot.val().username) || 'Anonymous';
  // ...
});

此外，从Firebase返回的值可能是long或String，具体取决于您要存储时间戳的数据类型。看来它是以String的形式发送的。

Answer 2

首先，时间戳是一个长值而不是映射。您必须更改聊天类

//...
private boolean isseen;
private long timestamp;
String MessageId;
//...

然后您可以将时间戳转换为日期字符串，如下所示：

public static  String longToDateString(long timestamp, String format){
    return DateFormat.format(format,new Date(timestamp)).toString();
}

使用

String date = longToDateString(mChat.get(position).getTimestamp, "dd.MM.yyyyy");

或

String time = longToDateString(mChat.get(position).getTimestamp, "HH:mm");

如何从Firebase实时数据库检索时间戳并将其显示为文本视图中的日期

2 个答案: