如何从Firebase子节点中检索时间戳，Android版。

huangapple
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英文:

How to retrieve time stamp from Firebase child Android

问题

以下是翻译好的内容：

我正在创建一个社交应用，当有人上传帖子时，上传帖子的时间也被记录下来。

我想要获取帖子上传的日期和时间，并以适当的形式展示给用户。例如，如果是在2小时前上传的，它将显示为"2小时前"，而不是完整的上传日期和时间，或上传日期的时间戳。那么，我应该如何展示它，哪种方式最简单？

这段代码：

  1. Post post = dataSnapshot.getValue(Post.class);
  2. dateAdded.setText(post.getDate_time());

我得到了这个错误：

java.lang.NullPointerException: 尝试在空对象引用上调用虚拟方法'java.lang.String com.example.gone.Model.Post.getDate_time()'

所以，如果有人知道如何实现这个，请帮助我一下，谢谢。

编辑---

我想要显示日期/时间的方法 -

  1. private void getDate(TextView dateAdded) {
  2.     DatabaseReference reference = FirebaseDatabase.getInstance().getReference().child("Posts").child("date_time");
  3.     reference.addValueEventListener(new ValueEventListener() {
  4.         @Override
  5.         public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
  6.             Post post = dataSnapshot.getValue(Post.class);
  7.             dateAdded.setText(post.getDate_time());
  8.         }
  10.         @Override
  11.         public void onCancelled(@NonNull DatabaseError error) {
  12.         }
  13.     });
  14. }

Post类：

  1. private String date_time;
  3. public String getDate_time() {
  4.     return date_time;
  5. }
  7. public void setDate_time(String date_time) {
  8.     this.date_time = date_time;
  9. }
  11. public Post(String date_time) {
  12.     this.date_time = date_time;
  13. }

JSON节点：

  1. "Posts" : {
  2.     "-MJ-VvX8zPdt2DY0pVqb" : {
  3.         "date_time" : "01-10-2020 22:17:43",
  4.         "description" : "",
  5.         "postid" : "-MJ-VvX8zPdt2DY0pVqb",
  6.         "postimage" : "https://firebasestorage.googleapis.com/v0/b/gone-b14f5.appspot.com/o/posts%2F1602031430356.null?alt=media&token=dc7c4a5c-d652-44be-bb2a-28283964da1e",
  7.         "publisher" : "gIt685Xex8eZaPBSsbcPbU1S5V93"
  8.     },
  9.     // 其他帖子的信息...
  10. }
英文:

I am creating a social app and when someone uploads a post the time they uploaded the post is also uploaded.

I want to get the date and time it was uploaded and show it to the user in a proper form. For example if it was uploaded 2 hours ago it will say 2hr instead of the entire date and time it was uploaded or the time stamp of the uploaded date. So how do I show it and which was is easiest ?

如何从Firebase子节点中检索时间戳，Android版。

This code:

  1. Post post = dataSnapshot.getValue(Post.class);
  2. dateAdded.setText(post.getDate_time());

I get this error:

> java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.example.gone.Model.Post.getDate_time()' on a null object reference

So if someone has a way of doing this can someone please help me ? Thanks

EDIT ---

The method where I want to show the date/time -

  1. private void getDate(TextView dateAdded) {
  3.     DatabaseReference reference = FirebaseDatabase.getInstance().getReference().child("Posts").child("date_time");
  4.     reference.addValueEventListener(new ValueEventListener() {
  5.         @Override
  6.         public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
  8.             //dateAdded.setText((CharSequence) dataSnapshot.child("date_time"));
  9.             Post post = dataSnapshot.getValue(Post.class);
  10.             dateAdded.setText(post.getDate_time());
  11.         }
  13.         @Override
  14.         public void onCancelled(@NonNull DatabaseError error) {
  15.         }
  16.     });
  17. }

Post.class:

  1. private String date_time;
  3. public String getDate_time() {
  4.     return date_time;
  5. }
  7. public void setDate_time(String date_time) {
  8.     this.date_time = date_time;
  9. }
  11. public Post(String date_time) {
  12.     this.date_time = date_time;
  13. }

JSON node:

  1.     "Posts" : {
  2.     "-MJ-VvX8zPdt2DY0pVqb" : {
  3.       "date_time" : "01-10-2020 22:17:43",
  4.       "description" : "",
  5.       "postid" : "-MJ-VvX8zPdt2DY0pVqb",
  6.       "postimage" : "https://firebasestorage.googleapis.com/v0/b/gone-b14f5.appspot.com/o/posts%2F1602031430356.null?alt=media&token=dc7c4a5c-d652-44be-bb2a-28283964da1e",
  7.       "publisher" : "gIt685Xex8eZaPBSsbcPbU1S5V93"
  8.     },
  9.     "-MJ-qP4mKkkXCTGQeqhq" : {
  10.       "date_time" : "06-10-2020 22:17:43",
  11.       "description" : "",
  12.       "postid" : "-MJ-qP4mKkkXCTGQeqhq",
  13.       "postimage" : "https://firebasestorage.googleapis.com/v0/b/gone-b14f5.appspot.com/o/posts%2F1602037062255.null?alt=media&token=5fde471b-f794-4376-8250-18c0893c716e",
  14.       "publisher" : "gIt685Xex8eZaPBSsbcPbU1S5V93"
  15.     },
  16.     "-MJUqKzwnZfC0cVRRohI" : {
  17.       "dateAdded" : "12-10-2020 22:45:41",
  18.       "date_time" : "1602557141467",
  19.       "description" : "",
  20.       "postid" : "-MJUqKzwnZfC0cVRRohI",
  21.       "postimage" : "https://firebasestorage.googleapis.com/v0/b/gone-b14f5.appspot.com/o/posts%2F1602557139321.null?alt=media&token=06af1115-481a-4c0f-8ba7-3bef13da3989",
  22.       "publisher" : "J51XZDETvNT86eCLtqU5XHUzEWu2"
  23.     }
  24.   }

答案1

得分: 1

date_time不是Posts的直接子项。请将date_time替换为-MJ-VvX8zPdt2DY0pVqb。

尝试如下：

  1. DatabaseReference reference = FirebaseDatabase
  2.     .getInstance()
  3.     .getReference()
  4.     .child("Posts")
  5.     .child("-MJ-VvX8zPdt2DY0pVqb");

更新：

要显示所有帖子，您需要使用RecyclerView。

这里是从Firebase Quickstart 中复制的代码。

  1. Query postsQuery = FirebaseDatabase
  2.     .getInstance().getReference().child("Posts").limitToFirst(100);
  4. FirebaseRecyclerOptions options = new FirebaseRecyclerOptions.Builder<Post>()
  5.     .setQuery(postsQuery, Post.class)
  6.     .build();
  8. mAdapter = new FirebaseRecyclerAdapter<Post, PostViewHolder>(options) {
  10.     @Override
  11.     public PostViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
  12.         LayoutInflater inflater = LayoutInflater.from(viewGroup.getContext());
  13.         return new PostViewHolder(inflater.inflate(R.layout.item_post, viewGroup, false));
  14.     }
  16.     @Override
  17.     protected void onBindViewHolder(PostViewHolder viewHolder, int position, final Post model) {
  18.         // model.date
  19.     }
  20. };
  21. mRecycler.setAdapter(mAdapter);

更新 2：

要显示时间：

  1. // 如果date_time是Long类型，例如：1602557141467
  2. val time = 1602557141467
  3. // 如果date_time是String类型，例如：01-10-2020 22:17:43
  4. val time = SimpleDateFormat(
  5.     "dd-MM-yyyy HH:mm:ss",
  6.     Locale.getDefault()
  7. ).parse("01-10-2020 22:17:43")?.time ?: 0
  9. val deltaTime = Date().time - time
  11. val minutes = (deltaTime / (60 * 1000)).toInt() % 60
  12. val hours = (deltaTime / (60 * 60 * 1000)).toInt() % 24
  13. val days = (deltaTime / (24 * 60 * 60 * 1000)).toInt()
  15. val result = buildString {
  16.     if (days != 0) append("${days}d ")
  17.     if (hours != 0) append("${hours}h ")
  18.     if (minutes != 0) append("${minutes}m")
  19. }
英文:

date_time is not direct child of Posts. Instead of date_time paste -MJ-VvX8zPdt2DY0pVqb.

Try like that:

  1. DatabaseReference reference = FirebaseDatabase
  2.     .getInstance()
  3.     .getReference()
  4.     .child(&quot;Posts&quot;)
  5.     .child(&quot;-MJ-VvX8zPdt2DY0pVqb&quot;);

Update:

To show all posts you need RecyclerView.

Here code that copied from Firebase Quickstart.

  1.     Query postsQuery = FirebaseDatabase
  2.         .getInstance().getReference().child(&quot;Posts&quot;).limitToFirst(100);
  4.     FirebaseRecyclerOptions options = new FirebaseRecyclerOptions.Builder&lt;Post&gt;()
  5.             .setQuery(postsQuery, Post.class)
  6.             .build();
  8.     mAdapter = new FirebaseRecyclerAdapter&lt;Post, PostViewHolder&gt;(options) {
  10.         @Override
  11.         public PostViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
  12.             LayoutInflater inflater = LayoutInflater.from(viewGroup.getContext());
  13.             return new PostViewHolder(inflater.inflate(R.layout.item_post, viewGroup, false));
  14.         }
  16.         @Override
  17.         protected void onBindViewHolder(PostViewHolder viewHolder, int position, final Post model) {
  18.             // model.date
  19.             });
  20.         }
  21.     };
  22.     mRecycler.setAdapter(mAdapter);

Update 2:

To show time:

  1.     // if date_time is Long like: 1602557141467
  2.     val time = 1602557141467
  3.     // if date_time is String like: 01-10-2020 22:17:43
  4.     val time = SimpleDateFormat(
  5.         &quot;dd-MM-yyyy HH:mm:ss&quot;,
  6.         Locale.getDefault()
  7.     ).parse(&quot;01-10-2020 22:17:43&quot;)?.time ?: 0
  9.     val deltaTime = Date().time - time
  11.     val minutes = (deltaTime / (60 * 1000)).toInt() % 60
  12.     val hours = (deltaTime / ( 60 * 60 * 1000)).toInt() % 24
  13.     val days = (deltaTime / ( 24 * 60 * 60 * 1000)).toInt()
  16.     val result = buildString {
  17.         if (days != 0) append(&quot;${days}d &quot;)
  18.         if (hours != 0) append(&quot;${hours}h &quot;)
  19.         if (minutes != 0) append(&quot;${minutes}m&quot;)
  20.     }

答案2

得分: 0

我使用Gson来转换我的数据，在build.gradle中：

  1. dependencies {
  2.     implementation 'com.google.code.gson:gson:2.8.6'
  3. }

在我的代码中：

  1. Gson gson = new Gson();
  2. JsonElement jsonElement = gson.toJsonTree(dataSnapshot.getValue());
  3. Post post = gson.fromJson(jsonElement, Post.class);
  4. dateAdded.setText(post.getDate_time());

请记得让你的Post类实现Serializable接口，以在运行时获得更好的结果：

  1. import java.io.Serializable;
  3. public class Post implements Serializable{}

因为某种原因，直接在Firebase中进行操作会失败。

英文:

I use Gson for convert my data, in build.gradle:

  1. dependencies {
  2.     implementation &#39;com.google.code.gson:gson:2.8.6&#39;
  3. }

In my code:

  1. Gson gson = new Gson();
  2. JsonElement jsonElement = gson.toJsonTree(dataSnapshot.getValue());
  3. Post post = gson.fromJson(jsonElement, Post.class);
  4. dateAdded.setText(post.getDate_time());

Remember make your Post class Serializable to have better results in runtime

  1. import java.io.Serializable;
  2. public class Post implements Serializable{}

For some reason doing it direct with Firebase fails

huangapple
  • 本文由 发表于 2020年10月14日 00:13:35
  • 转载请务必保留本文链接：https://go.coder-hub.com/64339099.html
  • android
  • firebase
  • firebase-realtime-database
  • java
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