如何将数据从 Firebase 检索到我的适配器 [英] How can I retrieve data from Firebase to my adapter

问题描述

我的结构

所以我有一个应用程序，用户可以在其中上传我的适配器中的帖子.我可以检索帖子描述和帖子图片，但是当我尝试检索海报的名称时，应用程序似乎崩溃了，要检索每个帖子的名称，数据库中会添加一个带有上传者 ID 的子项.这是我的类文件:

So I have an app in which users upload posts in my adapter. I can retrieve the post description and the post picture, but when I try to retrieve the poster's name the app seems to crash, to retrieve the name with every post there is a child added to the database with the uploader's id. This is my class file:

public String image_thumb;
public String user_id;
public String image_url;
public String desc;

public BlogPost(){}


public BlogPost(String user_id, String image_url, String desc, String image_thumb) {
    this.user_id = user_id;
    this.image_url = image_url;
    this.desc = desc;
    this.image_thumb = image_thumb;
}



public String getUser_id() {
    return user_id;
}

public void setUser_id(String user_id) {
    this.user_id = user_id;
}

public String getImage_url() {
    return image_url;
}

public void setImage_url(String image_url) {
    this.image_url = image_url;
}

public String getDesc() {
    return desc;
}

public void setDesc(String desc) {
    this.desc = desc;
}

public String getImage_thumb() {
    return image_thumb;
}

public void setImage_thumb(String image_thumb) {
    this.image_thumb = image_thumb;
}

这是我的一些适配器:

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

    String desc_data = blog_list.get(position).getDesc();
    holder.setDescText(desc_data);//this works

    String image_url = blog_list.get(position).getImage_url();
    holder.setBlogImage(image_url);//this works

    String user_id = blog_list.get(position).getUser_id();
    firebaseDatabase.child("Users").child(user_id).addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            if(dataSnapshot.exists()){
                String userName = dataSnapshot.child("name").getValue().toString();

                holder.setUserName(userName);
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
    public void setUserName(String name){
        blogUserName = mView.findViewById(R.id.blog_user_name);
        blogUserName.setText(name);
    }

我基本上想做的是在 user_id 中查找名称并在我的 TextView

What I basically wanna do is look inside the user_id for the name and retrieve it inside my TextView

推荐答案

为了使其正常工作，我建议您对模型类以及代码进行一些更改.您的模型类应如下所示:

In order to make it work correctly, I recommend you to do some changes in you model class as well as in your code. Your model class should look like:

public class BlogPost {
    public String imageThumb, userId, imageUrl, desc;

    public BlogPost() {}

    public BlogPost(String imageThumb, String userId, String imageUrl, String desc) {
        this.imageThumb = imageThumb;
        this.userId = userId;
        this.imageUrl = imageUrl;
        this.desc = desc;
    }

    public String getImageThumb() {return imageThumb;}
    public String getUserId() {return userId;}
    public String getImageUrl() {return imageUrl;}
    public String getDesc() {return desc;}
}

请参阅字段和 getter 的命名约定.

Please see the naming convention of the fields and getters.

为了使它工作，不要忘记删除旧数据并添加新数据.

In order to make it work, don't forget the remove the old data and add fresh one.

假设您的活动有一个 .XML 文件，其中包含一个 RecyclerView，如下所示:

Assuming your have a .XML file for your activity that contains a RecyclerView which looks like this:

<android.support.v7.widget.RecyclerView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/recycler_view"/>

还有一个用于您的项目文件的 .XML 文件，如下所示:

And a .XML file for your item file, which looks like this:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/image_thumb_text_view" />

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/user_id_text_view" />

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/image_url_text_view" />

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/desc_text_view" />
</LinearLayout>

要使用 FriebaseRecyclerAdapter 在 RecyclerView 中显示您的数据，请按照以下步骤操作:

To display your data in a RecyclerView using a FriebaseRecyclerAdapter, please follow the next steps:

首先，您需要在您的 Activity 中找到 RecyclerView 并像这样设置 LinearLayoutManager:

First, you need to find the RecyclerView in your activity and set the LinearLayoutManager like this:

RecyclerView recyclerView = findViewById(R.id.recycler_view);
recyclerView.setLayoutManager(new LinearLayoutManager(this));

然后您需要创建 Firebase 数据库的根引用和一个 Query 对象，如下所示:

Then you need to create the root reference of your Firebase database and a Query object like this:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
Query query = rootRef.child("Users");

然后你必须像这样创建一个 FirebaseRecyclerOptions 对象:

Then you'll have to create a FirebaseRecyclerOptions object like this:

FirebaseRecyclerOptions<BlogPost> firebaseRecyclerOptions = new FirebaseRecyclerOptions.Builder<BlogPost>()
        .setQuery(query, BlogPost.class)
        .build();

在您的活动类中，创建一个 holder 类，如下所示:

In your activity class, create a holder class that looks like this:

private class BlogPostHolder extends RecyclerView.ViewHolder {
    private TextView imageThumbtextView, userIdTextView, imageUrlTextView, descTextView;

    BlogPostHolder(View itemView) {
        super(itemView);
        imageThumbtextView = itemView.findViewById(R.id.image_thumb_text_view);
        userIdTextView = itemView.findViewById(R.id.user_id_text_view);
        imageUrlTextView = itemView.findViewById(R.id.image_url_text_view);
        descTextView = itemView.findViewById(R.id.desc_text_view);
    }

    void setBlogPost(BlogPost blogPost) {
        String imageThumb = blogPost.getImageThumb();
        imageThumbtextView.setText(imageThumb);
        String userId = blogPost.getUserId();
        userIdTextView.setText(userId);
        String imageUrl = blogPost.getImageUrl();
        imageUrlTextView.setText(imageUrl);
        String desc = blogPost.getDesc();
        descTextView.setText(desc);
    }
}

然后创建一个声明为全局的适配器:

Then create an adapter which is declared as global:

private FirebaseRecyclerAdapter<BlogPost, BlogPostHolder> firebaseRecyclerAdapter;

并在您的 Activity 中实例化它，如下所示:

And instantiate it in your activity like this:

firebaseRecyclerAdapter = new FirebaseRecyclerAdapter<BlogPost, BlogPostHolder>(firebaseRecyclerOptions) {
    @Override
    protected void onBindViewHolder(@NonNull BlogPostHolder blogPostHolder, int position, @NonNull BlogPost blogPost) {
        blogPostHolder.setBlogPost(blogPost);
    }

    @Override
    public BlogPostHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item, parent, false);

        return new BlogPostHolder(view);
    }
};
recyclerView.setAdapter(firebaseRecyclerAdapter);

最后不要忘记覆盖以下两个方法并开始监听变化:

In the end, don't forget to override the following two methods and start listening for changes:

@Override
protected void onStart() {
    super.onStart();
    firebaseRecyclerAdapter.startListening();
}

@Override
protected void onStop() {
    super.onStop();

    if (firebaseRecyclerAdapter!= null) {
        firebaseRecyclerAdapter.stopListening();
    }
}

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