FirebaseRecyclerAdapter - populateViewHolder是不是第一次运行它的数据填充？ [英] FirebaseRecyclerAdapter - populateViewHolder is not populating the data for first time it runs?

问题描述

FirebaseRecyclerAdapter - populateViewHolder 第一次运行时没有填充数据，但是当我关闭应用程序，打开它，数据绑定在 RecyclerView 查看持有人。

我不明白为什么数据不填充第一次，它显示空白屏幕

这是我的 MainActivity

  mDatabase = FirebaseDatabase.getInstance（）。getReference（）; 
 // [END create_database_reference] 
 
 mRecycler =（RecyclerView）findViewById（R.id.recycler_view）; 
 mRecycler.setHasFixedSize（true）; 
 setSupportActionBar（toolbar）; 
 final LinearLayoutManager layoutManager = new LinearLayoutManager（getApplicationContext（））; 
 layoutManager.setOrientation（LinearLayoutManager.VERTICAL）; 
 layoutManager.setReverseLayout（true）; 
 layoutManager.setStackFromEnd（true）; 
 mRecycler.setLayoutManager（layoutManager）; 
 
 
 
 $ b //使用Query 
设置FirebaseRecyclerAdapter //查询postsQuery = mDatabase.child（EN）。child（Courses ）; 
 DatabaseReference ref = FirebaseDatabase.getInstance（）。getReference（）。child（EN）。child（Courses）; 
 ref.addListenerForSingleValueEvent（new ValueEventListener（）{
 @Override $ b $ public void onDataChange（DataSnapshot dataSnapshot）{
 Toast.makeText（MainActivity.this，dataSnapshot.toString（），Toast .LENGTH_SHORT）.show（）; 
} 
 $ b $ @覆盖
 public void onCancelled（DatabaseError databaseError）{
 Toast.makeText（MainActivity.this，databaseError.toString （），Toast.LENGTH_SHORT）.show（）; 
} 
}）; 
 Log.d（ref，String.valueOf（ref））; 
 // Log.d（Query，String.valueOf（postsQuery））; 
 mAdapter = new FirebaseRecyclerAdapter< Course，CourseViewHolder>（Course.class，R.layout.item_home，
 CourseViewHolder.class，ref）{
 @Override 
 protected void populateViewHolder（final CourseViewHolder viewHolder，final Course model，final int position）{
 viewHolder.bindToPost（model）; 
} 
 
}; 
 mRecycler.setAdapter（mAdapter）; 
  

和 ViewHolder

  public class CourseViewHolder extends RecyclerView.ViewHolder {
 
 public TextView titleView; 
 public TextView descriptionView; 
 public ImageView IconView; 
 public TextView lessonCountView; 
 
 
 public CourseViewHolder（查看itemView）{
 super（itemView）; 
 
 titleView =（TextView）itemView.findViewById（R.id.title）; 
 descriptionView =（TextView）itemView.findViewById（R.id.description）; 
 // IconView =（ImageView）itemView.findViewById（R.id.star）; 
 
 
 public void bindToPost（Course post）{
 // Log.d（Post，String.valueOf（post））; 
 titleView.setText（post.getName（））; 
 descriptionView.setText（post.getDescription（））; 
 
 
 $ b  

My Model Pojo

  public class Course {
 
 public String description; 
 public String title; 
 $ b $ public Course（）{
 //调用DataSnapshot.getValue（Post.class）所需的默认构造函数
} 
 
 public Course（String标题，字符串描述）{
 // this.description = author; 
 this.title = title; 
 this.description = description; 
} 
 
 public String getName（）{
 return title; 
} 
 
 public String getDescription（）{
 return description; 
 
 
 
 $ div $解析方案

找到
$ b $问题是 RecyclerView 的高度 wrap_content 。所以请确保您的 RecyclerView 高度设置为 match_parent 。



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




FirebaseRecyclerAdapter - populateViewHolder is not populating the data for the first time it runs but when I closed the app and opened it, the data is binded in RecyclerView View Holder.

I am not getting why data is not populating for first time, it is showing blank screen

Here's my MainActivity

mDatabase = FirebaseDatabase.getInstance().getReference();
// [END create_database_reference]

mRecycler = (RecyclerView) findViewById(R.id.recycler_view);
mRecycler.setHasFixedSize(true);
setSupportActionBar(toolbar);
final LinearLayoutManager layoutManager = new LinearLayoutManager(getApplicationContext());
layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
layoutManager.setReverseLayout(true);
layoutManager.setStackFromEnd(true);
mRecycler.setLayoutManager(layoutManager);




// Set up FirebaseRecyclerAdapter with the Query
//Query postsQuery = mDatabase.child("EN").child("Courses") ;
DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child("EN").child("Courses");
ref.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        Toast.makeText(MainActivity.this, dataSnapshot.toString(), Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        Toast.makeText(MainActivity.this, databaseError.toString(), Toast.LENGTH_SHORT).show();
    }
});
Log.d("ref", String.valueOf(ref));
//   Log.d("Query", String.valueOf(postsQuery));
mAdapter = new FirebaseRecyclerAdapter<Course, CourseViewHolder>(Course.class, R.layout.item_home,
        CourseViewHolder.class, ref) {
    @Override
    protected void populateViewHolder(final CourseViewHolder viewHolder, final Course model, final int position) {
        viewHolder.bindToPost(model);
    }

};
mRecycler.setAdapter(mAdapter);

And the ViewHolder

public class CourseViewHolder extends RecyclerView.ViewHolder {

    public TextView titleView;
    public TextView descriptionView;
    public ImageView IconView;
    public TextView lessonCountView;


    public CourseViewHolder(View itemView) {
        super(itemView);

        titleView = (TextView) itemView.findViewById(R.id.title);
        descriptionView = (TextView) itemView.findViewById(R.id.description);
        //IconView = (ImageView) itemView.findViewById(R.id.star);
    }

    public void bindToPost(Course post) {
      //  Log.d("Post", String.valueOf(post));
        titleView.setText(post.getName());
        descriptionView.setText(post.getDescription());

    }
}

My Model Pojo

public class Course {

    public String description;
    public String title;

    public Course() {
        // Default constructor required for calls to DataSnapshot.getValue(Post.class)
    }

    public Course(String title, String description) {
      //  this.description = author;
        this.title = title;
        this.description =description;
    }

    public String getName() {
        return title;
    }

    public String getDescription() {
        return description;
    }
}

解决方案

Found the Solution.

The Problem is RecyclerView had a height of wrap_content. So Please make sure your RecyclerView height is set to match_parent. This will fix this issue.

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

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