RecyclerView不会在第一次启动时加载项目 [英] RecyclerView doesn't load items on first start of activity

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本文介绍了RecyclerView不会在第一次启动时加载项目的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

每次我们打开这个回收器适配器的活动，它都无法在第一次尝试时加载。退出活动并重新进入修复问题。例如，这是一个GIF。 https://gyazo.com/32dc664dd427ef1129704a09861a3708



我产卵的项目：

 <？xml version =1.0encoding =utf-8？> 
< LinearLayout xmlns：android =http://schemas.android.com/apk/res/android
 xmlns：app =http://schemas.android.com/apk/res -auto
 xmlns：card_view =http://schemas.android.com/tools
 android：id =@ + id / show_chat_single_item_layout
 android：layout_width =match_parent 
 android：layout_height =wrap_content
 android：orientation =horizo​​ntal> 
 
 android.support.v7.widget.CardView 
 android：layout_width =match_parent
 android：layout_height =70dp
 
 app ：cardBackgroundColor =＃dcdada
 app：cardCornerRadius =0dp
 app：contentPadding =3dp
 card_view：cardCornerRadius =5dp
 card_view：cardElevation =2dp 
 card_view：cardUseCompatPadding =true> 
 
< android.support.constraint.ConstraintLayout 
 android：layout_width =match_parent
 android：layout_height =wrap_content> 
 
 $ {
 
 $ android 
 $ android $ android $ layout bash $ $ b android：layout_marginBottom =8dp
 android：layout_marginLeft =8dp
 android：layout_marginTop =8dp
 app：layout_constraintBottom_toBottomOf =parent
 app：layout_constraintLeft_toLeftOf = parent
 app：layout_constraintTop_toTopOf =parent
 app：srcCompat =@ mipmap / ic_launcher/> 
 
 TextView 
 android：id =@ + id / chat_persion_name
 android：layout_width =wrap_content
 android：layout_height =wrap_content
 android：layout_marginLeft =10dp
 android：layout_marginTop =0dp
 android：text =Name
 android：textSize =18sp$ b $ android：textStyle = bold
 app：layout_constraintLeft_toRightOf =@ + id / chat_persion_image
 app：layout_constraintTop_toTopOf =@ + id / chat_persion_image/> 
 
 TextView 
 android：id =@ + id / chat_persion_email
 android：layout_width =wrap_content
 android：layout_height =wrap_content
 android：layout_marginLeft =0dp
 android：layout_marginTop =8dp
 android：text =Email
 app：layout_constraintLeft_toLeftOf =@ + id / chat_persion_name
 app：layout_constraintTop_toBottomOf =@ + id / chat_persion_name/> 
 < /android.support.v7.widget.CardView> 
< / LinearLayout>

我的对话版面： 

 <？xml version =1.0encoding =utf-8？> 
< RelativeLayout xmlns：android =http://schemas.android.com/apk/res/android
 xmlns：app =http://schemas.android.com/apk/res -auto
 android：id =@ + id / msgs_content
 android：layout_width =match_parent
 android：layout_height =match_parent
 android：orientation =vertical 
 app：theme =@ style / AppTheme2
 
> 
 
 
< android.support.v7.widget.RecyclerView 
 
 android：id =@ + id / active_chats
 android：layout_width = match_parent
 android：layout_height =510dp
 android：layout_alignParentBottom =true
 android：layout_alignParentTop =true
 android：layout_centerHorizo​​ntal =true
 android：layout_marginLeft =2dp
 android：layout_marginRight =2dp
 android：layout_marginTop =57dp> 
 
 
< /android.support.v7.widget.RecyclerView> 
 
 $ b $ include 
 android：id =@ + id / include2
 layout =@ layout / toolbar
 android：layout_width = match_parent
 android：layout_height =wrap_content
 
 /> 
 
 
< / RelativeLayout>

我的适配器：

  public class ActiveChatConvo extends RecyclerView.Adapter< ActiveChatConvo.ViewHolder> 
 {
 private ArrayList< User> mUsers; 
 private Context mContext; 
 
 public ActiveChatConvo（ArrayList< User> photos，Context dick）{
 mUsers = photos; 
 mContext = dick; 
} 
 
 private Context getContext（）{
 return mContext; 
 
 $ b @Override 
 public ActiveChatConvo.ViewHolder onCreateViewHolder（ViewGroup parent，int viewType）{
 Context context = parent.getContext（）; 
 LayoutInflater inflater = LayoutInflater.from（context）; 
 
 //膨胀自定义布局
查看contactView = inflater.inflate（R.layout.chat_single_item，parent，false）; 
 
 //返回一个新的持有者实例
 ViewHolder viewHolder = new ViewHolder（contactView）; 
返回viewHolder; 
 
 $ b @Override 
 public void onBindViewHolder（ViewHolder holder，int position）{
 //获取基于位置的数据模型
 User user = mUsers.get（位置）; 
 
 //根据您的视图和数据模型设置项目视图
 TextView name = holder.mItemName; 
 name.setText（user.getName（））; 
 TextView description = holder.mItemDescription; 
 description.setText（user.getEmail（））; 
 ImageView pic = holder.mItemImage; （pic.getContext（））。load（Uri.parse（user.getPic（）））。into（pic）; 
 Picasso.with（pic.getContext（） 
 
 
 $ b @Override 
 public int getItemCount（）{
 return mUsers.size（）; 
 
 
 public static class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
 $ b $ private ImageView mItemImage; 
私人TextView mItemName; 
私人TextView mItemDescription; 
私有的LinearLayout布局; 
 final LinearLayout.LayoutParams params; 
 
 
 public ViewHolder（View v）{
 super（v）; 
 
 mItemImage =（ImageView）v.findViewById（R.id.chat_persion_image）; 
 mItemName =（TextView）v.findViewById（R.id.chat_persion_name）; 
 mItemDescription =（TextView）v.findViewById（R.id.chat_persion_email）; 
 layout =（LinearLayout）itemView.findViewById（R.id.show_chat_single_item_layout）; 
 params = new LinearLayout.LayoutParams（ViewGroup.LayoutParams.MATCH_PARENT，ViewGroup.LayoutParams.WRAP_CONTENT）; 
 v.setOnClickListener（this）; 
 
 
 @Override 
 public void onClick（View v）{
 Context context = itemView.getContext（）; 
 Intent showChatIntent = new Intent（context，ChatConversationActivity.class）; 
 //showPhotoIntent.putExtra(PHOTO_KEY，mPhoto）; 
 context.startActivity（showChatIntent）; 
 
 
 
 
 
我的主类
  public class ConnectionsActivity extends AppCompatActivity {
 
 private Toolbar toolbar; 
私人ViewPager mViewPager; 
私人TextView person_name，person_email; 
私人RecyclerView recyclerView; 
 private DatabaseReference mRef; 
私有LinearLayoutManager mLinearLayoutManager; 
 private ArrayList< User>用户; 
 private FirebaseAuth mAuth; 
 
 @Override 
 protected void onCreate（Bundle savedInstanceState）{
 super.onCreate（savedInstanceState）; 
 
 
 setContentView（R.layout.activity_connections）; 
 
 //数据库
 mRef = FirebaseDatabase.getInstance（）。getReference（Users）; 
 mRef.keepSynced（true）; 
 
 mAuth = FirebaseAuth.getInstance（）; 
 FirebaseUser user = mAuth.getCurrentUser（）; 
 
 users = new ArrayList<>（）; 
 
 $ b mRef.addListenerForSingleValueEvent（new ValueEventListener（）{
 @Override $ b $ public void onDataChange（DataSnapshot dataSnapshot）{
 if（dataSnapshot.exists（） ）
 {
 
 for（DataSnapshot postSnapshot：dataSnapshot.getChildren（））{
 String name = postSnapshot.child（Name）。getValue（String.class）; $ $ b $ String String = postSnapshot.child（Email）。 b $ b users.add（new User（name，email，pic））; 
} 
} 
 
} 
 
 @Override 
 public void onCancelled（DatabaseError databaseError）{
 $ b} 
}）; 
 
 
 
 // Recycler View 
 recyclerView =（RecyclerView）findViewById（R.id.active_chats）; 
 ActiveChatConvo适配器=新的ActiveChatConvo（用户，这）; 
 recyclerView.setAdapter（adapter）; 
 mLinearLayoutManager =新的LinearLayoutManager（this）; 
 //mLinearLayoutManager.setStackFromEnd(true）; 
 recyclerView.setLayoutManager（mLinearLayoutManager）; 
 
 // VIEWS 
 
 toolbar =（工具栏）findViewById（R.id.tToolbar）; 
 if（toolbar！= null）
 setSupportActionBar（toolbar）; 
 
 ImageView profileActivity =（ImageView）toolbar.findViewById（R.id.action_profile）; 
 ImageView homeActivity =（ImageView）toolbar.findViewById（R.id.action_home）; 
 
 profileActivity.setOnClickListener（new View.OnClickListener（）{
 
 @Override 
 public void onClick（View v）{
 Intent profileActivity = new Intent （ConnectionsActivity.this，ProfileActivity.class）; 
 startActivity（profileActivity）; 
 finish（）; 
 overridePendingTransition（R.anim.push_right_in，R.anim.push_right_out）; 
 } 
 
}）; 
 
 homeActivity.setOnClickListener（new View.OnClickListener（）{
 
 @Override 
 public void onClick（View v）{
 Intent home = new Intent （ConnectionsActivity.this，HomeActivity.class）; 
 startActivity（home）; 
 finish（）; 
 overridePendingTransition（R.anim.push_right_in，R.anim.push_right_out）; 
 } 
 
}）; 
} 
 
 
 
 
 
 
 $ b} 
  
因此，如果recyclerView Activity是我访问的第一个活动，那么它将不会创建这些项目。 Firebase是同步的，所以它不会阻塞你的应用程序的主线程，这意味着你的应用程序继续执行，你需要通过在之后使用 adapter.notifiyDatasetChanged（）来完成他的工作之后通知适配器循环
 
Everytime we open the activity that bares the recycler adapter it fails to load on the first try. Exiting the activity and re-entering fixes the problem. Here is a gif for example. https://gyazo.com/32dc664dd427ef1129704a09861a3708



The Item i am spawning in:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:card_view="http://schemas.android.com/tools"
    android:id="@+id/show_chat_single_item_layout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal">

    <android.support.v7.widget.CardView
        android:layout_width="match_parent"
        android:layout_height="70dp"

        app:cardBackgroundColor="#dcdada"
        app:cardCornerRadius="0dp"
        app:contentPadding="3dp"
        card_view:cardCornerRadius="5dp"
        card_view:cardElevation="2dp"
        card_view:cardUseCompatPadding="true">

        <android.support.constraint.ConstraintLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

            <ImageView
                android:id="@+id/chat_persion_image"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginBottom="8dp"
                android:layout_marginLeft="8dp"
                android:layout_marginTop="8dp"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintLeft_toLeftOf="parent"
                app:layout_constraintTop_toTopOf="parent"
                app:srcCompat="@mipmap/ic_launcher" />

            <TextView
                android:id="@+id/chat_persion_name"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginLeft="10dp"
                android:layout_marginTop="0dp"
                android:text="Name"
                android:textSize="18sp"
                android:textStyle="bold"
                app:layout_constraintLeft_toRightOf="@+id/chat_persion_image"
                app:layout_constraintTop_toTopOf="@+id/chat_persion_image" />

            <TextView
                android:id="@+id/chat_persion_email"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginLeft="0dp"
                android:layout_marginTop="8dp"
                android:text="Email"
                app:layout_constraintLeft_toLeftOf="@+id/chat_persion_name"
                app:layout_constraintTop_toBottomOf="@+id/chat_persion_name" />
        </android.support.constraint.ConstraintLayout>
    </android.support.v7.widget.CardView>
</LinearLayout>

My conversation layout:
<?xml version="1.0" encoding="utf-8"?>
    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:id="@+id/msgs_content"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        app:theme="@style/AppTheme2"

        >


        <android.support.v7.widget.RecyclerView

            android:id="@+id/active_chats"
            android:layout_width="match_parent"
            android:layout_height="510dp"
            android:layout_alignParentBottom="true"
            android:layout_alignParentTop="true"
            android:layout_centerHorizontal="true"
            android:layout_marginLeft="2dp"
            android:layout_marginRight="2dp"
            android:layout_marginTop="57dp">


        </android.support.v7.widget.RecyclerView>


        <include
            android:id="@+id/include2"
            layout="@layout/toolbar"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"

            />


    </RelativeLayout>

My Adapter:
public class ActiveChatConvo extends RecyclerView.Adapter<ActiveChatConvo.ViewHolder>
{
    private ArrayList<User> mUsers;
    private Context mContext;

    public ActiveChatConvo(ArrayList<User> photos,Context dick) {
        mUsers = photos;
        mContext = dick;
    }

    private Context getContext() {
        return mContext;
    }

    @Override
    public ActiveChatConvo.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        Context context = parent.getContext();
        LayoutInflater inflater = LayoutInflater.from(context);

        // Inflate the custom layout
        View contactView = inflater.inflate(R.layout.chat_single_item, parent, false);

        // Return a new holder instance
        ViewHolder viewHolder = new ViewHolder(contactView);
        return viewHolder;
    }

    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        // Get the data model based on position
        User user = mUsers.get(position);

        // Set item views based on your views and data model
        TextView name = holder.mItemName;
        name.setText(user.getName());
        TextView description = holder.mItemDescription;
        description.setText(user.getEmail());
        ImageView pic = holder.mItemImage;
        Picasso.with(pic.getContext()).load(Uri.parse(user.getPic())).into(pic);

    }

    @Override
    public int getItemCount() {
        return mUsers.size();
    }

    public static class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

        private ImageView mItemImage;
        private TextView mItemName;
        private TextView mItemDescription;
        private LinearLayout layout;
        final LinearLayout.LayoutParams params;


        public ViewHolder(View v) {
            super(v);

            mItemImage = (ImageView) v.findViewById(R.id.chat_persion_image);
            mItemName = (TextView) v.findViewById(R.id.chat_persion_name);
            mItemDescription = (TextView) v.findViewById(R.id.chat_persion_email);
            layout = (LinearLayout) itemView.findViewById(R.id.show_chat_single_item_layout);
            params = new LinearLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT);
            v.setOnClickListener(this);
        }

        @Override
        public void onClick(View v) {
            Context context = itemView.getContext();
            Intent showChatIntent = new Intent(context, ChatConversationActivity.class);
            //showPhotoIntent.putExtra(PHOTO_KEY, mPhoto);
            context.startActivity(showChatIntent);
        }
    }
}

My main class
public class ConnectionsActivity extends AppCompatActivity {

    private Toolbar toolbar;
    private ViewPager mViewPager;
    private TextView person_name,person_email;
    private RecyclerView recyclerView;
    private DatabaseReference mRef;
    private LinearLayoutManager mLinearLayoutManager;
    private ArrayList<User> users;
    private FirebaseAuth mAuth;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);


        setContentView(R.layout.activity_connections);

        //Database
        mRef = FirebaseDatabase.getInstance().getReference("Users");
        mRef.keepSynced(true);

        mAuth = FirebaseAuth.getInstance();
        FirebaseUser user = mAuth.getCurrentUser();

        users = new ArrayList<>();


        mRef.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                if (dataSnapshot.exists())
                {

                    for (DataSnapshot postSnapshot: dataSnapshot.getChildren()) {
                        String name = postSnapshot.child("Name").getValue(String.class);
                        String email = postSnapshot.child("Email").getValue(String.class);
                        String pic = postSnapshot.child("image").getValue(String.class);

                        users.add(new User(name,email,pic));
                    }
                }

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });



        //Recycler View
        recyclerView = (RecyclerView)findViewById(R.id.active_chats);
        ActiveChatConvo adapter = new ActiveChatConvo(users,this);
        recyclerView.setAdapter(adapter);
        mLinearLayoutManager = new LinearLayoutManager(this);
        //mLinearLayoutManager.setStackFromEnd(true);
        recyclerView.setLayoutManager(mLinearLayoutManager);

        //VIEWS

        toolbar = (Toolbar) findViewById(R.id.tToolbar);
        if (toolbar != null)
            setSupportActionBar(toolbar);

        ImageView profileActivity = (ImageView) toolbar.findViewById(R.id.action_profile);
        ImageView homeActivity = (ImageView) toolbar.findViewById(R.id.action_home);

        profileActivity.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                Intent profileActivity = new Intent(ConnectionsActivity.this, ProfileActivity.class);
                startActivity(profileActivity);
                finish();
                overridePendingTransition(R.anim.push_right_in, R.anim.push_right_out);
            }

        });

        homeActivity.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                Intent home = new Intent(ConnectionsActivity.this, HomeActivity.class);
                startActivity(home);
                finish();
                overridePendingTransition(R.anim.push_right_in, R.anim.push_right_out);
            }

        });
    }







    }

So if the recyclerView Activity is the first activity I visit then it will not create the items. 
 解决方案 
Firebase is synchronize so it doesn't block the main thread of your application, that mean that your application continue executing, you need to notify the adapter after firebase finishing his job by using adapter.notifiyDatasetChanged() after the for loop


                        
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