RecyclerView 不会在活动第一次开始时加载项目 [英] RecyclerView doesn't load items on first start of activity

问题描述

每次我们打开暴露回收器适配器的活动时，它在第一次尝试时都无法加载.退出活动并重新进入可解决问题.例如，这是一个 gif.https://gyazo.com/32dc664dd427ef1129704a09861a3708

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

我生成的物品:

<?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>

我的对话布局:

<?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>

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;
    }

    @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);
        }
    }
}

我的主课

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);
            }

        });
    }







    }

因此，如果 recyclerView Activity 是我访问的第一个 Activity，则它不会创建项目.

So if the recyclerView Activity is the first activity I visit then it will not create the items.

推荐答案

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，你需要在 firebase 完成后通知适配器他的工作是在 for 循环

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

这篇关于RecyclerView 不会在活动第一次开始时加载项目的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！