在 android studio 中构建回收站视图时出错

Question

My problem 1:I'm using android studio to build a recycler view.However,when I run the code,this notification pop up.

My problem 2:In MainActivity.java ,an error that shown cannot find system variable Recyclerview in line 23 pop up.May I know how to solve it?becuz I declared it already.

以下是我的代码：

(MainActivity.java:)

package com.example.recyclerviewdemo;

import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.os.Bundle;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    RecyclerView recyclerView;
    List <Details> detailsList;
    MyAdapter myAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        recyclerView=findViewById(R.id.recyclerView);
        detailsList=new ArrayList<>();

        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setHasFixedSize(true);

        //passing data to model class

        for (int i=0;i<=10;i++){

            Details details=new Details("Java "+i,"This is description " +i);
            detailsList.add(details);

        }

        myAdapter=new MyAdapter(detailsList);
        recyclerView.setAdapter(myAdapter);

    }
}

---

(activity_main.xml:)

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 
xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <androidx.recyclerview.widget.RecyclerView
        android:layout_width="409dp"
        android:layout_height="729dp"
        tools:layout_editor_absoluteX="1dp"
        tools:layout_editor_absoluteY="1dp" />
</androidx.constraintlayout.widget.ConstraintLayout>

---

MyAdapter.java：

package com.example.recyclerviewdemo;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.core.widget.TextViewOnReceiveContentListener;
import androidx.recyclerview.widget.RecyclerView;

import org.jetbrains.annotations.NotNull;

import java.util.List;

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {

    private List<Details> detailsList;

    public MyAdapter(List<Details> detailsList) {
        this.detailsList = detailsList;
    }

    @NonNull
    @NotNull
    @Override
    public MyViewHolder onCreateViewHolder(@NonNull @NotNull ViewGroup parent, int viewType) {
        View view= LayoutInflater.from(parent.getContext()).inflate(
                R.layout.rv_item_list,
                parent,
                false
        );
        return new MyViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull @NotNull MyAdapter.MyViewHolder holder, int 
    position) {
        holder.tvTitle.setText(detailsList.get(position).getTitle());
        holder.tvDesc.setText(detailsList.get(position).getTitle());

    }

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

    public class MyViewHolder extends RecyclerView.ViewHolder {

        TextView tvTitle;
        TextView tvDesc;

        public MyViewHolder(@NonNull @org.jetbrains.annotations.NotNull View itemView) {
            super(itemView);

            tvTitle=itemView.findViewById(R.id.tvTitle);
            tvDesc=itemView.findViewById(R.id.tvDescription);

        }
    }
}

---

Details.java：

package com.example.recyclerviewdemo;

public class Details {

    private String title;
    private String description;

    public Details(String title, String description) {
        this.title = title;
        this.description = description;
    }

    public String getTitle() {
        return title;
    }

    public String getDescription() {
        return description;
    }
}

---

rv_item_list.xml：

<?xml version="1.0" encoding="utf-8"?>
<com.google.android.material.card.MaterialCardView 
xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    app:cardCornerRadius="5dp"
    app:cardElevation="5dp"
    android:layout_margin="5dp">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <ImageView
            android:id="@+id/imageView"
            android:layout_width="100dp"
            android:layout_height="100dp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:srcCompat="@drawable/a" />

        <TextView
            android:id="@+id/tvTitle"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="20dp"
            android:layout_marginTop="24dp"
            android:text="TextView"
            app:layout_constraintStart_toEndOf="@+id/imageView"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/tvDescription"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="20dp"
            android:layout_marginEnd="200dp"
            android:text="TextView"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toEndOf="@+id/imageView"
            app:layout_constraintTop_toBottomOf="@+id/tvTitle" />
    </androidx.constraintlayout.widget.ConstraintLayout>

</com.google.android.material.card.MaterialCardView>

Answer 1

您忘记在 XML 文件中声明 id。在您的活动 xml 中添加此 ID

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 
xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="409dp"
        android:layout_height="729dp"
        tools:layout_editor_absoluteX="1dp"
        tools:layout_editor_absoluteY="1dp" />
</androidx.constraintlayout.widget.ConstraintLayout>