androidx.cardview.widget.CardView 不能转换为 androidx.recyclerview.widget.RecyclerView

Question

I am making a project but when I compile my project and launch the app on Android Studio my app crashes.

In my Logcat error

Process: com.passionategeekz.learnC, PID: 5854
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.passionategeekz.learnC/com.passionategeekz.learnC.card}: java.lang.ClassCastException: androidx.cardview.widget.CardView cannot be cast to androidx.recyclerview.widget.RecyclerView
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2895)
    at android.app.ActivityThread.-wrap11(Unknown Source:0)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1616)
    at android.os.Handler.dispatchMessage(Handler.java:106)``

My card.java

  package com.passionategeekz.learnC;

    import android.os.Bundle;

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

    import java.util.ArrayList;


    public class card extends AppCompatActivity {

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


            ArrayList<model> list= new ArrayList();
            list.add(new model(model.TEXT_TYPE,"xxx",0));
            list.add(new model(model.IMAGE_TYPE,"xx",R.drawable.wtc));
            list.add(new model(model.AUDIO_TYPE,"xx",R.raw.sound));
            list.add(new model(model.IMAGE_TYPE,"xx",R.drawable.snow));

            MultiViewTypeAdapter adapter = new MultiViewTypeAdapter(list,this);
            LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this,OrientationHelper.VERTICAL,false);

            RecyclerView mRecyclerView = (RecyclerView) findViewById(R.id.recyclerView);
            mRecyclerView.setLayoutManager(linearLayoutManager);
            mRecyclerView.setItemAnimator(new DefaultItemAnimator());
            mRecyclerView.setAdapter(adapter);
        }
    }

My card.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"
    android:fitsSystemWindows="true"
    tools:context="com.passionategeekz.learnC.MainActivity">


    <androidx.cardview.widget.CardView
        android:id="@+id/recyclerView"
        android:layout_width="350dp"
        android:layout_height="447dp"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent">

    </androidx.cardview.widget.CardView>


</androidx.constraintlayout.widget.ConstraintLayout>

My Gradle:

implementation "androidx.cardview:cardview:1.0.0"
implementation 'androidx.recyclerview:recyclerview:1.1.0'

Answer 1

The problem is this row:

RecyclerView mRecyclerView = (RecyclerView) findViewById(R.id.recyclerView);

The view whith id "recyclerView" is a CardView which you are trying to cast to RecyclerView. Change it`s type to RecyclerView instead of CardView in your xml.

Answer 2

Replace cardview with this

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/recyclerView"
    android:layout_width="350dp"
    android:layout_height="447dp"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent">

</androidx.recyclerview.widget.RecyclerView>

Answer 3

In your xml change

<androidx.cardview.widget.CardView
    android:id="@+id/recyclerView"
    android:layout_width="350dp"
    android:layout_height="447dp"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent">

</androidx.cardview.widget.CardView>

TO

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/recyclerView"
    android:layout_width="350dp"
    android:layout_height="447dp"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent">

</androidx.recyclerview.widget.RecyclerView>