android - Error inflating class RecyclerView

Question

So my code simply makes a list of CardViews using RecyclerView. Upon running my code i kept getting a weird error claiming there was an error in my xml. After tinkering for a while i found out that in my layout file if i change <RecyclerView> to <android.support.v7.widget.RecyclerView> everything would work just fine. Why is this happening?
My activity.

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.Menu;
import android.view.MenuItem;

import java.util.ArrayList;


public class CardListActivity extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_card_list);
        RecyclerView recyclerView = (RecyclerView)findViewById(R.id.cardList);
        recyclerView.setHasFixedSize(true);

        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
        linearLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);
        recyclerView.setLayoutManager(linearLayoutManager);

        ArrayList<String> list = new ArrayList<>();
        for(int i = 0; i < 20; i++) {list.add("Item " + i);}
        CardListAdapter cardListAdapter = new CardListAdapter(list);
        recyclerView.setAdapter(cardListAdapter);
    }

}

My Adapter

    import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import java.util.List;

public class CardListAdapter extends RecyclerView.Adapter<CardListAdapter.CardListViewHolder> {

    private List<String> list;

    public CardListAdapter(List<String> list) {
        this.list = list;
    }

    @Override
    public CardListViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
        View v = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.card_layout,viewGroup,false);
        return new CardListViewHolder(v);
    }

    @Override
    public void onBindViewHolder(CardListViewHolder cardListViewHolder, int i) {
        String s = list.get(i);
        cardListViewHolder.title.setText(s);
    }

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


    public static class CardListViewHolder extends RecyclerView.ViewHolder {
        TextView title;
        public CardListViewHolder(View itemView) {
            super(itemView);
            title = (TextView)itemView.findViewById(R.id.title);
        }
    }

}

My layout file, note, changing <RecyclerView> to <android.support.v7.widget.RecyclerView> fixes the error.

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".CardListActivity">

<RecyclerView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/cardList">

    </RecyclerView>

When i run with <RecyclerView> i get this error, .

`Process: com.liquidink.lollipopmaterialui, PID: 7317
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.liquidink.lollipopmaterialui/com.liquidink.lollipopmaterialui.CardListActivity}: android.view.InflateException: Binary XML file line #8: Error inflating class RecyclerView
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
     Caused by: android.view.InflateException: Binary XML file line #8: Error inflating class RecyclerView
            at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:757)
            at android.view.LayoutInflater.rInflate(LayoutInflater.java:806)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:504)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:414)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:365)
            at android.support.v7.app.ActionBarActivityDelegateBase.setContentView(ActionBarActivityDelegateBase.java:228)
            at android.support.v7.app.ActionBarActivity.setContentView(ActionBarActivity.java:102)
            at com.liquidink.lollipopmaterialui.CardListActivity.onCreate(CardListActivity.java:18)
            at android.app.Activity.performCreate(Activity.java:5933)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
????????????at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
????????????at android.app.ActivityThread.access$800(ActivityThread.java:144)
????????????at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
????????????at android.os.Handler.dispatchMessage(Handler.java:102)
????????????at android.os.Looper.loop(Looper.java:135)
????????????at android.app.ActivityThread.main(ActivityThread.java:5221)
????????????at java.lang.reflect.Method.invoke(Native Method)
????????????at java.lang.reflect.Method.invoke(Method.java:372)
????????????at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
????????????at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
     Caused by: java.lang.ClassNotFoundException: Didn't find class "android.view.RecyclerView" on path: DexPathList[[zip file "/data/app/com.liquidink.lollipopmaterialui-2/base.apk"],nativeLibraryDirectories=[/vendor/lib, /system/lib]]
            at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
            at java.lang.ClassLoader.loadClass(ClassLoader.java:511)
            at java.lang.ClassLoader.loadClass(ClassLoader.java:469)
            at android.view.LayoutInflater.createView(LayoutInflater.java:571)
            at android.view.LayoutInflater.onCreateView(LayoutInflater.java:665)
            at com.android.internal.policy.impl.PhoneLayoutInflater.onCreateView(PhoneLayoutInflater.java:65)
            at android.view.LayoutInflater.onCreateView(LayoutInflater.java:682)
            at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:741)
????????????at android.view.LayoutInflater.rInflate(LayoutInflater.java:806)
????????????at android.view.LayoutInflater.inflate(LayoutInflater.java:504)
????????????at android.view.LayoutInflater.inflate(LayoutInflater.java:414)
????????????at android.view.LayoutInflater.inflate(LayoutInflater.java:365)
????????????at android.support.v7.app.ActionBarActivityDelegateBase.setContentView(ActionBarActivityDelegateBase.java:228)
????????????at android.support.v7.app.ActionBarActivity.setContentView(ActionBarActivity.java:102)
????????????at com.liquidink.lollipopmaterialui.CardListActivity.onCreate(CardListActivity.java:18)
????????????at android.app.Activity.performCreate(Activity.java:5933)
????????????at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
????????????at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
????????????at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
????????????at android.app.ActivityThread.access$800(ActivityThread.java:144)
????????????at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
????????????at android.os.Handler.dispatchMessage(Handler.java:102)
????????????at android.os.Looper.loop(Looper.java:135)
????????????at android.app.ActivityThread.main(ActivityThread.java:5221)
????????????at java.lang.reflect.Method.invoke(Native Method)
????????????at java.lang.reflect.Method.invoke(Method.java:372)
????????????at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
????????????at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
    Suppressed: java.lang.ClassNotFoundException: android.view.RecyclerView
            at java.lang.Class.classForName(Native Method)
            at java.lang.BootClassLoader.findClass(ClassLoader.java:781)
            at java.lang.BootClassLoader.loadClass(ClassLoader.java:841)
            at java.lang.ClassLoader.loadClass(ClassLoader.java:504)
            ... 26 more
     Caused by: java.lang.NoClassDefFoundError: Class not found using the boot class loader; no stack available

`

Answer 1

You should add the RecyclerView in the XML in this way:

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

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

Hope it helps!