Android 设置menu出现Failed to compile values file.错误，求解

设置menu，要求出现如图效果

代码编写过程中代码无错，但运行时产生Failed to compile values file.错误。

附代码：

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <item
        android:id="@+id/menu888"
        android:orderInCategory="100"
        android:icon="@drawable/ccut"
        android:title="@string/menu123"
        app:showAsAction="always"
        />


</menu>

<?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:background="#000000"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/textView3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/textview2"
        android:textSize="23sp"
        android:textColor="#ffffff"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.414" />
</androidx.constraintlayout.widget.ConstraintLayout>

package com.example.menurepeat2;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    TextView textView;
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textView=findViewById(R.id.textView3);

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main,menu);
        menu.add(1,1,1,"移动开发技术");
        menu.add(1,2,2,"python");
        menu.add(1,3,3,"英语");
        menu.add(1,4,4,"高数");
        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(@NonNull MenuItem item) {
        String data=item.getTitle().toString();
        switch (item.getItemId()){
            case 1:
            case 2:
            case 3:
            case 4:
                textView.setText("您选择了："+data);break;
        }
        return super.onOptionsItemSelected(item);
    }
}

1.检查资源文件是否正常，string是否在xml中添加
2.clean重新build
3.重启AS