Android Studio androidx.coordinatorlayout

Question

我有以下问题。我的 android studio 显示错误，它已经写在标题Screenshot 中。我试图在右上角实现漂亮的 3 点菜单。如果有人能告诉我问题是什么，那就太好了...尝试 gradle 时遇到的错误是：C:\Users\User\AndroidStudioProjects\BluetoothCar\app\src\main\java\com\car\bluetooth\bluetoothcar\MainActivity.java:11: error: package android.support.design.widget does not existimport android.support.design.widget.AppBarLayout;C:\Users\User\AndroidStudioProjects\BluetoothCar\app\src\main\java\com\car\bluetooth\bluetoothcar\MainActivity.java:12: error: package android.support.v7.widget does not existimport android.support.v7.widget.Toolbar;我已经尝试导入 v7.widget.toolbar，但它将 v7 标记为红色并表示无法解析符号。主活动.java :package com.car.bluetooth.bluetoothcar;import android.os.Bundle;import com.google.android.material.floatingactionbutton.FloatingActionButton;import com.google.android.material.snackbar.Snackbar;import androidx.appcompat.app.AppCompatActivity;import androidx.appcompat.widget.Toolbar;import android.support.design.widget.AppBarLayout;import android.support.v7.widget.Toolbar;import android.util.Log;import android.view.View;import android.view.Menu;import android.view.MenuItem;import android.widget.SeekBar;import android.widget.TextView;public class MainActivity extends AppCompatActivity {//SeekBarsprivate SeekBar seekBarGas;private TextView textViewGas;private SeekBar seekBarSteering;private TextView textViewSteering;@Overrideprotected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);    setSupportActionBar(toolbar);    seekBarGas = (SeekBar) findViewById(R.id.seekBarGas);    textViewGas = (TextView) findViewById(R.id.textViewGas);    seekBarGas.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {        @Override        public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {            textViewGas.setText(progress + "  /  " + seekBarGas.getMax());        }