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 exist

import 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 exist

import 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 {

//SeekBars

private SeekBar seekBarGas;

private TextView textViewGas;

private SeekBar seekBarSteering;

private TextView textViewSteering;

@Override

protected 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());

        }