在通过绑定启动服务时跟着视频敲代码：

package com.example.servicedemo;

import androidx.appcompat.app.AppCompatActivity;

import android.content.ComponentName;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.IBinder;
import android.util.Log;
import android.view.View;

import com.example.servicedemo.service.FirstService;

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";
    private boolean mIsServiceBinded;
    private FirstService.InnerBinder mremoteBinder;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.d(TAG, "onCreate...");
    }

    //开启服务
    public void startServiceClick(View view) {
        Intent intent = new Intent();
        intent.setClass(this, FirstService.class);
        startService(intent);
    }

    //停止服务
    public void stopServiceClick(View view) {
        Intent intent = new Intent();
        intent.setClass(this, FirstService.class);
        stopService(intent);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.d(TAG, "onDestroy...");
    }

    //绑定服务
    public void bindServiceClick(View view) {
        Intent intent = new Intent();
        intent.setClass(this, FirstService.class);

        mIsServiceBinded = bindService(intent, mConnection, BIND_AUTO_CREATE);
    }

    //解绑服务
    public void unbindServiceClick(View view) {
        if (mConnection != null && mIsServiceBinded) {
            unbindService(mConnection);
        }
    }

    private final ServiceConnection mConnection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
            if(service instanceof FirstService.InnerBinder){
                mremoteBinder = service;
            }
        }

        @Override
        public void onServiceDisconnected(ComponentName componentName) {

        }
    };
}