前言

本文主要说明一下service的生命周期

生命周期方法

在service中可以手动调用的方法为：
startService：开启服务
stopService: 关闭服务
bindService：绑定服务
unbindService：解绑服务

自动调用的方法
onCreate：服务创建时调用
onStartCommand：开启服务时调用
onBind：绑定服务时调用
onUnbind：解绑服务时调用
onDestory：销毁服务时调用

官方给出的声明周期图如下：

service生命周期.jpg

由图上可以看出调用startService会执行的声明周期：

onCreate->onStartCommand->服务运行->调用停止服务方法（系统杀死服务）->onDestory。

绑定服务会执行的声明周期：

onCreate->onBind->绑定服务->调用解绑服务方法（系统杀死服务）->onUnbind->onDestory

常见的声明周期调用

想要使用服务主要有两种方式：开启服务和绑定服务，两者也可以一块使用，但需要注意方法的调用问题。
MainActivity.java:

package com.zhqy.servicelifecycle;

import android.app.Service;
import android.content.ComponentName;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.IBinder;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{
    Button btn_service_start;
    Button btn_service_bind;
    Button btn_service_unbind;
    Button btn_service_stop;
    private MyService.MyBinder binder;
    private ServiceConnection serviceConnection=new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
              binder= (MyService.MyBinder) service;
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {

        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btn_service_start=findViewById(R.id.btn_service_start);
        btn_service_bind=findViewById(R.id.btn_service_bind);
        btn_service_unbind=findViewById(R.id.btn_service_unbind);
        btn_service_stop=findViewById(R.id.btn_service_stop);

        btn_service_start.setOnClickListener(this);
        btn_service_bind.setOnClickListener(this);
        btn_service_unbind.setOnClickListener(this);
        btn_service_stop.setOnClickListener(this);

    }

    @Override
    public void onClick(View v) {
        Intent intent;
        switch (v.getId()){
            case R.id.btn_service_start:
                intent=new Intent(this,MyService.class);
                startService(intent);
                break;
            case R.id.btn_service_bind:
                intent=new Intent(this,MyService.class);
                bindService(intent,serviceConnection, Service.BIND_AUTO_CREATE);
                break;
            case R.id.btn_service_unbind:
                unbindService(serviceConnection);
                break;
            case R.id.btn_service_stop:
                intent=new Intent(this,MyService.class);
                stopService(intent);
                break;
        }
    }
}

activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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"
    tools:context="com.zhqy.servicelifecycle.MainActivity">

    <Button
        android:id="@+id/btn_service_start"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="开启服务"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        />
    <Button
        android:id="@+id/btn_service_bind"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="绑定服务"
        app:layout_constraintTop_toBottomOf="@+id/btn_service_start"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        android:layout_marginTop="10dp"
        />
    <Button
        android:id="@+id/btn_service_unbind"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toBottomOf="@+id/btn_service_bind"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        android:layout_marginTop="10dp"
        android:text="解绑服务"
        />
    <Button
        android:id="@+id/btn_service_stop"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toBottomOf="@+id/btn_service_unbind"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        android:text="停止服务"
        android:layout_marginTop="10dp"
        />



</android.support.constraint.ConstraintLayout>

MyService:

package com.zhqy.servicelifecycle;

import android.app.Service;
import android.content.Intent;
import android.os.Binder;
import android.os.IBinder;
import android.support.annotation.Nullable;
import android.util.Log;

/**
 * Created by jackal on 2019/8/16.
 */

public class MyService extends Service {

    @Override
    public void onCreate() {
        Log.e("MyService","onCreate");
        super.onCreate();
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Log.e("MyService","onStartCommand");
        return super.onStartCommand(intent, flags, startId);
    }



    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        Log.e("MyService","onBind");
        return new MyBinder();
    }

    @Override
    public boolean onUnbind(Intent intent) {
        Log.e("MyService","onUnbind");
        return super.onUnbind(intent);
    }

    @Override
    public void onDestroy() {
        Log.e("MyService","onDestroy");
        super.onDestroy();
    }

    class  MyBinder extends Binder{

    }
}

manifest.xml

   <service android:name=".MyService" />

（1）开启服务->绑定服务->解绑服务->停止服务

测试结果

08-16 16:20:34.144 3773-3773/com.zhqy.servicelifecycle E/MyService: onCreate
08-16 16:20:34.145 3773-3773/com.zhqy.servicelifecycle E/MyService: onStartCommand
08-16 16:20:35.522 3773-3773/com.zhqy.servicelifecycle E/MyService: onBind
08-16 16:20:37.115 3773-3773/com.zhqy.servicelifecycle E/MyService: onUnbind
08-16 16:20:37.924 3773-3773/com.zhqy.servicelifecycle E/MyService: onDestroy

（2）开启服务->停止服务

测试结果

08-16 16:24:12.355 4632-4632/com.zhqy.servicelifecycle E/MyService: onCreate
08-16 16:24:12.356 4632-4632/com.zhqy.servicelifecycle E/MyService: onStartCommand
08-16 16:24:14.084 4632-4632/com.zhqy.servicelifecycle E/MyService: onDestroy

（3）开启服务->开启服务->停止服务

测试结果

08-16 16:25:25.163 4921-4921/com.zhqy.servicelifecycle E/MyService: onCreate
08-16 16:25:25.172 4921-4921/com.zhqy.servicelifecycle E/MyService: onStartCommand
08-16 16:25:25.836 4921-4921/com.zhqy.servicelifecycle E/MyService: onStartCommand

从测试结果来看onCreate只会调用一次，而每当调用startService方法就会执行onStartCommand方法

（4）绑定服务->解绑服务

08-16 16:27:29.658 5043-5043/com.zhqy.servicelifecycle E/MyService: onCreate
08-16 16:27:29.662 5043-5043/com.zhqy.servicelifecycle E/MyService: onBind
08-16 16:27:31.800 5043-5043/com.zhqy.servicelifecycle E/MyService: onUnbind
08-16 16:27:31.800 5043-5043/com.zhqy.servicelifecycle E/MyService: onDestroy

从测试结果来看不论是开启服务还是绑定服务，首次都会创建service并执行onCreate方法。

（5）绑定服务->开启服务->解绑服务->停止服务

08-16 16:31:02.905 5944-5944/com.zhqy.servicelifecycle E/MyService: onCreate
08-16 16:31:02.913 5944-5944/com.zhqy.servicelifecycle E/MyService: onBind
08-16 16:31:04.720 5944-5944/com.zhqy.servicelifecycle E/MyService: onStartCommand
08-16 16:31:07.967 5944-5944/com.zhqy.servicelifecycle E/MyService: onUnbind
08-16 16:31:10.533 5944-5944/com.zhqy.servicelifecycle E/MyService: onDestroy

绑定服务->开启服务->停止服务

08-16 16:33:17.622 6238-6238/com.zhqy.servicelifecycle E/MyService: onCreate
08-16 16:33:17.623 6238-6238/com.zhqy.servicelifecycle E/MyService: onStartCommand
08-16 16:33:19.554 6238-6238/com.zhqy.servicelifecycle E/MyService: onBind

从测试结果可以看出当绑定服务后必须先解绑服务才能停止服务

注意

当调用startService后即使调用者销毁了，服务仍然可以正常运行。
当调用bindService后，如果调用者被销毁了，服务也会随着销毁