Android 四大组件之Service的详解-阿里云开发者社区

一、Service的简介

Service是Android中实现程序后台运行的解决方案，适用于去执行那些不需要和用户交互而且还要求长期运行的任务。Service是android 系统中的四大组件之一（Activity、Service、BroadcastReceiver、ContentProvider），它跟Activity的级别差不多，但不能自己运行只能后台运行，并且可以和其他组件进行交互。

Service的分类如下

作用：提供需在后台长期运行的服务

特点：无用户界面、在后台运行、生命周期长

1、Service的生命周期官方说明图

启动服务

生命周期为：onCreate->onStartCommand->onDestory

1.startService开启服务时，生命周期为

执行onCreate->onStartCommand(Android2.0之后用的都是这个,Android2.0以前是onStart)

一旦启动，服务可以在后台无限期运行，即使启动它的组件已经被销毁。

For example:音乐播放器，退出APP后，依然可以听歌，这是服务在后台运行的作用，否则无法播放音乐。

stopService关闭服务时，执行onDestory

绑定服务

生命周期为：onCreate->onBind->onUnBind->onDestory

2.bindService 绑定服务时，执行onCreate->onBind

unbindSerivce解绑服务时，执行onUnBind->onDestory

1、首先创建MyService类继承Service

/**
 * 自定义本地服务
 */
/*
    1.startService()
      第一次调用：-->构造方法()-->onCreate()-->onStartCommand()
      后面再调用：-->onStartCommand()
      stopService():-->onDestroy()
    2.bindService(Intent service, ServiceConnection conn,int flags)
      第一次调用：-->构造方法()-->onCreate()-->onBind()-->onServiceConnected()
      unbindService(connection):-(只有当前Activity与Service连接)->onUnbind()-->onDestroy()
 */
public class MyService extends Service {
    public MyService() {
        Log.i("TAG", "MyService() ");
    }
    @Override
    public void onCreate() {
        super.onCreate();
        Log.i("TAG", "MyService onCreate() ");
    }
    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Log.i("TAG", "MyService onStartCommand() ");
        return super.onStartCommand(intent, flags, startId);
    }
    @Override
    public void onDestroy() {
        super.onDestroy();
        Log.i("TAG", "MyService onDestroy() ");
    }
    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        Log.i("TAG", "onBind() ");
        return new Binder();
    }
    @Override
    public boolean onUnbind(Intent intent) {
        Log.i("TAG", "onUnbind() ");
        return super.onUnbind(intent);
    }
}

2、在AndroidManifest.xml中进行注册

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

3、ServiceActivity代码如下

public class ServiceActivity extends AppCompatActivity {
    private ServiceConnection connection;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_service);
    }
    //启动服务
    public void startMyService(View view) {
        Intent intent = new Intent(this, MyService.class);
        startService(intent);
        Toast.makeText(this, "启动服务！", Toast.LENGTH_SHORT).show();
    }
    public void stopMyService(View view) {
        Intent intent = new Intent(this, MyService.class);
        stopService(intent);
        Toast.makeText(this, "停止服务！", Toast.LENGTH_SHORT).show();
    }
    //绑定服务
    public void bindMyService(View view) {
        Intent intent = new Intent(this, MyService.class);
        //创建连接对象
        if (connection == null) {
            connection = new ServiceConnection() {
                //当与服务连接上之后，回调该方法
                @Override
                public void onServiceConnected(ComponentName name, IBinder service) {
                    Log.i("TAG", "onServiceConnected()");
                }
        //这个方法始终不会执行，不用管它
                @Override
                public void onServiceDisconnected(ComponentName name) {
                    Log.i("TAG", "onServiceDisconnected()");
                }
            };
            //绑定service
            //BIND_AUTO_CREATE表示：创建之后自动绑定
            bindService(intent, connection, BIND_AUTO_CREATE);
            Toast.makeText(this, "绑定服务！", Toast.LENGTH_SHORT).show();
        } else {
            Toast.makeText(this, "已经绑定服务！", Toast.LENGTH_SHORT).show();
        }
    }
    //解绑服务
    public void unBindMyService(View view) {
        if (connection != null) {
            unbindService(connection);
            connection = null;
            Toast.makeText(this, "解绑服务！", Toast.LENGTH_SHORT).show();
        } else {
            Toast.makeText(this, "还未进行绑定服务！", Toast.LENGTH_SHORT).show();
        }
    }
  //当绑定服务后，不解绑服务直接退出，会有错误抛出，所以需要在
  //当前Activity页面销毁的时候，执行解绑服务
    @Override
    protected void onDestroy() {
        super.onDestroy();
        if (connection != null) {
            unbindService(connection);
            connection = null;
        }
    }
}

二、远程服务AIDL的讲解

AIDL的理解

具体需求如下

具体步骤如下，首先写服务端应用

1、创建远程服务类MyRemoteService继承Service类

/**
 * 远程服务
 */
public class MyRemoteService extends Service {
    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        Log.i("TAG", "onBind() ");
        return new StudentService();
    }
    @Override
    public boolean onUnbind(Intent intent) {
        Log.i("TAG", "onUnbind() ");
        return super.onUnbind(intent);
    }
    //处理Student相关的业务逻辑类
    class StudentService extends IStudentService.Stub {
        @Override
        public Student getStudentById(int id) throws RemoteException {
            Log.i("TAG", "Service getStudentById() " + id);
            return new Student(id, "Tom", 10000);
        }
    }
}

2、在AndroidManifest.xml文件中注册该服务

<service android:name=".local.MyRemoteService">
            <intent-filter>
                <action android:name="local.MyRemoteService.Action" />
            </intent-filter>
</service>

3、创建Student类，并实现Parcelable接口,传递对象

public class Student implements Parcelable {
    private int id;
    private String name;
    private double price;
    public Student(int id, String name, double price) {
        this.id = id;
        this.name = name;
        this.price = price;
    }
    protected Student(Parcel in) {
        id = in.readInt();
        name = in.readString();
        price = in.readDouble();
    }
    public static final Creator<Student> CREATOR = new Creator<Student>() {
        @Override
        public Student createFromParcel(Parcel in) {
            Log.i("TAG", "解包createFromParcel()");
            return new Student(in);
        }
        //返回一个指定大小的对象容器
        @Override
        public Student[] newArray(int size) {
            return new Student[size];
        }
    };
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public double getPrice() {
        return price;
    }
    public void setPrice(double price) {
        this.price = price;
    }
    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", price=" + price +
                '}';
    }
    @Override
    public int describeContents() {
        return 0;
    }
    @Override
    public void writeToParcel(Parcel dest, int flags) {
        Log.i("TAG", "打包 writeToParcel() ");
        dest.writeInt(id);
        dest.writeString(name);
        dest.writeDouble(price);
    }
}

4、在src的main目录下，创建aidl文件默认会生成aidl文件夹。创建两个aidl文件，分别为

IStudentService.aidl

package com.example.customviewproject.entity;
import com.example.customviewproject.entity.Student;
interface IStudentService {
    Student getStudentById(int id);
}

Student.aidl

// Student.aidl
package com.example.customviewproject.entity;
// Declare any non-default types here with import statements
parcelable Student;

AIDL的一些规则如下

服务端创建好后，客户端将服务端的aidl文件和Student类，原封不动的拷贝到客户端应用，意思就是说路径不要变。

客户端的界面如下

MainActivity中进行具体代码的编写，代码如下

public class MainActivity extends AppCompatActivity {
    private EditText edit_id;
    private ServiceConnection connection;
    private IStudentService iStudentService;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        edit_id = findViewById(R.id.edit_id);
    }
    //绑定远端服务
    public void bindRemoteService(View view) {
        Intent intent = new Intent("local.MyRemoteService.Action");
        intent.setPackage("com.example.customviewproject");
        if (connection == null) {
            connection = new ServiceConnection() {
                @Override
                public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
                    Log.i("TAG", "onServiceConnected() ");
                    iStudentService = IStudentService.Stub.asInterface(iBinder);
                }
                @Override
                public void onServiceDisconnected(ComponentName componentName) {
                }
            };
            bindService(intent, connection, BIND_AUTO_CREATE);
        } else {
            Toast.makeText(this, "已经绑定远端服务！", Toast.LENGTH_SHORT).show();
        }
    }
    //调用远程服务端的方法
    public void callRemoteMethod(View view) {
        if (iStudentService != null) {
            int id = Integer.parseInt(edit_id.getText().toString());
            try {
                Student student = iStudentService.getStudentById(id);
                Log.i("TAG", "callRemoteMethod() student.toString():" + student.toString());
            } catch (RemoteException e) {
                e.printStackTrace();
            }
        }
    }
    //解绑远端服务
    public void UnbindService(View view) {
        if (connection != null) {
            unbindService(connection);
            connection = null;
            iStudentService = null;
            Toast.makeText(this, "解绑远端服务！", Toast.LENGTH_SHORT).show();
        } else {
            Toast.makeText(this, "还未绑定远端服务！", Toast.LENGTH_SHORT).show();
        }
    }
}

当用户首次进入后，点击绑定远端服务按钮执行的流程依次为

点击调用远程服务端的按钮，执行的流程依次为

点击解绑远程服务按钮，执行的流程依次为

以上是Service讲解，有什么不当之处，可在评论区指正共同学习!

Android 四大组件之Service的详解

一、Service的简介

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