Android -Services 使用简介

Android Services 四大组件之一，主要用于后台长时间运行。没有界面。这里讲解两种services的启动还有AIDL通信方式。

1.startservices

a.建立继承services的类，复写方法（本地服务）

public class MyServices extends Service  {

    private static final String TAG="TestTag";

    @Override
    public IBinder onBind(Intent arg0) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public void onCreate() {
        Log.i(TAG, "onCreate");
        super.onCreate();
    }

    @Override
    public void onStart(Intent intent, int startId) {
        Log.i(TAG, "onStart");
        super.onStart(intent, startId);
    }

    @Override
    public void onDestroy() {
        Log.i(TAG, "onDestroy");
        super.onDestroy();
    }

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

}

b.声明AndroidManifest

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

c.启动关闭

switch(v.getId()){
                case R.id.btnStart:
                    startService(intent);
                    break;
                case R.id.btnStop:
                    stopService(intent);
                    break;
  }

后记：

服务生命周期：context.startService() ->onCreate()- >onStart()- >onStartCommand()->Service running ->context.stopService()  ->onDestroy() ->Service stop

如果Service还没有运行，则android先调用onCreate()然后调用onStartCommand()，每次调用startService(Intent)的时候，都会调用执行onStartCommand()；
如果Service已经运行，则只调用onStartCommand()。

2.bindservices

服务链接（ServiceConnection）或直接获取Service中状态和数据信息 
服务链接能够获取Service的对象，因此绑定Service的组件可以调用Service中的实现的函数 
使用Service的组件通过Context.bindService()建立服务链接，通过Context.unbindService()停止服务链接 
如果在绑定过程中Service没有启动，Context.bindService()会自动启动Service 
同一个Service可以绑定多个服务链接，这样可以同时为多个不同的组件提供服务

a.创建BindService继承Service

public class BindService extends Service {

    private static final String TAG="BindService";

    private BindServiceX myBinderServiceX=new BindServiceX();
    public class BindServiceX extends Binder{
        public BindService getBindService() {
            return BindService.this;
        }
    }

    @Override
    public IBinder onBind(Intent arg0) {
        // TODO Auto-generated method stub
        Log.i(TAG, "onBind");
        return myBinderServiceX;
    }

    @Override
    public void onCreate() {
        Log.i(TAG, "onCreate");
        super.onCreate();
    }

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

    @Override
    public void onDestroy() {
        Log.i(TAG, "onDestroy");
        super.onDestroy();
    }

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

    public void ShowLog(){
        Log.i(TAG, "BindService=>ShowLog");
    }

}

b.声明AndroidManifest

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

c.启动使用

public void onClick(View v) {
            Intent intentBind = new Intent(MainActivity.this, BindService.class);

            switch (v.getId()) {
                case R.id.btnStartBindService:
                    bindService(intentBind, conn, Context.BIND_AUTO_CREATE);
                    break;
                case R.id.btnStopBindService:
                    if (isConn) {
                        unbindService(conn); //不可以多次调用
                        isConn=false;
                    }
                    break;
            }

后记：

AndroidServiceActivity绑定方法，Context.BIND_AUTO_CREATE表明只要绑定存在，就自动建立Service；同时也告知Android系统，这个Service的重要程度与调用者相同，除非考虑终止调用者，否则不要关闭这个Service。

如果service没被创建，那么调用一次onCreate(),然后调用onBind()，多次绑定时，不会多次调用onBind()。

通过unbindService()函数取消绑定Servcie时，onUnbind()函数将被调用， 
如果onUnbind()函数的返回true，则表示在调用者绑定新服务时， 
onRebind()函数将被调用

取消绑定仅需要使用unbindService()方法，并将ServiceConnnection传递给unbindService()方法需注意的是，unbindService()方法成功后，系统并不会调用onServiceDisconnected()，因为onServiceDisconnected()仅在意外断开绑定时才被调用

3.AIDL IPC通信 services

Android系统中，各个应用都运行在自己的进程中，进程之间一般无法直接进行通信，为了实现进程通信（interprocess communication，简称IPC），android提供了AIDL Service；

Android需要AIDL（Android Interface Definition Language）来定义远程接口，这种接口定义语言并不是一种真正的变成语言，只是定义两个进程之间的通信接口；

与Java接口相似，但是存在如下几点差异：

• AIDL定义接口的源代码必须以.aidl结尾；

• AIDL用到的数据类型，除了基本类型、String、List、Map、CharSequence之外，其它类型全部都需要导包，即使它们在同一个包中也需要导包；

AIDL的步骤:

a.创建AIDL文件

package com.example.zcx.servicesdemo;

// Declare any non-default types here with import statements

//interface ICat {
//    /**
//     * Demonstrates some basic types that you can use as parameters
//     * and return values in AIDL.
//     */
//    void basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat,
//            double aDouble, String aString);
//}
interface ICat {
    String getColor();
    double getWeight();
}

b.服务端编写

public class AidlService extends Service {
    String[] colors = new String[] { "红色", "黄色", "黑色" };
    double[] weights = new double[] { 2.3, 3.1, 1.58 };
    private String color;
    private double weight;
    private CatBinder catBinder;
    Timer timer = new Timer();

    @Override
    public void onCreate() {
        super.onCreate();
        catBinder = new CatBinder();
        timer.schedule(new TimerTask() {

            @Override
            public void run() {
                // 随机地改变service组件内的color，weight属性的值
                int rand = (int) (Math.random() * 3);
                color = colors[rand];
                weight = weights[rand];
                System.out.println("---------" + rand);
            }
        }, 0, 800);
    }

    @Override
    public IBinder onBind(Intent arg0) {
        /**
         * 返回CatBinder对象，在绑定本地Service情况下，
         * 该catBinder会直接传给客户端的ServiceConnected对象的ServiceConnected
         * ()方法的第二个参数；在绑定远程Service的情况下
         * ，只将catBinder对象的代理传给客户端的ServiceConnected对象的ServiceConnected()方法的第二个参数
         */
        return catBinder;
    }

    @Override
    public void onDestroy() {
        timer.cancel();
    }

    /**
     * 继承Stub,也就是实现了ICat接口，并实现了IBinder接口
     *
     * @author pengcx
     *
     */
    public class CatBinder extends ICat.Stub {
        @Override
        public String getColor() throws RemoteException {
            return color;
        }

        @Override
        public double getWeight() throws RemoteException {
            return weight;
        }
    }
}

androidmanifest:

<service android:name=".AidlService" android:process=":remote">
            <intent-filter>
                <action android:name="org.crazyit.aidl.AIDL_SERVICE" />
            </intent-filter>
</service>

c.客户端使用

首先需要建立aidl,注意要在相同的包名下,否则报错： java.lang.SecurityException: Binder invocation to an incorrect interface

// ICat.aidl
package com.example.zcx.servicesdemo;

// Declare any non-default types here with import statements

//interface ICat {
//    /**
//     * Demonstrates some basic types that you can use as parameters
//     * and return values in AIDL.
//     */
//    void basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat,
//            double aDouble, String aString);
//}
interface ICat {
    String getColor();
    double getWeight();
}

编写客户端：

public class MainActivity extends AppCompatActivity {

    private ICat catService;
    private Button getButton;
    private EditText colorEditText, weightEditText;

    private ServiceConnection conn = new ServiceConnection() {
        @Override
        public void onServiceDisconnected(ComponentName name) {
            catService = null;
        }

        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            // 获取远程Service的onBinder方法返回的对象代理
            catService = ICat.Stub.asInterface(service);
            Log.d("zcx","catService");
        }
    };
    public static Intent getExplicitIntent(Context context, Intent implicitIntent) {
        // Retrieve all services that can match the given intent
        PackageManager pm = context.getPackageManager();
        List<ResolveInfo> resolveInfo = pm.queryIntentServices(implicitIntent, 0);
        // Make sure only one match was found
        if (resolveInfo == null || resolveInfo.size() != 1) {
            return null;
        }
        // Get component info and create ComponentName
        ResolveInfo serviceInfo = resolveInfo.get(0);
        String packageName = serviceInfo.serviceInfo.packageName;
        String className = serviceInfo.serviceInfo.name;
        ComponentName component = new ComponentName(packageName, className);
        // Create a new intent. Use the old one for extras and such reuse
        Intent explicitIntent = new Intent(implicitIntent);
        // Set the component to be explicit
        explicitIntent.setComponent(component);
        return explicitIntent;
    }
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        getButton = (Button) findViewById(R.id.getbutton);
        colorEditText = (EditText) findViewById(R.id.coloredittext);
        weightEditText = (EditText) findViewById(R.id.weightedittext);

        // 创建所需要绑定的Service的Intent
        Intent intent = new Intent();
        intent.setAction("org.crazyit.aidl.AIDL_SERVICE");
        //intent.setPackage(getPackageName());
        Intent eintent = new Intent(getExplicitIntent(this,intent));
        Log.e("zcx","eintent = "+eintent);
        // 绑定远程的服务
        Log.e("zcx"," "+bindService(eintent, conn, Service.BIND_AUTO_CREATE));

        getButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // 获取并显示远程service的状态
                try {
                    colorEditText.setText(catService.getColor());
                    weightEditText.setText(catService.getWeight() + "");
                } catch (RemoteException e) {
                    e.printStackTrace();
                }
            }
        });
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        // 解除绑定
        this.unbindService(conn);
    }
}