37.Android Service 及 AIDL

37.Android Service 及 AIDL

Android Service介绍

├── Context
│   ├── ContextWrapper (Service)
│   │   ├── ContextThemeWrapper (Activity)

• Service只是一个没有界面（Theme）的Activity，它继承的是ContextWrapper。

• Activity继承的是ContextThemeWrapper，所以有主题，有界面。

Service的等级和Activity差不多。由于Service没有界面，用户不可见的。所以，Service一般作为运行在后台的服务，做一个后台的工作（监听什么，记录什么，刷新什么）。

说这么多很多东西可能被概念混淆：Service虽然是不可以见的，运行的后台的，说到底也只是一个没有主题的Activity，但是还是运行在主线程中的。即使是Activity，不开子线程也是运行在主线程中的，所以Service也一样，即使用了Service，要做一些耗时的操作，也必须在子线程中，或者异步任务中。

要实现IPC（跨进程调用）时，Service上只能用AIDL的方式调用bindService；其次，还有使用BroadcastReceiver。

Android Service类型

• Local Service ：运行在主进程中，因为在主进程中，所以不需要IPC，那就更不需要写一AIDL，这里的话用bindService比较方便，绑定Service的Context销毁的时候，再unbindService，就可以停止服务了。

• Remote Service ：在AndroidMainfest.xml的< service >标签中指定android:process=":remote"即可。此时，Service启动后将作为一个独立的进程。启动Service的Context所在的进程被回收后，Service一样可以运行。这样的话，有助于不同App之间的通信。

Android Service bind 和 start

startService流程图：

Created with Raphaël 2.1.0 startService() onCreate() onStartCommand() Service was running... stopService() or stopSelf() onDestroy() service was destroyed

bindService流程图：

Created with Raphaël 2.1.0 bindService() onCreate() onBind() Service was running and it was bound unbindService() onUnbind() onDestroy() service was destroyed

• startService：

  • 就是简单的开启一个Service，然后服务运行，不能进行通信，除非调用stopService。

  • startService 方法被调用N次，onCreate方法只会调用一次，onStartCommand将会被调用多次（和startService的次数一致）。

• bindService：

  • 绑定Service需要一个ServiceConnection，通过这个ServiceConnection可以拿到IBinder对象，就可以和这个Service进行通信。如果要停止服务，则要使用unbindService。相当于把Service的生命周期交给绑定它的Context去管理（对应的onCreate去bind，对用的onDestory去unbind）。

  • 调用 bindService 调用N次，onCreate方法都只会调用一次，同时onStartCommand方法始终不会被调用。

• startService + bindService：

  • 调用unbindService已经不能停止Service，必须调用stopService 或 Service自身的stopSelf。

  • 启动又绑定Service，Service后一直会在后台运行，当然onCreate也只会调用一次，后面的onStartCommand会被调用N次。

Local Service 实现

要做成什么样子呢？就做一个绑定Service，然后进行通信。然后，下载图片，再将图片渲染在Activity的ImageView上。

还引用了一个AsyncTask模板。

先写一个Activity的回调接口 IBinderView

public interface IBinderView {
    /** * 开始下载 */
    void downloadStart();

    /** * 下载成功 * * @param imageFilePath */
    void downloadSuccess(String imageFilePath);

    /** * 下载失败 */
    void downloadFailure();
}

DownloadService

public class DownloadService extends Service {

    private static final String TAG = "DownloadService";
    private IBinder binder;

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return this.binder;
    }

    /** * Called by the system when the service is first created. Do not call this method directly. */
    @Override
    public void onCreate() {
        super.onCreate();
        this.binder = new DownloadServiceBinder();
    }

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

    /** * Called by the system to notify a Service that it is no longer used and is being removed. The * service should clean up any resources it holds (threads, registered * receivers, etc) at this point. Upon return, there will be no more calls * in to this Service object and it is effectively dead. Do not call this method directly. */
    @Override
    public void onDestroy() {
        super.onDestroy();
    }

    /** * Service Binder */
    public class DownloadServiceBinder extends Binder {
        public IBinderView iBinderView;

        public DownloadService getService() {
            return DownloadService.this;
        }
    }

    public void startDownload(String imageUrl) {
        ((DownloadServiceBinder) DownloadService.this.binder).iBinderView.downloadStart();
        new DownloadImageAsyncTask(this).execute(imageUrl);
    }

    /** * 下载图片异步任务 */
    public class DownloadImageAsyncTask extends AsyncTask<String, Integer, String> {

        private Service service;
        private String localFilePath;

        public DownloadImageAsyncTask(Service service) {
            super();
            this.service = service;
        }

        /** * 对应AsyncTask第一个参数 * 异步操作，不在主UI线程中，不能对控件进行修改 * 可以调用publishProgress方法中转到onProgressUpdate(这里完成了一个handler.sendMessage(...)的过程) * * @param params The parameters of the task. * @return A result, defined by the subclass of this task. * @see #onPreExecute() * @see #onPostExecute * @see #publishProgress */
        @Override
        protected String doInBackground(String... params) {
            URL fileUrl = null;
            try {
                fileUrl = new URL(params[0]);
            } catch (MalformedURLException e) {
                e.printStackTrace();
            }
            if (fileUrl == null) return null;
            try {
                HttpURLConnection connection = (HttpURLConnection) fileUrl.openConnection();
                connection.setRequestMethod("GET");
                connection.setDoInput(true);
                connection.connect();

                //计算文件长度
                int lengthOfFile = connection.getContentLength();
                /** * 不存在SD卡，就放到缓存文件夹内 */
                File cacheDir = this.service.getCacheDir();
                File downloadFile = new File(cacheDir, UUID.randomUUID().toString() + ".jpg");
                this.localFilePath = downloadFile.getPath();
                if (!downloadFile.exists()) {
                    File parent = downloadFile.getParentFile();
                    if (parent != null) parent.mkdirs();
                }
                FileOutputStream output = new FileOutputStream(downloadFile);
                InputStream input = connection.getInputStream();
                InputStream bitmapInput = connection.getInputStream();
                //下载
                byte[] buffer = new byte[1024];
                int len;
                long total = 0;
                // 计算进度
                while ((len = input.read(buffer)) > 0) {
                    total += len;
                    this.publishProgress((int) ((total * 100) / lengthOfFile));
                    output.write(buffer, 0, len);
                }
                output.close();
                input.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return null;
        }

        /** * 对应AsyncTask第三个参数 (接受doInBackground的返回值) * 在doInBackground方法执行结束之后在运行，此时已经回来主UI线程当中 能对UI控件进行修改 * * @param string The result of the operation computed by {@link #doInBackground}. * @see #onPreExecute * @see #doInBackground * @see #onCancelled(Object) */
        @Override
        protected void onPostExecute(String string) {
            super.onPostExecute(string);
            ((DownloadServiceBinder) DownloadService.this.binder).iBinderView.downloadSuccess(this.localFilePath);
        }

        /** * 对应AsyncTask第二个参数 * 在doInBackground方法当中，每次调用publishProgress方法都会中转(handler.sendMessage(...))到onProgressUpdate * 在主UI线程中，可以对控件进行修改 * * @param values The values indicating progress. * @see #publishProgress * @see #doInBackground */
        @Override
        protected void onProgressUpdate(Integer... values) {
            super.onProgressUpdate(values);
        }

        /** * 运行在主UI线程中，此时是预执行状态，下一步是doInBackground * * @see #onPostExecute * @see #doInBackground */
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

        /** * <p>Applications should preferably override {@link #onCancelled(Object)}. * This method is invoked by the default implementation of * {@link #onCancelled(Object)}.</p> * <p/> * <p>Runs on the UI thread after {@link #cancel(boolean)} is invoked and * {@link #doInBackground(Object[])} has finished.</p> * * @see #onCancelled(Object) * @see #cancel(boolean) * @see #isCancelled() */
        @Override
        protected void onCancelled() {
            super.onCancelled();
            ((DownloadServiceBinder) DownloadService.this.binder).iBinderView.downloadFailure();
        }

    }

}

DownloadServiceActivity

public class DownloadServiceActivity extends AppCompatActivity implements View.OnClickListener, IBinderView {

    private static final String OBJECT_IMAGE_URL = "http://img.blog.csdn.net/20150913233900119";

    private Button startBT;
    private ImageView imageIV;
    private DownloadService service;

    private ServiceConnection connection;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        this.setContentView(R.layout.activity_download_service);
        this.initViews();
        this.initData();
        this.initListeners();
    }

    private void initViews() {
        TextView imageTV = (TextView) this.findViewById(R.id.image_tv);
        imageTV.setText(OBJECT_IMAGE_URL);

        this.startBT = (Button) this.findViewById(R.id.start_service_bt);
        this.imageIV = (ImageView) this.findViewById(R.id.image_iv);
    }

    private void initData() {
        this.connection = new ServiceConnection() {
            @Override
            public void onServiceConnected(ComponentName name, IBinder service) {
                DownloadService.DownloadServiceBinder binder = (DownloadService.DownloadServiceBinder) service;
                binder.iBinderView = DownloadServiceActivity.this;
                DownloadServiceActivity.this.service = binder.getService();
            }

            @Override
            public void onServiceDisconnected(ComponentName name) {
                DownloadServiceActivity.this.service = null;
            }
        };

        DownloadServiceActivity.this.bindService(
                new Intent(DownloadServiceActivity.this, DownloadService.class),
                DownloadServiceActivity.this.connection,
                Context.BIND_AUTO_CREATE
        );
    }

    private void initListeners() {
        this.startBT.setOnClickListener(this);
    }

    /** * Called when a view has been clicked. * * @param v The view that was clicked. */
    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.start_service_bt:
                this.service.startDownload(OBJECT_IMAGE_URL);
                break;
        }
    }

    /** * 开始下载 */
    @Override
    public void downloadStart() {
        this.startBT.setEnabled(false);
    }

    /** * 下载成功 * * @param imageFilePath */
    @Override
    public void downloadSuccess(String imageFilePath) {
        /** * 设置按钮可用，并隐藏Dialog */
        this.startBT.setEnabled(true);
        DisplayMetrics metrics = new DisplayMetrics();
        getWindowManager().getDefaultDisplay().getMetrics(metrics);
        int screenWidth = metrics.widthPixels;
        int screenHeight = metrics.heightPixels;
        /** * ImageUtil.decodeScaleImage 解析图片 */
        Bitmap bitmap = ImageUtil.decodeScaleImage(imageFilePath, screenWidth, screenHeight);
        DownloadServiceActivity.this.imageIV.setImageBitmap(bitmap);
    }

    /** * 下载失败 */
    @Override
    public void downloadFailure() {
        this.startBT.setEnabled(true);
    }

}

AndroidManifest.xml

<service android:name="com.camnter.newlife.service.DownloadService" />

Remote Service 实现

这里就需要写一个AIDL文件，提供给Activity与Remote Service通讯。

IPushMessage.aidl

interface IPushMessage {
    /** * 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);

    String onMessage();

}

写完AIDL文件后，此时，会自动生成一个 IPushMessage 接口的代码。

IPushMessage

/* * This file is auto-generated. DO NOT MODIFY. * Original file: /Users/CaMnter/GitHub/AndroidLife/app/src/main/aidl/com/camnter/newlife/aidl/IPushMessage.aidl */
package com.camnter.newlife.aidl;
// Declare any non-default types here with import statements

public interface IPushMessage extends android.os.IInterface {
    /** * Local-side IPC implementation stub class. */
    public static abstract class Stub extends android.os.Binder implements com.camnter.newlife.aidl.IPushMessage {
        private static final java.lang.String DESCRIPTOR = "com.camnter.newlife.aidl.IPushMessage";

        /** * Construct the stub at attach it to the interface. */
        public Stub() {
            this.attachInterface(this, DESCRIPTOR);
        }

        /** * Cast an IBinder object into an com.camnter.newlife.aidl.IPushMessage interface, * generating a proxy if needed. */
        public static com.camnter.newlife.aidl.IPushMessage asInterface(android.os.IBinder obj) {
            if ((obj == null)) {
                return null;
            }
            android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
            if (((iin != null) && (iin instanceof com.camnter.newlife.aidl.IPushMessage))) {
                return ((com.camnter.newlife.aidl.IPushMessage) iin);
            }
            return new com.camnter.newlife.aidl.IPushMessage.Stub.Proxy(obj);
        }

        @Override
        public android.os.IBinder asBinder() {
            return this;
        }

        @Override
        public boolean onTransact(int code, android.os.Parcel data, android.os.Parcel reply, int flags) throws android.os.RemoteException {
            switch (code) {
                case INTERFACE_TRANSACTION: {
                    reply.writeString(DESCRIPTOR);
                    return true;
                }
                case TRANSACTION_basicTypes: {
                    data.enforceInterface(DESCRIPTOR);
                    int _arg0;
                    _arg0 = data.readInt();
                    long _arg1;
                    _arg1 = data.readLong();
                    boolean _arg2;
                    _arg2 = (0 != data.readInt());
                    float _arg3;
                    _arg3 = data.readFloat();
                    double _arg4;
                    _arg4 = data.readDouble();
                    java.lang.String _arg5;
                    _arg5 = data.readString();
                    this.basicTypes(_arg0, _arg1, _arg2, _arg3, _arg4, _arg5);
                    reply.writeNoException();
                    return true;
                }
                case TRANSACTION_onMessage: {
                    data.enforceInterface(DESCRIPTOR);
                    java.lang.String _result = this.onMessage();
                    reply.writeNoException();
                    reply.writeString(_result);
                    return true;
                }
            }
            return super.onTransact(code, data, reply, flags);
        }

        private static class Proxy implements com.camnter.newlife.aidl.IPushMessage {
            private android.os.IBinder mRemote;

            Proxy(android.os.IBinder remote) {
                mRemote = remote;
            }

            @Override
            public android.os.IBinder asBinder() {
                return mRemote;
            }

            public java.lang.String getInterfaceDescriptor() {
                return DESCRIPTOR;
            }

            /** * Demonstrates some basic types that you can use as parameters * and return values in AIDL. */
            @Override
            public void basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat, double aDouble, java.lang.String aString) throws android.os.RemoteException {
                android.os.Parcel _data = android.os.Parcel.obtain();
                android.os.Parcel _reply = android.os.Parcel.obtain();
                try {
                    _data.writeInterfaceToken(DESCRIPTOR);
                    _data.writeInt(anInt);
                    _data.writeLong(aLong);
                    _data.writeInt(((aBoolean) ? (1) : (0)));
                    _data.writeFloat(aFloat);
                    _data.writeDouble(aDouble);
                    _data.writeString(aString);
                    mRemote.transact(Stub.TRANSACTION_basicTypes, _data, _reply, 0);
                    _reply.readException();
                } finally {
                    _reply.recycle();
                    _data.recycle();
                }
            }

            @Override
            public java.lang.String onMessage() throws android.os.RemoteException {
                android.os.Parcel _data = android.os.Parcel.obtain();
                android.os.Parcel _reply = android.os.Parcel.obtain();
                java.lang.String _result;
                try {
                    _data.writeInterfaceToken(DESCRIPTOR);
                    mRemote.transact(Stub.TRANSACTION_onMessage, _data, _reply, 0);
                    _reply.readException();
                    _result = _reply.readString();
                } finally {
                    _reply.recycle();
                    _data.recycle();
                }
                return _result;
            }
        }

        static final int TRANSACTION_basicTypes = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);
        static final int TRANSACTION_onMessage = (android.os.IBinder.FIRST_CALL_TRANSACTION + 1);
    }

    /** * Demonstrates some basic types that you can use as parameters * and return values in AIDL. */
    public void basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat, double aDouble, java.lang.String aString) throws android.os.RemoteException;

    public java.lang.String onMessage() throws android.os.RemoteException;
}

可以看到：

• 1.生成了一个静态抽象类 Stub ，用于提供给Service实现 Service 的 IBinder，然后返回给ServiceConnection。

• 2.生成了抽象类 Stub 的一个静态内部类 Proxy ，作为AIDL代理服务类，进行远程通信。

• 3.生成了AIDL文件中自定义的方法（basicTypes、onMessage）。

注意！！！！！！，在Service的实现中，要实现自动生成的 IPushMessage 接口中的静态抽象类 Stub ，以此作为 Service 的 Binder 对象，进行通信。

PushMessageService

public class PushMessageService extends Service {

    private static final String TAG = "MessageService";

    private IPushMessageImpl binder;

    /** * AIDL implement * 实现AIDL生成静态抽象类 IPushMessage.Stub */
    private class IPushMessageImpl extends IPushMessage.Stub {
        /** * Demonstrates some basic types that you can use as parameters * and return values in AIDL. * * @param anInt * @param aLong * @param aBoolean * @param aFloat * @param aDouble * @param aString */
        @Override
        public void basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat, double aDouble, String aString) throws RemoteException {

        }

        @Override
        public String onMessage() throws RemoteException {
            return UUID.randomUUID().toString();
        }

    }

    /** * Called by the system when the service is first created. Do not call this method directly. */
    @Override
    public void onCreate() {
        super.onCreate();
        this.binder = new IPushMessageImpl();
    }


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

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return this.binder;
    }

}

当使用ServiceConnection桥接好Service 与 Activity成功后，我们能拿到IBinder service 对象。注意！！！！！！，此时，的IBinder对象只是BinderProxy对象，不能直接转换为Binder对象，我们只能再调用AIDL生成类IPushMessage中的内部静态抽象类 Stub 的静态方法 public static com.camnter.newlife.aidl.IPushMessage asInterface(android.os.IBinder obj) 将其转为IPushMessage类型，以此来跟Service通信。

AIDLActivity

public class AIDLActivity extends AppCompatActivity {

    private static final String TAG = "AIDLActivity";

    private TextView aidlTV;

    private String pushMessage;
    private IPushMessage iPushMessage;
    private ServiceConnection connection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            /* * 这里的 service 不是 Binder对象 * 而是 BinderProxy对象 * 不能 直接转为Binder（ (Binder)service ），是错误的。 */
            AIDLActivity.this.iPushMessage = IPushMessage.Stub.asInterface(service);
            try {
                AIDLActivity.this.pushMessage = AIDLActivity.this.iPushMessage.onMessage();
                AIDLActivity.this.aidlTV.setText(AIDLActivity.this.pushMessage);
            } catch (RemoteException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {
            AIDLActivity.this.iPushMessage = null;
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        this.setContentView(R.layout.activity_aidl);
        this.aidlTV = (TextView) this.findViewById(R.id.aidl_tv);
        Intent intent = new Intent(this, PushMessageService.class);
        this.startService(intent);
        this.bindService(intent, this.connection, Context.BIND_AUTO_CREATE);
    }

    @Override
    protected void onDestroy() {
        this.unbindService(this.connection);
        super.onDestroy();
    }

}

AndroidManifest.xml

<!-- action 写上 aidl生成类的所在包 -->
<service  android:name=".aidl.PushMessageService" android:process=":remote">
    <intent-filter>
        <action android:name="com.camnter.newlife.aidl.IPushMessage" />
    </intent-filter>
</service>

然后，可以看到Service作为单独进程存在了：