39.Android BroadcastReceiver

Android BroadcastReceiver 介绍

现在的BroadcastReceiver好多都用在了做推送上。比如极光推送、信鸽推送等等。

推送用BroadcastReceiver发多都是提示一个Notification。服务端发送推送，推送Android SDK内的通信机制接受到了推送，然后发送广播通知，BroadcastReceiver接收到了通知，进而区分通知类型，执行对应的操作，很多时候，我们都是看到一个Notification（QQ消息通知、微信消息通知等等）。

Android BroadcastReceiver 功能

就是简单的三句话。

• 1.Android的跨组件通信
• 2.Android的跨线程通信
• 3.Android的跨进程（App）通信

为什么会这样子呢？请见下面的浅淡机制。

Android BroadcastReceiver 浅淡机制

Android BroadcastReceiver 的实现使用的是观察者模式。

观察者模式：假如，所有事件的都要实现Event接口，监听事件都需要将View的引用作为参数传入Event的构造方法中。有N个View添加了A事件的监听，M个View添加了B事件的监听。那么，就有N+M个View的引用放在观察者池里。此时，假如随便从哪发来了一个A事件，都要遍历那个长度为N+M的观察者池，查看里面的哪个引用的事件是A事件，然后调用引用的事件响应方法。从而，完成一次观察者模式的事件监听。

Android BroadcastReceiver 的实现原理就是如此：使用了观察者模式的监听方式，在动态或静态注册广播时，添加对应的Action作为与BroadcastReceiver通信的通道，发送广播等于消息的发布，添加Action等于订阅事件。这样大大解耦了发送者和接收者，流程大题如下：

• 1.BroadcastReceiver 通过Binder机制在AMS（Activity Manager Service）注册。

• 2.View发送广播时，也是通过Binder机制向AMS（Activity Manager Service）发送广播通知。

• 3.AMS根据发来的Intent里的Action查找对应的IntentFilter或者Permission，筛选出BroadcastReceiver，然后将广播转发到BroadcastReceiver上相应的消息循环队列中。

• 4.在BroadcastReceiver的消息循环队列执行循环时，拿到了此广播，回调BroadcastReceiver的onReceive()方法。

从此看来，这里的BroadcastReceiver充当了观察者；View充当了消息发送者；AMS就相当于消息处理中心，其内部包含了一个观察者池。

静态BroadcastReceiver 实现

静态BroadcastReceiver就需要在AndroidMainfest.xml文件里配置<receiver>：

receiver标签属性

<!--
    enabled: "true" 或者 "false"
    exported: "true" 或者 "false"
    icon: 资源Id
    label: 资源Id
    name: 字符串
    permission: 字符串
    process: 字符串
-->
<receiver
    android:enabled="true"
    android:exported="true" 
    android:icon="@drawable/*"
    android:label="@string/*"
    android:name="String"
    android:permission="String"
    android:process="String">

</receiver>

android:exported：表示的是该BroadcastReceiver是否接受其他App的广播。true为接收；false为不接收。其默认值：如果有intent-filter，默认值为true；没有intent-filter，默认值为false。（ Activity 或 Service中的android:exported的默认值是这样设置的 ）这里区分的是App，不是进程，因为一个App中可能有多进程。

StaticReceiver

public class StaticReceiver extends BroadcastReceiver {

    public static final String INTENT_ACTION = "com.camnter.android.intent.static";
    public static final String STATIC_MESSAGE = "message";

    @TargetApi(Build.VERSION_CODES.JELLY_BEAN)
    @Override
    public void onReceive(Context context, Intent intent) {
        String message = intent.getStringExtra(STATIC_MESSAGE);
        Intent data = new Intent();
        PendingIntent pendingIntent = PendingIntent.getActivity(
                context,
                0,
                data,
                PendingIntent.FLAG_CANCEL_CURRENT
        );
        NotificationManager notificationManager = (NotificationManager)
                context.getSystemService(Context.NOTIFICATION_SERVICE);
        Notification notification = new Notification.Builder(context)
                .setContentTitle("StaticBroadcastReceiver")
                .setContentText(message)
                .setSmallIcon(R.mipmap.zzmbs_2)
                .setLargeIcon(BitmapFactory.decodeResource(context.getResources(), R.mipmap.zzmbs_2))
                .setContentIntent(pendingIntent)
                .build();
        notificationManager.notify(206, notification);
        Toast.makeText(context, message, Toast.LENGTH_SHORT).show();
    }

}

AndroidManifest.xml

<receiver
    android:name=".broadcastreceiver.StaticReceiver"
    android:exported="true"
    android:process=":remotereceiver">
    <intent-filter>
        <action android:name="com.camnter.android.intent.static" />
    </intent-filter>
</receiver>

StaticReceiverActivity

public class StaticReceiverActivity extends AppCompatActivity implements View.OnClickListener {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        this.setContentView(R.layout.activity_static_broadcast_receiver);
        this.findViewById(R.id.static_broadcast_receiver_bt).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.static_broadcast_receiver_bt:
                Intent intent = new Intent(StaticReceiver.INTENT_ACTION);
                intent.putExtra(StaticReceiver.STATIC_MESSAGE, UUID.randomUUID().toString());
                this.sendBroadcast(intent);
                break;
        }
    }
}

动态BroadcastReceiver 实现

动态BroadcastReceiver就不需要在AndroidManifest.xml里配置，需要手动代码注册。

涉及到两个API：

• 1.Context.registerReceiver(BroadcastReceiver receiver, IntentFilter filter)
  public Intent registerReceiver(BroadcastReceiver receiver, IntentFilter filter)

• 2.IntentFilter.addAction(String action)
  public final void addAction(String action)

DynamicReceiver

public class DynamicReceiver extends BroadcastReceiver {

    public static final String INTENT_ACTION = "com.camnter.android.intent.dynamic";
    public static final String DYNAMIC_MESSAGE = "message";

    public static DynamicReceiver instance;

    private DynamicReceiver() {
    }

    public static DynamicReceiver getInstance() {
        if (instance == null) instance = new DynamicReceiver();
        return instance;
    }

    /**
     * 提供给外部注册广播
     *
     * @param context
     */
    public static void register(Context context) {
        IntentFilter intentFilter = new IntentFilter();
        intentFilter.addAction(INTENT_ACTION);
        context.registerReceiver(getInstance(), intentFilter);
    }

    @TargetApi(Build.VERSION_CODES.JELLY_BEAN)
    @Override
    public void onReceive(Context context, Intent intent) {
        String message = intent.getStringExtra(DYNAMIC_MESSAGE);
        Intent data = new Intent();
        PendingIntent pendingIntent = PendingIntent.getActivity(
                context,
                0,
                data,
                PendingIntent.FLAG_CANCEL_CURRENT
        );
        NotificationManager notificationManager = (NotificationManager)
                context.getSystemService(Context.NOTIFICATION_SERVICE);
        Notification notification = new Notification.Builder(context)
                .setContentTitle("StaticBroadcastReceiver")
                .setContentText(message)
                .setSmallIcon(R.mipmap.zzmbs_2)
                .setLargeIcon(BitmapFactory.decodeResource(context.getResources(), R.mipmap.zzmbs_2))
                .setContentIntent(pendingIntent)
                .build();
        notificationManager.notify(206, notification);
        Toast.makeText(context, message, Toast.LENGTH_SHORT).show();
    }

}

DynamicReceiverActivity

public class DynamicReceiverActivity extends AppCompatActivity implements View.OnClickListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        this.setContentView(R.layout.activity_dynamic_broadcast_receiver);

        DynamicReceiver.register(this);
        this.findViewById(R.id.dynamic_broadcast_receiver_bt).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.dynamic_broadcast_receiver_bt:
                Intent intent = new Intent(DynamicReceiver.INTENT_ACTION);
                intent.putExtra(DynamicReceiver.DYNAMIC_MESSAGE, UUID.randomUUID().toString());
                this.sendBroadcast(intent);
                break;
        }

    }
}

BroadcastReceiver 启动 Service

要做一个这样工作： Activity发送广播，BroadcastReceiver接收到了广播，启动Service去开启一个AsyncTask下载图片，下载好图片再发送数据给BroadcastReceiver，广播再将数据带给Activity，渲染到ImageView上，最后再保存相册。

参考了如下：

• 1. AsyncTask模板
• 2. Android 下载图片保存到相册
• 3. Android Service 及 AIDL

DownloadReceiverActivity

public class DownloadReceiverActivity extends AppCompatActivity implements View.OnClickListener {

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

    private Button downloadBT;
    private ImageView downloadIV;

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

    private void registerReceiver() {
        DownloadReceiver downloadReceiver = new DownloadReceiver();
        IntentFilter intentFilter = new IntentFilter();
        intentFilter.addAction(DownloadReceiver.INTENT_ACTION);
        this.registerReceiver(downloadReceiver, intentFilter);
    }

    private void initViews() {
        TextView downloadTV = (TextView) this.findViewById(R.id.down_broadcast_image_tv);
        downloadTV.setText(OBJECT_IMAGE_URL);
        this.downloadBT = (Button) this.findViewById(R.id.down_broadcast_start_bt);
        this.downloadIV = (ImageView) this.findViewById(R.id.down_broadcast_image_iv);
    }

    private void initListeners() {
        this.downloadBT.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.down_broadcast_start_bt:
                v.setEnabled(false);
                Intent intent = new Intent(DownloadReceiver.INTENT_ACTION);
                intent.putExtra(DownloadReceiver.INTENT_DATA_IMAGE_URL, OBJECT_IMAGE_URL);
                intent.putExtra(DownloadReceiver.INTENT_TYPE, DownloadReceiver.TYPE_DOWNLOAD_START);
                this.sendBroadcast(intent);
                break;
        }
    }

    /**
     * 下载广播
     */
    public class DownloadReceiver extends BroadcastReceiver {

        public static final String INTENT_ACTION = "com.camnter.android.intent.download";
        public static final String INTENT_TYPE = "type";
        public static final String INTENT_DATA_IMAGE_URL = "image_url";
        public static final String INTENT_DATA_IMAGE_PATH = "image_path";
        public static final int TYPE_DOWNLOAD_START = 2061;
        public static final int TYPE_DOWNLOAD_SUCCESS = 2062;
        public static final int TYPE_DOWNLOAD_FAILURE = 2063;

        @Override
        public void onReceive(Context context, Intent intent) {
            int type = intent.getIntExtra(INTENT_TYPE, -1);
            if (type == -1) return;
            switch (type) {
                case TYPE_DOWNLOAD_START: {
                    String url = intent.getStringExtra(INTENT_DATA_IMAGE_URL);
                    DownloadIntentService.startActionDownload(context, url);
                    break;
                }
                case TYPE_DOWNLOAD_SUCCESS: {
                    String imageFilePath = intent.getStringExtra(INTENT_DATA_IMAGE_PATH);
                    /**
                     * 设置按钮可用，并隐藏Dialog
                     */
                    DownloadReceiverActivity.this.downloadBT.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);
                    DownloadReceiverActivity.this.downloadIV.setImageBitmap(bitmap);

                    /**
                     * 保存图片到相册
                     */
                    String imageName = System.currentTimeMillis() + ".jpg";
                    MediaStore.Images.Media.insertImage(DownloadReceiverActivity.this.getApplicationContext().getContentResolver(), bitmap, imageName, "camnter");
                    Toast.makeText(DownloadReceiverActivity.this, "已保存：" + imageName, Toast.LENGTH_LONG).show();
                    break;
                }
                case TYPE_DOWNLOAD_FAILURE: {
                    DownloadReceiverActivity.this.downloadBT.setEnabled(true);
                    break;
                }
            }
        }

    }

}

DownloadIntentService

public class DownloadIntentService extends IntentService {
    // TODO: Rename actions, choose action names that describe tasks that this
    // IntentService can perform, e.g. ACTION_FETCH_NEW_ITEMS
    private static final String ACTION_DOWNLOAD = "com.camnter.newlife.service.action.download";

    // TODO: Rename parameters
    private static final String IMAGE_URL = "com.camnter.newlife.service.extra.image.url";

    /**
     * Starts this service to perform action Foo with the given parameters. If
     * the service is already performing a task this action will be queued.
     *
     * @see IntentService
     */
    // TODO: Customize helper method
    public static void startActionDownload(Context context, String url) {
        Intent intent = new Intent(context, DownloadIntentService.class);
        intent.setAction(ACTION_DOWNLOAD);
        intent.putExtra(IMAGE_URL, url);
        context.startService(intent);
    }


    public DownloadIntentService() {
        super("DownIntentService");
    }

    @Override
    protected void onHandleIntent(Intent intent) {
        if (intent != null) {
            final String action = intent.getAction();
            if (ACTION_DOWNLOAD.equals(action)) {
                final String url = intent.getStringExtra(IMAGE_URL);
                this.handleActionDownload(url);
            }
        }
    }

    /**
     * Handle action Download in the provided background thread with the provided
     * parameters.
     */
    private void handleActionDownload(String url) {
        // TODO: Handle action Download
        new DownloadImageAsyncTask(this).execute(url);
    }

    /**
     * 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);
            Intent intent = new Intent(DownloadReceiverActivity.DownloadReceiver.INTENT_ACTION);
            intent.putExtra(
                    DownloadReceiverActivity.DownloadReceiver.INTENT_TYPE,
                    DownloadReceiverActivity.DownloadReceiver.TYPE_DOWNLOAD_SUCCESS
            );
            intent.putExtra(
                    DownloadReceiverActivity.DownloadReceiver.INTENT_DATA_IMAGE_PATH,
                    this.localFilePath
            );
            DownloadIntentService.this.sendBroadcast(intent);
        }

        /**
         * 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();
            Intent intent = new Intent(DownloadReceiverActivity.DownloadReceiver.INTENT_ACTION);
            intent.putExtra(
                    DownloadReceiverActivity.DownloadReceiver.INTENT_TYPE,
                    DownloadReceiverActivity.DownloadReceiver.TYPE_DOWNLOAD_FAILURE
            );
            DownloadIntentService.this.sendBroadcast(intent);
        }

    }

}

AndroidManifest.xml

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

效果图