39.Android BroadcastReceiver
Android BroadcastReceiver 介紹
現在的BroadcastReceiver好多都用在了做推送上。比如極光推送、信鴿推送等等。
推送用BroadcastReceiver發多都是提示一個Notification。服務端發送推送，推送Android SDK內的通信機制接受到了推送，然後發送廣播通知，BroadcastReceiver接收到了通知，進而區分通知類型，執行對應的操作，很多時候，我們都是看到一個Notification（QQ消息通知、微信消息通知等等）。
Android BroadcastReceiver 功能
就是簡單的三句話。
- 1.Android的跨組件通信
- 2.Android的跨線程通信
- 3.Android的跨進程（App）通信
爲什麼會這樣子呢？請見下面的淺淡機制。
Android BroadcastReceiver 淺淡機制
Android BroadcastReceiver 的實現使用的是觀察者模式。
觀察者模式：假如，所有事件的都要實現Event接口，監聽事件都需要將View的引用作爲參數傳入Event的構造方法中。有N個View添加了A事件的監聽，M個View添加了B事件的監聽。那麼，就有N+M個View的引用放在觀察者池裏。此時，假如隨便從哪發來了一個A事件，都要遍歷那個長度爲N+M的觀察者池，查看裏面的哪個引用的事件是A事件，然後調用引用的事件響應方法。從而，完成一次觀察者模式的事件監聽。
Android BroadcastReceiver 的實現原理就是如此：使用了觀察者模式的監聽方式，在動態或靜態註冊廣播時，添加對應的Action作爲與BroadcastReceiver通信的通道，發送廣播等於消息的發佈，添加Action等於訂閱事件。這樣大大解耦了發送者和接收者，流程大題如下：
1.BroadcastReceiver 通過Binder機制在AMS（Activity Manager Service）註冊。
2.View發送廣播時，也是通過Binder機制向AMS（Activity Manager Service）發送廣播通知。
3.AMS根據發來的Intent裏的Action查找對應的IntentFilter或者Permission，篩選出BroadcastReceiver，然後將廣播轉發到BroadcastReceiver上相應的消息循環隊列中。
4.在BroadcastReceiver的消息循環隊列執行循環時，拿到了此廣播，回調BroadcastReceiver的onReceive()方法。
從此看來，這裏的BroadcastReceiver充當了觀察者；View充當了消息發送者；AMS就相當於消息處理中心，其內部包含了一個觀察者池。
靜態BroadcastReceiver 實現
靜態BroadcastReceiver就需要在AndroidMainfest.xml文件裏配置<receiver>：
receiver標籤屬性
<!--
enabled: "true" 或者 "false"
exported: "true" 或者 "false"
icon: 資源Id
label: 資源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：表示的是該BroadcastReceiver是否接受其他App的廣播。true爲接收；false爲不接收。其默認值：如果有intent-filter，默認值爲true；沒有intent-filter，默認值爲false。（ Activity 或 Service中的android:exported的默認值是這樣設置的 ）這裏區分的是App，不是進程，因爲一個App中可能有多進程。
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;
}
}
}動態BroadcastReceiver 實現
動態BroadcastReceiver就不需要在AndroidManifest.xml裏配置，需要手動代碼註冊。
涉及到兩個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;
}
/**
* 提供給外部註冊廣播
*
* @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 啓動 Service
要做一個這樣工作： Activity發送廣播，BroadcastReceiver接收到了廣播，啓動Service去開啓一個AsyncTask下載圖片，下載好圖片再發送數據給BroadcastReceiver，廣播再將數據帶給Activity，渲染到ImageView上，最後再保存相冊。
參考瞭如下：
DownloadReceiverActivity
public class DownloadReceiverActivity extends AppCompatActivity implements View.OnClickListener {
private static final String OBJECT_IMAGE_URL = "https://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;
}
}
/**
* 下載廣播
*/
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);
/**
* 設置按鈕可用，並隱藏Dialog
*/
DownloadReceiverActivity.this.downloadBT.setEnabled(true);
DisplayMetrics metrics = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(metrics);
int screenWidth = metrics.widthPixels;
int screenHeight = metrics.heightPixels;
/**
* ImageUtil.decodeScaleImage 解析圖片
*/
Bitmap bitmap = ImageUtil.decodeScaleImage(imageFilePath, screenWidth, screenHeight);
DownloadReceiverActivity.this.downloadIV.setImageBitmap(bitmap);
/**
* 保存圖片到相冊
*/
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);
}
/**
* 下載圖片異步任務
*/
public class DownloadImageAsyncTask extends AsyncTask<String, Integer, String> {
private Service service;
private String localFilePath;
public DownloadImageAsyncTask(Service service) {
super();
this.service = service;
}
/**
* 對應AsyncTask第一個參數
* 異步操作，不在主UI線程中，不能對控件進行修改
* 可以調用publishProgress方法中轉到onProgressUpdate(這裏完成了一個handler.sendMessage(...)的過程)
*
* @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();
//計算文件長度
int lengthOfFile = connection.getContentLength();
/**
* 不存在SD卡，就放到緩存文件夾內
*/
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();
//下載
byte[] buffer = new byte[1024];
int len;
long total = 0;
// 計算進度
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;
}
/**
* 對應AsyncTask第三個參數 (接受doInBackground的返回值)
* 在doInBackground方法執行結束之後在運行，此時已經回來主UI線程當中 能對UI控件進行修改
*
* @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);
}
/**
* 對應AsyncTask第二個參數
* 在doInBackground方法當中，每次調用publishProgress方法都會中轉(handler.sendMessage(...))到onProgressUpdate
* 在主UI線程中，可以對控件進行修改
*
* @param values The values indicating progress.
* @see #publishProgress
* @see #doInBackground
*/
@Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
}
/**
* 運行在主UI線程中，此時是預執行狀態，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" />效果圖
