Service使用AlarmManager实现后台定时任务

在Android 4.0.3版本中, 使用AlarmManager实现后台定时任务是比较好的方案, 其实现机制, 是利用Service的 onStartCommand() 方法, 在每次被AlarmManager唤醒后, 执行任务并注册下一次唤醒到AlarmManager. 涉及的代码

1. 新建DaemonService, 实现 onStartCommand() 方法, 在这个方法中新开线程执行任务, 并再次将AlarmReceiver注册到AlarmManager. 注: 同样的注册多次调用时, 不会注册多个, 而是会进行更新. 这个方法会在Activity中调用 startService(intent); 方法时被调用.

@Override    public int onStartCommand(Intent intent, int flags, int startId) {        new DaemonThread().start();        AlarmManager manager = (AlarmManager) getSystemService(ALARM_SERVICE);        long triggerAtTime = SystemClock.elapsedRealtime() + 5 * 1000;        Intent i = new Intent(this, AlarmReceiver.class);        PendingIntent pi = PendingIntent.getBroadcast(this, 0, i, 0);        manager.set(AlarmManager.ELAPSED_REALTIME_WAKEUP, triggerAtTime, pi);        return super.onStartCommand(intent, flags, startId);    }

 2. onDestroy() 方法在调用 Activity stopService(intent) 时会被调用, 此时需要将AlarmReceiver从AlarmManager中cancel掉.

@Override    public void onDestroy() {        Log.d(TAG, "onDestroy");        AlarmManager manager = (AlarmManager) getSystemService(ALARM_SERVICE);        Intent i = new Intent(this, AlarmReceiver.class);        PendingIntent pi = PendingIntent.getBroadcast(this, 0, i, 0);        manager.cancel(pi);        super.onDestroy();    }

3. 新建Receiver, 用来注册到AlarmManager, 用于将来响应Alarm消息. 在内部的onReceive方法中, 启动DaemonService

public class AlarmReceiver extends BroadcastReceiver {    @Override    public void onReceive(Context context, Intent intent) {        Intent i = new Intent(context, DaemonService.class);        context.startService(i);    }}

4. 在AndroidManifest.xml中添加Service和Receiver

5. 在Activity中, 对应控件的点击响应中添加service的启动, 停止代码

@Override    public boolean onOptionsItemSelected(MenuItem item) {        // ...        if (id == R.id.action_start) {            Intent intent = new Intent(this, DaemonService.class);            startService(intent);            return true;        }        if (id == R.id.action_stop) {            Intent intent = new Intent(this, DaemonService.class);            stopService(intent);            return true;        }        // ...        return super.onOptionsItemSelected(item);    }

定时任务中使用 AsyncTask和 httpUrlConnection访问网址, 使用Callback进行结果回调

1. 新建HttpAsyncCallback接口, 要接收AsyncTask返回数据的, 都要实现这个接口

public interface HttpAsyncCallback {    // This function will be called from inside of your AsyncTask when you are ready to callback to    // your controllers (like a fragment, for example) The object in the completionHandler will be    // whatever it is that you need to send to your controllers    void completionHandler(Boolean success, int type, Object object);}

2. 新建HttpAsyncTask类, 进行实际的HTTP访问

public class HttpAsyncTask extends AsyncTask
     
       {    public static final int METHOD_GET = 0;    public static final int METHOD_POST = 1;    private static final String TAG = HttpAsyncTask.class.getSimpleName();    private String postData;    private int method;    private int connectTimeout;    private int readTimeout;    private String encoding;    private int type;    private HttpAsyncCallback callback;    public HttpAsyncTask(int method, String encoding) {        this(null, method, encoding, 10000, 10000, 0, null);    }    public HttpAsyncTask(int method, String encoding, int type, HttpAsyncCallback callback) {        this(null, method, encoding, 10000, 10000, type, callback);    }    public HttpAsyncTask(String postData, int method, String encoding, int type, HttpAsyncCallback callback) {        this(postData, method, encoding, 10000, 10000, type, callback);    }    public HttpAsyncTask(String postData, int method, String encoding, int connectTimeout, int readTimeout, int type, HttpAsyncCallback callback) {        this.postData = postData;        this.method = method;        this.encoding = encoding;        this.connectTimeout = connectTimeout;        this.readTimeout = readTimeout;        this.type = type;        this.callback = callback;    }    @Override    protected Void doInBackground(String... strings) {        Log.d(TAG, "Timestamp:" + System.currentTimeMillis());        HttpURLConnection connection = null;        try {            connection = (HttpURLConnection) new URL(strings[0]).openConnection();            connection.setConnectTimeout(connectTimeout);            connection.setReadTimeout(readTimeout);            if (method == METHOD_GET) {                connection.setRequestMethod("GET");            } else {                // get请求的话默认就行了，post请求需要setDoOutput(true)，这个默认是false的。                connection.setDoOutput(true);                connection.setRequestMethod("POST");                if (this.postData != null) {                    OutputStreamWriter writer = new OutputStreamWriter(connection.getOutputStream());                    writer.write(postData);                    writer.flush();                }            }            int statusCode = connection.getResponseCode();            if (statusCode ==  200) {                InputStream in = connection.getInputStream();                byte[] bytes = getBytesByInputStream(in);                String response = new String(bytes, encoding);                Log.d(TAG, response);                // From here you can convert the string to JSON with whatever JSON parser you like to use                // After converting the string to JSON, I call my custom callback. You can follow this                // process too, or you can implement the onPostExecute(Result) method                // Use the response to create the object you need                if (callback != null) {                    callback.completionHandler(true, type, "Timestamp:" + System.currentTimeMillis() + ", " + response);                }            } else {                Log.d(TAG, statusCode+"");                if (callback != null) {                    callback.completionHandler(false, type, statusCode);                }            }        } catch (IOException e) {            Log.e(TAG, e.getMessage(), e);        } finally {            if (connection != null){                connection.disconnect();            }        }        return null;    }    private byte[] getBytesByInputStream(InputStream is) {        ByteArrayOutputStream bos = new ByteArrayOutputStream();        byte[] buffer = new byte[1024];        int length;        try {            while ((length = is.read(buffer)) != -1) {                bos.write(buffer, 0, length);            }        } catch (IOException e) {            Log.e(TAG, e.getMessage());        } finally {            try {                bos.close();            } catch (IOException e) {                Log.e(TAG, e.getMessage());            }        }        return bos.toByteArray();    }    public static String formDataToString(Map
      
        data, String encoding) {        StringBuilder sb = new StringBuilder();        String con = "";        for (String key : data.keySet()) {            String value = data.get(key);            try {                key = URLEncoder.encode(key, encoding);                value = URLEncoder.encode(value, encoding);                sb.append(con).append(key).append("=").append(value);                con = "&";            } catch (UnsupportedEncodingException e) {                Log.e(TAG, "UnsupportedEncodingException " + encoding + " in processing:" + key);            }        }        return sb.toString();    }    public static String formDataToJson(Map
       
         data, String encoding) {        if (data != null) {            JSONObject jsonObject = new JSONObject(data);            return jsonObject.toString();        }        return null;    }}
       
      
     

 

使用 Callback和BroadcastReceiver实现消息通信

1. 在DaemonService中实现HttpAsyncCallback接口, 用于接收HttpAsyncTask任务执行结果

public class DaemonService extends Service implements HttpAsyncCallback {    private static final String TAG = DaemonService.class.getSimpleName();    // ...    @Override    public void completionHandler(Boolean success, int type, Object object) {        Log.d(TAG, "completionHandler");    }}

2. 在DaemonService的onStartCommand()方法中, 将自己做为参数传给HttpAsyncTask. 1和2是为了将AsyncTask的结果传回Service

@Override    public int onStartCommand(Intent intent, int flags, int startId) {        Map
     
       map = new HashMap<>();        map.put("phone", "13800138000");        HttpAsyncTask task = new HttpAsyncTask(HttpAsyncTask.formDataToString(map, "UTF-8"), HttpAsyncTask.METHOD_POST, "UTF-8", 0, this);        task.execute("https://www.toutiao.com/api/pc/realtime_news/");        //new DaemonThread("").start();        AlarmManager manager = (AlarmManager) getSystemService(ALARM_SERVICE);        long triggerAtTime = SystemClock.elapsedRealtime() + 5 * 1000;        Intent i = new Intent(this, AlarmReceiver.class);        PendingIntent pi = PendingIntent.getBroadcast(this, 0, i, 0);        manager.set(AlarmManager.ELAPSED_REALTIME_WAKEUP, triggerAtTime, pi);        return super.onStartCommand(intent, flags, startId);    }
     

3. 为了从Service将结果传回Fragment, 需要在Fragment中注册一个BroadcastReceiver, 实现onReceive方法, 在这个方法中将结果更新到TextView, 在onCreateView中初始化这个receiver, 在onStart和onStop方法中进行注册和取消. 注意: 从fragment中获取TextView时, 需要在onActivityCreated方法中才行, 在其他的事件方法(onCreateView, onAttach中, findViewById拿到的是null

public class MainActivityFragment extends Fragment {    private static final String TAG = MainActivityFragment.class.getSimpleName();    private BroadcastReceiver receiver;    private TextView tv;    ...    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {        Log.d(TAG, "onCreateView");        receiver = new BroadcastReceiver() {            @Override            public void onReceive(Context context, Intent intent) {                String s = intent.getStringExtra("msg");                tv.setText(s);            }        };        return inflater.inflate(R.layout.fragment_main, container, false);    }    @Override    public void onAttach(Context context) {        Log.d(TAG, "onAttach");        super.onAttach(context);    }    @Override    public void onActivityCreated(@Nullable Bundle savedInstanceState) {        Log.d(TAG, "onActivityCreated");        super.onActivityCreated(savedInstanceState);        tv = getActivity().findViewById(R.id.sample_text);    }    @Override    public void onStart() {        Log.d(TAG, "onStart");        super.onStart();        if (receiver != null) {            IntentFilter intentFilter = new IntentFilter(MainActivityFragment.class.getName() + ".TextView");            getActivity().registerReceiver(receiver, intentFilter);        }    }    @Override    public void onStop() {        Log.d(TAG, "onStop");        if (receiver != null) {            getActivity().unregisterReceiver(receiver);        }        super.onStop();    }}

 

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