Android学习之IntentService执行耗时任务

一、概述
我们都知道在Service里面我们不能直接进行耗时操作，一般都需要去开启子线程去做一些事情，自己去管理Service的生命周期以及子线程并非是个优雅的做法；好在Android给我们提供了一个类，叫做IntentService。
IntentService是一个基于Service的一个类，用来处理异步的请求。可以通过startService(Intent)来提交请求，该Service会在需要的时候创建，当完成所有的任务以后自己关闭，且请求是在工作线程处理的。
IntentService负责执行后台的耗时的任务，也因为IntentService是服务的原因，这导致它的优先级比单纯的线程要高。
所以IntentService适用于执行高优先级的后台任务。
使用IntentService最起码有两个好处，一方面不需要自己去new Thread了；另一方面不需要考虑在什么时候关闭该Service。
二、代码示例

package com.aldx.presidentcockpit.service;

import android.app.IntentService;
import android.content.Context;
import android.content.Intent;
import android.support.v4.content.LocalBroadcastManager;

import com.aldx.presidentcockpit.model.MonitorInfo;
import com.aldx.presidentcockpit.utils.LogUtil;
import com.aldx.presidentcockpit.utils.Utils;
import com.hikvision.netsdk.HCNetSDK;
import com.hikvision.netsdk.INT_PTR;
import com.hikvision.netsdk.NET_DVR_JPEGPARA;

/**
 * author: chenzheng
 * created on: 2018/4/24 14:59
 * description:
 */

public class DownloadImgService extends IntentService {
    public static final String DOWNLOAD_RESULT = "com.aldx.presidentcockpit.service.DOWNLOAD_RESULT";
    private static final String ACTION_DOWNLOAD_IMG = "com.aldx.presidentcockpit.service.action.DOWNLOAD_IMAGE";

    public static void startDownloadImg(Context context,int loginId, int channel, String path) {
        Intent intent = new Intent(context, DownloadImgService.class);
        intent.setAction(ACTION_DOWNLOAD_IMG);
        intent.putExtra("hk_login_id", loginId);
        intent.putExtra("hk_channel", channel);
        intent.putExtra("hk_image_path", path);
        context.startService(intent);
    }


    public DownloadImgService() {
        super("DownloadImgService");
    }

    @Override
    protected void onHandleIntent(Intent intent) {
        if (intent != null) {
            final String action = intent.getAction();
            if (ACTION_DOWNLOAD_IMG.equals(action)) {
                String path = intent.getStringExtra("hk_image_path");
                int loginId = intent.getIntExtra("hk_login_id", -1);
                int channel = intent.getIntExtra("hk_channel", -1);
                handleUploadImg(loginId, channel, path);
            }
        }
    }

    private void handleUploadImg(int loginId, int channel, String path) {
        try {
            NET_DVR_JPEGPARA jpeg = new NET_DVR_JPEGPARA();
            // 设置图片的分辨率
            jpeg.wPicSize = 2;
            // 设置图片质量
            jpeg.wPicQuality = 2;
            boolean is = HCNetSDK.getInstance().NET_DVR_CaptureJPEGPicture(loginId,
                    channel, jpeg, path);
            if (is) {
                LogUtil.e("成功：" + path);
            } else {
                LogUtil.e("失败：" + path);
                LogUtil.e(HCNetSDK.getInstance().NET_DVR_GetErrorMsg(new INT_PTR()));
            }

            LocalBroadcastManager localBroadcastManager = LocalBroadcastManager.getInstance(this);
            Intent intent = new Intent(DOWNLOAD_RESULT);
            localBroadcastManager.sendBroadcast(intent);

        } catch (Exception e) {
            e.printStackTrace();
        }


    }

    @Override
    public void onCreate() {
        super.onCreate();
        LogUtil.e("TAG", "onCreate");
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        LogUtil.e("TAG", "onDestroy");
    }
}

public static final String UPLOAD_RESULT = "com.aldx.presidentcockpit.service.DOWNLOAD_RESULT";

//注册广播接收器
        LocalBroadcastManager localBroadcastManager = LocalBroadcastManager.getInstance(getActivity());
        IntentFilter intentFilter = new IntentFilter(UPLOAD_RESULT);
        localBroadcastManager.registerReceiver(downloadHkImgReceiver, intentFilter);

private BroadcastReceiver downloadHkImgReceiver = new BroadcastReceiver() {

        @Override
        public void onReceive(Context context, Intent intent) {
            LogUtil.e("接收图片下载结果广播");
            if (mWorkering && intent.getAction().equals(UPLOAD_RESULT)) {
                videoRecyclerview.refreshComplete();
                if (playMonitorList.size() > 0) {
                    loadingLayout.showContent();
                } else {
                    loadingLayout.showEmpty();
                }
                adapter.setItems(playMonitorList);
            }
        }
    };

for (int i = 0; i < playMonitorList.size(); i++) {
            MonitorInfo monitorInfo = playMonitorList.get(i);
            String imgPath = Utils.getHikvisionCapturePath(getActivity()) + "/" + System.currentTimeMillis() + ".jpg";
            monitorInfo.imagePath = imgPath;
            DownloadImgService.startDownloadImg(getActivity(), m_iLogID, monitorInfo.chanl, imgPath);
        }

@Override
    public void onDestroy() {
        super.onDestroy();
        mWorkering = false;
        if (downloadHkImgReceiver != null) {
            LocalBroadcastManager.getInstance(getActivity()).unregisterReceiver(downloadHkImgReceiver);
            downloadHkImgReceiver = null;
        }
    }

<service android:name="com.aldx.presidentcockpit.service.DownloadImgService" />

当Service的每个任务完成的时候，会发送一个广播，我们在Activity/Fragment里面分别注册和解注册了广播；当收到广播则更新指定的UI。