Android学习笔记——服务最佳实践

2017-08-12

参考书籍:Android第一行代码(第二版).郭霖著

实现完整下载功能。

创建ServiceBestPractice项目。首先在app/build.gradle中dependencies下添加OKHttp库依赖(网络相关功能使用):

compile 'com.squareup.okhttp3:okhttp:3.8.1'

定义一个回调接口,用于对下载过程中各种状态进行监听和回调:

public interface DownloadListener {
    void onProgress(int progress);//通知当前下载进度
    void onSuccess();//通知下载成功事件
    void onFailed();//通知下载失败事件
    void onPaused();//通知下载暂停事件
    void onCanceled();//通知下载取消事件
}

编写下载功能,新建DownloadTask继承自AsyncTask:

public class DownloadTask extends AsyncTask<String, Integer, Integer> {//三个泛型参数,第一个表示在执行AsyncTask时需传入一个字符串参数给后台任务,
    //第二个使用整型数据最为进度显示单位,第三个表示使用整型数据来反馈结果执行

    //定义四个整型常量分别表示下载的不同状态
    public static final int TYPE_SUCCESS = 0;
    public static final int TYPE_FAILED = 1;
    public static final int TYPE_PAUSE = 2;
    public static final int TYPE_CANCELED = 3;

    private DownloadListener listener;
    private boolean isCanceled = false;
    private boolean isPaused = false;
    private int lastProgress;

    public DownloadTask(DownloadListener listener){
        this.listener = listener;//将下载的状态通过此参数进行回调
    }

    //在后台执行具体的下载逻辑
    @Override
    protected Integer doInBackground(String... params) {//String... params:可变长参数列表,必须是String类型,转化为数组处理
        InputStream is = null;
        RandomAccessFile savedFile = null;
        File file = null;
        try{
            long downloadedLength = 0;//记录已下载的文件长度
            String downloadUrl = params[0];//获取下载的URL地址
            String fileName = downloadUrl.substring(downloadUrl.lastIndexOf("/"));//根据URL地址解析出下载的文件名
            String directory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath();//指定下载路径Environment.DIRECTORY_DOWNLOADS,SD卡的Download目录
            file = new File(directory + fileName);
            if (file.exists()){//判断是否已存在要下载的文件,存在则读取已下载的字节数(可启用断点续传功能)
                downloadedLength = file.length();
            }
            long contentLength = getContentLength(downloadUrl);//获取待下载文件的总长度
            if (contentLength == 0){//总长度为0,说明文件有问题
                return TYPE_FAILED;
            }else if (contentLength == downloadedLength){//已下载字节和文件总字节相等,说明已经下载完成了
                return TYPE_SUCCESS;
            }
            OkHttpClient client = new OkHttpClient();
            Request request = new Request.Builder()
                    //断点下载,指定从哪个字节开始下载(已下载部分不需再重新下载)
                    .addHeader("RANGE", "bytes=" + downloadedLength + "-")
                    .url(downloadUrl)
                    .build();
            Response response = client.newCall(request).execute();
            if (response != null){//使用Java文件流方式不断从网络上读取数据,不断写入到本地,直到文件全部下载完
                is = response.body().byteStream();
                savedFile = new RandomAccessFile(file, "rw");
                savedFile.seek(downloadedLength);//跳过已下载的字节
                byte[] b = new byte[1024];
                int total = 0;
                int len;
                while ((len = is.read(b)) != -1){
                    if (isCanceled){//判断用户有没触发暂停或取消操作,如果有则返回相应值来中断下载
                        return TYPE_CANCELED;
                    }else if (isPaused){
                        return TYPE_PAUSE;
                    }else {
                        total += len;
                        savedFile.write(b, 0, len);
                        //计算已下载的百分比
                        int progress = (int) ((total + downloadedLength) * 100 / contentLength);
                        publishProgress(progress);//通知进度
                    }
                }
                response.body().close();
                return TYPE_SUCCESS;
            }
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            try {
                if (is != null){
                    is.close();
                }
                if (savedFile != null){
                    savedFile.close();
                }
                if (isCanceled && file != null){
                    file.delete();
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return TYPE_FAILED;
    }

    //在界面更新当前的下载进度
    @Override
    protected void onProgressUpdate(Integer... values) {
        int progress  = values[0];//获取当前下载进度
        if (progress > lastProgress){//与上一次下载进度对比
            listener.onProgress(progress);//有变化则调用DownloadListener的onProgress()通知下载进度更新
            lastProgress = progress;
        }
    }

    //通知最终下载结果
    @Override
    protected void onPostExecute(Integer status) {
        switch (status){//根据传入的下载状态进行回调
            case TYPE_SUCCESS:
                listener.onSuccess();
                break;
            case TYPE_FAILED:
                listener.onFailed();
                break;
            case TYPE_PAUSE:
                listener.onPaused();
                break;
            case TYPE_CANCELED:
                listener.onCanceled();
                break;
            default:
                break;
        }
    }

    public void pauseDownload(){
        isPaused = true;
    }
    public void cancelDownload(){
        isCanceled = true;
    }

    private long getContentLength(String downloadUrl) throws IOException{
        OkHttpClient client = new OkHttpClient();
        Request request = new Request.Builder().url(downloadUrl).build();
        Response response = client.newCall(request).execute();
        if (response != null && response.isSuccessful()){
            long contentLength = response.body().contentLength();
            response.close();
            return contentLength;
        }
        return 0;
    }

}

为了保证DownliadTask可一直在后台运行,需创建一个下载的服务DownloadService(使用快捷方式创建):

public class DownloadService extends Service {
    private DownloadTask downloadTask;
    private String downloadUrl;
    //创建DownloadListener匿名类实例
    private DownloadListener listener = new DownloadListener() {
        @Override
        public void onProgress(int progress) {
            getNotificationManager().notify(1, getNotification("Downloading...", progress));
        }

        @Override
        public void onSuccess() {
            downloadTask = null;
            //下载成功时将前台服务通知关闭,并创建一个下载成功的通知
            stopForeground(true);
            getNotificationManager().notify(1, getNotification("Download Success", -1));
            Toast.makeText(DownloadService.this, "Download Success", Toast.LENGTH_SHORT).show();

        }

        @Override
        public void onFailed() {
            downloadTask  = null;
            //下载失败时将前台服务通知关闭,并创建一个下载失败的通知
            stopForeground(true);
            getNotificationManager().notify(1, getNotification("Download Failed", -1));
            Toast.makeText(DownloadService.this, "Download Failed", Toast.LENGTH_SHORT).show();

        }

        @Override
        public void onPaused() {
            downloadTask  = null;
            Toast.makeText(DownloadService.this, "Paused", Toast.LENGTH_SHORT).show();

        }

        @Override
        public void onCanceled() {
            downloadTask  = null;
            stopForeground(true);
            Toast.makeText(DownloadService.this, "Canceled", Toast.LENGTH_SHORT).show();

        }
    };

    private DownloadBinder mBinder = new DownloadBinder();

    @Override
    public IBinder onBind(Intent intent) {
        return mBinder;
    }

    class DownloadBinder extends Binder{
        public void startDownload(String url){
            if (downloadTask == null){
                downloadUrl = url;
                downloadTask = new DownloadTask(listener);
                downloadTask.execute(downloadUrl);
                startForeground(1, getNotification("Downloading...", 0));
                Toast.makeText(DownloadService.this, "Downloading...", Toast.LENGTH_SHORT).show();
            }
        }
        public void pauseDownload(){
            if (downloadTask != null){
                downloadTask.pauseDownload();
            }
        }
        public void cancelDownload(){
            if (downloadTask != null){
                downloadTask.cancelDownload();
            }else {
                if (downloadUrl != null){
                    //取消下载时需将文件删除,并将通知关闭
                    String fileName = downloadUrl.substring(downloadUrl.lastIndexOf("/"));
                    String directroy = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath();
                    File file = new File(directroy + fileName);
                    if (file.exists()){
                        file.delete();
                    }
                    getNotificationManager().cancel(1);
                    stopForeground(true);
                    Toast.makeText(DownloadService.this, "Canceled", Toast.LENGTH_SHORT).show();
                }
            }
        }
    }
    private NotificationManager getNotificationManager(){
        return (NotificationManager)getSystemService(NOTIFICATION_SERVICE);
    }
    private Notification getNotification(String title, int progress){
        Intent intent = new Intent(this, MainActivity.class);
        PendingIntent pi = PendingIntent.getActivity(this, 0, intent, 0);
        NotificationCompat.Builder builder = new NotificationCompat.Builder(this);
        builder.setSmallIcon(R.mipmap.ic_launcher);
        builder.setLargeIcon(BitmapFactory.decodeResource(getResources(), R.mipmap.ic_launcher));
        builder.setContentIntent(pi);
        builder.setContentTitle(title);
        if (progress > 0){
            //当progress大于或等于0时才需显示下载进度
            builder.setContentText(progress + "%");
            builder.setProgress(100, progress, false);//三个参数:通知的最大进度,通知的当前进度,是否使用模糊进度条
        }
        return builder.build();
    }
}

后端基本完成,编写前端,修改布局文件,放置三个按钮分别用于开始下载、暂停下载和取消下载。
修改MainActivity:

public class MainActivity extends AppCompatActivity implements View.OnClickListener{
    private DownloadService.DownloadBinder downloadBinder;
    private ServiceConnection connection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            downloadBinder = (DownloadService.DownloadBinder) service;
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {

        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button startDownload = (Button) findViewById(R.id.start_download);
        Button pauseDownload = (Button) findViewById(R.id.pause_download);
        Button cancelDownload = (Button) findViewById(R.id.cancel_download);
        startDownload.setOnClickListener(this);
        pauseDownload.setOnClickListener(this);
        cancelDownload.setOnClickListener(this);
        Intent intent =new Intent(this, DownloadService.class);
        startService(intent);//启动服务,保证服务一直在后台运行
        bindService(intent, connection, BIND_AUTO_CREATE);//绑定服务,让MainActivity和服务进行通信
        if (ContextCompat.checkSelfPermission(MainActivity.this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED){
            ActivityCompat.requestPermissions(MainActivity.this, new String[]{
                    Manifest.permission.WRITE_EXTERNAL_STORAGE}, 1);
        }
    }

    @Override
    public void onClick(View v) {
        if (downloadBinder == null){
            return;
        }
        switch (v.getId()){
            case R.id.start_download:
                String url = "https://raw.githubusercontent.com/guolindev/eclipse/master/eclipse-inst-win64.exe";
                downloadBinder.startDownload(url);
                break;
            case R.id.pause_download:
                downloadBinder.pauseDownload();
                break;
            case R.id.cancel_download:
                downloadBinder.cancelDownload();
                break;
            default:
                break;
        }

    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        switch (requestCode){
            case 1:
                if (grantResults.length > 0 && grantResults[0] != PackageManager.PERMISSION_GRANTED){
                    Toast.makeText(this, "拒绝权限将无法使用程序", Toast.LENGTH_SHORT).show();
                    finish();
                }
                break;
            default:
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        unbindService(connection);//解绑服务,避免内存泄漏
    }
}

最后还要声明网络和SD卡访问权限:

<uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

运行程序:这里写图片描述

允许之后,点击按钮测试:
这里写图片描述

点击停止、取消都会弹出相应提示,下载完成也会提示:这里写图片描述

再次点击开始下载就不会再下载了,同样会弹出这个提示,点击取消之后再点下载又会开始下载。



注明:本文章属于转载,仅供行业人员学习交流使用,文章版权属于原创作者,在此向原创者致敬,感谢原创作者为大家学习交流提供精品内容。

站方声明:IThao123是为广大互联网从业者免费提供学习交流的平台,如果侵犯了原创著作权,请联系站方删除,给你带来不便,深表歉意。

顶部