《第一行代码Android》学习总结第十章 Service实践——下载功能示例

1、在app/build.gradle文件，dependencies闭包中添加依赖。

compile 'com.squareup.okhttp3:okhttp:3.4.1'

2、定义DownloadListener回调接口，用于对下载过程中的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}

3、新建DownloadTask继承自AsyncTask。

public class DownloadTask extends AsyncTask {//下载状态通过该参数回调    public static final int TYPE_SUCCESS = 0;    public static final int TYPE_FAILED = 1;    public static final int TYPE_PAUSED = 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) {//下载状态会根据该参数回调        this.listener = listener;    }//后台执行下载逻辑    @Override    protected Integer doInBackground(String... params) {        InputStream is = null;        RandomAccessFile saveFile = null;        File file = null;        try {            long downloadedLength = 0;  //记录已下载的文件长度            String downloadUrl = params[0];            String fileName = downloadUrl.substring(downloadUrl.lastIndexOf("/"));            String directory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath();            file = new File(directory + fileName);            if(file.exists()){//读取已下载的字节数，用于断点续传                downloadedLength = file.length();            }            long contentLength = getContentLength(downloadUrl);  //文件总字节            if(contentLength == 0){                return TYPE_FAILED;            }else if(contentLength == downloadedLength){                return TYPE_SUCCESS;            }            OkHttpClient client = new OkHttpClient();            Request request = new Request.Builder()//断点续传                    .addHeader("RANGE", "bytes=" + downloadedLength + "-")                    .url(downloadUrl)                    .build();            Response response = client.newCall(request).execute();            if(request != null){                is = response.body().byteStream();                saveFile = new RandomAccessFile(file, "rw");                saveFile.seek(downloadedLength);                byte[] b = new byte[1024];                int total = 0;                int len;//读取数据写入本地                while((len = is.read(b)) != -1){                    if(isCanceled){                        return TYPE_CANCELED;                    }else if(isPaused){                        return TYPE_PAUSED;                    }else {                        total += len;                        saveFile.write(b, 0, len);                        int progress = (int) ((total + downloadedLength) * 100 / contentLength);                        publishProgress(progress);                    }                }                response.body().close();                return TYPE_SUCCESS;            }        }catch (Exception e){            e.printStackTrace();        }finally {            try {                if(is != null){                    is.close();                }                if(saveFile != null){                    saveFile.close();                }                if(isCanceled && file != null){                    file.delete();                }            }catch (Exception e){                e.printStackTrace();            }        }        return TYPE_FAILED;    }//界面更新下载进度    @Override    protected void onProgressUpdate(Integer... values) {        int progress = values[0];        if(progress > lastProgress){            listener.onProgress(progress);            lastProgress = progress;        }    }//通知最终下载结果    @Override    protected void onPostExecute(Integer status) {        switch (status){            case TYPE_SUCCESS:                listener.onSuccess();                break;            case TYPE_FAILED:                listener.onFailed();                break;            case TYPE_PAUSED:                listener.onPaused();                break;            case TYPE_CANCELED:                listener.onCanceled();                break;            default:                break;        }    }//暂停    public void  pauseDownload(){        isPaused = true;}//取消    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.body().close();            return contentLength;        }        return 0;    }}

4、新建DownloadService继承自Service。

public class DownloadService extends Service {    private DownloadTask downloadTask;    private String downloadUrl;//匿名类    private DownloadListener listener = new DownloadListener() {        @Override        public void onProgress(int progress) {//触发通知            getNotificationManager().notify(1, getNotification("Downloading...", progress));        }        @Override        public void onSuccess() {            downloadTask = null;//下载成功时关闭前台服务，并创建下载成功的通知。            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;//下载失败时关闭前台服务，并创建下载失败的通知。            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;    }//用于活动与服务通信    class DownloadBinder extends Binder{        public void startDownload(String url){            if(downloadTask == null){                downloadUrl = url;                downloadTask =new DownloadTask(listener);//执行DownloadTask后台下载                downloadTask.execute(downloadUrl);//开始前台服务                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();            }            if(downloadUrl != null){//取消下载时需删除文件并将通知关闭                String fileName = downloadUrl.substring(downloadUrl.lastIndexOf("/"));                String directory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath();                File file =new File(directory + 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){            builder.setContentText(progress + "%");// setProgress()方法：在通知上设置进度条，参数一传入通知最大进度，参数二传入通知当前进度，参数三表示是否使用模糊进度条            builder.setProgress(100, progress, false);        }        return builder.build();    }}

5、修改activity_main中代码，添加三个按钮用于开始下载，暂停下载和取消下载。

6、修改MainActivity中代码。

public class MainActivity extends AppCompatActivity implements View.OnClickListener{private DownloadService.DownloadBinder downloadBinder;//匿名类    private ServiceConnection connection = new ServiceConnection() {        @Override        public void onServiceConnected(ComponentName componentName, IBinder service) {//获取DownloadService实例，用于活动与服务通信            downloadBinder = (DownloadService.DownloadBinder) service;        }        @Override        public void onServiceDisconnected(ComponentName componentName) {        }    };    @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//绑定服务，让活动与服务通信        bindService(intent, connection, BIND_AUTO_CREATE);          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 view) {        if(downloadBinder == null){            return;        }        switch (view.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, "You deny the permission", Toast.LENGTH_SHORT).show();                    finish();                }                break;            default:        }    }    @Override    protected void onDestroy() {        super.onDestroy();        unbindService(connection);   //解绑服务    }}

7、在AndroidManifest中进行权限声明。

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