serviceStation

项目流程1为项目添加依赖库app/build.gradle2为项目添加依赖库app/build.gradle3为项目添加依赖库app/build.gradle4具体下载功能完成后，为保证DownloadTadk在后台运行，新建DownService5现在后端工作基本完成，现在看前段。修改activity_main.xml6修改MainActivity中的代码7AndroidManifest.xml注册声明得到权限 

为项目添加依赖库app/build.gradle

dependencies {    compile fileTree(dir: 'libs', include: ['*.jar'])    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {        exclude group: 'com.android.support', module: 'support-annotations'    })    compile 'com.android.support:appcompat-v7:24.2.1'    testCompile 'junit:junit:4.12'    compile 'com.squareup.okhttp3:okhttp:3.4.1'}

对下载过程中各种状态进行监听，新建DownloadListener接口

五个回调方法

onProgress
onSuccess
onFailed
onPaused
onCanceled
 
public interface DownloadListener {    void onProgress(int Progress);    void onSuccess();    void onFailed();    void onPaused();    void onCanceled();}
编写下载功能，新建DownloadTask继承自AsyncTask
1AsyncTask三个泛型参数 2  4个整型常量用于表示下载状态3 重写doInBackgrund（）、onProgressUpdate（）、onPostExecute（）
public class DownloadTask extends AsyncTask<String, Integer, Integer> {    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) {        this.listener = listener;    }    @Override    protected Integer doInBackground(String... params) {        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];            String fileName = downloadUrl.substring(downloadUrl.lastIndexOf("/"));            String directory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath();            file = new File(directory + fileName);            if (file.exists()) {                downloadedLength = file.length();            }            long contentLength = getContentLength(downloadUrl);            if (contentLength == 0) {                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                    .addHeader("RANGE", "bytes=" + downloadedLength + "-")                    .url(downloadUrl)                    .build();            Response response = client.newCall(request).execute();            if (response != null) {                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) {                        return TYPE_CANCELED;                    } else if(isPaused) {                        return TYPE_PAUSED;                    } 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);                    }                }                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;    }    @Override    protected void onProgressUpdate(Integer... values) {        int progress = values[0];        if (progress > lastProgress) {            listener.onProgress(progress);            lastProgress = progress;        }    }    @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();            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;    }
具体下载功能完成后，为保证DownloadTadk在后台运行，新建DownService
主要用上面五个回调方法
创建了DownloadBinder，提供方法如下
   startDownload（）pauseDownload（）cancelDownload（）
public class DownloadService extends Service {    private DownloadTask downloadTask;    private String downloadUrl;    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 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) {            // 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);        }        return builder.build();    }}
现在后端工作基本完成，现在看前段。修改activity_main.xml
开始下载暂停下载取消下载
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="vertical"    android:layout_width="match_parent"    android:layout_height="match_parent">    <Button        android:id="@+id/start_download"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:text="Start Download" />    <Button        android:id="@+id/pause_download"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:text="Pause Download" />    <Button        android:id="@+id/cancel_download"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:text="Cancel Download" /></LinearLayout>

修改MainActivity中的代码

public class MainActivity extends AppCompatActivity implements View.OnClickListener{    private DownloadService.DownloadBinder downloadBinder;    private ServiceConnection connection = new ServiceConnection() {        @Override        public void onServiceDisconnected(ComponentName name) {        }        @Override        public void onServiceConnected(ComponentName name, IBinder service) {            downloadBinder = (DownloadService.DownloadBinder) service;        }    };    @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        bindService(intent, connection, BIND_AUTO_CREATE); // 绑定服务        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, String[] permissions, 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);    }}

在AndroidManifest.xml注册声明得到权限
<manifest xmlns:android="http://schemas.android.com/apk/res/android"    package="servicebestpractice.example.com.servicebestpractice">    <uses-permission android:name="android.permission.INTERNET" />    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />    <application        android:allowBackup="true"        android:icon="@mipmap/ic_launcher"        android:label="@string/app_name"        android:supportsRtl="true"        android:theme="@style/AppTheme">        <activity android:name=".MainActivity">            <intent-filter>                <action android:name="android.intent.action.MAIN" />                <category android:name="android.intent.category.LAUNCHER" />            </intent-filter>        </activity>        <service            android:name=".DownloadService"            android:enabled="true"            android:exported="true"/>    </application></manifest>