《第一行代码》10.6节 服务的最佳实践-完整版的下载示例

在app/build.grandle文件的dependencies包下添加

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

1、新建回调接口：DownloadListener

public interface DownloadListener {

    void onProgress(int progress);
    void onSuccess();
    void onFailed();
    void onPaused();
    void onCanceled();

}

2、新建：DownloadTask类，继承：AsyncTask，该类实现下载功能（分部注释在代码中）

public class DownloadTask extends AsyncTask {//下载功能

    public static final int TYPE_SUCCESS = 0;//下载成功
    public static final int TYPE_FAILED = 1;//下载失败
    public static final int TYPE_PAUSED = 2;//下载暂停
    public static final int TYPE_CANCELED = 3;//取消下载

    private DownloadListener listener;//通过此参数将将下载状态进行回调
    private boolean isCanceled = false;
    private boolean isPaused = false;
    private int lastProgress;

    public DownloadTask(DownloadListener listener){
        this.listener = listener;
    }

    @Override
    protected Integer doInBackground(String... params) {//后台执行具体的下载逻辑
        InputStream is = null;//输入流
        RandomAccessFile savedFile = null;//保存文件的地址
        File file = null;
        try {
            long downloadedLength = 0;//记录已下载文件的长度
            String downloadUrl = params[0];//通过传入的参数，获取到下载的URL地址
            String fileName = downloadUrl.substring(downloadUrl.lastIndexOf("/"));//从downloadUrl中截取出下载的文件名
            String directory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath();//下载到指定目录
            file = new File(directory + fileName);//下载的文件
            if (file.exists()){//若文件已经存在
                downloadedLength = file.length();//获取已下载的字节数，下面可以设置断点接着下载
            }
            long contentLength = getContentLength(downloadUrl);//获取待下载文件的总长度
            if (contentLength == 0){//若为0，则失败
                return TYPE_FAILED;
            }else if (contentLength == downloadedLength){//若文件长度等于已下载的文件长度，则已经下载完成
                return TYPE_SUCCESS;
            }
            OkHttpClient client = new OkHttpClient();//创建实例
            Request request = new Request.Builder()
                    .addHeader("RANGE", "bytes=" + downloadedLength + "-")//创建断点继续下载
                    .url(downloadUrl)
                    .build();
            Response response = client.newCall(request).execute();//发送请求并获取服务端数据
            if (response != null){//不断从网络上获取数据
                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){//读取文件
                    if (isCanceled){//判断是否取消
                        return TYPE_CANCELED;
                    }else if (isPaused){//判断是否暂停
                        return TYPE_PAUSED;
                    }else {
                        total += len;
                        savedFile.write(b, 0, len);
                        int progress = (int) ((total + downloadedLength) * 100 / contentLength);//计算下载的百分比
                        publishProgress(progress);
                    }
                }
                response.body().close();//得到具体内容
                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) {//界面上更新下载进度
        int progress = values[0];
        if (progress > lastProgress){//和上一次下载进度相比，若有变化，则更新
            listener.onProgress(progress);
            lastProgress = progress;
        }
    }

    @Override
    protected void onPostExecute(Integer status) {//通知最后下载进度
        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;
        }
    }

    public void pauseDownload(){
        isPaused = true;
    }

    public void cancelDownload(){
        isCanceled = true;
    }

    private long getContentLength(String downloadUrl) throws IOException{//获取文件长度
        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;
    }
}

3、新建一个服务：DownloadServices，使得DownloadTask可以一直在后台运行

public class DownloadService extends Service {

    private DownloadTask downloadTask;
    private String downloadUrl;

    private DownloadListener listener = new DownloadListener() {//匿名类
        @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，创建一个新的通知用于告诉用户下载成功了
            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，创建一个新的通知用于告诉用户下载失败
            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();

//    public DownloadService() {
//    }

    @Override
    public IBinder onBind(Intent intent) {
        return mBinder;
    }
    class DownloadBinder extends Binder{//为了让DownloadService与活动进行通信，创建了DownloadBinder类

        public void startDownload(String url){//开始下载
            if (downloadTask == null){
                downloadUrl = url;
                downloadTask = new DownloadTask(listener);
                downloadTask.execute(downloadUrl);//开启下载
                startForeground(1, getNotification("Downloading...", 0));//成为前台服务，，创建一个持续运行的通知
                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){//将正在下载的文件删除
                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(){//触发下载进度的这个通知
        return (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
    }

    private Notification getNotification(String title, int progress){//显示下载进度的通知，具体代码为通知显示的写法
        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，才需要显示下载进度
            builder.setContentText(progress + "%");
            builder.setProgress(100, progress, false);
        }
        return builder.build();
    }
}

4、修改activity_main.xml中的代码

5、修改MainActivity中的代码

public class MainActivity extends AppCompatActivity implements View.OnClickListener{

    private DownloadService.DownloadBinder downloadBinder;

    private ServiceConnection connection = new ServiceConnection() {//在活动中调用服务提供的各种方法
        @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);//开启服务
        bindService(intent,connection,BIND_AUTO_CREATE);//绑定服务
        if (ContextCompat.checkSelfPermission(MainActivity.this, Manifest.permission.WRITE_EXTERNAL_STORAGE)//运行时权限
                != 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){//运行时权限将会回调的方法
        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() {//程序销毁前，进行解绑
        super.onDestroy();
        unbindService(connection);
    }
}

但是运行后，安装到手机上，app会闪退，这是怎么回事？寻找原因ing