編輯:關於Android編程
AsyncTask不僅方便我們在子線程中對UI進行更新操作,還可以借助其本身的線程池來實現多線程任務。下面是一個使用AsyncTask來實現的多線程下載例子。
01 效果圖
02 核心類 - DownloadTask.class
public class DownloadTask extends AsyncTask<String, Integer, Integer> { public static final int TYPE_SUCCESS = 0; public static final int TYPE_FAILURE = 1; public static final int TYPE_PAUSE = 2; public static final int TYPE_CANCEL = 3; public int positionDownload; private boolean isPaused = false; private boolean isCancelled = false; private DownloadListener downloadListener; private int lastProgress; public DownloadTask(DownloadListener downloadListener){ this.downloadListener = downloadListener; } public void setDownloadListener(DownloadListener downloadListener){ this.downloadListener = downloadListener; } @Override protected Integer doInBackground(String... params) { InputStream is = null; RandomAccessFile savedFile = null; File file = null; long downloadLength = 0; String downloadUrl = params[0]; positionDownload = Integer.parseInt(params[1]); String fileName = downloadUrl.substring(downloadUrl.lastIndexOf("/")); String directory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath(); file = new File(directory + fileName); if(file.exists()){ downloadLength = file.length(); } long contentLength = getContentLength(downloadUrl); if(contentLength == 0){ return TYPE_FAILURE; } else if(contentLength == downloadLength){ return TYPE_SUCCESS; } OkHttpClient client = new OkHttpClient(); Request request = new Request.Builder() .addHeader("RANGE", "bytes="+downloadLength+"-") .url(downloadUrl) .build(); try { Response response = client.newCall(request).execute(); if(response != null){ is = response.body().byteStream(); savedFile = new RandomAccessFile(file, "rw"); savedFile.seek(downloadLength); byte[] buffer = new byte[1024]; int total = 0; int length; while((length = is.read(buffer)) != -1){ if(isCancelled){ response.body().close(); return TYPE_CANCEL; } else if(isPaused) { response.body().close(); return TYPE_PAUSE; } total += length; savedFile.write(buffer, 0, length); int progress = (int) ((total + downloadLength) * 100 / contentLength); int currentDownload = (int) (total + downloadLength); publishProgress(positionDownload, progress, currentDownload, (int) contentLength); } response.body().close(); return TYPE_SUCCESS; } } catch (IOException e) { e.printStackTrace(); } finally { try { if(is != null) is.close(); if(savedFile != null) savedFile.close(); if(isCancelled && file != null) file.delete(); } catch (IOException e) { e.printStackTrace(); } } return TYPE_FAILURE; } @Override protected void onProgressUpdate(Integer... values) { int progress = values[1]; if(progress > lastProgress){ downloadListener.onProgress(values[0], progress, values[2], values[3]); lastProgress = progress; } } @Override protected void onPostExecute(Integer status) { switch (status){ case TYPE_SUCCESS: downloadListener.onSuccess(positionDownload); break; case TYPE_FAILURE: downloadListener.onFailure(); break; case TYPE_PAUSE: downloadListener.onPause(); break; case TYPE_CANCEL: downloadListener.onCancel(); break; } } public void pauseDownload(){ isPaused = true; } public void cancelDownload(){ isCancelled = true; } private long getContentLength(String downloadUrl) { OkHttpClient client = new OkHttpClient(); Request request = new Request.Builder() .url(downloadUrl) .build(); Response response = null; try { response = client.newCall(request).execute(); if(response != null && response.isSuccessful()){ long contentLength = response.body().contentLength(); response.body().close(); return contentLength; } } catch (IOException e) { e.printStackTrace(); } return 0; } }
03 核心類 - DownloadService.class
public class DownloadService extends Service { private Map<String, DownloadTask> downloadTaskMap = new HashMap<>(); private DownloadBinder mBinder = new DownloadBinder(); @Override public IBinder onBind(Intent intent) { return mBinder; } private Notification getNotification(String title, int progress) { Intent intent = new Intent(this, MainActivity.class); PendingIntent pendingIntent = 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(pendingIntent); builder.setContentTitle(title); if(progress > 0){ builder.setContentText(progress + "%"); builder.setProgress(100, progress, false); } return builder.build(); } private NotificationManager getNotificationManager() { return (NotificationManager) getSystemService(NOTIFICATION_SERVICE); } class DownloadBinder extends Binder { public void startDownload(String url, int position, DownloadListener listener){ if(!downloadTaskMap.containsKey(url)){ DownloadTask downloadTask = new DownloadTask(listener); downloadTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, url, position+""); downloadTaskMap.put(url, downloadTask); if(downloadTaskMap.size() == 1){ startForeground(1, getNotification("正在下載" + downloadTaskMap.size(), -1)); } else{ getNotificationManager().notify(1, getNotification("正在下載" + downloadTaskMap.size(), -1)); } } } public void updateDownload(String url, DownloadListener listener){ if(downloadTaskMap.containsKey(url)){ DownloadTask downloadTask = downloadTaskMap.get(url); if(downloadTask != null){ downloadTask.setDownloadListener(listener); } } } public void pauseDownload(String url){ if(downloadTaskMap.containsKey(url)){ DownloadTask downloadTask = downloadTaskMap.get(url); if(downloadTask != null){ downloadTask.pauseDownload(); } downloadTaskMap.remove(url); if(downloadTaskMap.size() > 0){ getNotificationManager().notify(1, getNotification("正在下載" + downloadTaskMap.size(), -1)); } else { stopForeground(true); getNotificationManager().notify(1, getNotification("全部暫停下載", -1)); } } } public void downloadSuccess(String url){ if(downloadTaskMap.containsKey(url)){ DownloadTask downloadTask = downloadTaskMap.get(url); downloadTaskMap.remove(url); if(downloadTask != null){ downloadTask = null; } if(downloadTaskMap.size() > 0){ getNotificationManager().notify(1, getNotification("正在下載" + downloadTaskMap.size(), -1)); } else { stopForeground(true); getNotificationManager().notify(1, getNotification("下載成功", -1)); } } } public boolean isDownloading(String url){ if(downloadTaskMap.containsKey(url)){ return true; } return false; } public void cancelDownload(String url){ if(downloadTaskMap.containsKey(url)){ DownloadTask downloadTask = downloadTaskMap.get(url); if(downloadTask != null){ downloadTask.cancelDownload(); } downloadTaskMap.remove(url); if(downloadTaskMap.size() > 0){ getNotificationManager().notify(1, getNotification("正在下載" + downloadTaskMap.size(), -1)); } else { stopForeground(true); getNotificationManager().notify(1, getNotification("全部取消下載", -1)); } } if(url != null){ String fileName = url.substring(url.lastIndexOf("/")); String directory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath(); File file = new File(directory + fileName); if(file.exists()){ file.delete(); Toast.makeText(DownloadService.this, "Deleted", Toast.LENGTH_SHORT).show(); } } } } }
04 源碼
下載地址
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