我正在开发一个 Android 应用程序来从我的网络服务器下载图像。所有代码都运行良好。我正在使用 Asynctask 将图像下载到我的 SD 卡。
我的连接速度为 4mbps，但我的应用程序需要大约 8 分钟才能下载 3 张图像 (2.5 MB)。我已经阅读了 Asynctask 自动管理线程创建的其他地方，那么现在我可以做些什么来实现并发？
我在下面发布我的代码。下面的代码用于我的 Asynctask 活动，该活动将图像从服务器下载到 sdcard。
public class BitmapDownloaderTask extends AsyncTask<String, Void, Bitmap> {
private String url;
Bitmap bitmap1;
String sdCard;
private final WeakReference<ImageView> imageViewReference;
public BitmapDownloaderTask(ImageView imageView) {
imageViewReference = new WeakReference<ImageView>(imageView);
}
@Override
// Actual download method, run in the task thread
protected Bitmap doInBackground(String... params) {
// params comes from the execute() call: params[0] is the url.
bitmap1 = downloadBitmap(params[0]);
boolean avail = isMemorySizeAvailableAndroid(bitmap1.getRowBytes(),
Environment.isExternalStorageEmulated());
if (avail) {
try {
sdCard = Environment.getExternalStorageDirectory().toString()
+ "/MyCatalogue";
File f1 = new File(sdCard);
if (!f1.exists()) {
f1.mkdirs();
}
String filename1 = params[0].substring(params[0]
.lastIndexOf("/") + 1);
File file1 = new File(f1.toString(), filename1);
OutputStream stream1 = new FileOutputStream(file1);
bitmap1.compress(CompressFormat.JPEG, 100, stream1);
Log.w("Abhishek", "card is " + sdCard);
} catch (Exception e) {
e.printStackTrace();
}
}
Log.w("ImageDownloader", "Success bitmap is" + bitmap1);
return downloadBitmap(params[0]);
}
protected static boolean isMemorySizeAvailableAndroid(long download_bytes,
boolean isExternalMemory) {
boolean isMemoryAvailable = false;
long freeSpace = 0;
// if isExternalMemory get true to calculate external SD card available
// size
if (isExternalMemory) {
try {
StatFs stat = new StatFs(Environment
.getExternalStorageDirectory().getPath());
freeSpace = (long) stat.getAvailableBlocks()
* (long) stat.getBlockSize();
if (freeSpace > download_bytes) {
isMemoryAvailable = true;
} else {
isMemoryAvailable = false;
}
} catch (Exception e) {
e.printStackTrace();
isMemoryAvailable = false;
}
} else {
// find phone available size
try {
StatFs stat = new StatFs(Environment.getDataDirectory()
.getPath());
freeSpace = (long) stat.getAvailableBlocks()
* (long) stat.getBlockSize();
if (freeSpace > download_bytes) {
isMemoryAvailable = true;
} else {
isMemoryAvailable = false;
}
} catch (Exception e) {
e.printStackTrace();
isMemoryAvailable = false;
}
}
return isMemoryAvailable;
}
@Override
// Once the image is downloaded, associates it to the imageView
protected void onPostExecute(Bitmap bitmap) {
if (isCancelled()) {
bitmap = null;
}
if (imageViewReference != null) {
ImageView imageView = imageViewReference.get();
if (imageView != null) {
imageView.setImageBitmap(bitmap);
}
}
}
static Bitmap downloadBitmap(String url) {
final AndroidHttpClient client = AndroidHttpClient
.newInstance("Android");
final HttpGet getRequest = new HttpGet(url);
try {
HttpResponse response = client.execute(getRequest);
final int statusCode = response.getStatusLine().getStatusCode();
if (statusCode != HttpStatus.SC_OK) {
Log.w("ImageDownloader", "Error " + statusCode
+ " while retrieving bitmap from " + url);
return null;
} else {
Log.w("ImageDownloader", "Success " + statusCode
+ " while retrieving bitmap from " + url);
}
final HttpEntity entity = response.getEntity();
if (entity != null) {
InputStream inputStream = null;
try {
inputStream = entity.getContent();
final Bitmap bitmap = BitmapFactory
.decodeStream(inputStream);
return bitmap;
} finally {
if (inputStream != null) {
inputStream.close();
}
entity.consumeContent();
}
}
} catch (Exception e) {
// Could provide a more explicit error message for IOException or
// IllegalStateException
getRequest.abort();
Log.w("ImageDownloader", "Error while retrieving bitmap from "
+ url);
} finally {
if (client != null) {
client.close();
}
}
return null;
}
}