使用 AsyncTask 加载图像时行为不一致

Question

该应用程序的作用非常简单。它加载两个 RSS 源，并且在每个 RSS 源上，它包含两个带有标题、图像和链接的项目。然后它下载图像，将其保存到本地文件夹并显示它们。两个 RSS 提要和 4 个图像下载。

我使用 AsyncTask 来执行此操作。因此，调用两个 AsyncTasks 对象来加载两个 RSS feed，调用 4 个 AsyncTasks 来加载 4 个图像。当它尝试下载图像时会出现问题。对于第一次运行，效果很好。但如果我继续重新加载它们，有时 AsyncTask 不会执行任何操作。有时它无法读取输入流......非常奇怪。

使用 AsyncTask 是否缺少任何规则？

下面是我的代码片段。

public class TunesAppsWidgetProvider extends AppWidgetProvider {

private Intent taService = null;
private static boolean widgetEnabled = false;

@Override
public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {
    taService = new Intent(context, UpdateService.class);
    context.startService(taService);
}

public static class UpdateService extends Service {


    @Override
    public void onStart(Intent intent, int startId) {
        Log.d(Constants.TAG, "Service: onStart()");
        Context context = getApplicationContext();
        mViews = new RemoteViews(context.getPackageName(), R.layout.tunesappswidget);

        thisWidget = new ComponentName(this, TunesAppsWidgetProvider.class);
        manager = AppWidgetManager.getInstance(this);

        buildFeedUpdate();

        this.stopSelf();
        Log.d(Constants.TAG, "Stop Service");
    }

    public void buildFeedUpdate() {
        Log.d(Constants.TAG, "buildFeedUpdate");
        Context context = getApplicationContext();

        feedParser_0 = new FeedParser(context, Constants.FEED_ID_0);
        feedParser_1 = new FeedParser(context, Constants.FEED_ID_1);

        feedTask_0 = new LoadFeedTask();
        feedTask_0.execute(
                new LoadFeedTask.Payload(
                        feedParser_0,
                        UpdateService.this
                )
        );

        feedTask_1 = new LoadFeedTask();
        feedTask_1.execute(
                new LoadFeedTask.Payload(
                        feedParser_1,
                        UpdateService.this
                )
        );
    }

    public void buildCoverUpdate(byte feedID, List<Message> feedRSS, String operator) {
        Context context = getApplicationContext();

        Log.d(Constants.TAG, "buildCoverUpdate: " + feedID);
        try {
            switch(feedID) {
                case Constants.FEED_ID_0:
                        coverImage_0 = new CoverImage(context, feedRSS.get(Constants.ITEM_IDX_0).getImageLink(), Constants.SLOT_0);

            coverImageTask_0 = new LoadCoverImageTask();
                        coverImageTask_0.execute(
                            new LoadCoverImageTask.Payload(
                                    coverImage_0,
                                    UpdateService.this
                            )
                        );

                        coverImage_1 = new CoverImage(context, feedRSS.get(Constants.ITEM_IDX_1).getImageLink(), Constants.SLOT_1);

                        coverImageTask_1 = new LoadCoverImageTask();
                            coverImageTask_1.execute(
                                new LoadCoverImageTask.Payload(
                                    coverImage_1,
                                    UpdateService.this
                                )
                        );
                    break;

                case Constants.FEED_ID_1:
                        coverImage_2 = new CoverImage(context, feedRSS.get(Constants.ITEM_IDX_0).getImageLink(), Constants.SLOT_2, operator);
                    coverImageTask_2 = new LoadCoverImageTask();
                        coverImageTask_2.execute(
                                new LoadCoverImageTask.Payload(
                                        coverImage_2,
                                        UpdateService.this
                                )
                        );

                        coverImage_3 = new CoverImage(context, feedRSS.get(Constants.ITEM_IDX_1).getImageLink(), Constants.SLOT_3, operator);
                        bm_3 = coverImage_3.getDefaultCoverImage();
                            coverImageTask_3 = new LoadCoverImageTask();
                            coverImageTask_3.execute(
                                new LoadCoverImageTask.Payload(
                                    coverImage_3,
                                    UpdateService.this
                                )
                        );
                    break;

                default:
                    break;
            }
        }
        catch(Exception e) {
            Log.d(Constants.TAG, "buildCoverUpdate: " + e.toString());
        }
    }

下面

的代码用于加载图像。有时，即使调用了“execute”，这个 doInBackground 也永远不会被调用。有时它会卡在'Bitmap bitmap = BitmapFactory.decodeStream(in)'这里并且永远不会逃脱。

    protected LoadCoverImageTask.Payload doInBackground(LoadCoverImageTask.Payload... param) {
    HttpURLConnection httpConn = null;
    InputStream in;
    File imageFile;
    FileOutputStream fos;
    int slotIdx = param[0].coverImage.getSlotIndex();
    System.setProperty("http.keepAlive", "false");

    try{
        URL fileURL = new URL(param[0].coverImage.getFileURL());
        httpConn = (HttpURLConnection) fileURL.openConnection();
        Log.d(Constants.TAG , "openConn: Slot " + slotIdx);

        httpConn.setConnectTimeout(10000);

        if(httpConn.getResponseCode() == HttpURLConnection.HTTP_OK) {
            Log.d(Constants.TAG , "200OK: Slot " + slotIdx + ": " + fileURL.toString());

            in = httpConn.getInputStream();
            imageFile = new File(param[0].coverImage.getFullFilePath());
            fos = new FileOutputStream(imageFile);

            try {
                Bitmap bitmap = BitmapFactory.decodeStream(in);
                Log.d(Constants.TAG , "200OK: Slot " + slotIdx + " decodeStream(in);");
                if(bitmap.compress(Bitmap.CompressFormat.JPEG, 80, fos) == true) {
                    fos.flush();
                    fos.close();
                    in.close();
                    Log.d(Constants.TAG , "200OK-decodeOK: Slot " + slotIdx);
                    param[0].result = Constants.TRUE;
                }
                else {
                    fos.flush();
                    fos.close();
                    in.close();
                    Log.d(Constants.TAG , "200OK-decodeFail: Slot " + slotIdx);
                    param[0].result = Constants.FALSE;
                }
            }
            catch(NullPointerException e) {
                Log.d(Constants.TAG , "Slot " + slotIdx + ":" + e.toString());
                param[0].result = Constants.RETRY;
            }
        }
        else {
            Log.d(Constants.TAG , "Slot " + slotIdx + ":" + httpConn.getResponseCode());
            param[0].result = Constants.FALSE;
        }

    } catch(SocketTimeoutException e) {
        Log.d(Constants.TAG , "Time Out: " + slotIdx + ":" + e.toString());
    } catch(Exception e) {
        Log.d(Constants.TAG , "Slot " + slotIdx + ":" + e.toString());
        param[0].result = Constants.FALSE;
    }
    finally {
        if(httpConn != null) httpConn.disconnect();
        Log.d(Constants.TAG , "Slot " + slotIdx + ":httpConn.disconnect");
    }
    return param[0];
}

我被困在这个问题上几天了..请帮忙...

Answer 1

也许问题不在你的代码中。 BitmapFactory.decodeStream 中存在一个错误，如果您通过 http 连接使用 InputStream，有时无法很好地加载图像。

请参阅 http://code.google.com/p/android/issues /detail?id=6066 了解更多信息

对我有用的简单解决方案是将整个内容数据下载到缓冲区中，然后
使用 BitmapFactory.decodeByteArray 方法：

InputStream is = httpCon.getInputStream();
byte [] content = inputStreamToByteArray2(is);
image = BitmapFactory.decodeByteArray(content, 0, content.length);


public static final byte[] inputStreamToByteArray(InputStream is) throws IOException {
    BufferedInputStream bis = new BufferedInputStream(is);
    ByteArrayOutputStream buf = new ByteArrayOutputStream();
    int result = bis.read();
    while(result !=-1) {
        byte b = (byte)result;
        buf.write(b);
        result = bis.read();
    }
    return buf.toByteArray();
}

或者如果您不想按 1 个字节读取：

public static final byte[] inputStreamToByteArray(InputStream is) throws IOException {
    BufferedInputStream bis = new BufferedInputStream(is);
    ByteArrayOutputStream buf = new ByteArrayOutputStream();
    byte[] buffer = new byte[256];
    int result = bis.read(buffer);
    while(result > 0) {
        buf.write(buffer, 0, result);
        result = bis.read(buffer);
    }
    return buf.toByteArray();
}