Question

我试图在我的Android应用中用Fresco替换Picasso。但是我不确定如何使用Fresco简单地加载位图。

毕加索我会做以下事情。

Bitmap poster = Picasso.with(getActivity())
                    .load(url)
                    .resize(Utils.convertDpToPixel(WIDTH,HEIGHT))
                    .centerCrop()
                    .get();

我一直无法弄清楚如何使用这个Fresco创建一个Bitmap。有任何想法吗？

Answer 1

正如弗雷斯科所说：

如果您对管道的请求是针对解码图像（Android位图），您可以利用我们更容易使用的BaseBitmapDataSubscriber：

dataSource.subscribe(new BaseBitmapDataSubscriber() {
    @Override
    public void onNewResultImpl(@Nullable Bitmap bitmap) {
       // You can use the bitmap in only limited ways
      // No need to do any cleanup.
    }

    @Override
    public void onFailureImpl(DataSource dataSource) {
      // No cleanup required here.
    }
  },
  executor);

您不能将位图分配给不在onNewResultImpl方法范围内的任何变量。

http://frescolib.org/docs/datasources-datasubscribers.html#_

我的代码：

public void setDataSubscriber(Context context, Uri uri, int width, int height){
    DataSubscriber dataSubscriber = new BaseDataSubscriber<CloseableReference<CloseableBitmap>>() {
        @Override
        public void onNewResultImpl(
                DataSource<CloseableReference<CloseableBitmap>> dataSource) {
            if (!dataSource.isFinished()) {
                return;
            }
            CloseableReference<CloseableBitmap> imageReference = dataSource.getResult();
            if (imageReference != null) {
                final CloseableReference<CloseableBitmap> closeableReference = imageReference.clone();
                try {
                    CloseableBitmap closeableBitmap = closeableReference.get();
                    Bitmap bitmap  = closeableBitmap.getUnderlyingBitmap();
                    if(bitmap != null && !bitmap.isRecycled()) {
                        //you can use bitmap here
                    }
                } finally {
                    imageReference.close();
                    closeableReference.close();
                }
            }
        }
        @Override
        public void onFailureImpl(DataSource dataSource) {
            Throwable throwable = dataSource.getFailureCause();
            // handle failure
        }
    };
    getBitmap(context, uri, width, height, dataSubscriber);
}

/**
 *
 * @param context
 * @param uri
 * @param width          
 * @param height         
 * @param dataSubscriber
 */
public void getBitmap(Context context, Uri uri, int width, int height, DataSubscriber dataSubscriber){
    ImagePipeline imagePipeline = Fresco.getImagePipeline();
    ImageRequestBuilder builder = ImageRequestBuilder.newBuilderWithSource(uri);
    if(width > 0 && height > 0){
        builder.setResizeOptions(new ResizeOptions(width, height));
    }
    ImageRequest request = builder.build();
    DataSource<CloseableReference<CloseableImage>>
            dataSource = imagePipeline.fetchDecodedImage(request, context);
    dataSource.subscribe(dataSubscriber, UiThreadExecutorService.getInstance());
}

Answer 2

您可以直接使用Fresco的图像管道：

http://frescolib.org/docs/using-image-pipeline.html

虽然如果你不介意我的问题 - 这里的动机是什么？你为什么需要Bitmap？

Answer 3

您可以直接使用Fresco的CacheKey：

public class DownloadVideoThumbnail extends AsyncTask<String, Void, Bitmap> {
private ImageView bmImage;
private Bitmap bitmapVideo;
private Context context;

public DownloadVideoThumbnail(Context context, ImageView bmImage) {
    this.bmImage = (ImageView) bmImage;
    this.context = context;
}

protected Bitmap doInBackground(String... urls) {

    String urlStr = urls[0];
    if (readFromCacheSync(urlStr) == null) {
        try {
            //Your method call here
            bitmapVideo = retriveVideoFrameFromVideo(urlStr);

        } catch (Throwable throwable) {
            throwable.printStackTrace();
        }
    } else {
        bitmapVideo = readFromCacheSync(urlStr);
    }
    return null;
}

protected void onPostExecute(Bitmap result) {
    if (bitmapVideo != null) {
        //Load your bitmap here
        bmImage.setImageBitmap(bitmapVideo);
        bmImage.setScaleType(ImageView.ScaleType.CENTER_CROP);
    }
}


public void cacheBitmap(Bitmap bitmap, String url) {
    try {
        CacheKey cacheKey = new SimpleCacheKey(url);
        ByteArrayOutputStream stream = new ByteArrayOutputStream();
        bitmap.compress(Bitmap.CompressFormat.JPEG, 100, stream);
        final byte[] byteArray = stream.toByteArray();
        Fresco.getImagePipelineFactory().getMainFileCache().insert(cacheKey, new WriterCallback() {
            @Override
            public void write(OutputStream outputStream) throws IOException {
                outputStream.write(byteArray);
            }
        });
    } catch (IOException cacheWriteException) {

    }
}

public static Bitmap readFromCacheSync(String imageUrl) {
    CacheKey cacheKey = DefaultCacheKeyFactory.getInstance().getEncodedCacheKey(ImageRequest.fromUri(imageUrl), null);
    StagingArea stagingArea = StagingArea.getInstance();
    EncodedImage encodedImage = stagingArea.get(cacheKey);
    if (encodedImage != null) {

        return BitmapFactory.decodeStream(encodedImage.getInputStream());
    }

    try {
        return BitmapFactory.decodeStream(readFromDiskCache(cacheKey));
    } catch (Exception e) {
        return null;
    }
}


private static InputStream readFromDiskCache(final CacheKey key) throws IOException {
    try {
        FileCache fileCache = ImagePipelineFactory.getInstance().getMainFileCache();
        final BinaryResource diskCacheResource = fileCache.getResource(key);
        if (diskCacheResource == null) {
            FLog.v(TAG, "Disk cache miss for %s", key.toString());
            return null;
        }
        PooledByteBuffer byteBuffer;
        final InputStream is = diskCacheResource.openStream();
        FLog.v(TAG, "Successful read from disk cache for %s", key.toString());
        return is;
    } catch (IOException ioe) {
        return null;
    }
}

public Bitmap retriveVideoFrameFromVideo(String videoPath) throws Throwable {

    Bitmap bitmap = null;
    MediaMetadataRetriever mediaMetadataRetriever = null;
    try {
        mediaMetadataRetriever = new MediaMetadataRetriever();
        if (Build.VERSION.SDK_INT >= 14)
            mediaMetadataRetriever.setDataSource(videoPath, new HashMap<String, String>());
        else
            mediaMetadataRetriever.setDataSource(videoPath);
        bitmap = mediaMetadataRetriever.getFrameAtTime();
        if (bitmap != null) {
            ByteArrayOutputStream stream = new ByteArrayOutputStream();
            bitmap.compress(Bitmap.CompressFormat.JPEG, 70, stream);
            cacheBitmap(bitmap, videoPath);
        }
    } catch (Exception e) {
        e.printStackTrace();
        throw new Throwable(
                "Exception in retriveVideoFrameFromVideo(String videoPath)"
                        + e.getMessage());

    } finally {
        if (mediaMetadataRetriever != null) {
            mediaMetadataRetriever.release();
        }
    }
    return bitmap;
}
}

Answer 4

从this开始，我创建了一个快速实现，该实现使用Kotlin扩展和RxJava从int中获取ClosableBitmap：

ImageRequest

由于合同规定，一旦使用了位图，就必须关闭引用，因此我创建了这个util函数：

fun ImageRequest.getBitmap(context: Context): Maybe<CloseableReference<CloseableBitmap>> {
    val dataSource = Fresco.getImagePipeline().fetchDecodedImage(this, context)
    return Maybe.create { emitter ->
        dataSource.subscribe(
            object : BaseDataSubscriber<CloseableReference<CloseableImage>>() {
                override fun onFailureImpl(dataSource: DataSource<CloseableReference<CloseableImage>>) {
                    emitter.onComplete()
                }

                override fun onNewResultImpl(dataSource: DataSource<CloseableReference<CloseableImage>>) {
                    if (!dataSource.isFinished) {
                        return
                    }

                    dataSource.result
                        ?.takeIf { it.get() is CloseableBitmap }
                        ?.let {
                            @Suppress("UNCHECKED_CAST")
                            emitter.onSuccess(it as CloseableReference<CloseableBitmap>)
                        }

                    emitter.onComplete()
                }
            },
            DefaultExecutorSupplier(1).forBackgroundTasks()
        )
    }
}

Answer 5

我使用Kotlin的协程找到了这种解决方案：

suspend fun getBitmapFromUri(imageUri: Uri): Bitmap = withContext(Dispatchers.Default) {
    val imageRequest = ImageRequestBuilder.newBuilderWithSource(imageUri).build()
    val dataSource = Fresco.getImagePipeline().fetchDecodedImage(imageRequest, this)
    val result = DataSources.waitForFinalResult(dataSource) as CloseableReference<CloseableBitmap>

    val bitmap = result.get().underlyingBitmap

    CloseableReference.closeSafely(result)
    dataSource.close()

    return@withContext bitmap
}

使用Facebook的Fresco加载位图

5 个答案: