在android中改变位图的大小以避免OOM

Question

我一直在努力改变我从服务器下载的位图的大小，因为我知道这是我的OOM错误的问题。我试过下面的其他例子，这个也是https://developer.android.com/training/displaying-bitmaps/load-bitmap.html，但我不能让头或尾关于如何使用它，在哪里使用它。我想将位图缩小到屏幕分辨率，但无法解决这个问题。谢谢你的帮助。

也不是在AsyncTask中这样做，如果这有区别的话。

下面是我设置位图的代码:

public class ImageDownloaderTask extends AsyncTask<String, Void, Bitmap> {
BitmapFactory.Options options = new BitmapFactory.Options();
private final WeakReference<ImageView> imageViewReference;
Resources resources;
public ImageDownloaderTask(ImageView imageView) {
    imageViewReference = new WeakReference<ImageView>(imageView);
}

@Override
protected Bitmap doInBackground(String... params)
{
    return downloadBitmap(params[0]);
}
@Override
protected void onPostExecute(Bitmap bitmap) {
    if (isCancelled()) {
        bitmap = null;
        Log.d("HTTPS No go", bitmap.toString());
    }
    if (imageViewReference != null) {
        ImageView imageView = imageViewReference.get();
        if (imageView != null) {
            if (bitmap != null) {
                //Scale the bitmap to a smaller size
                imageView.setImageBitmap(bitmap);
            } else {
                Log.d("Downloading the image: ", "No Image found");
            }
        }
    }
}
//URL connection to download the image
private Bitmap downloadBitmap(String url) {
    HttpURLConnection urlConnection = null;
            try{
            URL uri = new URL(url);
            urlConnection = (HttpURLConnection) uri.openConnection();
            urlConnection.setRequestMethod("GET");
            int statusCode = urlConnection.getResponseCode();
            //check if the HTTP status code is equal to 200, which means that it is ok
            if (statusCode != 200) {
                return null;
            }
            InputStream inputStream = urlConnection.getInputStream();
            if (inputStream != null) {
                /*
                options.inJustDecodeBounds = true;
                Bitmap bitmap = BitmapFactory.decodeStream(inputStream, null, options);
                int imageHeight = options.outHeight;
                int imageWidth = options.outWidth;
                String imageType = options.outMimeType;
                int sampleSize = calculateInSampleSize(options, imageWidth, imageHeight);
                */
                Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
                return bitmap;
            }
            }catch (ProtocolException e) {
                e.printStackTrace();
            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } {}
    return null;
}
public static int calculateInSampleSize(
        BitmapFactory.Options options, int reqWidth, int reqHeight) {
    // Raw height and width of image
    final int height = options.outHeight;
    final int width = options.outWidth;
    int inSampleSize = 1;
    if (height > reqHeight || width > reqWidth) {
        final int halfHeight = height / 2;
        final int halfWidth = width / 2;
        // Calculate the largest inSampleSize value that is a power of 2 and keeps both
        // height and width larger than the requested height and width.
        while ((halfHeight / inSampleSize) >= reqHeight
                && (halfWidth / inSampleSize) >= reqWidth) {
            inSampleSize *= 2;
        }
    }
    return inSampleSize;
}
}

更新:

这修复了一点。它允许我只注销一次，但当我注销第二次它崩溃与好旧的OOM错误。

InputStream inputStream = urlConnection.getInputStream();
            if (inputStream != null) {
                BitmapFactory.Options options = new BitmapFactory.Options();
                options.inSampleSize=1; //try to decrease decoded image
                Bitmap bitmap = BitmapFactory.decodeStream(inputStream , null, options);
                return bitmap;
            }
            }catch (ProtocolException e) {
                e.printStackTrace();
            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } {}

Answer 1

几天前我也遇到过同样的问题。理论上有两种方法可以做到这一点。要么你完全下载图像，然后调整图像大小，或者你必须要求你的服务器这样做，而不是应用程序。我喜欢第二个解决方案，在那里我发送所需的宽度，高度和所需的图像。服务器计算可能的比例，然后减小尺寸并返回，打印图像。之后，我只是使用HttpURLConnection下载位图，并从我的连接的输入流中创建位图，没有任何问题。

你的错误是什么，也许你试图先从流计算，然后创建它。当然，这将导致崩溃，因为您正在尝试第二次读取输入流。在读取图像元数据以了解大小时，光标已经移动到流中。现在当它尝试创建位图时，它失败了，因为它不是从流的第0个字节开始的。而是在中间的某个地方，你上次光标停的地方。因此，如果需要读取两次流，您需要首先将输入流复制到某个地方，以便能够读取两次流。

Answer 2

我使用了以下代码:

    Bitmap outBitmap;
    // Decode image size
    BitmapFactory.Options o = new BitmapFactory.Options();
    o.inJustDecodeBounds = true;
    BitmapFactory.decodeFile(photoPath, o);
    // The new size we want to scale to ensure memory usage is optimal
    int targetWidth;
    int targetHeight;
    if (o.outHeight > o.outWidth) {
        targetWidth = getResources().getInteger(R.integer.pic_width_px);
        targetHeight = getResources().getInteger(R.integer.pic_height_px);
    } else if (o.outHeight == o.outWidth) {
        targetWidth = targetHeight = getResources().getInteger(R.integer.pic_width_px);
    } else {
        targetWidth = getResources().getInteger(R.integer.pic_width_px);
        targetHeight = getResources().getInteger(R.integer.pic_height_px);
    }
    if (o.outWidth <= targetWidth && o.outHeight <= targetHeight) {
        // Return image as is without any additional scaling
        Bitmap origBitmap = BitmapFactory.decodeFile(photoPath, null);
        outBitmap = Bitmap.createBitmap(origBitmap, 0, 0, o.outWidth, o.outHeight, m, true);
        origBitmap.recycle();
        return outBitmap;
    }
    // Find the correct scale value. It should be the power of 2.
    int scale = 1;
    while(o.outWidth / scale / 2 >= targetWidth &&
            o.outHeight / scale / 2 >= targetHeight) {
        scale *= 2;
    }
    // Decode with inSampleSize
    BitmapFactory.Options scaleOptions = new BitmapFactory.Options();
    scaleOptions.inSampleSize = scale;
    Bitmap scaledBitmap = BitmapFactory.decodeFile(photoPath, scaleOptions);
    return Bitmap.createBitmap(scaledBitmap, 0, 0, scaledBitmap.getWidth(), scaledBitmap.getHeight(), m, true);

Answer 3

我认为你需要改变你的图像的大小之前，你读到内存

private Bitmap downloadBitmap(String url) {
    HttpURLConnection urlConnection = null;
            try{
            URL uri = new URL(url);
            urlConnection = (HttpURLConnection) uri.openConnection();
            urlConnection.setRequestMethod("GET");
            int statusCode = urlConnection.getResponseCode();
            //check if the HTTP status code is equal to 200, which means that it is ok
            if (statusCode != 200) {
                return null;
            }
            InputStream inputStream = urlConnection.getInputStream();
            if (inputStream != null) {
                //scale down the image and load
                options.inJustDecodeBounds = true;
                Bitmap bitmap = BitmapFactory.decodeStream(inputStream, null, options);
                options.inSampleSize = calculateInSampleSize(options, 100, 100);
                options.inJustDecodeBounds = false;
                return BitmapFactory.decodeStream(inputStream, null, options);   //I'm not sure here, because the inputStream used twice.
            }
            }catch (ProtocolException e) {
                e.printStackTrace();
            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } {}
    return null;
}

Answer 4

感谢所有帮助我的人。我发现我的问题不是下载位图的大小，因为我每次将它们添加到我的回收视图时都会自动调整它们的大小。这是由于我在登录页面上播放的一个动图占用了太多的内存，一旦其他东西占用了内存，它就会关闭设备。

我真的很感激这里的每一个人，谢谢你们。