android - BitmapFactory.decodeStream 在下载图像表单时返回 null

Question

我正在尝试使用Google Example Page从 URL 下载图像。我读过当我在 BitmapFactory.decodeStream 方法中使用 InputStream 时，我不能使用两次。我正在尝试这样做，但它不起作用，因为它在解码图像中返回 null，而且我不知道我能做什么。

这是我的代码：

这部分在 AsyncTask 类的 doInBackground 方法中

Bitmap bitmapImage;
URL imageUrl = null;
try {
imageUrl = new URL(url[0]);

HttpGet httpRequest = null;
httpRequest = new HttpGet(imageUrl.toURI());

HttpClient httpclient = new DefaultHttpClient();
HttpResponse response = (HttpResponse) httpclient.execute(httpRequest);

HttpEntity entity = response.getEntity();
BufferedHttpEntity bufHttpEntity = new BufferedHttpEntity(entity);
InputStream instream = bufHttpEntity.getContent();

    bitmapImage = CommonMethods.decodeSampledBitmapFromResource(instream, thumb_width, thumb_width);

instream.close();
return bitmapImage;

 } catch (URISyntaxException e) {
    e.printStackTrace();
    return null;
 } catch (MalformedURLException e) {
    e.printStackTrace();
    return null;
 } catch (IOException e) {
    e.printStackTrace();
    return null;
 }


 public static Bitmap decodeSampledBitmapFromResource(InputStream instream,
        int reqWidth, int reqHeight) throws IOException {

    //Copy instream for decode twice 
ByteArrayOutputStream out = new ByteArrayOutputStream();
    copy(instream,out);
    ByteArrayInputStream instream2 = new ByteArrayInputStream(out.toByteArray());

    // First decode with inJustDecodeBounds=true to check dimensions
    final BitmapFactory.Options options = new BitmapFactory.Options();
    options.inJustDecodeBounds = true;
    BitmapFactory.decodeStream(instream, null, options);
    instream2.close();

    options.inJustDecodeBounds = false;

    // Calculate inSampleSize
    options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

    // Decode bitmap with inSampleSize set
    return BitmapFactory.decodeStream(instream, null, options);
 }

 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) {
         if (width > height) {
         inSampleSize = Math.round((float) height / (float) reqHeight);
     } else {
             inSampleSize = Math.round((float) width / (float) reqWidth);
     }
     }

     return inSampleSize;
}

//Copy instream method
public static void copy(InputStream input, OutputStream output) throws IOException{

     byte[] buffer = new byte[Constants.IO_BUFFER_SIZE];

 int n = 0;

 while (-1 != (n = input.read(buffer))) {

     output.write(buffer, 0, n);
 }
 }

score 6 · Accepted Answer

BitmapFactory.decodeStream 返回 null 因为输入流被使用了两次，我没有尝试过你的代码，但它接缝没问题，或者我错了。无论如何，我有一个更好的解决方案。只需使用 BufferedInputStream 包装 inputStream，然后在第二次读取之前，先调用“reset”。注意普通的 inputStreams 不支持“reset”，你可以调用它但什么都不会发生。我的代码：

    public static Bitmap decodeSampledBitmapFromStream(InputStream inputStream,
                                                   int reqWidth, int reqHeight)
                             throws IOException {
    if (!widthHeightCheck(reqWidth, reqHeight)) 
        return BitmapFactory.decodeStream(inputStream);
    // First decode with inJustDecodeBounds=true to check dimensions
    if (!(inputStream instanceof BufferedInputStream)) {
        inputStream = new BufferedInputStream(inputStream);
    }
    final BitmapFactory.Options options = new BitmapFactory.Options();
    options.inJustDecodeBounds = true;
    Rect rect = new Rect(-1, -1, -1, -1);
    BitmapFactory.decodeStream(inputStream, rect, options);

    // Calculate inSampleSize
    options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

    // Decode bitmap with inSampleSize set
    options.inJustDecodeBounds = false;
    inputStream.reset();
    return BitmapFactory.decodeStream(inputStream, rect, options);
}

score 1 · Accepted Answer

我认为您可以通过将您从 httpEntity 获得的流包装在自定义 WrappedStream 中来实现这一点。这个 WrappedStream 将在读取原始流时提供第二个输入流。（这是通过 PipedStream 完成的）

使用此代码获取图像大小后：

options.inJustDecodeBounds = true;
WrappedStream wrappedStream = new WrappedStream(instream);
BitmapFactory.decodeStream(wrappedStream, null, options);

你可以打电话

InputStream reReadStream = wrappedStream.getReReadStream();
options.inJustDecodeBounds = false;
// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

// Decode bitmap with inSampleSize set
return BitmapFactory.decodeStream(reReadStream, null, options);

最后，这是 WrappedStream 的实现（它只是将所有调用委托给包装的 inputStream，并将所有读取（或跳过）的字节写入 pipedOutputStream）

import java.io.IOException;
import java.io.InputStream;
import java.io.PipedInputStream;
import java.io.PipedOutputStream;

/** Simple class wrapping an InputStream and feeding a secondary InputStream
 *  to re-read the data that was originally available in the inputStream.
**/

public class WrappedStream extends InputStream {

private InputStream urlStream;
private PipedOutputStream pipedStream;

public WrappedStream(InputStream urlStream) {
    this.urlStream = urlStream;
    this.pipedStream = new PipedOutputStream();
}

/**
 * return a fresh InputStream to re-read the data
 */
public InputStream getReReadStream() throws IOException {
    return new PipedInputStream(pipedStream);
}
@Override
public int available() throws IOException {
    return urlStream.available();
}

@Override
public void close() throws IOException {
    urlStream.close();
}

@Override
public void mark(int readlimit) {
    urlStream.mark(readlimit);
}

@Override
public boolean markSupported() {
    return urlStream.markSupported();
}

@Override
public int read() throws IOException {
    int b = urlStream.read();
    pipedStream.write(b);
    return b;
}

@Override
public int read(byte[] buffer) throws IOException {
    int l = urlStream.read(buffer);
    pipedStream.write(buffer);
    return l;
}

@Override
public int read(byte[] buffer, int offset, int length) throws IOException {
    int l = urlStream.read(buffer, offset, length);
    pipedStream.write(buffer, offset, length);
    return l;
}

@Override
public void reset() throws IOException {
    urlStream.reset();
}

@Override
//bytes skipped must available on the re-read stream so we read and write them.
public long skip(long byteCount) throws IOException {
    long bytesToSkip = byteCount;
    long skippedBytes = 0;
//ugly trick required to not loosing bytes if we ever skip more than Integer.MAX_VALUE bytes
    while(bytesToSkip>Integer.MAX_VALUE){
        _skip(Integer.MAX_VALUE);
        bytesToSkip -=Integer.MAX_VALUE;
        skippedBytes +=Integer.MAX_VALUE;
    }
    byte[] b = new byte[(int)bytesToSkip];
    skippedBytes += read(b);
    return skippedBytes;
}

private int _skip(int byteCount) throws IOException {
    byte[] b = new byte[(int)byteCount];
    return read(b);
}
}

请注意，我没有测试此代码。这只是为了给你一些关于如何解决你的问题的想法。

另一点：即使这段代码从未创建过巨大的位图，整个流将保留在内存中，直到构建缩放的位图。

score 0 · Accepted Answer

这是从服务器下载位图的方法，代码较少，您可以满足您的要求

Bitmap downloadBitmap(String url)
        {
            Bitmap image = null;
            InputStream in = null;
            try
                {
                    in = new java.net.URL(url).openStream();
                    BitmapFactory.Options opts = new BitmapFactory.Options();
                    opts.inSampleSize = 2;
                    image = BitmapFactory.decodeStream(new FlushedInputStream(in),null,opts);
                    in.close();
                }
            catch (MalformedURLException e)
                {
                    e.printStackTrace();
                }
            catch (IOException e)
                {
                    e.printStackTrace();
                }
            return image;
        }

在上面的代码中我们使用 opts.inSampleSize = 2; 这意味着位图将减少到其原始大小的一半以避免内存异常如果我们正在加载大量图像，我们必须这样做

其中使用的其他一些类

        static class FlushedInputStream extends FilterInputStream
        {
            public FlushedInputStream( InputStream inputStream )
                {
                    super(inputStream);
                }

            @Override
            public long skip(long n) throws IOException
                {
                    long totalBytesSkipped = 0L;
                    while (totalBytesSkipped < n)
                        {
                            long bytesSkipped = in.skip(n - totalBytesSkipped);
                            if (bytesSkipped == 0L)
                                {
                                    int byte1 = read();
                                    if (byte1 < 0)
                                        {
                                            break; // we reached EOF
                                        }
                                    else
                                        {
                                            bytesSkipped = 1; // we read one byte
                                        }
                                }
                            totalBytesSkipped += bytesSkipped;
                        }
                    return totalBytesSkipped;
                }
        }

score 0 · Accepted Answer

找到适合您的代码

final HttpEntity entity = response.getEntity();
            if (entity != null) {
                InputStream inputStream = null;
                try {
                    inputStream = entity.getContent();
                    BitmapFactory.Options options = new BitmapFactory.Options();
                    //options.inSampleSize = 2;
                    final Bitmap bitmap = BitmapFactory
                            .decodeStream(inputStream, null, options);
                    return bitmap;
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    if (inputStream != null) {
                        inputStream.close();
                    }
                    entity.consumeContent();
                }
            }

请替换适当的变量，如果您想缩放图像，您可以在获取位图后对其进行缩放。

score 0 · Accepted Answer

请使用以下代码将图像下载并显示到 imageview 中。

public class image extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        Bitmap bitmap = DownloadImage("http://www.gophoto.it/view.php?i=http://1.bp.blogspot.com/-2LTvCCufBKc/T3L3KgcTj2I/AAAAAAAABbQ/Ki60e1LU9sE/s1600/Sachin%2BTendulkar.png");
        ImageView img = (ImageView) findViewById(R.id.img);
        img.setImageBitmap(bitmap);
    }

    private InputStream OpenHttpConnection(String urlString) throws IOException {
        InputStream in = null;
        int response = -1;

        URL url = new URL(urlString);
        URLConnection conn = url.openConnection();

        if (!(conn instanceof HttpURLConnection))
            throw new IOException("Not an HTTP connection");

        try {
            HttpURLConnection httpConn = (HttpURLConnection) conn;
            httpConn.setAllowUserInteraction(false);
            httpConn.setInstanceFollowRedirects(true);
            httpConn.setRequestMethod("GET");
            httpConn.connect();
            response = httpConn.getResponseCode();
            if (response == HttpURLConnection.HTTP_OK) {
                in = httpConn.getInputStream();
            }
        } catch (Exception ex) {
            throw new IOException("Error connecting");
        }
        return in;
    }

    private Bitmap DownloadImage(String URL) {
        Bitmap bitmap = null;
        InputStream in = null;
        try {
            in = OpenHttpConnection(URL);
            bitmap = BitmapFactory.decodeStream(in);
            in.close();
        } catch (IOException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }
        return bitmap;
    }
}

android - BitmapFactory.decodeStream 在下载图像表单时返回 null

5 回答 5

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