Question

我在图像上做一个应用程序，在GridView中显示它们，我从服务器获取20个图像。每个图像的分辨率为720 * 540.I使用JSON解析来获取url，并使用下面的代码转换为Bitmap以设置图像。

public static Bitmap loadImageFromUrl(String url) {
    InputStream inputStream;Bitmap b;
    try {
        inputStream = (InputStream) new URL(url).getContent();
        BitmapFactory.Options bpo=  new BitmapFactory.Options();
        if(bpo.outWidth>500) {
            bpo.inSampleSize=8;
            b=BitmapFactory.decodeStream(inputStream, null,bpo );
        } else {
            bpo.inSampleSize=2;
            b=BitmapFactory.decodeStream(inputStream, null,bpo );
        }
        return  b;
    } catch (IOException e) {
        throw new RuntimeException(e);
    }
}

我的应用程序工作正常，但加载图片需要花费太多时间。所以我的应用程序变得缓慢。我应该降低图像的分辨率吗？

如何摆脱这个问题？

Answer 1

如果您正在进行网格视图以加载此类分辨率的20张图像，我建议如下：

绝对减小图像的大小。除非你的目标是平板电脑，否则你会很好，因为大多数智能手机无法通过20张图像达到分辨率。
如果可以，请缓存图片。
在不同的主题上下载图像。存储HashMap会让您轻松，只需将所有图像视图与图像文件名或其他形式的ID一起作为键。下载图像时向处理程序发送消息，并在解码后更新视图。您可以直接检索您的视图。只记得检查它们是否仍在窗口中。这样，图像将一个接一个地快速显示出来。我不认为多线程图像会有所帮助，只需确保使用另一个线程“推送图像”和主UI线程更新。用户体验将大大改善。

希望这会有所帮助。

---一些实现，我现在没有完整的代码 -

拥有一个数据结构，使视图与来自的数据相匹配。这里非常方便。

private HashMap<String,ImageView> pictures;

获得图片网址列表后，请仔细阅读：

 pictures.put(id,view);
        try{
            FileInputStream in = openFileInput(id);
            Bitmap bitmap = null;
            bitmap = BitmapFactory.decodeStream(in, null, null);
        view.setImageBitmap(bitmap);
        }catch(Exception e){
            new Thread(new PictureGetter(this,mHandler,id)).start();
        }

（这里图片获取器只是在没有缓存的情况下获取图像并缓存它）

更新图片视图的代码：

 if(id!=null){
        ImageView iv = pictures.get(id);
        if(iv!=null){
            try{
                FileInputStream in = openFileInput(id);
                Bitmap bitmap = null;
                bitmap = BitmapFactory.decodeStream(in, null, null);
                iv.setImageBitmap(bitmap);
            }catch(Exception e){
        }
    }

Answer 2

我猜测大部分加载时间是因为大量图像与图像大小相结合。

有两种可能的解决方案：

调整图像大小或降低图像质量，使文件大小低于75kb左右。
使用多线程一次检索多个图像。如果用户的连接速度非常慢，这可能没有用，但是如果将它与足够小的文件大小结合起来，它可能会有足够的帮助。您可能想要确定设备的当前带宽是什么，并根据您运行的线程数量来确定。

例如：20个图像，每个75KB，可用连接200 KB / s = 3或4个并发线程。

希望这有帮助。

Answer 3

我在Android应用程序中遇到同样的问题。当您从大尺寸图像解码位图并将其设置为imageBitmap到图像视图时，您的应用程序可能会变慢，经过几次尝试后，您将获得＆＃34;内存不足异常＆＃34;

您可以尝试处理此问题的两种可能方法： 1-从文件解码时减小位图大小 2-使用图像库。

我更喜欢第二种方式并使用Universal Image Loader。 https://github.com/nostra13/Android-Universal-Image-Loader

String url = "file://" + your_file_path
com.nostra13.universalimageloader.core.ImageLoader.getInstance().displayImage(url, ivPicture, options);

Answer 4

 public class clothImageLoader {

// the simplest in-memory cache implementation. This should be replaced with
// something like SoftReference or BitmapOptions.inPurgeable(since 1.6)
// public static HashMap<String, Bitmap> cache = new HashMap<String,
// Bitmap>();

private static File cacheDir;

public clothImageLoader(Context context) {
    // Make the background thead low priority. This way it will not affect
    // the UI performance
    photoLoaderThread.setPriority(Thread.NORM_PRIORITY - 1);

    // Find the dir to save cached images
    if (android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED))
        // cacheDir=new
        // File(android.os.Environment.getExternalStorageDirectory(),"LazyList");
        cacheDir = new File(ConstValue.MY_ClothBitmap_DIR);
    else
        cacheDir = context.getCacheDir();
    if (!cacheDir.exists())
        cacheDir.mkdirs();
}

final int stub_id = R.drawable.icon;

public void DisplayImage(String url, Activity activity, ImageView imageView) {
    if (ConstValue.ClothRoomcache.containsKey(url))
        imageView.setImageBitmap(ConstValue.ClothRoomcache.get(url));
    else {
        queuePhoto(url, activity, imageView);
        imageView.setImageResource(stub_id);
    }
}

private void queuePhoto(String url, Activity activity, ImageView imageView) {
    // This ImageView may be used for other images before. So there may be
    // some old tasks in the queue. We need to discard them.
    photosQueue.Clean(imageView);
    PhotoToLoad p = new PhotoToLoad(url, imageView);
    synchronized (photosQueue.photosToLoad) {
        photosQueue.photosToLoad.push(p);
        photosQueue.photosToLoad.notifyAll();
    }

    // start thread if it's not started yet
    if (photoLoaderThread.getState() == Thread.State.NEW)
        photoLoaderThread.start();
}

private Bitmap getBitmap(String url) {
    // I identify images by hashcode. Not a perfect solution, good for the
    // demo.
    String filename = String.valueOf(url.hashCode());
    File f = new File(cacheDir, filename);

    // from SD cache
    Bitmap b = decodeFile(f);
    if (b != null)
        return b;

    // from web
    try {
        Bitmap bitmap = null;
        /*
         * InputStream is=new URL(url).openStream(); OutputStream os = new
         * FileOutputStream(f); Utils.CopyStream(is, os); os.close();
         */
        URL url1 = new URL(url);
        bitmap = decodeFile(f);
        /* Open a connection to that URL. */
        URLConnection ucon = url1.openConnection();

        /*
         * Define InputStreams to read from the URLConnection.
         */
        InputStream is = ucon.getInputStream();
        // FlushedInputStream a = new FlushedInputStream(is);
        BufferedInputStream bis = new BufferedInputStream(is);

        /*
         * Read bytes to the Buffer until there is nothing more to read(-1).
         */
        ByteArrayBuffer baf = new ByteArrayBuffer(5000);
        int current = 0;
        while ((current = bis.read()) != -1) {
            baf.append((byte) current);
        }

        /* Convert the Bytes read to a String. */
        FileOutputStream fos = new FileOutputStream(f);
        fos.write(baf.toByteArray());
        fos.flush();
        fos.close();

        bitmap = decodeFile(f);
        return bitmap;
    } catch (Exception ex) {
        ex.printStackTrace();
        return null;
    }
}

// decodes image and scales it to reduce memory consumption
private Bitmap decodeFile(File f) {
    try {
        // decode image size
        BitmapFactory.Options o = new BitmapFactory.Options();
        o.inJustDecodeBounds = true;
        BitmapFactory.decodeStream(new FileInputStream(f), null, o);
        // Find the correct scale value. It should be the power of 2.
        final int REQUIRED_SIZE = ConstValue.bmpSize;
        int width_tmp = o.outWidth, height_tmp = o.outHeight;
        int scale = 1;
        while (true) {
            if (width_tmp / 2 < REQUIRED_SIZE || height_tmp / 2 < REQUIRED_SIZE)
                break;
            width_tmp /= 2;
            height_tmp /= 2;
            scale++;
        }

        // decode with inSampleSize
        BitmapFactory.Options o2 = new BitmapFactory.Options();
        o2.inSampleSize = scale;
        return BitmapFactory.decodeStream(new FileInputStream(f), null, o2);
    } catch (FileNotFoundException e) {
    }
    return null;
}

// Task for the queue
private class PhotoToLoad {
    public String url;
    public ImageView imageView;

    public PhotoToLoad(String u, ImageView i) {
        url = u;
        imageView = i;
    }
}

PhotosQueue photosQueue = new PhotosQueue();

public void stopThread() {
    photoLoaderThread.interrupt();
}

// stores list of photos to download
class PhotosQueue {
    private Stack<PhotoToLoad> photosToLoad = new Stack<PhotoToLoad>();

    // removes all instances of this ImageView
    public void Clean(ImageView image) {
        for (int j = 0; j < photosToLoad.size();) {
            if (photosToLoad.get(j).imageView == image)
                photosToLoad.remove(j);
            else
                ++j;
        }
    }
}

class PhotosLoader extends Thread {
    public void run() {
        try {
            while (true) {
                // thread waits until there are any images to load in the
                // queue
                if (photosQueue.photosToLoad.size() == 0)
                    synchronized (photosQueue.photosToLoad) {
                        photosQueue.photosToLoad.wait();
                    }
                if (photosQueue.photosToLoad.size() != 0) {
                    PhotoToLoad photoToLoad;
                    synchronized (photosQueue.photosToLoad) {
                        photoToLoad = photosQueue.photosToLoad.pop();

                        // photoToLoad=photosQueue.photosToLoad.get(0);
                        // photosQueue.photosToLoad.remove(photoToLoad);
                    }
                    Bitmap bmp = getBitmap(photoToLoad.url);
                    ConstValue.ClothRoomcache.put(photoToLoad.url, bmp);
                    if (((String) photoToLoad.imageView.getTag()).equals(photoToLoad.url)) {
                        BitmapDisplayer bd = new BitmapDisplayer(bmp, photoToLoad.imageView);
                        Activity a = (Activity) photoToLoad.imageView.getContext();
                        a.runOnUiThread(bd);
                    }
                }
                if (Thread.interrupted())
                    break;
            }
        } catch (InterruptedException e) {
            // allow thread to exit
        }
    }
}

PhotosLoader photoLoaderThread = new PhotosLoader();

// Used to display bitmap in the UI thread
class BitmapDisplayer implements Runnable {
    Bitmap bitmap;
    ImageView imageView;

    public BitmapDisplayer(Bitmap b, ImageView i) {
        bitmap = b;
        imageView = i;
    }

    public void run() {
        if (bitmap != null)
            imageView.setImageBitmap(bitmap);
        else
            imageView.setImageResource(stub_id);
    }
}

public static void clearCache() {
    // clear memory cache
    ConstValue.ClothRoomcache.clear();

    // clear SD cache
    File[] files = cacheDir.listFiles();
    for (File f : files)
        f.delete();
}

public 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 a = read();
                if (a < 0) {
                    break; // we reached EOF
                } else {
                    bytesSkipped = 1; // we read one byte
                }
            }
            totalBytesSkipped += bytesSkipped;
        }
        return totalBytesSkipped;
    }
}

}

当你在gridView getView方法中调用方法时：

holder.image.setTag(ChoseInfo.get(position).getLink());
        imageLoader.DisplayImage(ChoseInfo.get(position).getLink(), activity, holder.image);

ChoseInfo.get（位置）.getLink（））

此处getLink()是互联网链接。

Answer 5

Picasso library

解决方案是代替使用位图直接加载图像使用一个名为Picasso的超棒库它只是超级快我知道你真的很喜欢这个你可以这样做吗

将picasso jar文件添加到您的项目中（在此处下载picasso jar文件）使用picasso加载此类图像

Picasso.with(context).load(new File(title)).centerCrop()
    .resize(150, 150).error(R.drawable.ic_launcher).into(image);

其中title是您要加载的图像路径。裁剪，调整大小，错误是可选的。

应用程序在Android中的图像很慢

5 个答案: