Android 位图使用优化

Question

我一直在阅读使用位图的不同方法，每种方法各有优缺点。

所以我有一个问题在我的搜索中没有得到真正的回答。我的应用程序中有大量内存泄漏。所以我解决了这个问题，我使用了几个位图。特别是一个位图被不同的对象多次使用。我调用位图图像并使用 Canvas 在其上绘制文本，然后以适合使用它的设备的分辨率压缩并保存图像。

目前，每次我需要绘制新文本并创建图像的更新版本时，我都会使用 BitmapFactory.decodeResource(Resources, ResourceID) 获取位图。

有没有更好的方法来获取图像？就像在某处缓存它：1）可能吗？ 2) 与从可绘制文件夹中解码它相比，多次引用同一图像的更好方法？

注意：此过程是使用 AsyncTask 完成的，因此根据设备的不同，从技术上讲，图像可以被使用一次访问服务时间。不确定这是否会导致资源冲突。

谢谢大家，我觉得答案不需要代码，但如果需要，我可以添加它。

Answer 1

如果您正在寻找简单的 Android 中的位图缓存，以下实现将缓存在内存和文件中。当它再次加载位图资源（由图像文件名标识）时，它会尝试在内存中搜索位图，然后在文件缓存中搜索。

用法：

imageLoader.DisplayImage("image_filename_in_resource_folder", imageView);

public class ImageLoader {
        final int stub_id = R.drawable.ic_thumbnail;
    private Context mContext;
    MemoryCache memoryCache = new MemoryCache();
    FileCache fileCache;
    ExecutorService executorService;
    private Map<ImageView, String> imageViews = Collections.synchronizedMap(new WeakHashMap<ImageView, String>());

    public ImageLoader(Context context) {
        fileCache = new FileCache(context);
        executorService = Executors.newFixedThreadPool(5);
        this.mContext = context;
    }

    public void DisplayImage(String url, ImageView imageView) {
        imageViews.put(imageView, url);
        Bitmap bitmap = memoryCache.get(url);
        if (bitmap != null)
            imageView.setImageBitmap(bitmap);
        else {
            queuePhoto(url, imageView);
            imageView.setImageResource(stub_id);
        }
    }

    private void queuePhoto(String url, ImageView imageView) {
        PhotoToLoad p = new PhotoToLoad(url, imageView);
        executorService.submit(new PhotosLoader(p));
    }



    //decodes image and scales it to reduce memory consumption
    protected 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 = 150;
            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 *= 2;
            }

            //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;
    }

    boolean imageViewReused(PhotoToLoad photoToLoad) {
        String tag = imageViews.get(photoToLoad.imageView);
        if (tag == null || !tag.equals(photoToLoad.url))
            return true;
        return false;
    }

    public void clearCache() {
        memoryCache.clear();
        fileCache.clear();
    }

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

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

    Bitmap getBitmap(String imageFileName) {
        File f = fileCache.getFile(imageFileName);

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

        try {
            Resources resource = mContext.getResources();
            int imageId = resource.getIdentifier(imageFileName, "drawable", mContext.getPackageName());
            Bitmap bitmap = null;
            InputStream is = resource.openRawResource(imageId);
            OutputStream os = new FileOutputStream(f);
            IOUtils.copy(is, os);
            os.close();
            bitmap = decodeFile(f);
            return bitmap;
        } catch (IOException e) {
            return null;
        }
    }
    class PhotosLoader implements Runnable {
        PhotoToLoad photoToLoad;

        PhotosLoader(PhotoToLoad photoToLoad) {
            this.photoToLoad = photoToLoad;
        }

        public void run() {
            if (imageViewReused(photoToLoad))
                return;
            Bitmap bmp = getBitmap(photoToLoad.url);
            memoryCache.put(photoToLoad.url, bmp);
            if (imageViewReused(photoToLoad))
                return;
            BitmapDisplayer bd = new BitmapDisplayer(bmp, photoToLoad);
            Activity a = (Activity) photoToLoad.imageView.getContext();
            a.runOnUiThread(bd);
        }
    }

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

        public BitmapDisplayer(Bitmap b, PhotoToLoad p) {
            bitmap = b;
            photoToLoad = p;
        }

        public void run() {
            if (imageViewReused(photoToLoad))
                return;
            if (null != bitmap) {
                photoToLoad.imageView.setImageBitmap(bitmap);

            }
        }
    }
}

内存缓存类

public class MemoryCache {
    private HashMap<String, SoftReference<Bitmap>> cache = new HashMap<String, SoftReference<Bitmap>>();

    public Bitmap get(String id) {
        if (!cache.containsKey(id))
            return null;
        SoftReference<Bitmap> ref = cache.get(id);
        return ref.get();
    }

    public void put(String id, Bitmap bitmap) {
        cache.put(id, new SoftReference<Bitmap>(bitmap));
    }

    public void clear() {
        cache.clear();
    }
}

文件缓存类

public class FileCache {

    private File cacheDir;

    public FileCache(Context context) {
        //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");
        else
            cacheDir = context.getCacheDir();
        if (!cacheDir.exists())
            cacheDir.mkdirs();
    }

    public File getFile(String url) {
        //Identify images by hashcode. Not a perfect solution.
        String filename = String.valueOf(url.hashCode());

        //Another possible solution, using cypto hashing functions like md5
        //String filename = md5(url);
        File f = new File(cacheDir, filename);
        return f;

    }

    public void clear() {
        File[] files = cacheDir.listFiles();
        if (files == null)
            return;
        for (File f : files)
            f.delete();
    }

}