android - 使用 LruCache 在内存中存储位图

Question

我一直在尝试在我的应用程序中实现 LruCache，但我在连接点和在不同组件之间传递位图时遇到困难。

我想知道如何在我的应用程序中集成 LruCache。我也想了解实现 LruCache 的过程，所以越详细越好

第一类是 AsyncTask 图像加载器，第二类是我的自定义适配器

异步任务

 public class GetImagesBitmap extends AsyncTask<ImageView, Void, Bitmap>{
    InputStream inputStream;
    ImageView imageView = null;
    String path;




    @Override
    protected Bitmap doInBackground(ImageView... imageViews) {
        this.imageView = imageViews[0];
        return download_Image((String)imageView.getTag());
    }

    @Override
    protected void onPostExecute(Bitmap result) {

        imageView.setImageBitmap(result);
    }

    private Bitmap download_Image(String url) {


        final AndroidHttpClient client = AndroidHttpClient.newInstance("Android");
        HttpGet httpGet = new HttpGet(url);
        try {
            HttpResponse httpResponse = client.execute(httpGet);
            final int statusCode = httpResponse.getStatusLine().getStatusCode();
            if (statusCode != HttpStatus.SC_OK) {
                Log.w("ImageDownloader", "Error " + statusCode
                        + " while retrieving bitmap from " + url);
                return null;
            }

            final HttpEntity entity = httpResponse.getEntity();
            if(entity != null){
                inputStream = null;
                inputStream = entity.getContent();
                final Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
                return bitmap;
            }
                if(inputStream != null){
                    inputStream.close();
                }
                entity.consumeContent();

        } catch (IOException e) {

            httpGet.abort();
             Log.w("ImageDownloader", "Error while retrieving bitmap from " + url);
        }finally{
            if(client != null){
                client.close();
            }
        }

        return null;
        }



    }

自定义 View 适配器类

 public class CustomListingListAdapter extends ArrayAdapter<HashMap<String, String>> {





    private ArrayList<HashMap<String, String>> data;
    private Context context;
    private LayoutInflater mInflater;
    private int viewId;
    private String[] tag;
    HashMap<String, String> currentData = new HashMap<String, String>();

    //private static final String TAG_CONTENT = "content";
    //private static final String TAG_RATING = "rating";
    private static final String TAG_NAME = "name";
    private static final String TAG_IMAGE_PATH = "image_path";
    private static final String TAG_PRODUCT_ID = "product_id";
    private static final String TAG_RATING = "rating";

    public CustomListingListAdapter(Context c,
            ArrayList<HashMap<String, String>> data,
            int viewId, String[] tag) {
        super( c, viewId, data);

        this.context = c;
        this.data= data;
        this.viewId = viewId ;
    }

    @Override
    public int getCount() {

        return data.size();
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        View vi = convertView;
        Holder holder;

        if (convertView == null) {

            // Inflate the view since it does not exist
            if (vi == null) {
                mInflater = (LayoutInflater) getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
                vi = mInflater.inflate(R.layout.list_item_layout, null);

            }

            holder = new Holder();

            holder.Name = (TextView) vi.findViewById(R.id.name);
            holder.pid = (TextView) vi.findViewById(R.id.pid);
            holder.imageView = (ImageView) vi.findViewById(R.id.list_image);
            holder.ratingView = (ImageView) vi.findViewById(R.id.num_stars);

            vi.setTag(holder);  
        }else {
            holder = (Holder) vi.getTag();
        }


        currentData = (HashMap<String, String>) data.get(position);
        holder.imageView.setTag(currentData.get(TAG_IMAGE_PATH));





        if (currentData != null) {

            holder.Name.setText(currentData.get(TAG_NAME));
            holder.pid.setText(currentData.get(TAG_PRODUCT_ID));
        }   

        new GetImagesBitmap().execute(holder.imageView);
    return vi;


    }
    private static class Holder {

        public ImageView imageView;
        public ImageView ratingView;
        public TextView pid;
        public TextView Name;

       } 
    }

Answer 1

您走在正确的轨道上，但我无法确定您在代码中的哪个位置考虑了 List/GridView 中的 View 回收。您确实在重用传递给 getView 的 convertView，但在每个 getView 中启动一个新的 AsyncTask 将导致任务加载图像，但如果启动它的 View 被回收，则将它们插入错误的列表行中。我的建议是查看 Google 的新网络库 Volley。它有一个 NetworkImageView 类，可以将图像异步加载到 ImageView 中。我推荐它的原因是缓存，在磁盘和内存中， View 回收都为您处理。

截击: https://developers.google.com/events/io/sessions/325304728

如果您确实想自己解决这个问题，我会查看有关在 ListView 中加载位图的 Android 开发人员博客文章。它演示了如何像您想要的那样使用 AsyncTasks，但它正确地处理了 View 回收。

文章: http://developer.android.com/training/displaying-bitmaps/process-bitmap.html

最后一个小提示:不要为每个网络调用都实例化一个新的 HttpClient。创建一个需要一些时间，首选方法是保留一个配置为多线程的 HttpClient 作为 Singleton 实例，并将其用于网络调用。或者，您可以为每个请求创建一个新的 HttpUrlConnection；这对那个类(class)来说没问题。

编辑:抱歉，我刚刚意识到我实际上并没有回答这个问题。要为 Bimap 实现 LruCache，您可以通过一些调整从支持库扩展 LruCache 类。这是我用于缓存 Bitamps 以与 Volley 库一起使用的类:

// From com.android.volley.toolbox.ImageLoader
public interface ImageCache {
    public Bitmap getBitmap(String url);
    public void putBitmap(String url, Bitmap bitmap);
}

// My ImageCache implementation
public class BitmapLruCache extends LruCache<String, Bitmap> implements ImageCache {
    private static final int DEFAULT_CACHE_SIZE = (int) (Runtime.getRuntime().maxMemory() / 1024) / 8;

    public BitmapLruCache() {
        this(DEFAULT_CACHE_SIZE);
    }

    public BitmapLruCache(int maxSize) {
        super(maxSize);
    }

    @Override
    public Bitmap getBitmap(String url) {
        return get(url);
    }

    @Override
    public void putBitmap(String url, Bitmap bitmap) {
        put(url, bitmap);
    }

    @Override
    protected int sizeOf(String key, Bitmap value) {
        return value == null ? 0 : value.getRowBytes() * value.getHeight() / 1024;
    }
}