android - 如何让 Volley NetworkImageView 离线工作

Question

我使用 Volley NetworkImageView 从互联网下载图像并显示在我的 listview 中。现在我想让 Volley NetworkImageView 在没有可用网络时显示保存的图像。 Volley 已经通过 URL 作为键缓存了图像，因为当我使用

Entry entry = SingletonRequestQueue.getInstance(context).getRequestQueue().getCache().get(imageURL);

entry.data 不为空。但我的问题是图像分辨率很高，我无法使用

Bitmap b = BitmapFactory.decodeByteArray(entry.data, 0, entry.data.length);

因为它造成了很多滞后，我不得不重新发明轮子，因为我必须再次创建 asynctask 查看 listview 何时滚动以取消解码，回收 位图，在内存缓存中创建，找到最佳采样值和...

所以更好的想法是做一些技巧，使 Volley NetworkImageView 使用它自己的 DiskLRUCache 在没有网络时显示它们。

有什么想法吗？

我的代码:

public class SingletonRequestQueue {


    private static SingletonRequestQueue mInstance;
    private RequestQueue mRequestQueue;
    private ImageLoader mImageLoader;
    private static Context mCtx;
    private LruBitmapCache mLruBitmapCache;

    private SingletonRequestQueue(Context context) {
        mCtx = context;
        mRequestQueue = getRequestQueue();
        mLruBitmapCache = new LruBitmapCache(LruBitmapCache.getCacheSize(context));
        mImageLoader = new ImageLoader(mRequestQueue,mLruBitmapCache);

    }

    public static synchronized SingletonRequestQueue getInstance(Context context) {
        if (mInstance == null) {
            mInstance = new SingletonRequestQueue(context);
        }
        return mInstance;
    }

    public RequestQueue getRequestQueue() {
        if (mRequestQueue == null) {

            // getApplicationContext() is key, it keeps you from leaking the
            // Activity or BroadcastReceiver if someone passes one in.

            mRequestQueue = Volley.newRequestQueue(mCtx.getApplicationContext(),new OkHttpStack());
//          mRequestQueue = Volley.newRequestQueue(mCtx.getApplicationContext());
        }
        return mRequestQueue;
    }

    public <T> void addToRequestQueue(Request<T> req) {
        getRequestQueue().add(req);
    } 

    public ImageLoader getImageLoader() {
        return mImageLoader;
    }

    public LruBitmapCache getLruBitmapCache() {
        return mLruBitmapCache;
    }

    public void setLruBitmapCache(LruBitmapCache lruBitmapCache) {
        mLruBitmapCache = lruBitmapCache;
    }


}

在我的适配器中:

public IssueListAdapter(Context context, int resource, List<Issue> objects) {
        super(context, resource, objects);
        this.context = context;
        this.mIssueList = objects;
        mImageLoader = SingletonRequestQueue.getInstance(context).getImageLoader();
}

public static class ViewHolder{

    public  NetworkImageView mNetworkImageView;
    public  TextView mFee;
    public  TextView mName;
}


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


    ViewHolder holder;

    if(convertView == null){
        holder = new ViewHolder();
        LayoutInflater inflater =    
                (LayoutInflater) context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
        convertView = inflater.inflate(R.layout.gridview_issuelist_item, parent, false);

        holder.mNetworkImageView = (NetworkImageView)convertView.findViewById(R.id.NetworkImageView_MainActivity_issue_image);
        holder.mName = (TextView)convertView.findViewById(R.id.TextView_MainActivity_name);
        holder.mFee = (TextView)convertView.findViewById(R.id.TextView_MainActivity_fee);
        Utility.settingTypfaceFont(context, holder.mName);
        Utility.settingTypfaceFont(context, holder.mFee);

        convertView.setTag(holder);

    }else{
        holder = (ViewHolder)(convertView.getTag());
    }

    final Issue issue = mIssueList.get(position);
    holder.mName.setText(issue.getTitle());
    holder.mFee.setText(String.valueOf(issue.getFee()));
    String imageURL = issue.getPublicCover();

    holder.mNetworkImageView.setImageUrl(imageURL, mImageLoader);
    holder.mNetworkImageView.setDefaultImageResId(R.drawable.placeholder2);;

    /*
    Entry entry = SingletonRequestQueue.getInstance(context).getRequestQueue().getCache().get(imageURL);
    if(entry != null && entry.data != null){
        byte[] imageByte = entry.data;
        loadBitmap(imageByte, holder.mNetworkImageView,imageURL);
    }else{
        holder.mNetworkImageView.setImageUrl(imageURL, mImageLoader);
    }*/

    return convertView;
}

@Override
public int getCount() {
    if(mIssueList != null){
        return mIssueList.size();           
    }
    else{
        return 0;
    }
}

public List<Issue> getIssueList() {
    return mIssueList;
}

}

Answer 1

我更喜欢使用 Volley/retrofit 和 Android-Universal-Image-Loader/Picasso ，图片加载器库确实在加载和缓存图像方面做得很好。

默认情况下，他们用一行代码处理所有事情:

Picasso.with(context).load("http://i.imgur.com/DvpvklR.png").into(imageView);

您还可以在图片加载时设置动画、调整图片大小和添加占位符。