RecyclerView lazy loading

问题

I'm doing lazy loading on a RecyclerView adapter. First I fetch the image metadata (if it has any) and then let Picasso download the actual image.

public class PostHolder extends RecyclerView.ViewHolder implements Callback<Photo>{
    private PostImageView cover;
    private TextView content;
    private long id;

    public PostHolder(View itemView) {
        super(itemView);
        this.itemView.setOnClickListener(onClickListener);
        content = (TextView) itemView.findViewById(R.id.post_content);
        cover = (PostImageView) itemView.findViewById(R.id.post_image);
    }

    public void setPost(final Post post, int i){
        cover.unsetImage();
        this.id = post.getPhotoId();
        itemView.setTag(i);
        content.setText(post.getMessage());

        if("photo".equals(post.getType()) || "video".equals(post.getType()) && id != 0L){
            cache.get(id, this);
        }else{
            cover.setUrl(post.getImageUrl());
        }
    }

    @Override
    public void result(Photo result) {
        if(result != null && result.getId() == PostHolder.this.id){
            cover.setPhoto(result);
        }
    }
}

cache.get() loads my metadata from the cache, the result is returned with result().setPost() gets called in onBindViewHolder(). Now I'm getting everyone's favorite viewholder issue - my ImageView displays a different image before switching to the correct one. I know that Picasso correctly handles this and I have a check for my own loading where i compare the holder's id to the metadata id. I've spent a few hours on this already. Internet, you are my only hope.

回答1:

It's fixed now, though I'm not exactly sure why. I believe it's

Picasso
    .with(getContext())
    .cancelRequest(this);

inside unsetImage() because of the double request needed to load it.

What I think happens:

1. Picasso is still loading the previous image.
2. A call for the current image metadata is dispatched.
3. Picasso loads the preVious image. Since Picasso doesn't know about the metadata, it's not automatically canceled.
4. The metadata get's loaded, and Picasso starts loading the current image.

来源：https://stackoverflow.com/questions/27460779/recyclerview-lazy-loading