How to get a context in a recycler view adapter

问题:

I'm trying to use picasso library to be able to load url to imageView, but I'm not able to get the context to use the picasso library correctly.

public class FeedAdapter extends RecyclerView.Adapter<FeedAdapter.ViewHolder> {
    private List<Post> mDataset;



    // Provide a reference to the views for each data item
    // Complex data items may need more than one view per item, and
    // you provide access to all the views for a data item in a view holder
    public class ViewHolder extends RecyclerView.ViewHolder {
        // each data item is just a string in this case
        public TextView txtHeader;
        public ImageView pub_image;
        public ViewHolder(View v) {
            super(v);
            txtHeader = (TextView) v.findViewById(R.id.firstline);
            pub_image = (ImageView) v.findViewById(R.id.imageView);


        }
    }




    // Provide a suitable constructor (depends on the kind of dataset)
    public FeedAdapter(List<Post> myDataset) {
        mDataset = myDataset;
    }

    // Create new views (invoked by the layout manager)
    @Override
    public FeedAdapter.ViewHolder onCreateViewHolder(ViewGroup parent,
                                                   int viewType) {
        // create a new view
        View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.feedholder, parent, false);
        // set the view's size, margins, paddings and layout parameters
        ViewHolder vh = new ViewHolder(v);
        return vh;
    }

    // Replace the contents of a view (invoked by the layout manager)
    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        // - get element from your dataset at this position
        // - replace the contents of the view with that element

        holder.txtHeader.setText(mDataset.get(position).getPost_text());

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


    }

    // Return the size of your dataset (invoked by the layout manager)
    @Override
    public int getItemCount() {
        return mDataset.size();
    }

}

回答1:

You have a few options here:

1. Pass Context as an argument to FeedAdapter and keep it as class field
2. Use dependency injection to inject Context when you need it. I strongly suggest reading about it. There is a great tool for that -- Dagger by Square

3. Get it from any View object. In your case this might work for you:

   holder.pub_image.getContext()

   As pub_image is a ImageView.

回答2:

You can add global variable:

private Context context;

then assign the context from here:

@Override
public FeedAdapter.ViewHolder onCreateViewHolder(ViewGroup parent,int viewType) {
    // create a new view
    View v=LayoutInflater.from(parent.getContext()).inflate(R.layout.feedholder, parent, false);
    // set the view's size, margins, paddings and layout parameters
    ViewHolder vh = new ViewHolder(v);
    // set the Context here 
    context = parent.getContext();
    return vh;
}

Happy Codding :)

回答3:

You can use pub_image context (holder.pub_image.getContext()) :

@Override
public void onBindViewHolder(ViewHolder ViewHolder, int position) {

    holder.txtHeader.setText(mDataset.get(position).getPost_text());

    Picasso.with(holder.pub_image.getContext()).load("http://i.imgur.com/DvpvklR.png").into(holder.pub_image);


}

回答4:

Short answer:

Context context;

@Override
public void onAttachedToRecyclerView(RecyclerView recyclerView) {
    super.onAttachedToRecyclerView(recyclerView);
    context = recyclerView.getContext();
}

Explanation why other answers are not great:

1. Passing Context to the adapter is completely unnecessary, since RecyclerView you can access it from inside the class
2. Obtaining Context at ViewHolder level means that you do it every time you bind or create a ViewHolder. You duplicate operations.
3. I don't think you need to worry about any memory leak. If your adapter lingers outside your Activity lifespan (which would be weird) then you already have a leak.

回答5:

Create a constructor of FeedAdapter :

Context context; //global
public FeedAdapter(Context context)
{
   this.context = context;  
}

and in Activity

FeedAdapter obj = new FeedAdapter(this);

回答6:

First globally declare

Context mContext;

pass context with the constructor, by modifying it.

public FeedAdapter(List<Post> myDataset, Context context) {
    mDataset = myDataset;
    this.mContext = context;
}

then use the mContext whereever you need it

回答7:

You can use like this view.getContext()

Example

holder.tv_room_name.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            Toast.makeText(v.getContext(), "", Toast.LENGTH_SHORT).show();


        }
    });

回答8:

First add a global variable

Context mContext;

Then change your constructor to this

public FeedAdapter(Context context, List<Post> myDataset) {
    mContext = context;
    mDataset = myDataset;
}

The pass your context when creating the adapter.

FeedAdapter myAdapter = new FeedAdapter(this,myDataset);

回答9:

you can use this:

itemView.getContext()

回答10:

You can define:

Context ctx; 

And on onCreate initialise ctx to:

ctx=parent.getContext(); 

Note: Parent is a ViewGroup.