Question

所以我关注这个tutorial，我有 RecyclerView 和 GridLayoutManager 实现。 GridLayoutManager 有2列。我想要两种视图类型，所以我使用了两个扩展 RecyclerView.ViewHolder 的 ViewHolders ，我正在重写这个方法： getItemViewType（int position）< / em>，但我采取了Cast异常。 Logcat 显示：

java.lang.ClassCastException：adapter.AdapterListItemHome $ CommentViewHolder0无法强制转换为adapter.AdapterListItemHome $ CommentViewHolder1 在adapter.AdapterListItemHome.onBindViewHolder（AdapterListItemHome.java:200）在adapter.AdapterListItemHome.onBindViewHolder（AdapterListItemHome.java:25）

但是我没有使用CommentViewHolder0对CommentViewHolder1使用强制转换，例如Line问题是这样的：

Remote Address:127.0.0.1:80 Request URL:http://localhost/project_dir/public/user/check Request Method:POST Status Code:200 OK Response Headers view source Access-Control-Allow-Origin:http://localhost:9000 Cache-Control:no-cache Connection:Keep-Alive Content-Length:4 Content-Type:text/html; charset=UTF-8 Date:Wed, 29 Jul 2015 13:41:51 GMT Keep-Alive:timeout=5, max=100 Server:Apache/2.4.9 (Win64) PHP/5.5.12 Vary:Origin X-Powered-By:PHP/5.5.12 Request Headers view source Accept:application/json, text/plain, */* Accept-Encoding:gzip, deflate Accept-Language:en-US,en;q=0.8 Cache-Control:max-age=0 Connection:keep-alive Content-Length:0 Host:localhost Origin:http://localhost:9000 Referer:http://localhost:9000/ User-Agent:Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/44.0.2403.107 Safari/537.36

这是来自适配器的代码（AdapterListItemHome.java）：

final CommentViewHolder0 vh0 = (CommentViewHolder0)cvh;

这是 Fragment ， RecyclerView 正在实施

public class AdapterListItemHome extends RecyclerView.Adapter<RecyclerView.ViewHolder> { ArrayList<GadgetItem> mListItem; Context mContext; private int choice; public static OnItemClickListener listener;// Define listener member variable public static final int FIRST_ITEM = 0; public static final int REST_ITEMS = 1; /** * Defines the listener interface */ public interface OnItemClickListener { void onItemClick(View itemView, int position); } // Define the method that allows the parent activity or fragment to define the listener public void setOnItemClickListener(OnItemClickListener listener) { this.listener = listener; } /** * view holder - holds the widgets - classical */ public class CommentViewHolder1 extends RecyclerView.ViewHolder { public ProgressBar pgLoading; public TextView tv_title; public ImageView imgView; //constructor public CommentViewHolder1(final View itemView) { super(itemView); // Find the TextView in the LinearLayout tv_title = ((TextView) itemView.findViewById(R.id.namgeItem)); pgLoading = (ProgressBar) itemView.findViewById(R.id.pbLoadingImage); imgView = (ImageView) itemView.findViewById(R.id.imgItem); itemView.setOnClickListener(new View.OnClickListener(){ @Override public void onClick(View v) { // Triggers click upwards to the adapter on click if (listener != null) listener.onItemClick(itemView, getPosition()); } }); } } /** * second viewHolder */ public class CommentViewHolder0 extends RecyclerView.ViewHolder { public ProgressBar pgLoading; public TextView tv_title; public ResizableImageView imgView; public TextView tv_date; //constructor public CommentViewHolder0(final View itemView) { super(itemView); // Find the TextView in the LinearLayout tv_title = ((TextView) itemView.findViewById(R.id.namgeItem)); tv_date = ((TextView) itemView.findViewById(R.id.tv_date)); pgLoading = (ProgressBar) itemView.findViewById(R.id.pbLoadingImage); imgView = (ResizableImageView) itemView.findViewById(R.id.resizable_image); imgView.setOnClickListener(new View.OnClickListener(){ @Override public void onClick(View v) { // Triggers click upwards to the adapter on click if (listener != null) listener.onItemClick(imgView, getPosition()); } }); } } /* * VF: Constructor */ public AdapterListItemHome(Context pContext, ArrayList<GadgetItem> pListGadget) { this.mContext = pContext; this.mListItem = pListGadget; } /** * Replace the contents of a view (invoked by the layout manager) * @param viewGroup * @param ViewType * @return */ @Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup viewGroup, int ViewType){ View v; //Log.d("bill", "viewtype = " + String.valueOf(ViewType)); switch(ViewType){ case REST_ITEMS: v = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.row_item, viewGroup, false); CommentViewHolder1 cvh1 = new CommentViewHolder1(v); return cvh1; case FIRST_ITEM: v = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.row_item_home, viewGroup, false); CommentViewHolder0 cvh0 = new CommentViewHolder0(v); return cvh0; default: v = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.row_item, viewGroup, false); CommentViewHolder1 cvh2 = new CommentViewHolder1(v); return cvh2; } } @Override public void onBindViewHolder(RecyclerView.ViewHolder cvh, int position) { Transformation transformation; GadgetItem item; switch ( cvh.getItemViewType () ){ case REST_ITEMS: final CommentViewHolder1 vh1 = (CommentViewHolder1)cvh; item = mListItem.get(position); vh1.tv_title.setText(item.gadget_title); vh1.pgLoading.setVisibility(View.VISIBLE); vh1.imgView.setImageDrawable(null); /** * clicking on the image view */ transformation = new Transformation() { @Override public Bitmap transform(Bitmap source) { int targetWidth = vh1.imgView.getWidth(); double aspectRatio = (double) source.getHeight() / (double) source.getWidth(); int targetHeight = (int) (targetWidth * aspectRatio); // Bitmap result = Bitmap.createScaledBitmap(source, // targetWidth, // targetHeight, false); Bitmap result = scaleAndCropImage(source, 300); if (result != source) { // Same bitmap is returned if sizes are the same source.recycle(); } return result; } @Override public String key() { return "transformation" + " desiredWidth"; } }; Picasso.with(mContext).load(item.gadget_image).into(vh1.imgView, new Callback() { @Override public void onError() { } @Override public void onSuccess() { vh1.pgLoading.setVisibility(View.GONE); } }); case FIRST_ITEM: final CommentViewHolder0 vh0 = (CommentViewHolder0)cvh; item = mListItem.get(position); vh0.tv_title.setText(item.gadget_title); vh0.pgLoading.setVisibility(View.VISIBLE); vh0.imgView.setImageDrawable(null); vh0.tv_date.setText(item.gadget_pubDate); /** * clicking on the image view */ transformation = new Transformation() { @Override public Bitmap transform(Bitmap source) { int targetWidth = vh0.imgView.getWidth(); double aspectRatio = (double) source.getHeight() / (double) source.getWidth(); int targetHeight = (int) (targetWidth * aspectRatio); // Bitmap result = Bitmap.createScaledBitmap(source, // targetWidth, // targetHeight, false); Bitmap result = scaleAndCropImage(source, 300); if (result != source) { // Same bitmap is returned if sizes are the same source.recycle(); } return result; } @Override public String key() { return "transformation" + " desiredWidth"; } }; Picasso.with(mContext).load(item.gadget_image).into(vh0.imgView, new Callback() { @Override public void onError() { } @Override public void onSuccess() { vh0.pgLoading.setVisibility(View.GONE); } }); } } // Return the size of dataset (invoked by the layout manager) @Override public int getItemCount() { return mListItem.size(); } /* (non-Javadoc) * VF: creating a item to show */ Bitmap scaleAndCropImage(Bitmap image, int height) { float ratio = (float) (height) / (float) image.getHeight(); int width = (int) ((float) image.getWidth() * ratio); return ScalingUtilities.createScaledBitmap(image, width, height, ScalingUtilities.ScalingLogic.CROP); } @Override public int getItemViewType(int position) { int viewType; if (position == 1) viewType = FIRST_ITEM; else viewType = REST_ITEMS; return viewType; } }

我一直在各地搜索，实施方法是一样的，我无法弄清问题在哪里。谢谢你的帮助

Answer 1

这段代码对我来说很好用：

public class AdapterListItemHome extends RecyclerView.Adapter<AdapterListItemHome.MainHolder>  {
ArrayList<GadgetItem> mListItem;
Context mContext;
public static OnItemClickListener listener;// Define listener member variable
public static final int FIRST_ITEM = 0;
public static final int REST_ITEMS = 1;
/**
 * Defines the listener interface
 */
public interface OnItemClickListener {
    void onItemClick(View itemView, int position);
}
// Define the method that allows the parent activity or fragment to define the listener
public void setOnItemClickListener(OnItemClickListener listener) {
    this.listener = listener;
}
public class MainHolder extends RecyclerView.ViewHolder {

    public MainHolder(View itemView){
        super(itemView);
    }
}
/**
 * view holder - holds the widgets 
 */
public class CommentViewHolder1 extends MainHolder {
    public ProgressBar pgLoading;
    public TextView tv_title;
    public ImageView imgView;

    //constructor
    public CommentViewHolder1(final View itemView) {
        super(itemView);
        // Find the TextView in the LinearLayout
        tv_title = ((TextView) itemView.findViewById(R.id.namgeItem));
        pgLoading = (ProgressBar) itemView.findViewById(R.id.pbLoadingImage);
        imgView = (ImageView) itemView.findViewById(R.id.imgItem);
        itemView.setOnClickListener(new View.OnClickListener(){

            @Override
            public void onClick(View v) {
                // Triggers click upwards to the adapter on click
                if (listener != null)
                    listener.onItemClick(itemView, getPosition());
            }
        });
    }   
}
/**
 * second viewHolder
 */
public class CommentViewHolder0 extends MainHolder {

    public ProgressBar pgLoading;
    public TextView tv_title;
    public ResizableImageView imgView;
    public TextView tv_date;

    //constructor
    public CommentViewHolder0(final View itemView) {
        super(itemView);
        // Find the TextView in the LinearLayout
        tv_title = ((TextView) itemView.findViewById(R.id.namgeItem_home));
        tv_date = ((TextView) itemView.findViewById(R.id.tv_date));
        pgLoading = (ProgressBar) itemView.findViewById(R.id.pbLoadingImage_home);
        imgView = (ResizableImageView) itemView.findViewById(R.id.resizable_image);
        imgView.setOnClickListener(new View.OnClickListener(){

            @Override
            public void onClick(View v) {
                // Triggers click upwards to the adapter on click
                if (listener != null)
                    listener.onItemClick(imgView, getPosition());

            }
        });
    }

}
public AdapterListItemHome(Context pContext, ArrayList<GadgetItem> pListGadget,ArrayList<String> pDateList) {
    this.mContext = pContext;
    this.mListItem = pListGadget;
    this.mDateList = pDateList;
    p = new Picasso.Builder(mContext)
            .memoryCache(new LruCache(cacheSize))
            .build();
}

/**
 * Replace the contents of a view (invoked by the layout manager)
 */
@Override
public MainHolder onCreateViewHolder(ViewGroup viewGroup, int ViewType){
    View v
    switch(ViewType){
        case REST_ITEMS:
            v = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.row_item, viewGroup, false);
            CommentViewHolder1 cvh1 = new CommentViewHolder1(v);
            return cvh1;
        case FIRST_ITEM:
            v = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.row_item_home, viewGroup, false);
            CommentViewHolder0 cvh0 = new CommentViewHolder0(v);
            return cvh0;
        default:
            v = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.row_item, viewGroup, false);
            CommentViewHolder1 cvh2 = new CommentViewHolder1(v);
            return cvh2;
    }
}

@Override
public void onBindViewHolder(MainHolder cvh, int position) {

    switch ( cvh.getItemViewType () ){

        case REST_ITEMS:

            final CommentViewHolder1 vh1 = (CommentViewHolder1)cvh;
            GadgetItem item1 = mListItem.get(position);
            vh1.tv_title.setText(fixTitleText(20, item1.gadget_title) + item1.gadget_price);
            vh1.pgLoading.setVisibility(View.VISIBLE);
            vh1.imgView.setImageDrawable(null);
            final int y = 200;
            final int x = 200;
            //picasso
            p.with(mContext).load(item1.gadget_image).resize(x, y).centerCrop().into(vh1.imgView, new Callback() {
                @Override
                public void onError() {
                }

                @Override
                public void onSuccess() {
                    vh1.pgLoading.setVisibility(View.GONE);
                }

            });
            break;
        case FIRST_ITEM:
            final CommentViewHolder0 vh0 = (CommentViewHolder0)cvh;
            GadgetItem item = mListItem.get(position);
            vh0.tv_title.setText(fixTitleText(63, item.gadget_title) + item.gadget_price);
            vh0.pgLoading.setVisibility(View.VISIBLE);
            vh0.imgView.setImageDrawable(null);
            String dateTime = fixdateTime(item.gadget_pubDate);
            String date = null;
            try {
                date = calculateDate(dateTime);
            } catch (ParseException e) {
                e.printStackTrace();
            }
            vh0.tv_date.setText(date + " " + dateTime);

            final int y1 = 335;
            final int x1 = 400;
            //picasso
            p.with(mContext).
                    load(item.gadget_image).resize(x1, y1).centerCrop().into(vh0.imgView, new Callback() {
                @Override
                public void onError() {

                }

                @Override
                public void onSuccess() {
                    vh0.pgLoading.setVisibility(View.GONE);
                }

            });

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

    return mListItem.size();
}
/*  (non-Javadoc)
 *  VF: creating a item to show
 */
@Override
public int getItemViewType(int position) {
    int viewType;

        if (position == 0 || (!(mDateList.get(position).equals(mDateList.get(position -1 )))))
            viewType = FIRST_ITEM;
        else
            viewType = REST_ITEMS;

    return viewType;
}
}

具有多种视图类型的RecyclerView GridLayoutManager，Viewholder强制转换异常

1 个答案: