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如果arraylist为空,为什么显示recyclerview no头?

android-recyclerview android java

Jakob · 技术社区 · 7 年前

我的 RecyclerView 显示器 CardViews 还有一个标题。这个 Cardviews 从中获取值 json 头部从之前活动中给定的参数中获取值。

我的问题是 Reyclerview 仅在以下情况下显示标题: 杰森 对于 CardView 不是空的,但如果 杰森 不向发送空值 卡地维 显示标题。

回收视图适配器 :

        public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

            Context context;

            private Activity activity;

            List<GetDataAdapter> getDataAdapter;
            List<ExerciseAdapter> exerciseAdapter;
            private static final int TYPE_HEADER = 0;

            private static final int TYPE_ITEM = 1;
            public RecyclerViewAdapter(Context context, List<GetDataAdapter> getDataAdapter, List<ExerciseAdapter> exerciseAdapter){

                super();

                this.exerciseAdapter = exerciseAdapter;
                this.getDataAdapter = getDataAdapter;
                this.context = context;
            }

            private GetDataAdapter getItem(int position)
            {
                return getDataAdapter.get(position);

            }


            @Override
            public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
                if (viewType == TYPE_ITEM) {
                     View itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.item, parent, false);
                     return new ViewHolder(itemView);
                }
                if (viewType == TYPE_HEADER) {
                    //Inflating header view
                    View itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.header, parent, false);
                    return new HeaderViewHolder(itemView);
                }
                return null;
            }



            class ViewHolder extends RecyclerView.ViewHolder{

                public TextView edit;
                public TextView NameTextView;
                public TextView PhoneNumberTextView;
                public TextView SubjectTextView;
                public NetworkImageView imageView1;
                public NetworkImageView imageView2;
                public NetworkImageView imageView3;
                public NetworkImageView imageView4;
                public NetworkImageView imageView5;
                public TextView ratebutton;


                public ViewHolder(View itemView) {

                    super(itemView);
                    edit = (TextView)itemView.findViewById(R.id.edit);
                    NameTextView = (TextView) itemView.findViewById(R.id.textView4) ;
                    PhoneNumberTextView = (TextView) itemView.findViewById(R.id.textView6) ;
                    SubjectTextView = (TextView) itemView.findViewById(R.id.textView8) ;
                    imageView1 = (NetworkImageView)itemView.findViewById(R.id.imageView1t);
                    imageView2 = (NetworkImageView)itemView.findViewById(R.id.imageView2t);
                    imageView3 = (NetworkImageView)itemView.findViewById(R.id.imageView3t);
                    imageView4 = (NetworkImageView)itemView.findViewById(R.id.imageView4t);
                    imageView5 = (NetworkImageView)itemView.findViewById(R.id.imageView5t);
                    ratebutton = (TextView)itemView.findViewById(R.id.ratebutton);



                }
            }



            @Override
            public void onBindViewHolder(final RecyclerView.ViewHolder holder, int position) {
                if (holder instanceof ViewHolder) {

                    if (position != 0) {
                      final GetDataAdapter current = getItem(position - 1);


                        final ViewHolder holder1 = (ViewHolder) holder;
                        final ImageLoader imageLoader = ImageAdapter.getInstance(context).getImageLoader();
                        final ImageLoader imageLoader2 = ImageAdapter.getInstance(context).getImageLoader();
                        final ImageLoader imageLoader3 = ImageAdapter.getInstance(context).getImageLoader();
                        final ImageLoader imageLoader4 = ImageAdapter.getInstance(context).getImageLoader();
                        final ImageLoader imageLoader5 = ImageAdapter.getInstance(context).getImageLoader();

                        imageLoader.get(current.getImageUrl(),
                                ImageLoader.getImageListener(
                                        holder1.imageView1,
                                        R.mipmap.ic_launcher_image,
                                        android.R.drawable.ic_dialog_alert
                                )
                        );
                        imageLoader2.get(current.getImageUrl2(),
                                ImageLoader.getImageListener(
                                        holder1.imageView2,
                                        R.mipmap.ic_launcher_image,
                                        android.R.drawable.ic_dialog_alert
                                )
                        );
                        imageLoader3.get(current.getImageUrl3(),
                                ImageLoader.getImageListener(
                                        holder1.imageView3,
                                        R.mipmap.ic_launcher_image,
                                        android.R.drawable.ic_dialog_alert
                                )
                        );
                        imageLoader4.get(current.getImageUrl4(),
                                ImageLoader.getImageListener(
                                        holder1.imageView4,
                                        R.mipmap.ic_launcher_image,
                                        android.R.drawable.ic_dialog_alert
                                )
                        );
                        imageLoader5.get(current.getImageUrl5(),
                                ImageLoader.getImageListener(
                                        holder1.imageView5,
                                        R.mipmap.ic_launcher_image,
                                        android.R.drawable.ic_dialog_alert
                                )
                        );


                        holder1.imageView1.setImageUrl(current.getImageUrl(), imageLoader);
                        holder1.imageView2.setImageUrl(current.getImageUrl2(), imageLoader2);
                        holder1.imageView3.setImageUrl(current.getImageUrl3(), imageLoader3);
                        holder1.imageView4.setImageUrl(current.getImageUrl4(), imageLoader4);
                        holder1.imageView5.setImageUrl(current.getImageUrl5(), imageLoader5);
                        holder1.NameTextView.setText(current.getName());
                        holder1.PhoneNumberTextView.setText(current.getPhone_number());
                        holder1.SubjectTextView.setText(current.getSubject2());



                    } else{
                        final GetDataAdapter current = getItem(position);
                        final ViewHolder holder1 = (ViewHolder) holder;
                        final ImageLoader imageLoader = ImageAdapter.getInstance(context).getImageLoader();
                        final ImageLoader imageLoader2 = ImageAdapter.getInstance(context).getImageLoader();
                        final ImageLoader imageLoader3 = ImageAdapter.getInstance(context).getImageLoader();
                        final ImageLoader imageLoader4 = ImageAdapter.getInstance(context).getImageLoader();
                        final ImageLoader imageLoader5 = ImageAdapter.getInstance(context).getImageLoader();

                        imageLoader.get(current.getImageUrl(),
                                ImageLoader.getImageListener(
                                        holder1.imageView1,
                                        R.mipmap.ic_launcher_image,
                                        android.R.drawable.ic_dialog_alert
                                )
                        );
                        imageLoader2.get(current.getImageUrl2(),
                                ImageLoader.getImageListener(
                                        holder1.imageView2,
                                        R.mipmap.ic_launcher_image,
                                        android.R.drawable.ic_dialog_alert
                                )
                        );
                        imageLoader3.get(current.getImageUrl3(),
                                ImageLoader.getImageListener(
                                        holder1.imageView3,
                                        R.mipmap.ic_launcher_image,
                                        android.R.drawable.ic_dialog_alert
                                )
                        );
                        imageLoader4.get(current.getImageUrl4(),
                                ImageLoader.getImageListener(
                                        holder1.imageView4,
                                        R.mipmap.ic_launcher_image,
                                        android.R.drawable.ic_dialog_alert
                                )
                        );
                        imageLoader5.get(current.getImageUrl5(),
                                ImageLoader.getImageListener(
                                        holder1.imageView5,
                                        R.mipmap.ic_launcher_image,
                                        android.R.drawable.ic_dialog_alert
                                )
                        );


                        holder1.imageView1.setImageUrl(current.getImageUrl(), imageLoader);
                        holder1.imageView2.setImageUrl(current.getImageUrl2(), imageLoader2);
                        holder1.imageView3.setImageUrl(current.getImageUrl3(), imageLoader3);
                        holder1.imageView4.setImageUrl(current.getImageUrl4(), imageLoader4);
                        holder1.imageView5.setImageUrl(current.getImageUrl5(), imageLoader5);
                        holder1.NameTextView.setText(current.getName());
                        holder1.PhoneNumberTextView.setText(current.getPhone_number());
                        holder1.SubjectTextView.setText(current.getSubject2());


                    }
                }
                if (holder instanceof HeaderViewHolder) {
                    final GetDataAdapter current = getItem(position);
                    final HeaderViewHolder holder1 = (HeaderViewHolder) holder;

                    //set text of header textviews;



                }

            }



            @Override
            public int getItemViewType(int position) {
                if (position == 0) {
                    return TYPE_HEADER;
                }
                    return TYPE_ITEM;

        }


            @Override
            public int getItemCount() {
               if (!getDataAdapter.isEmpty()) {
                   return getDataAdapter.size() + 1;
               } else

                   return getDataAdapter.size();

            }
            private class HeaderViewHolder extends RecyclerView.ViewHolder {
                TextView //some Textviews for Header;
                ImageView exerciseimage;

                public HeaderViewHolder(View view) {
                    super(view);


                  // declaring textviews;



                }
            }




        }

用

@Override
        public int getItemCount() {
           if (!getDataAdapter.isEmpty()) {
               return getDataAdapter.size() + 1;
           } else

               return getDataAdapter.size();

        }

我试图改变 getDataAdapter 如果它是空的,只显示标题,但不起作用。

也与

else{
                    final GetDataAdapter current = getItem(position);
                    final ViewHolder holder1 = (ViewHolder) holder;
                    final ImageLoader imageLoader = ImageAdapter.getInstance(context).getImageLoader();
                    final ImageLoader imageLoader2 = ImageAdapter.getInstance(context).getImageLoader();
                    final ImageLoader imageLoader3 = ImageAdapter.getInstance(context).getImageLoader();
                    final ImageLoader imageLoader4 = ImageAdapter.getInstance(context).getImageLoader();
                    final ImageLoader imageLoader5 = ImageAdapter.getInstance(context).getImageLoader();

                    imageLoader.get(current.getImageUrl(),
                            ImageLoader.getImageListener(
                                    holder1.imageView1,
                                    R.mipmap.ic_launcher_image,
                                    android.R.drawable.ic_dialog_alert
                            )
                    );
                    imageLoader2.get(current.getImageUrl2(),
                            ImageLoader.getImageListener(
                                    holder1.imageView2,
                                    R.mipmap.ic_launcher_image,
                                    android.R.drawable.ic_dialog_alert
                            )
                    );
                    imageLoader3.get(current.getImageUrl3(),
                            ImageLoader.getImageListener(
                                    holder1.imageView3,
                                    R.mipmap.ic_launcher_image,
                                    android.R.drawable.ic_dialog_alert
                            )
                    );
                    imageLoader4.get(current.getImageUrl4(),
                            ImageLoader.getImageListener(
                                    holder1.imageView4,
                                    R.mipmap.ic_launcher_image,
                                    android.R.drawable.ic_dialog_alert
                            )
                    );
                    imageLoader5.get(current.getImageUrl5(),
                            ImageLoader.getImageListener(
                                    holder1.imageView5,
                                    R.mipmap.ic_launcher_image,
                                    android.R.drawable.ic_dialog_alert
                            )
                    );


                    holder1.imageView1.setImageUrl(current.getImageUrl(), imageLoader);
                    holder1.imageView2.setImageUrl(current.getImageUrl2(), imageLoader2);
                    holder1.imageView3.setImageUrl(current.getImageUrl3(), imageLoader3);
                    holder1.imageView4.setImageUrl(current.getImageUrl4(), imageLoader4);
                    holder1.imageView5.setImageUrl(current.getImageUrl5(), imageLoader5);
                    holder1.NameTextView.setText(current.getName());
                    holder1.PhoneNumberTextView.setText(current.getPhone_number());
                    holder1.SubjectTextView.setText(current.getSubject2());


                }
            }

我试图改变 position 在里面 final GetDataAdapter current = getItem(position); 我认为这样做是必要的 position - 1 或类似: size + 1 ,因为数组开始计数 0 尺寸为 1 .

也许你可以给我一个提示或者解决我的问题。

1 回复 | 直到 7 年前

Jack Meister 7 年前

假设你的名单, getDataAdapter ,为空。然后 getDataAdapter.size() == 0 和 getItemCount() 也回报 0 . 因为你总是想让标题显示出来, 获取项计数() 至少应该总是返回 1 . 我会简单地重写它:

@Override
public int getItemCount() {
    return getDataAdapter.size() + 1;
}

有了这个更改,RecyclerView列表中总是有第零个项目。什么时候? getItemViewType() 被调用,它将正确返回 TYPE_HEADER 对于第零项,所以 RecyclerView.ViewHolder 第0项中的将是 HeaderViewHolder . (我知道你说过要改变 获取数据适配器 当它是空的,但这似乎是一个迂回的方式来实现这里的目标。您的数据模型不需要更改以适应您的视图。)

关于 onBindViewHolder() :您不需要嵌套的if-else语句。由于头始终位于RecyclerView列表的顶部,因此 position 参数将为 一 当RecyclerView绑定到第一个“Normal”列表项时。但第一个正常项对应于 获取数据适配器 ,所以减去 一 :

@Override
public void onBindViewHolder(final RecyclerView.ViewHolder holder, int position) {
    if (holder instanceof ViewHolder) {
        final ViewHolder viewHolder = (ViewHolder) holder;
        final GetDataAdapter current = getItem(position - 1);
        //bind to normal views
    } else if (holder instanceof HeaderViewHolder) {
        final HeaderViewHolder headerViewHolder = (HeaderViewHolder) holder;
        //set text of header textviews
    }
}