Question

我在Google的RoomWithAView代码实验室中添加了一个复选框和分页库，并且对DiffUtil.ItemCallback的调用似乎正在将实体的更新版本传递给oldItem和newItem参数。

我的复选框处于选中状态是由数据库中名为“ isSelected”的布尔字段驱动的，该字段在单击该行时会更新，这将导致复选框状态发生变化。

问题是，当我更新“ isSelected”字段（例如，从false更改为true）时，以下日志打印对两个项目均返回true。我的复选框状态不会更改，因为areContentsTheSame返回true，并且不会调用onBindViewHolder。我可以强迫它返回false，但是我想了解出了什么问题：

private static DiffUtil.ItemCallback<WordEntity> DIFF_CALLBACK =
            new DiffUtil.ItemCallback<WordEntity>() {
                @Override
                public boolean areItemsTheSame(WordEntity oldItem, WordEntity newItem) {
                    Log.i("CLEAN_LOG","areItemsTheSame: " +
                            Boolean.toString(oldItem.getWordId()==newItem.getWordId()));
                    return oldItem.getWordId() == newItem.getWordId();
                }

                @Override
                public boolean areContentsTheSame(WordEntity oldItem, WordEntity newItem) {
                    Log.i("CLEAN_LOG","oldItem: " +
                            Boolean.toString(oldItem.getIsSelected()));
                    Log.i("CLEAN_LOG","newItem: " +
                            Boolean.toString(newItem.getIsSelected()));
                    Log.i("CLEAN_LOG","areContentsTheSame: " +
                            Boolean.toString(oldItem.getIsSelected() == newItem.getIsSelected()));
                    return oldItem.getIsSelected() == newItem.getIsSelected();
                }
            };

这是我的PagedListAdapter：

public static class WordListAdapter extends PagedListAdapter<WordEntity, WordListAdapter.WordViewHolder> {

    protected WordListAdapter() {
        super(DIFF_CALLBACK);
        setHasStableIds(true);
    }

    @NonNull
    @Override
    public WordViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.recyclerview_item, parent, false);
        return new WordViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(@NonNull WordViewHolder holder, int position) {

        WordEntity current = getItem(position);

        if (current != null) {
            holder.bindTo(current);
        }
    }

    private static DiffUtil.ItemCallback<WordEntity> DIFF_CALLBACK =
            new DiffUtil.ItemCallback<WordEntity>() {
                @Override
                public boolean areItemsTheSame(WordEntity oldItem, WordEntity newItem) {
                    Log.i("CLEAN_LOG","areItemsTheSame: " +
                            Boolean.toString(oldItem.getWordId()==newItem.getWordId()));
                    return oldItem.getWordId() == newItem.getWordId();
                }

                @Override
                public boolean areContentsTheSame(WordEntity oldItem, WordEntity newItem) {
                    Log.i("CLEAN_LOG","oldItem: " +
                            Boolean.toString(oldItem.getIsSelected()));
                    Log.i("CLEAN_LOG","newItem: " +
                            Boolean.toString(newItem.getIsSelected()));
                    Log.i("CLEAN_LOG","areContentsTheSame: " +
                            Boolean.toString(oldItem.getIsSelected() == newItem.getIsSelected()));
                    return oldItem.getIsSelected() == newItem.getIsSelected();
                }
            };

    @Override
    public long getItemId(int position) {
        WordEntity current = getItem(position);
        return current.mWordId;
    }

    class WordViewHolder extends RecyclerView.ViewHolder {

        TextView wordItemView;
        CheckBox checkBox;
        LinearLayout viewForeground;

        public void bindTo(WordEntity word) {
            wordItemView.setText(word.mWord);
            checkBox.setChecked(word.mIsSelected);
        }

        private WordViewHolder(View itemView) {
            super(itemView);
            viewForeground = itemView.findViewById(R.id.viewForeground);
            wordItemView = itemView.findViewById(R.id.textView);
            checkBox = itemView.findViewById(R.id.checkBox);

            checkBox.setClickable(false);

            viewForeground.setOnLongClickListener(new View.OnLongClickListener() {
                @Override
                public boolean onLongClick(View view) {
                    final WordEntity thisWord = getItem(getAdapterPosition());
                    if (thisWord != null) {
                        Toast.makeText(context,
                                "You long-clicked: " + thisWord.getWord(),
                                Toast.LENGTH_LONG).show();
                    }
                    // returning false here will alow onClickListener to trigger as well
                    return true;
                }
            });

            viewForeground.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    final WordEntity thisWord = getItem(getAdapterPosition());

                    if (thisWord != null) {
                        if (thisWord.getIsSelected()) {
                            thisWord.setIsSelected(false);
                        } else {
                            thisWord.setIsSelected(true);
                        }
                        mWordViewModel.update(thisWord);
                    }
                }
            });
        }
    }
}

这是我的观察者：

mWordViewModel = ViewModelProviders.of(this).get(WordViewModel.class);
    mWordViewModel.getAllWords().observe(this, new Observer<PagedList<WordEntity>>() {
        @Override
        public void onChanged(@Nullable final PagedList<WordEntity> words) {
            // Update the cached copy of the words in the adapter.
            adapter.submitList(words);
            if (words != null) {
                wordCount = words.size();
            } else {
                wordCount = 0;
            }
            Log.i(LOG_TAG,"Word Count: " + Integer.toString(wordCount));
        }
    });

所有Room数据库更新正常发生
基于日志，似乎在敲击一行时两次调用了areItemsTheSame，一次调用了一次areContentsTheSame

我期望oldItem.getIsSelected（）为false，而new.Item.getIsSelected（）为true，然后会触发onBindViewHolder。我还希望areItemsTheSame和areContentsTheSame只能为每个项目调用一次。

有人可以帮助我了解这里出了什么问题吗？如果我的期望与应该发生的事情相符？

这是我的示例应用程序的GitHub： https://github.com/DanglaGT/RoomWithAViewPaging

Answer 1

由于this answer，我和您遇到了同一个程序，我终于发现要使用Paging Library，您需要确保PagedList和它是{{1} } 两者都是旧对象。

有我的解决方案：

item

PagedListAdapter将newItem作为oldItem传递到DiffUtil.ItemCallback

1 个答案: