為什么RecyclerView.OnScrollListener（）僅影響recyclerview的最后一項

Question

我想在我的應用程序中擁有此功能

意味着每當RecyclerView滾動時，顯示時間的TextView就會出現一小段時間，然后消失，我的工作就是這樣，目標TextView具有Visiblity.GONE和適配器看起來像

public class ChatMessageAdapter extends RecyclerView.Adapter<ViewHolder> {

    private List<ChatMessage> mMessageList;
    private Context mContext;
    private boolean isMe = false;

    private ThemMessageHolder messageHolder;

    public ChatMessageAdapter(Context mContext, List<ChatMessage> mMessageList){
        this.mContext = mContext;
        this.mMessageList = mMessageList;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View rootView = LayoutInflater.from(mContext).inflate( R.layout.chat_them_container, parent, false );
        return new ThemMessageHolder(rootView);
    }

    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        messageHolder = (ThemMessageHolder) holder;
        messageHolder.mMessageTextView.setText(mMessageList.get(position).getMessage());
        messageHolder.mSentAtTextView.setText(mMessageList.get(position).getSentAt());
    }

    @Override
    public int getItemCount() {
        return mMessageList.size();
    }

    public void showAndHideDate(){
        messageHolder.mSentAtTextView.setVisibility(View.VISIBLE);
        Handler handler = new Handler();
        handler.postDelayed(new Runnable() {
            @Override
            public void run() {
                messageHolder.mSentAtTextView.setVisibility(View.GONE);
            }
        },3500);

    }

}

在MainActivity中，我只是

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);        

        mMessageList = new CopyOnWriteArrayList<>();

        mChatMessagesRecyclerView = (RecyclerView) findViewById(R.id.chat_msg_rv);
        mChatMessagesRecyclerView.setLayoutManager(new LinearLayoutManager(MainActivity.this));
        mChatMessageAdapter = new ChatMessageAdapter(MainActivity.this, mMessageList);
        mChatMessagesRecyclerView.setAdapter(mChatMessageAdapter);

        mChatMessagesRecyclerView.setOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                super.onScrollStateChanged(recyclerView, newState);
                mChatMessageAdapter.showAndHideDate(); // Here I'm calling the method defined in Adapter class
            }

            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);
            }
        });
    }

通過上面的代碼，我僅對RecyclerView的最后一項獲得了預期的效果，如圖所示

如何在RecyclerView的所有項目上應用所需的效果？

Answer 1

問題是您在適配器中僅使用一個ThemMessageHolder變量。 意味着，每次onBindViewHolder()調用都會覆蓋該變量。 然后， messageHolder將指向最后創建的所有者，而showAndHideDate()將僅與它一起使用。

該解決方案可以找到所有可見的持有人（偽代碼）：

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        if (initChatBarUI()){
            mSendImageButton.setOnClickListener(MainActivity.this);
            mEmoImageButton.setOnClickListener(MainActivity.this);
        }

        mMessageList = new CopyOnWriteArrayList<>();

        final LinearLayoutManager layoutManager = new LinearLayoutManager(MainActivity.this);
        mChatMessagesRecyclerView = (RecyclerView) findViewById(R.id.chat_msg_rv);
        mChatMessagesRecyclerView.setLayoutManager(layoutManager);
        mChatMessageAdapter = new ChatMessageAdapter(MainActivity.this, mMessageList);
        mChatMessagesRecyclerView.setAdapter(mChatMessageAdapter);

        mChatMessagesRecyclerView.setOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                super.onScrollStateChanged(recyclerView, newState);
                final int firstVisibleItemPosition = layoutManager.findFirstVisibleItemPosition();
                final int lastVisibleItemPosition = layoutManager.findLastVisibleItemPosition();
                mChatMessageAdapter.showAndHideDate(mChatMessagesRecyclerView, firstVisibleItemPosition, lastVisibleItemPosition); // Here I'm calling the method defined in Adapter class
            }

            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);
            }
        });   
    }

和showAndHideDate（）可能看起來像

public void showAndHideDate(RecyclerView mRecyclerView, int firstVisibleItemPosition, int lastVisibleItemPosition){

    for (int i = firstVisibleItemPosition; i <= lastVisibleItemPosition; ++i) {
        final ThemMessageHolder holder = (ThemMessageHolder) mRecyclerView.findViewHolderForAdapterPosition(i);
        holder.mSentAtTextView.setVisibility(View.VISIBLE);
        Handler handler = new Handler();
        handler.postDelayed(new Runnable() {
            @Override
            public void run() {
                holder.mSentAtTextView.setVisibility(View.GONE);
            }
        },3500);
    }       

}