Java OnBackpress（）后notifydatasetchanged（）不工作 单击“后退”按钮后，我的recyclerview未正确更新 按 按下后退按钮之前，recyclerview工作正常 数据已正确更新（见日志），但recyclerview未反映更改 处理程序的目的是轮询数据库以获取通知（正常工作） 每次都会显示通知土司 我没有收到任何错误

如果我能提供任何其他信息帮助，请不要犹豫询问

Main:

 public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_chat_room);
        recView = (RecyclerView) findViewById(R.id.recyclerViewMessages);
        linearLayoutManager = new LinearLayoutManager(this) {};
        linearLayoutManager.setReverseLayout(true);
        recView.setLayoutManager(linearLayoutManager);
        listData = (ArrayList) MessagingData.getMessageListData();
        adapter = new RecyclerViewAdapterMessaging(listData, this);
        recView.setAdapter(adapter);
        adapter.setItemClickCallback(this);
        final Handler h = new Handler();
        final int delay = 2000; //milliseconds

        h.postDelayed(new Runnable(){
          public void run(){

            Notify_Message_Async notify_message_async = new Notify_Message_Async(ctx);
            notify_message_async.execute(NOTIFICATION, message_id);

            System.out.println(global.getNotification());
            if(global.getNotification()==1){
                Toast.makeText(ctx, "Notified",
                        Toast.LENGTH_LONG).show();
                try {
                    refresh_receive();
                } catch (ExecutionException e) {
                    Toast.makeText(ctx, "catch",
                            Toast.LENGTH_LONG).show();
                    e.printStackTrace();
                } catch (InterruptedException e) {
                    Toast.makeText(ctx, "catch",
                            Toast.LENGTH_LONG).show();
                    e.printStackTrace();
                }
            }
            h.postDelayed(this, delay);
        }
    }, delay);
}

 public void refresh_receive() throws ExecutionException, InterruptedException {
        String method = "receive_message";
        Receive_Live_Message_Async receive_live_message_async = new Receive_Live_Message_Async(this);
        receive_live_message_async.execute(method, message_id).get();// Setup the message
        adapter.setListData((ArrayList)MessagingData.getMessageListData());
        adapter.notifyDataSetChanged();
        global.setNotification(0);//reset notification
 }

public class RecyclerViewAdapterMessaging extends RecyclerView.Adapter<RecyclerViewAdapterMessaging.Holder> {
    private View v;
    private List<List_Item_Messaging> listData;
    private LayoutInflater inflater;
    Global global = new Global();
    private ItemClickCallback itemClickCallback;
    Context context;

    public interface ItemClickCallback {
        void onItemClick(View v, int p);

        void onSecondaryIconClick(int p);
    }

    public void setItemClickCallback(final ItemClickCallback itemClickCallback) {
        this.itemClickCallback = itemClickCallback;
    }

    public RecyclerViewAdapterMessaging(List<List_Item_Messaging> listData, Context c) {
        inflater = LayoutInflater.from(c);
        context = c;
        this.listData = listData;
    }

    @Override
    public int getItemViewType(int position) {//0 for self... /1 for Other
        List_Item_Messaging item = listData.get(position);
        //ENSURE GLOBAL USERNAME NOT NULL
        String other_username = item.getMessage_username();
        if (other_username == null) {
            ((Activity) context).finish();
        }
        if (item.getMessage_username().trim().equals(global.getUserName())) {
            System.out.println("The usernames are the same");
            return 0;
        } else {
            System.out.println("The usernames are the NOT same");
            return 1;
        }

    }

    @Override
    public Holder onCreateViewHolder(ViewGroup parent, int viewType) {

        switch (viewType) {
            case 0:
                View view = inflater.inflate(R.layout.chat_thread, parent, false);// Self
                v = view;
                break;
            case 1:
                View view2 = inflater.inflate(R.layout.chat_thread_other, parent, false);// Not self
                int width2 = global.getScreenWidth();
                v = view2;
                break;
        }
        return new Holder(v);
    }

    @Override
    public void onBindViewHolder(Holder holder, int position) {
        List_Item_Messaging item = listData.get(position);
        holder.conversation.setText(item.getMessage_conversation());
    }

    public void setListData(ArrayList<List_Item_Messaging> exerciseList) {
        this.listData.clear();
        this.listData.addAll(exerciseList);
    }

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

    class Holder extends RecyclerView.ViewHolder implements View.OnClickListener {

        ImageView thumbnail;
        //ImageView secondaryIcon;
        TextView conversation;
        View message_container;

        public Holder(View itemView) {
            super(itemView);

            conversation = (TextView) itemView.findViewById(R.id.conversation_textview);
            message_container = itemView.findViewById(R.id.message_container);
            message_container.setOnClickListener(this);
        }

        @Override
        public void onClick(View v) {
            if (v.getId() == R.id.message_container) {
                itemClickCallback.onItemClick(v, getAdapterPosition());
            } else {
                itemClickCallback.onSecondaryIconClick(getAdapterPosition());
            }
        }
    }

    public void clearItems() {
        listData.clear();
        this.notifyDataSetChanged();
    }
}

适配器：

 public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_chat_room);
        recView = (RecyclerView) findViewById(R.id.recyclerViewMessages);
        linearLayoutManager = new LinearLayoutManager(this) {};
        linearLayoutManager.setReverseLayout(true);
        recView.setLayoutManager(linearLayoutManager);
        listData = (ArrayList) MessagingData.getMessageListData();
        adapter = new RecyclerViewAdapterMessaging(listData, this);
        recView.setAdapter(adapter);
        adapter.setItemClickCallback(this);
        final Handler h = new Handler();
        final int delay = 2000; //milliseconds

        h.postDelayed(new Runnable(){
          public void run(){

            Notify_Message_Async notify_message_async = new Notify_Message_Async(ctx);
            notify_message_async.execute(NOTIFICATION, message_id);

            System.out.println(global.getNotification());
            if(global.getNotification()==1){
                Toast.makeText(ctx, "Notified",
                        Toast.LENGTH_LONG).show();
                try {
                    refresh_receive();
                } catch (ExecutionException e) {
                    Toast.makeText(ctx, "catch",
                            Toast.LENGTH_LONG).show();
                    e.printStackTrace();
                } catch (InterruptedException e) {
                    Toast.makeText(ctx, "catch",
                            Toast.LENGTH_LONG).show();
                    e.printStackTrace();
                }
            }
            h.postDelayed(this, delay);
        }
    }, delay);
}

 public void refresh_receive() throws ExecutionException, InterruptedException {
        String method = "receive_message";
        Receive_Live_Message_Async receive_live_message_async = new Receive_Live_Message_Async(this);
        receive_live_message_async.execute(method, message_id).get();// Setup the message
        adapter.setListData((ArrayList)MessagingData.getMessageListData());
        adapter.notifyDataSetChanged();
        global.setNotification(0);//reset notification
 }

public class RecyclerViewAdapterMessaging extends RecyclerView.Adapter<RecyclerViewAdapterMessaging.Holder> {
    private View v;
    private List<List_Item_Messaging> listData;
    private LayoutInflater inflater;
    Global global = new Global();
    private ItemClickCallback itemClickCallback;
    Context context;

    public interface ItemClickCallback {
        void onItemClick(View v, int p);

        void onSecondaryIconClick(int p);
    }

    public void setItemClickCallback(final ItemClickCallback itemClickCallback) {
        this.itemClickCallback = itemClickCallback;
    }

    public RecyclerViewAdapterMessaging(List<List_Item_Messaging> listData, Context c) {
        inflater = LayoutInflater.from(c);
        context = c;
        this.listData = listData;
    }

    @Override
    public int getItemViewType(int position) {//0 for self... /1 for Other
        List_Item_Messaging item = listData.get(position);
        //ENSURE GLOBAL USERNAME NOT NULL
        String other_username = item.getMessage_username();
        if (other_username == null) {
            ((Activity) context).finish();
        }
        if (item.getMessage_username().trim().equals(global.getUserName())) {
            System.out.println("The usernames are the same");
            return 0;
        } else {
            System.out.println("The usernames are the NOT same");
            return 1;
        }

    }

    @Override
    public Holder onCreateViewHolder(ViewGroup parent, int viewType) {

        switch (viewType) {
            case 0:
                View view = inflater.inflate(R.layout.chat_thread, parent, false);// Self
                v = view;
                break;
            case 1:
                View view2 = inflater.inflate(R.layout.chat_thread_other, parent, false);// Not self
                int width2 = global.getScreenWidth();
                v = view2;
                break;
        }
        return new Holder(v);
    }

    @Override
    public void onBindViewHolder(Holder holder, int position) {
        List_Item_Messaging item = listData.get(position);
        holder.conversation.setText(item.getMessage_conversation());
    }

    public void setListData(ArrayList<List_Item_Messaging> exerciseList) {
        this.listData.clear();
        this.listData.addAll(exerciseList);
    }

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

    class Holder extends RecyclerView.ViewHolder implements View.OnClickListener {

        ImageView thumbnail;
        //ImageView secondaryIcon;
        TextView conversation;
        View message_container;

        public Holder(View itemView) {
            super(itemView);

            conversation = (TextView) itemView.findViewById(R.id.conversation_textview);
            message_container = itemView.findViewById(R.id.message_container);
            message_container.setOnClickListener(this);
        }

        @Override
        public void onClick(View v) {
            if (v.getId() == R.id.message_container) {
                itemClickCallback.onItemClick(v, getAdapterPosition());
            } else {
                itemClickCallback.onSecondaryIconClick(getAdapterPosition());
            }
        }
    }

    public void clearItems() {
        listData.clear();
        this.notifyDataSetChanged();
    }
}

公共类RecycleWebAdapterMessageing扩展了RecycleWebView.Adapter{ 私人观点v； 私有列表数据； 私人充气机； 全局全局=新全局（）； 私有项ClickCallback项ClickCallback； 语境； 公共接口项ClickCallback{ void onItemClick（视图v，int p）； 第二次连接无效（INTP）； } 公共无效设置项ClickCallback（最终项ClickCallback项ClickCallback）{ this.itemClickCallback=itemClickCallback； } 公共RecycleServiceAdapterMessageing（列表数据，上下文c）{ 充气机=来自（c）的充气机； 上下文=c； this.listData=listData； } @凌驾 public int getItemViewType（int位置）{//0表示自身…/1表示其他 List\u Item\u messageing Item=listData.get（位置）； //确保全局用户名不为空 字符串other_username=item.getMessage_username（）； 如果（其他用户名==null）{ （（活动）上下文）.finish（）； } if（item.getMessage_username（）.trim（）.equals（global.getUserName（）））{ System.out.println（“用户名相同”）； 返回0； }否则{ System.out.println（“用户名不一样”）； 返回1； } } @凌驾 public Holder onCreateViewHolder（视图组父级，int-viewType）{ 开关（视图类型）{ 案例0： 视图=充气器。充气（R.layout.chat_thread，parent，false）；//Self v=视图； 打破 案例1： View view2=充气机。充气（R.layout.chat_thread_other，parent，false）；//非自我 int width2=global.getScreenWidth（）； v=视图2； 打破 } 返还新持有人（五）； } @凌驾 公共无效onBindViewHolder（Holder Holder，内部位置）{ List\u Item\u messageing Item=listData.get（位置）； holder.conversation.setText（item.getMessage_conversation（））； } public void setListData（ArrayList exerciseList）{ 此参数为.listData.clear（）； this.listData.addAll（exerciseList）； } @凌驾 public int getItemCount（）{ 返回listData.size（）； } 类持有者扩展了RecyclerView.ViewHolder实现了View.OnClickListener{ 图像视图缩略图； //图像视图第二图标； 文本视图会话； 查看消息容器； 公共持有人（查看项目视图）{ 超级（项目视图）； conversation=（TextView）itemView.findViewById（R.id.conversation\u TextView）； message\u container=itemView.findviewbyd（R.id.message\u container）； message_container.setOnClickListener（此）； } @凌驾 公共void onClick（视图v）{ if（v.getId（）==R.id.message_容器）{ itemClickCallback.onItemClick（v，getAdapterPosition（））； }否则{ itemClickCallback.onSecondaryInclick（getAdapterPosition（））； } } } 公共物品{ listData.clear（）； this.notifyDataSetChanged（）； } } 我引用了以下无解决方案：

---

在代码中稍作更改

super.onCreate(savedInstanceState);
setContentView(R.layout.activity_chat_room);
    recView = (RecyclerView) findViewById(R.id.recyclerViewMessages);
    linearLayoutManager = new LinearLayoutManager(this) {};
    linearLayoutManager.setReverseLayout(true);
    recView.setLayoutManager(linearLayoutManager);
    // change here
    if (listData != null)
        listData.clear();
    else listData = new <> ArrayList();
    listData.addAdd((ArrayList)MessagingData.getMessageListData());
    adapter = new RecyclerViewAdapterMessaging(listData, this);
    recView.setAdapter(adapter);
    adapter.setItemClickCallback(this);
    final Handler h = new Handler();
    final int delay = 2000; //milliseconds

代码中的另一个问题是，您正在使用receive\u live\u message\u async AsyncTask 将更新代码放入onPostExecute

public class receive_live_message_async extends AsyncTask {

        @Override
        protected Object doInBackground(Object[] objects) {
            return null;
        }

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

        @Override
        protected void onPostExecute(Object o) {
            // call your refresh_receive(); here
            super.onPostExecute(o);
        }
    }

    @Override
    protected void onPostExecute(Object o) {
        dataList.clear();
        dataList.addAll((ArrayList)MessagingData.getMessageListData());
        adapter.notifyDataSetChanged();
        super.onPostExecute(o);
    }

类似地，在调用receive_live_message_async.execute（）时；在onPostExecute中更新您的recyclerView

public class receive_live_message_async extends AsyncTask {

        @Override
        protected Object doInBackground(Object[] objects) {
            return null;
        }

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

        @Override
        protected void onPostExecute(Object o) {
            // call your refresh_receive(); here
            super.onPostExecute(o);
        }
    }

    @Override
    protected void onPostExecute(Object o) {
        dataList.clear();
        dataList.addAll((ArrayList)MessagingData.getMessageListData());
        adapter.notifyDataSetChanged();
        super.onPostExecute(o);
    }

---

在代码中稍加修改

super.onCreate(savedInstanceState);
setContentView(R.layout.activity_chat_room);
    recView = (RecyclerView) findViewById(R.id.recyclerViewMessages);
    linearLayoutManager = new LinearLayoutManager(this) {};
    linearLayoutManager.setReverseLayout(true);
    recView.setLayoutManager(linearLayoutManager);
    // change here
    if (listData != null)
        listData.clear();
    else listData = new <> ArrayList();
    listData.addAdd((ArrayList)MessagingData.getMessageListData());
    adapter = new RecyclerViewAdapterMessaging(listData, this);
    recView.setAdapter(adapter);
    adapter.setItemClickCallback(this);
    final Handler h = new Handler();
    final int delay = 2000; //milliseconds

代码中的另一个问题是，您正在使用receive\u live\u message\u async AsyncTask 将更新代码放入onPostExecute

public class receive_live_message_async extends AsyncTask {

        @Override
        protected Object doInBackground(Object[] objects) {
            return null;
        }

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

        @Override
        protected void onPostExecute(Object o) {
            // call your refresh_receive(); here
            super.onPostExecute(o);
        }
    }

    @Override
    protected void onPostExecute(Object o) {
        dataList.clear();
        dataList.addAll((ArrayList)MessagingData.getMessageListData());
        adapter.notifyDataSetChanged();
        super.onPostExecute(o);
    }

类似地，在调用receive_live_message_async.execute（）时；在onPostExecute中更新您的recyclerView

public class receive_live_message_async extends AsyncTask {

        @Override
        protected Object doInBackground(Object[] objects) {
            return null;
        }

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

        @Override
        protected void onPostExecute(Object o) {
            // call your refresh_receive(); here
            super.onPostExecute(o);
        }
    }

    @Override
    protected void onPostExecute(Object o) {
        dataList.clear();
        dataList.addAll((ArrayList)MessagingData.getMessageListData());
        adapter.notifyDataSetChanged();
        super.onPostExecute(o);
    }

---

Where调用

refresh\u receive（）

method？使用其他代码更新Where调用

refresh\u receive（）

method？使用其他代码更新我感谢您的回答，但我收到了关于else listData=new ArrayList（）的错误；（菱形运算符不适用于非参数化类型）。所以我尝试了新的ArrayList（）；它运行了，但生成了一个完全空白的recyclerview。哦，对不起，错误是由我的代码引起的。请执行此操作

else listData=new ArrayList（）谢谢您的回复，我按照您的要求更改了线路。最初会填充recyclerview，但调用refreshreceive（）后，会显示相同的空白recyclerview请删除此行
adapter.setListData（dataList）来自refresh_receiveadapter=新的RecycleServiceAdapterMessageing（listData，this）；请给我看一下你的RecycleServiceAdapterMessage构造函数，你正在初始化你的代码。我很感激你的回答，但是我得到了一个关于else listData=new ArrayList（）的错误；（菱形运算符不适用于非参数化类型）。所以我尝试了新的ArrayList（）；它运行了，但生成了一个完全空白的recyclerview。哦，对不起，错误是由我的代码引起的。请执行此操作
else listData=new ArrayList（）谢谢您的回复，我按照您的要求更改了线路。最初会填充recyclerview，但调用refreshreceive（）后，会显示相同的空白recyclerview请删除此项