如何保存 RecyclerView 中添加的項目？

Question

我有一個 RecyclerView 但我面臨一些問題。 每當我向回收站視圖添加一些東西時，例如切換片段或關閉應用程序，RecyclerView 中的所有項目都會消失。 有辦法拯救他們嗎？ 你能幫忙的話，我會很高興！

這是一些代碼，看看是否有人需要它：

適配器

package com.example.freetrialtracker;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import java.util.ArrayList;

public class SubTrialAdapter extends RecyclerView.Adapter<SubTrialAdapter.MyViewHolder>{
    private ArrayList<SubTrial> listData;
    private Context context;
    private OnEditListener onEditListener;

    public SubTrialAdapter(Context context, ArrayList<SubTrial> list,OnEditListener onEditListener){
        this.listData=list;
        this.context=context;
        this.onEditListener=onEditListener;
    }

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

        View viewItem= LayoutInflater.from(parent.getContext()).inflate(R.layout.subscription_card_view,parent,false);
        return new MyViewHolder(viewItem);
    }

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

        SubTrial dataObj=listData.get(position);

        holder.nameTxt.setText(dataObj.getNamee());
        holder.startDate.setText(dataObj.getStartDate());
        holder.endDate.setText(dataObj.getEndDate());
        holder.description.setText(dataObj.getDescription());
        holder.link.setText(dataObj.getLink());

        holder.imgDelete.setOnClickListener(v->{
            listData.remove(position);
            notifyDataSetChanged();

        });
        holder.imgEdit.setOnClickListener(v->{
            onEditListener.onEditClick(listData.get(position),position);
        });


    }

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

    class MyViewHolder extends RecyclerView.ViewHolder {


        TextView nameTxt,startDate,endDate,description,link;
        ImageView imgEdit,imgDelete;

        public MyViewHolder(@NonNull View itemView) {
            super(itemView);

            nameTxt=itemView.findViewById(R.id.nameTxtId);
            startDate=itemView.findViewById(R.id.startDateTxtId);
            endDate = itemView.findViewById(R.id.endDateTxtId);
            description = itemView.findViewById(R.id.descriptionId);
            link = itemView.findViewById(R.id.linkId);
            imgEdit=itemView.findViewById(R.id.imgEdit);
            imgDelete=itemView.findViewById(R.id.imgDelete);

        }
    }



    public void editData(SubTrial listDataObj,int currentPosition){

        listData.get(currentPosition).setLink(listDataObj.getLink());
        listData.get(currentPosition).setDescription(listDataObj.getDescription());
        listData.get(currentPosition).setEndDate(listDataObj.getEndDate());
        listData.get(currentPosition).setStartDate(listDataObj.getStartDate());
        listData.get(currentPosition).setNamee(listDataObj.getNamee());
        notifyDataSetChanged();


    }

    public interface OnEditListener{
        void onEditClick(SubTrial listCurrentData, int CurrentPosition);

    }
}

分段

import android.app.AlertDialog;
import android.os.Bundle;
import android.os.Parcelable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import com.google.android.material.button.MaterialButton;
import com.google.android.material.floatingactionbutton.FloatingActionButton;

import java.util.ArrayList;

public class SubscriptionFragment extends Fragment implements SubscriptionDialogFragment.OnInputSelected {


    AlertDialog alertDialog;
    TextView textView1;
    RecyclerView subscriptionList;
    private FloatingActionButton mOpenDialog;
    SubTrialAdapter subscriptionAdapterList;


    ArrayList<SubTrial> subTrialArrayList;

    @Override
    public void sendInput(String name, String startDate, String endDate, String description, String link) {
        addSubscription(name, startDate, endDate, description, link);
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_subscription, container, false);
        mOpenDialog = view.findViewById(R.id.fabSub);
        subTrialArrayList = new ArrayList<>();
        subscriptionList = view.findViewById(R.id.activityListSub);
        subscriptionList.setHasFixedSize(true);
        subscriptionList.setLayoutManager(new LinearLayoutManager(this.getActivity(), LinearLayoutManager.VERTICAL, false));
        textView1 = view.findViewById(R.id.textView1);
        mOpenDialog.setOnClickListener(v -> {
            SubscriptionDialogFragment dialog = new SubscriptionDialogFragment();
            dialog.setTargetFragment(SubscriptionFragment.this, 1);
            dialog.show(getFragmentManager(), "Dialog");
        });



        return view;
    }

    public void addSubscription(String strName, String strStartDate, String strEndDate, String strDescription, String strLink) {
        textView1.setText(strStartDate);
        SubTrial obj = new SubTrial();
        obj.setNamee(strName);
        obj.setStartDate(strStartDate);
        obj.setEndDate(strEndDate);
        obj.setDescription(strDescription);
        obj.setLink(strLink);

        subTrialArrayList.add(obj);
        subscriptionAdapterList = new SubTrialAdapter(this.getContext(), subTrialArrayList, this::onEditClick);
        subscriptionList.setAdapter(subscriptionAdapterList);


    }

    private void onEditClick(SubTrial listCurrentData, int currentPosition) {
        View view=LayoutInflater.from(this.getContext()).inflate(R.layout.edit_subscription,null);
        AlertDialog.Builder builderObj=new AlertDialog.Builder(view.getContext());

        EditText mSubscriptionName = view.findViewById(R.id.subscriptionName);
        EditText mStartDate = view.findViewById(R.id.startDate);
        EditText mEndDate = view.findViewById(R.id.endDate);
        EditText mDescription = view.findViewById(R.id.description);
        EditText mLink = view.findViewById(R.id.link);
        MaterialButton btnEdit=view.findViewById(R.id.btnEdit);


        mSubscriptionName.setText(listCurrentData.getNamee());
        mStartDate.setText(listCurrentData.getStartDate());
        mEndDate.setText(listCurrentData.getEndDate());
        mDescription.setText(listCurrentData.getDescription());
        mLink.setText(listCurrentData.getLink());

        ImageView closeAlert = view.findViewById(R.id.closeAlert);
        builderObj.setView(view);
        builderObj.setCancelable(false);

        closeAlert.setOnClickListener(v -> {
            alertDialog.cancel();
        });

        btnEdit.setOnClickListener(v->{
            String strName = "", strStartDate = "", strEndDate = "", strDescription = "", strLink = "";
            if (mSubscriptionName.getText() != null) {
                strName = mSubscriptionName.getText().toString();
            }

            if (strName.equals("")) {
                Toast.makeText(this.getContext(), "Please enter Subscription Name", Toast.LENGTH_LONG).show();
                return;
            }

            if (mStartDate.getText() != null) {
                strStartDate = mStartDate.getText().toString();
            }
            if (strStartDate.equals("")) {
                Toast.makeText(this.getContext(), "Please enter Start Date", Toast.LENGTH_LONG).show();
                return;
            }
            if (mEndDate.getText() != null) {
                strEndDate = mEndDate.getText().toString();
            }
            if (strEndDate.equals("")) {
                Toast.makeText(this.getContext(), "Please enter End Date", Toast.LENGTH_LONG).show();
                return;
            }
            if (mDescription.getText() != null) {
                strDescription= mDescription.getText().toString();
            }
            if (strDescription.equals("")) {
                Toast.makeText(this.getContext(), "Please enter Description", Toast.LENGTH_LONG).show();
                return;
            }
            if (mLink.getText() != null) {
                strLink = mLink.getText().toString();
            }
            if (strLink.equals("")) {
                Toast.makeText(this.getContext(), "Please enter Link", Toast.LENGTH_LONG).show();
                return;
            }

            editContact(strName, strStartDate, strEndDate, strDescription, strLink, currentPosition);

        });

        alertDialog=builderObj.create();
        alertDialog.show();

    }

    public void editContact(String strUserName, String strStartDate, String strEndDate, String strDescription, String strLink, int currentPosition){


        SubTrial obj = new SubTrial();

        obj.setNamee(strUserName);
        obj.setStartDate(strStartDate);
        obj.setEndDate(strEndDate);
        obj.setDescription(strDescription);
        obj.setLink(strLink);


        subscriptionAdapterList.editData(obj,currentPosition);
        alertDialog.cancel();


    }

}

Answer 1

是的。 因為一旦您退出應用程序，應用程序內存就會在后台進程中被殺死，並且打開應用程序會創建一個新實例。 例如，您創建了一個 editText 和一個按鈕，該按鈕在單擊時顯示用戶向用戶輸入的 Toast + 文本。 應用程序內存將在您關閉后停止，一旦您將其從后台內存中刪除，它將關閉。 此方法稱為 onDestroy() 。

因此，為了防止這種情況，您可以使用 android 默認本地存儲，例如SQlite Database 、 Shared Preferences 、 Room Database

1. Sqlite數據庫是android的離線本地數據庫，不需要互聯網訪問來存儲數據。 並且要存儲在 SQlite 數據庫中的數據應該是字符串格式，如 uri 路徑。 不建議在 SQLite 數據庫中存儲更大的文件或內容，如圖像、音頻、視頻，以防止出現以下異常：

FATAL EXCEPTION: main
11-06 15:16:17.199: E/AndroidRuntime(1789): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.demodbimage/com.example.demodbimage.ImagesList}: java.lang.IllegalStateException: Couldn't read row 0, col 0 from CursorWindow.  Make sure the Cursor is initialized correctly before accessing data from it.

2. Shared Preferences 適合以字符串、布爾值、整數等鍵的形式存儲非常小的數據值。 例如，您希望在第一次登錄成功后阻止用戶登錄，或者您希望在用戶第一次選擇加入后下次顯示深色主題。

3. Room Database 和 Sqlite 數據庫一樣，但是 Google 推薦我們使用它，因為它易於使用，還提供數據庫語法，並且對錯誤非常敏感。

或者您可以使用在線數據庫，例如 mySQL、MongoDB、Firebase 數據庫、mariaDb 等。

Answer 2

基本上，RecyclerView 與 Room（本地數據庫）或 API（遠程數據庫，如 MySQL）等數據庫結合使用。
但是，如果您正在為您的投資組合創建一個非常輕量級的項目，我認為使用數據存儲或sharedPrefereces並不是一個壞主意。 與任何程序一樣，Kotlin 中常用的List和Array當然是易變的。