ArrayAdapter SQLite和customListView

Question

我在Android工作室为我的作业建立一个基本的购物清单应用程序。我是Java的新手，在从SQLite传递数据时会对ArrayAdapter感到困惑。请看一下我的代码，我会尽力解释我面临的问题=（

DatabaseHelper类

package com.puyakul.prin.psychic_shopping;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DatabaseHelper extends SQLiteOpenHelper {

    private static final String DB_NAME = "shoppinglist";
    private static final int DN_VERSION = 2;

    public DatabaseHelper(Context context){
        super (context,DB_NAME, null, DN_VERSION);

    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String sqlLists = "CREATE TABLE lists(id INTEGER PRIMARY KEY AUTOINCREMENT, name VARCHAR)";
        String sqlItems = "CREATE TABLE items(id INTEGER PRIMARY KEY AUTOINCREMENT, name VARCHAR, list_id INTEGER, FOREIGN KEY(list_id) REFERENCES lists(id))";

        db.execSQL(sqlLists);
        db.execSQL(sqlItems);
    }

    public boolean addLists(String name){
        //Open database
        SQLiteDatabase db = getReadableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put("name", name);
        db.insert("lists", null, contentValues);
        //Close database
        db.close();
        return true;
    }

    public boolean addListsItem(String name, int id){
        //Open database
        SQLiteDatabase db = getReadableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put("name", name);
        contentValues.put("list_id", id);
        db.insert("items", null, contentValues);
        //Close database
        db.close();
        return true;
    }

    public  int deleteItem (String id){
        SQLiteDatabase db= getReadableDatabase();
        return db.delete("item", "ID = ?", new String[] {id});
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        String sqlLists = "DROP TABLE IF EXISTS lists";
        String sqlItems = "DROP TABLE IF EXISTS items";
        db.execSQL(sqlLists);
        db.execSQL(sqlItems);
        onCreate(db);
    }

    public Cursor getList(){
        SQLiteDatabase db = this.getReadableDatabase();
        String sql = "SELECT * FROM lists";
        return db.rawQuery(sql, null);
    }

    public Cursor getListDetail(int id){
        SQLiteDatabase db = this.getReadableDatabase();
        String sql = "SELECT items.name FROM items WHERE items.list_id = '" + id + "'";
        //String sql = "SELECT items.name FROM items INNER JOIN lists ON lists.id=items.list_id WHERE items.list_id = '" + id + "'";
        return  db.rawQuery(sql,null);
    }

    public Cursor getListID(String name){
        SQLiteDatabase db = this.getReadableDatabase();
        String sql = "SELECT ID FROM lists WHERE name = '" + name + "'";
        return db.rawQuery(sql, null);
    }
}

MainListDetail类

package com.puyakul.prin.psychic_shopping;

import android.content.Context;
import android.content.Intent;
import android.database.Cursor;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.TextUtils;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

import java.sql.Time;
import java.util.ArrayList;
import java.util.List;

public class MainListsDetail extends AppCompatActivity {

    private Button btn_deleteItem, btn_editListName;
    private EditText editText_ListName, editText_addNewItemName;
    private TextView textView_listName;
    private ListView ListView_ListDetail;

    private DatabaseHelper db;

    private String selectedList;
    private int selectedID;

    public ArrayList<String> listDetailData = new ArrayList<>();

    //Time stamp code, matching current time zone
    //private Time today = new Time(Time.getCurrentTimezone());

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

        //declare layout elements
        ListView_ListDetail = findViewById(R.id.ListView_ListDetail);
        textView_listName = findViewById(R.id.textVie_listName);
        editText_addNewItemName = findViewById(R.id.editText_addNewItemName);



        //declare database
        db = new DatabaseHelper(this);

        //get the intent extra from MainListView
        Intent receivedIntent = getIntent();

        //now get the listID we passed on extra
        selectedID = receivedIntent.getIntExtra("id",0); // -1 for the default value

        //now get the name we passed on extra
        selectedList = receivedIntent.getStringExtra("name");

        //set text to show the current selected name
        textView_listName.setText(selectedList);


//        ArrayAdapter aa = new ArrayAdapter(..., itemsList);
//        ArrayAdapter itemListAdapter = new ArrayAdapter();
        ListView_ListDetail.setAdapter(new ListItemAdapter(this, R.layout.activity_item_detail_list, listDetailData));
        getListDetail();


        btn_editListName = findViewById(R.id.btn_addNewItem);
        btn_editListName.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                addItem();
                editText_addNewItemName.getText().clear();
            }
        });
    }

    public void addItem(){

        String newItemName = editText_addNewItemName.getText().toString().trim();
        if(TextUtils.isEmpty(newItemName)){
            Toast.makeText(this, "Please enter a new item", Toast.LENGTH_SHORT).show();
            // ****Must have return to make it work****
            return;
        }

        if(db.addListsItem(newItemName,selectedID)){

            Toast.makeText(this, "New item added to the list", Toast.LENGTH_SHORT).show();
        }
        else{
            Toast.makeText(this, "Error, no item add to the list", Toast.LENGTH_SHORT).show();
        }

        getListDetail();

    }

    public void getListDetail(){

        listDetailData.clear();

        Cursor cursor = db.getListDetail(selectedID);
        //Log.d("TAG", "selected ID" +selectedID);
        //ArrayList<String> listDetailData = new ArrayList<>();
        while(cursor.moveToNext()){
            listDetailData.add(cursor.getString(0));
        }

        //ListAdapter listDetailAdapter = new ArrayAdapter<>(this, android.R.layout.simple_expandable_list_item_1, listDetailData);
        //ListView_ListDetail.setAdapter(listDetailAdapter);


        ((ArrayAdapter<String>)ListView_ListDetail.getAdapter()).notifyDataSetChanged();
    }


}

ListAdapter类

package com.puyakul.prin.psychic_shopping;

import android.content.Context;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;

public class ListItemAdapter extends ArrayAdapter<String> {

    private static final String TAG = "ListItemAdapter";

    public ListItemAdapter(@NonNull Context context, int resource, @NonNull ArrayList<String> objects) {
        super(context, resource, objects);
    }

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {

        if (convertView == null){
//            LayoutInflater inflater = LayoutInflater.from(getContext());
//            convertView = inflater.inflate(layout, parent, false);
            convertView = LayoutInflater.from(getContext()).inflate(R.layout.activity_item_detail_list, parent, false);
        }

        ViewHolder viewHolder = new ViewHolder();
        viewHolder.listItem_Thumbnail = convertView.findViewById(R.id.img_thumbnail);
        viewHolder.listItem_Name = convertView.findViewById(R.id.textView_listItemText);
        viewHolder.listItem_Remove_btn = convertView.findViewById(R.id.btn_listItemRemove);
        viewHolder.listItem_Name.setText(getItem(position));
        convertView.setTag(viewHolder);
        return convertView;
    }

    public class ViewHolder {
        ImageView listItem_Thumbnail;
        TextView listItem_Name;
        Button listItem_Remove_btn;
    }
}

首先，代码运行正常，没有错误。我可以从文本字段插入一个新数据，但据我所知，我的函数是直接将数据插入数据库，它只保存一个字符串。我面临的问题是，每当我将此数据传递到ArrayAdapter时，例如在此代码行public class ListItemAdapter extends ArrayAdapter<String>中，它只指向单个字符串对吗？ 问题是我如何传递一个类，如果我想创建一个单独的GET-SET类来处理所有这些信息而不是直接用数据库String处理它。

我希望这里的某些人有意义，我很抱歉英语不是我的第一语言=（加上我真的不懂java，这让我很难写出来。

我非常感谢所有帮助。

Answer 1

  

我面临的问题是，每当我将此数据传递到ArrayAdapter时，例如在这行代码public class ListItemAdapter extends ArrayAdapter<String>中，它只指向单个字符串吗？

第一步是改变

class ListItemAdapter extends ArrayAdapter<String>

到

class ListItemAdapter extends ArrayAdapter<MyClass>

然后在getView()中，您可以使用position运算符来获取对MyClass的正确实例的引用，并使用其值填充视图。

由于您使用的是数据库，我建议您了解CursorAdapter以替换ArrayAdapter。从SimpleCursorAdapter开始，因为它提供了许多基本用途。