ListView 正在填充 List 的整个大小的相同值

Question

/*
this is the class which is called when a button is pressed in main activity. onResume is called along with onCreate first, and the list is getting populated with the last row input from the database multiple times.

目的是用数据库表中的数据填充列表视图。 什么时候调用 onResume？ */

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

import android.app.Activity;
import android.content.Intent;
import android.database.Cursor;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.ListView;
import android.widget.Toast;

public class Expenses extends Activity {
    ListView l;Databasehelper mydb;List<ListViewItem> items;
    MyAdapter adapter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_expenses);
        l= (ListView)findViewById(R.id.lv1);
        mydb=new Databasehelper(this);
         items= new ArrayList<Expenses.ListViewItem>();


        //adapter= new MyAdapter(this, items);
        //l.setAdapter(adapter);
    }

    @Override
    protected void onResume() {
        // TODO Auto-generated method stub
        super.onResume();
        items.clear();
        ListViewItem a= new ListViewItem();
        Cursor cur=mydb.getData();
        if(cur.getCount()==0)
            Toast.makeText(this, "No expenses to display", Toast.LENGTH_LONG).show();

        cur.moveToFirst();
        do
        {
            a.category=cur.getString(0);
            a.status=cur.getString(1);
            a.amount=cur.getString(2);
            items.add(a);
        }while(cur.moveToNext());
        adapter= new MyAdapter(this, items);
        l.setAdapter(adapter);
        for(int i=0; i<items.size(); i++)
        {
            System.out.print(items.get(i).category+" "+items.get(i).status+" "+items.get(i).amount);
            System.out.println();
        }

    }
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.expenses, menu);
        return true;
    }

    public class ListViewItem{
        public String category, amount, status;
    }

    public void onAdd(View v){
        Intent in= new Intent(this, Input.class);
        startActivityForResult(in, 10);
    }

}

//请帮助填充表。我怀疑恢复方法有问题。当我//使用打印命令打印时，列表包含相同//行的多个副本。但是数据库中的表包含正确的元组.

Answer 1

问题是你的 do while 循环。当您遍历游标时，您使用的是相同的 ListViewItem 对象来设置值。您应该在光标的每次迭代上创建一个新的 ListViewItem 对象。像这样的：

    do {
        ListViewItem a = new ListViewItem()
        a.category=cur.getString(0);
        a.status=cur.getString(1);
        a.amount=cur.getString(2);
        items.add(a);
    } while(cur.moveToNext());