C# 为什么我的C代码只显示数据库的第一行？

我的目标

您好，我正在尝试编写一个C应用程序，其中我希望从Microsoft Access 2016名为FruitsDatabase.accdb的数据库中名为Fruits_table的表中检索值。然后，我想以label1、label2、label3的形式在标签中显示这些值

仅供参考，我在另一个名为Fruits.cs的类文件中使用了名为Fruitstring Name、string Color的构造函数。然后我将这个构造函数传递到我的PresentationUI表单中

我的数据库

数据库有一个名为FROUTS\ U table的表，该表中有两列：水果名称的名称和颜色的颜色。数据库中记录了三个条目：苹果红、香蕉黄、梨绿

到目前为止，我所做的工作

我成功地连接到了我的数据库。所以没必要担心。从数据库中检索值也很好

我的问题

我的问题是：

无论我点击哪个水果图片框，似乎都只显示数据库中的第一个条目。换句话说，无论我点击picBox1、picBox2或picBox3，它都只会显示“苹果”和“红色”

如何遍历数据库中的行

using System;
...
using system.Windows.Forms;
using system.Data.OleDb;

namespace project1
{
     public partial class PresentationGUI : Form
     {
          private OleDbConnection aConn;
          private OleDbCommand aCmd;
          private OleDbDataReader aReader;

          private string aConnection;
          private string sql;

          Fruit[] aFruit = new Fruit[10];

     public PresentationGUI()
     {
          Initialize Component;

          //This is working fine.
          aConnection = "Provider = Microsoft.ACE.OLEDB.12.0; Data Source = FruitsDatabase.accdb;";

          sql = "SELECT * FROM Fruits_Table";
          aCmd = new OleDbCommand();
          aCmd.CommandText = sql;

          aCmd.Connection = aConn;
          aReader = aCmd.ExecuteReader();

          while (aReader.Read())
          {

             //I have a Fruit constructor that goes:  Fruit(string Name, string Color) in another class named Fruit.cs, and I use it here for this form.
             aFruit[0] = new Fruit(aReader["Name"].ToString(), aReader["Color"].ToString());
             aFruit[1] = new Fruit(aReader["Name"].ToString(), aReader["Color"].ToString());
             aFruit[2] = new Fruit(aReader["Name"].ToString(), aReader["Color"].ToString());
          }

     private void PresentationGUI_Load(object sender, EventArgs e) {...}

     //Intended Output:  when the user clicks on picBox1 (showing an image of an apple) it should display 'Apple' for label1 and 'red' for label2
    //Reality:  it displays 'Apple' for label1 and 'Red' for label2
     private void picBox1_Click(object sender, EventArgs e)
     {
         try
         {
               this.label1.Text = aFruit[0].Name.ToString();
               this.label2.Text = aFruit[0].Color.ToString();
         }
         catch (NullReferenceException) {....}
     }

     //Intended Output:  when the user clicks on picBox2 (showing an image of an Banana) it should display 'Banana' for label1 and 'yellow' for label2
    //Reality:  it displays 'Apple' for label1 and 'Red' for label2
     private void picBox2_Click(object sender, EventArgs e)
     {
         try
         {
               this.label1.Text = aFruit[1].Name.ToString();
               this.label2.Text = aFruit[1].Color.ToString();
         }
         catch (NullReferenceException) {....}
     }

     //Intended Output:  when the user clicks on picBox2 (showing an image of an Pear) it should display 'Pear' for label1 and 'green' for label2
    //Reality:  it displays 'Apple' for label1 and 'Red' for label2
    private void picBox3_Click(object sender, EventArgs e)
     {
         try
         {
               this.label1.Text = aFruit[2].Name.ToString();
               this.label2.Text = aFruit[2].Color.ToString();
         }
         catch (NullReferenceException) {....}
     }

     }
}    

---

为什么它只显示“我的数据库”的第一行？

您正在将相同的值加载到数组中三次，因此请尝试如下更改您的While语句：

using System;
...
using system.Windows.Forms;
using system.Data.OleDb;

namespace project1
{
     public partial class PresentationGUI : Form
     {
          private OleDbConnection aConn;
          private OleDbCommand aCmd;
          private OleDbDataReader aReader;

          private string aConnection;
          private string sql;

          Fruit[] aFruit = new Fruit[10];

     public PresentationGUI()
     {
          Initialize Component;

          //This is working fine.
          aConnection = "Provider = Microsoft.ACE.OLEDB.12.0; Data Source = FruitsDatabase.accdb;";

          sql = "SELECT * FROM Fruits_Table";
          aCmd = new OleDbCommand();
          aCmd.CommandText = sql;

          aCmd.Connection = aConn;
          aReader = aCmd.ExecuteReader();

          while (aReader.Read())
          {

             //I have a Fruit constructor that goes:  Fruit(string Name, string Color) in another class named Fruit.cs, and I use it here for this form.
             aFruit[0] = new Fruit(aReader["Name"].ToString(), aReader["Color"].ToString());
             aFruit[1] = new Fruit(aReader["Name"].ToString(), aReader["Color"].ToString());
             aFruit[2] = new Fruit(aReader["Name"].ToString(), aReader["Color"].ToString());
          }

     private void PresentationGUI_Load(object sender, EventArgs e) {...}

     //Intended Output:  when the user clicks on picBox1 (showing an image of an apple) it should display 'Apple' for label1 and 'red' for label2
    //Reality:  it displays 'Apple' for label1 and 'Red' for label2
     private void picBox1_Click(object sender, EventArgs e)
     {
         try
         {
               this.label1.Text = aFruit[0].Name.ToString();
               this.label2.Text = aFruit[0].Color.ToString();
         }
         catch (NullReferenceException) {....}
     }

     //Intended Output:  when the user clicks on picBox2 (showing an image of an Banana) it should display 'Banana' for label1 and 'yellow' for label2
    //Reality:  it displays 'Apple' for label1 and 'Red' for label2
     private void picBox2_Click(object sender, EventArgs e)
     {
         try
         {
               this.label1.Text = aFruit[1].Name.ToString();
               this.label2.Text = aFruit[1].Color.ToString();
         }
         catch (NullReferenceException) {....}
     }

     //Intended Output:  when the user clicks on picBox2 (showing an image of an Pear) it should display 'Pear' for label1 and 'green' for label2
    //Reality:  it displays 'Apple' for label1 and 'Red' for label2
    private void picBox3_Click(object sender, EventArgs e)
     {
         try
         {
               this.label1.Text = aFruit[2].Name.ToString();
               this.label2.Text = aFruit[2].Color.ToString();
         }
         catch (NullReferenceException) {....}
     }

     }
}    

int fruitCounter = 0
while (aReader.Read())
{
    //I have a Fruit constructor that goes:  Fruit(string Name, string Color) in another class named Fruit.cs, and I use it here for this form.
    aFruit[fruitCounter] = new Fruit(aReader["Name"].ToString(), aReader["Color"].ToString());
    fruitCounter++;

    if(fruitCounter > aFruit.Length)
    {
          break;
    }
}

---

我建议您首先获取查询返回的行数，然后根据该值初始化数组。

您要将相同的值加载到数组中三次，因此请尝试如下更改您的While语句：

int fruitCounter = 0
while (aReader.Read())
{
    //I have a Fruit constructor that goes:  Fruit(string Name, string Color) in another class named Fruit.cs, and I use it here for this form.
    aFruit[fruitCounter] = new Fruit(aReader["Name"].ToString(), aReader["Color"].ToString());
    fruitCounter++;

    if(fruitCounter > aFruit.Length)
    {
          break;
    }
}

---

我建议您首先获取查询返回的行数，然后根据该值初始化数组。

Nice！那起作用了。。。有点。但现在我的行似乎颠倒过来了：它显示的是梨，第一行是绿色，然后是香蕉，第二行是黄色，最后一行是苹果，反之则是红色。我应该将计数器设置为3并将其减量吗？在Select语句中添加一个Order by如何；美好的那起作用了。。。有点。但现在我的行似乎颠倒过来了：它显示的是梨，第一行是绿色，然后是香蕉，第二行是黄色，最后一行是苹果，反之则是红色。我应该将计数器设置为3并将其减量吗？在Select语句中添加一个Order by如何；