VB 实例学习笔记

简介

Visual Basic（VB）是一种非常流行的事件驱动编程语言，它可以用来开发桌面应用程序、Web 应用程序和数据库应用程序等。在本学习笔记中，我们将通过多个实例来学习 VB 编程。

实例 1：计算器应用程序

这个实例展示了如何使用 VB 来创建一个简单的计算器应用程序。在这个应用程序中，用户将能够输入两个数字，选择一个运算符（如加、减、乘、除），然后计算结果。

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Public Class Form1
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        ' 获取用户输入的两个数字
        Dim num1 As Double = Double.Parse(TextBox1.Text)
        Dim num2 As Double = Double.Parse(TextBox2.Text)

        ' 根据用户选择的操作符来计算结果
        Dim result As Double
        If RadioButton1.Checked Then
            result = num1 + num2
        ElseIf RadioButton2.Checked Then
            result = num1 - num2
        ElseIf RadioButton3.Checked Then
            result = num1 * num2
        ElseIf RadioButton4.Checked Then
            result = num1 / num2
        End If

        ' 将结果显示在 Label 控件上
        Label1.Text = "计算结果：" & result.ToString()
    End Sub
End Class

实例 2：图书管理系统

这个实例展示了如何使用 VB 和 Microsoft Access 数据库来创建一个简单的图书管理系统。在这个应用程序中，用户可以添加、修改和删除图书记录，并查询图书库存。

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Public Class Form1
    Dim conn As New OleDb.OleDbConnection
    Dim da As OleDb.OleDbDataAdapter
    Dim ds As New DataSet

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        ' 连接到数据库
        conn.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\BookDatabase.accdb"
        conn.Open()

        ' 加载数据到 DataGridView 控件上
        Dim sql As String = "SELECT * FROM Books"
        da = New OleDb.OleDbDataAdapter(sql, conn)
        da.Fill(ds, "Books")
        DataGridView1.DataSource = ds.Tables("Books")

        ' 关闭数据库连接
        conn.Close()
    End Sub

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        ' 连接到数据库
        conn.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\BookDatabase.accdb"
        conn.Open()

        ' 插入新的图书记录
        Dim cmd As New OleDb.OleDbCommand
        cmd.Connection = conn
        cmd.CommandText = "INSERT INTO Books (Title, Author, Publisher, Price) VALUES (@Title, @Author, @Publisher, @Price)"
        cmd.Parameters.AddWithValue("@Title", TextBox1.Text)
        cmd.Parameters.AddWithValue("@Author", TextBox2.Text)
        cmd.Parameters.AddWithValue("@Publisher", TextBox3.Text)
        cmd.Parameters.AddWithValue("@Price", TextBox4.Text)
        cmd.ExecuteNonQuery()

        ' 加载数据到 DataGridView 控件上
        Dim sql As String = "SELECT * FROM Books"
        da = New OleDb.OleDbDataAdapter(sql, conn)
        ds.Tables("Books").Clear()
        da.Fill(ds, "Books")
        DataGridView1.DataSource = ds.Tables("Books")

        ' 关闭数据库连接
        conn.Close()
    End Sub

    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
        ' 连接到数据库
        conn.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\BookDatabase.accdb"
        conn.Open()

        ' 更新选中的图书记录
        Dim cmd As New OleDb.OleDbCommand
        cmd.Connection = conn
        cmd.CommandText = "UPDATE Books SET Title=@Title, Author=@Author, Publisher=@Publisher, Price=@Price WHERE ID=@ID"
        cmd.Parameters.AddWithValue("@Title", TextBox1.Text)
        cmd.Parameters.AddWithValue("@Author", TextBox2.Text)
        cmd.Parameters.AddWithValue("@Publisher", TextBox3.Text)
        cmd.Parameters.AddWithValue("@Price", TextBox4.Text)
        cmd.Parameters.AddWithValue("@ID", DataGridView1.SelectedCells(0).Value)
        cmd.ExecuteNonQuery()

        ' 加载数据到 DataGridView 控件上
        Dim sql As String = "SELECT * FROM Books"
        da = New OleDb.OleDbDataAdapter(sql, conn)
        ds.Tables("Books").Clear()
        da.Fill(ds, "Books")
        DataGridView1.DataSource = ds.Tables("Books")

        ' 关闭数据库连接
        conn.Close()
    End Sub

    Private Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click
        ' 连接到数据库
        conn.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\BookDatabase.accdb"
        conn.Open()

        ' 删除选中的图书记录
        Dim cmd As New OleDb.OleDbCommand
        cmd.Connection = conn
        cmd.CommandText = "DELETE FROM Books WHERE ID=@ID"
        cmd.Parameters.AddWithValue("@ID", DataGridView1.SelectedCells(0).Value)
        cmd.ExecuteNonQuery()

        ' 加载数据到 DataGridView 控件上
        Dim sql As String = "SELECT * FROM Books"
        da = New OleDb.OleDbDataAdapter(sql, conn)
        ds.Tables("Books").Clear()
        da.Fill(ds, "Books")
        DataGridView1.DataSource = ds.Tables("Books")

        ' 关闭数据库连接
        conn.Close()
    End Sub

    Private Sub Button4_Click(sender As Object, e As EventArgs) Handles Button4.Click
        ' 连接到数据库
        conn.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\BookDatabase.accdb"
        conn.Open()

        ' 根据关键字查询图书记录
        Dim sql As String = "SELECT * FROM Books WHERE Title LIKE '%" & TextBox5.Text & "%'"
        da = New OleDb.OleDbDataAdapter(sql, conn)
        ds.Tables("Books").Clear()
        da.Fill(ds, "Books")
        DataGridView1.DataSource = ds.Tables("Books")

        ' 关闭数据库连接
        conn.Close()
    End Sub
End Class

结论

通过以上两个示例，我们可以看到 VB 是一种非常有效的编程语言，可以用于创建各种类型的应用程序。希望这些学习笔记能够帮助你开始学习 VB 编程。