Question

对于所有人，我正在学习Visual Basic，我目前正在研究Windows应用程序。我有两个文本框方法（usernameTextBox，passwordTextBox）。用户将在其中输入数据，然后点击提交按钮（Button1_Click）。该方法将调用connect。我希望能够做的是让用户键入他们的用户名和密码。然后在Button方法中调用它时，按值传递，而不是引用到connect()。

有点像认证页面。现在我在connect(FirstName:="JohnDoe", Password:="password")中有值 - 这基本上是用于测试MySQL服务器以及演示我想要尝试的内容。

Imports MySql.Data.MySqlClient
Public Class SecurePasswordList
    Dim conn As New MySqlConnection
    Public Sub connect(ByVal FirstName As String, ByVal Password As String)
        Dim DatabaseName As String = "mysql"
        Dim server As String = "10.1.0.0"
        If Not conn Is Nothing Then conn.Close()
        conn.ConnectionString = String.Format("server={0}; user id={1}; password={2}; database={3}; pooling=false", server, FirstName, Password, DatabaseName)
        Try
            conn.Open()
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
        conn.Close()
    End Sub
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        connect(FirstName:="JohnDoe", Password:="password")
    End Sub

    Private Sub SecurePasswordList_Load(sender As Object, e As EventArgs) Handles MyBase.Load

    End Sub

    Private Sub usernameTextBox_TextChanged(sender As Object, e As EventArgs) Handles usernameTextBox.TextChanged
        Dim FirstName As String
        FirstName = usernameTextBox.Text
    End Sub

    Private Sub passwordTextBox_TextChanged(sender As Object, e As EventArgs) Handles passwordTextBox.TextChanged
        Dim Password As String
        Password = passwordTextBox.Text
    End Sub
End Class

Answer 1

更改

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    connect(FirstName:="JohnDoe", Password:="password")
End Sub

到

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    connect(FirstName, Password)
End Sub

但是你应该确保FirstName和Password被初始化并保存为类变量。移动

Dim FirstName As String
Dim FirstName As String

在课堂上，而不是事件处理函数（点击等）。像这样：

Public Class SecurePasswordList
    Dim conn As New MySqlConnection
    Dim FirstName As String
    Dim FirstName As String

但是你真的可以像这样重做你的代码（因为你想要的只是控件中的Text）：

Imports MySql.Data.MySqlClient
Public Class SecurePasswordList
    Dim conn As New MySqlConnection
    Public Sub connect(ByVal FirstName As String, ByVal Password As String)
        Dim DatabaseName As String = "mysql"
        Dim server As String = "10.1.0.0"
        If Not conn Is Nothing Then conn.Close()
        conn.ConnectionString = String.Format("server={0}; user id={1}; password={2}; database={3}; pooling=false", server, FirstName, Password, DatabaseName)
        Try
            conn.Open()
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
        conn.Close()
    End Sub
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        connect(usernameTextBox.Text, passwordTextBox.Text)
    End Sub

End Class

我不认为通过价值或参考传递是这里的问题。你想连接函数修改传递给它的字符串吗？我对此表示怀疑。所以在这种情况下，价值或参考是好的。字符串由引用的复制实例传递，因此它们实际上是由Value传递的，除非在函数声明中使用Byref。默认情况下，每个类（int，string等）在VB中以不同方式传递。如果指定Byval或Byref，则需要检查每种类型以了解它将执行的操作。如果使用Byval，String会创建String的副本，但实际上是使用指向新创建的String的指针来访问它。所以这取决于你想要深入挖掘的深度

按值传递参数

1 个答案: