VB串口通信程序,该如何解决

VB串口通信程序
我从网上找了一个PC机与单片机通信的串口通信程序，但运行时会报错,好像是接口出了问题，有人说根据自己电脑上的串口状态修改串口号，在SerialPort1属性里修改即可。所以我想把COM2换为COM4，但是只学过C语言，没学过VB，求各路大神帮帮忙，应该怎么改。最好能贴个图供学习参考，在此先行谢过 VB串口通信程序,该如何解决

代码如下
<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _
Partial Class Form1
    Inherits System.Windows.Forms.Form

    'Form 重写 Dispose，以清理组件列表。
    <System.Diagnostics.DebuggerNonUserCode()> _
    Protected Overrides Sub Dispose(ByVal disposing As Boolean)
        Try
            If disposing AndAlso components IsNot Nothing Then
                components.Dispose()
            End If
        Finally
            MyBase.Dispose(disposing)
        End Try
    End Sub

    'Windows 窗体设计器所必需的
    Private components As System.ComponentModel.IContainer

    '注意: 以下过程是 Windows 窗体设计器所必需的
    '可以使用 Windows 窗体设计器修改它。
    '不要使用代码编辑器修改它。
    <System.Diagnostics.DebuggerStepThrough()> _
    Private Sub InitializeComponent()
        Me.components = New System.ComponentModel.Container()
        Me.TextBox1 = New System.Windows.Forms.TextBox()
        Me.Button1 = New System.Windows.Forms.Button()
        Me.Button2 = New System.Windows.Forms.Button()
        Me.SerialPort1 = New System.IO.Ports.SerialPort(Me.components)
        Me.SuspendLayout()
        '
        'TextBox1
        '
        Me.TextBox1.Location = New System.Drawing.Point(12, 50)
        Me.TextBox1.Name = "TextBox1"
        Me.TextBox1.Size = New System.Drawing.Size(268, 21)
        Me.TextBox1.TabIndex = 0
        '
        'Button1
        '
        Me.Button1.Location = New System.Drawing.Point(12, 122)
        Me.Button1.Name = "Button1"
        Me.Button1.Size = New System.Drawing.Size(75, 23)
        Me.Button1.TabIndex = 1
        Me.Button1.Text = "发送"
        Me.Button1.UseVisualStyleBackColor = True
        '
        'Button2
        '
        Me.Button2.Location = New System.Drawing.Point(116, 122)
        Me.Button2.Name = "Button2"
        Me.Button2.Size = New System.Drawing.Size(72, 23)
        Me.Button2.TabIndex = 2
        Me.Button2.Text = "清除"
        Me.Button2.UseVisualStyleBackColor = True
        '
        'SerialPort1
        '
        Me.SerialPort1.PortName = "COM2"
        '
        'Form1
        '
        Me.AutoScaleDimensions = New System.Drawing.SizeF(6.0!, 12.0!)
        Me.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font
        Me.ClientSize = New System.Drawing.Size(292, 273)
        Me.Controls.Add(Me.Button2)
        Me.Controls.Add(Me.Button1)
        Me.Controls.Add(Me.TextBox1)
        Me.Name = "Form1"
        Me.Text = "Form1"
        Me.ResumeLayout(False)
        Me.PerformLayout()

    End Sub
    Friend WithEvents TextBox1 As System.Windows.Forms.TextBox
    Friend WithEvents Button1 As System.Windows.Forms.Button
    Friend WithEvents Button2 As System.Windows.Forms.Button
    Friend WithEvents SerialPort1 As System.IO.Ports.SerialPort

End Class
还有另外一部分代码是
Public Class Form1

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        TextBox1.Text = ""
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        SerialPort1.Write(TextBox1.Text)
    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        SerialPort1.Open()
        SerialPort1.Encoding = System.Text.Encoding.GetEncoding("GB2312")
    End Sub
End Class VB串口通信程序,该如何解决

------解决思路----------------------
先到”设备管理器 “－》‘端口（com和lpt)’里面看看你的电脑支持那些COM端口，不是你想用COM4就能用的，要看你的电脑支不支持
------解决思路----------------------
在窗体的Load过程中设置:

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        SerialPort1.BaudRate = 9600 '波特率设为

        SerialPort1.PortName = "com4" '端口为串口

        If SerialPort1.IsOpen = False Then SerialPort1.Open() '打开串口

    End Sub

VB串口通信程序,该如何解决

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