vb中的elseif not
时间: 2024-01-24 09:13:09 浏览: 17
在VB中,elseif not是指如果某个条件不成立,则执行elseif not后面的语句。在引用中的代码中,elseif not isDate(Text1.Text)则是判断Text1.Text是否为日期类型,如果不是,则弹出提示框并清空Text1.Text的值,将光标移动到Text1上并退出子程序。如果是日期类型,则将Text1.Text的值赋给MyDate变量。
相关问题
VB多个if else写法
VB 中有多种方式可以编写多个 if else 语句,以下是其中几种常见的方法:
1. 使用嵌套的 if else 语句:
```
If condition1 Then
' do something
ElseIf condition2 Then
' do something else
ElseIf condition3 Then
' do another thing
Else
' do default action
End If
```
2. 使用多个 if 语句:
```
If condition1 Then
' do something
End If
If condition2 Then
' do something else
End If
If condition3 Then
' do another thing
End If
If Not (condition1 Or condition2 Or condition3) Then
' do default action
End If
```
3. 使用 Select Case 语句:
```
Select Case variable
Case value1
' do something
Case value2
' do something else
Case value3
' do another thing
Case Else
' do default action
End Select
```
以上是几种常见的多个 if else 语句的写法,开发人员可以根据实际情况选择最适合自己的编码方式。
VB中modbus tcp 示例
在VB中使用Modbus TCP进行通信的示例代码如下:
```vb
Imports System.Net.Sockets
Public Class Form1
Dim client As TcpClient
Dim stream As NetworkStream
Private Sub btnConnect_Click(sender As Object, e As EventArgs) Handles btnConnect.Click
Try
client = New TcpClient(txtIPAddress.Text, Integer.Parse(txtPort.Text))
stream = client.GetStream()
MessageBox.Show("Connected to Modbus TCP device.")
Catch ex As Exception
MessageBox.Show("Connection failed: " & ex.Message)
End Try
End Sub
Private Sub btnRead_Click(sender As Object, e As EventArgs) Handles btnRead.Click
If client IsNot Nothing AndAlso client.Connected Then
Try
Dim request As Byte() = {0, 3, 0, 0, 0, 2, 197, 209} ' Modbus TCP Read Holding Register command
stream.Write(request, 0, request.Length)
Dim response(8) As Byte
stream.Read(response, 0, response.Length)
' Process the response data
Dim value As Integer = response(3) * 256 + response(4)
MessageBox.Show("Read value: " & value.ToString())
Catch ex As Exception
MessageBox.Show("Read failed: " & ex.Message)
End Try
Else
MessageBox.Show("Not connected to Modbus TCP device.")
End If
End Sub
Private Sub btnDisconnect_Click(sender As Object, e As EventArgs) Handles btnDisconnect.Click
If client IsNot Nothing AndAlso client.Connected Then
stream.Close()
client.Close()
MessageBox.Show("Disconnected from Modbus TCP device.")
End If
End Sub
End Class
```
这个示例代码演示了通过VB中的TCPClient类实现与Modbus TCP设备的通信。在点击"Connect"按钮后,会尝试连接到指定的Modbus TCP设备。在点击"Read"按钮后,会发送Modbus TCP的读保持寄存器命令,并接收并处理设备返回的数据。在点击"Disconnect"按钮后,会断开与Modbus TCP设备的连接。
请注意,此示例仅演示了基本的连接、读取和断开连接操作,实际使用中可能需要根据具体的Modbus设备和数据进行相应的命令编码和数据解析。