vb.net读usb的简单介绍

vb.net编程接受U盘准备卸载用的windows消息 DBT_DEVICEQUERYREMOVE总是没反应，据说是因为默认注册的消息里

在我的XP+VB2010环境下，测试U盘插入拔出，没有问题：

Private WM_DEVICECHANGE As Integer = H219

Public Enum WM_DEVICECHANGE_WPPARAMS As Integer

DBT_CONFIGCHANGECANCELED = H19

DBT_CONFIGCHANGED = H18

DBT_CUSTOMEVENT = H8006

DBT_DEVICEARRIVAL = H8000

DBT_DEVICEQUERYREMOVE = H8001

DBT_DEVICEQUERYREMOVEFAILED = H8002

DBT_DEVICEREMOVECOMPLETE = H8004

DBT_DEVICEREMOVEPENDING = H8003

DBT_DEVICETYPESPECIFIC = H8005

DBT_DEVNODES_CHANGED = H7

DBT_QUERYCHANGECONFIG = H17

DBT_USERDEFINED = HFFFF

End Enum

Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message)

If m.Msg = WM_DEVICECHANGE Then

Select Case m.WParam

Case WM_DEVICECHANGE_WPPARAMS.DBT_DEVICEARRIVAL

MsgBox("USB device is just plugged in!")

Case WM_DEVICECHANGE_WPPARAMS.DBT_DEVICEREMOVECOMPLETE

MsgBox("USB device is just taken out")

End Select

End If

MyBase.WndProc(m)

End Sub

相关问答

Q1: vb.net 如何判断u盘是否接入

窗体上添加两个标签：Label1和Label2

下面代码经过VB 2005测试通过。

Imports System.IO

Public Class Form1

Public Const WM_DEVICECHANGE = H219

Public Const DBT_DEVICEARRIVAL = H8000

Public Const DBT_CONFIGCHANGECANCELED = H19

Public Const DBT_CONFIGCHANGED = H18

Public Const DBT_CUSTOMEVENT = H8006

Public Const DBT_DEVICEQUERYREMOVE = H8001

Public Const DBT_DEVICEQUERYREMOVEFAILED = H8002

Public Const DBT_DEVICEREMOVECOMPLETE = H8004

Public Const DBT_DEVICEREMOVEPENDING = H8003

Public Const DBT_DEVICETYPESPECIFIC = H8005

Public Const DBT_DEVNODES_CHANGED = H7

Public Const DBT_QUERYCHANGECONFIG = H17

Public Const DBT_USERDEFINED = HFFFF

Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message)

If m.Msg = WM_DEVICECHANGE Then

Select Case m.WParam

Case WM_DEVICECHANGE

Case DBT_DEVICEARRIVAL 'U盘插入

Dim s() As DriveInfo = DriveInfo.GetDrives

For Each drive As DriveInfo In s

If drive.DriveType = DriveType.Removable Then

Label2.Text = "U盘已经插入！盘符为:" + drive.Name.ToString()

End If

Next

Case DBT_CONFIGCHANGECANCELED

Case DBT_CONFIGCHANGED

Case DBT_CUSTOMEVENT

Case DBT_DEVICEQUERYREMOVE

Case DBT_DEVICEQUERYREMOVEFAILED

Case DBT_DEVICEREMOVECOMPLETE 'U盘卸载

Label2.Text = "U盘已经拔出！"

Case DBT_DEVICEREMOVEPENDING

Case DBT_DEVICETYPESPECIFIC

Case DBT_DEVNODES_CHANGED

Case DBT_QUERYCHANGECONFIG

Case DBT_USERDEFINED

End Select

End If

MyBase.WndProc(m)

End Sub

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

Label1.Text = "请操作U盘！"

Label2.Text = ""

End Sub

End Class

Q2: VB.NET怎样把USB摄像头在显示器上输出的实时画面（像素信息），引入到数据库.

用directshow获取帧缓存,转换为标准图像格式(比如jpg,png这些),存储到数据库的image字段里就行了.

Q3: vb.net 二进制读取文件

VB.NET打开二进制文件用fileopen完成，打开二进制文件的形式为：openmode.binary

读取二进制文件用的是fileget方法，写入二进制文件用的是fileput方法。

应用示例：将一批随机数保存在一个dat文件中，然后再将其提取到文本框中。

二进制文件的读写一批随机数的存取，程序为：

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

Dim x, i, fn As Integer

Dim s As String = ""

fn = FreeFile()

FileOpen(fn, "d:\data.dat", OpenMode.Binary)

For i = 1 To 8

x = Int(Rnd() * 100)

s = s + Str(x)

FilePut(fn, x)

Next

FileClose(fn)

TextBox1.Text = s

End Sub

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click

Dim x, fn As Integer

Dim s As String = ""

fn = FreeFile()

FileOpen(fn, "d:\data.dat", OpenMode.Binary)

Do While Not EOF(fn)

FileGet(fn, x)

s = s + Str(x) + " "

Loop

FileClose(fn)

TextBox1.Text = s

End Sub

Q4: vb.net 怎么用事件触发的方式读取串口数据

首先：

textbox里没有显示，是因为SerialPort1和TextBox2不是同一线程创建vb.net读usb的，需要跨线程操作。需要用到委托，这样才能显示出来。

其次：

vb.net读usb我觉得用串口的接收数据事件更好一些。

下面代码供参考：

'----------------------

'串口接收数据事件，其实比用定时器更好，

'触发事件的条件可以自己在form_load中设置ReceivedBytesThreshold属性数值，默认为ReceivedBytesThreshold=1

Private Sub SerialPort1_DataReceived(ByVal sender As Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles SerialPort1.DataReceived

Dim strRecvData As String = ""

strRecvData = SerialPort1.ReadExisting

Call disPlayComData(strRecvData)

End Sub

Delegate Sub callback(ByVal strT As String) '定义委托

Sub showString(ByVal comdata As String) '显示结果

Me.TextBox1.Text = "结果：" comdata

End Sub

Sub disPlayComData(ByVal strTmp As String) '判定是否为跨线程

If Me.TextBox1.InvokeRequired Then

Dim d As New callback(AddressOf showString)

Me.Invoke(d, New Object() {strTmp})

Else

Me.TextBox1.Text = strTmp

End If

End Sub

Q5: vb.net 读取扫描枪USB接口数据的实例

USB比较难抓数据，建议是USB模拟串口，或者直接就是串口，这样数据比较好抓。

USB上传模式是鼠标光标在哪数据就上传在哪，所以你抓USB的数据的很难！

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