vb怎么读取或修改opc变量值?

Option Base 1

Dim WithEvents ServerObj As OPCServer 'OPC Server对象，连接OPC服务器

Dim GroupsObj As OPCGroups 'OPC Groups对象，添加OPC组

Dim WithEvents GroupObj As OPCGroup 'OPC Group对象

Dim ItemsObj As OPCItems 'OPC Item集合

Dim ServerHandles() As Long '服务器端OPC Item的句柄

Dim ClientHandles() as Long'客户端OPC Item的句柄

Dim ItemId(2) As String

Dim Errors() As Long

接下来，生成各个对象：

If ServerObj Is Nothing Then Set ServerObj = New OPCServer

'连接OPC服务器

If ServerObj.ServerState = OPCDisconnected Then

ServerObj.Connect ("OPC.SimaticNET") '假设OPC服务器运行在本机

End If

If GroupsObj Is Nothing Then Set GroupsObj = ServerObj.OPCGroups

If GroupObj Is Nothing Then Set GroupObj = GroupsObj.Add

If ItemsObj Is Nothing Then Set ItemsObj = GroupObj.OPCItems

GroupObj.IsActive = True '设置组为活动状态

'假设有两个数据源，一个是8位开关量输入，一个是8位开关量输出

ItemId(1) = "S7:[S7 connection_1]IB0"

ItemId(2) = "S7:[S7 connection_1]QB0"

ClientHandles(1) = 1

ClientHandles(2) = 2

'添加组项目，ServerHandles数组的值为各个OPC Item的服务器句柄,

' ClientHandles数组的值为各个OPC Item的客户端句柄，由应用程序设定

Call ItemsObj.AddItems(2, ItemId, ClientHandles, ServerHandles, Errors)

比如

dim a as string

默认a=""

判断时就if a="" then a=string(1,0)

最好用 if len(a)=0 then a=string(1,0)

但是像 long ,integer ,byte ,Double....这样的初始都是0

只有对象刚申请时为 Nothing

dim k as object

初始时要, set k=new object

这里的object就是任何对象