Control Properties in Visual Basic 6

问题:

Is there a way to ask for a control property in a loop??

I need somethig like this:

For each p in control.properties
    if p = "Value" then
        msgbox "I Have Value Property"
    elseif p = "Caption" then
        msgbox "I Have Caption Property"
    end if 
next

It could be done somehow?

回答1:

Found this code on Experts Exchange. Add a reference to TypeLib Information.

Public Enum EPType
    ReadableProperties = 2
    WriteableProperties = 4
End Enum

Public Function EnumerateProperties(pObject As Object, pType As EPType) As Variant
    Dim rArray() As String
    Dim iVal As Long
    Dim TypeLib As TLI.InterfaceInfo
    Dim Prop As TLI.MemberInfo
    On Error Resume Next
    ReDim rArray(0) As String
    Set TypeLib = TLI.InterfaceInfoFromObject(pObject)
    For Each Prop In TypeLib.Members
        If Prop.InvokeKind = pType Then
            iVal = UBound(rArray)
            rArray(iVal) = UCase$(Prop.Name)
            ReDim Preserve rArray(iVal + 1) As String
        End If
    Next
    ReDim Preserve rArray(UBound(rArray) - 1) As String
    EnumerateProperties = rArray
End Function

You can ask for a list of the readable, or writeable properties.

Bonus, ask if a specific property exists.

Public Function DoesPropertyExist(pObject As Object, ByVal _
    PropertyName As String, pType As EPType) As Boolean
    Dim Item As Variant
    PropertyName = UCase$(PropertyName)
    For Each Item In EnumerateProperties(pObject, pType)
        If Item = PropertyName Then
            DoesPropertyExist = True
            Exit For
        End If
    Next
End Function

回答2:

Beaner has given an excellent direct answer to the question you have asked.

I'm guessing what you might be trying to do. Perhaps you're trying to get the "text" from a control but you don't know the type of the control at runtime. You could consider something like this, which tries a number of hard-coded property names in turn until something works.

Function sGetSomeText(ctl As Object) As String 
  On Error Resume Next 
  sGetSomeText = ctl.Text
  If Err = 0 Then Exit Function 
  sGetSomeText = ctl.Caption
  If Err = 0 Then Exit Function 
  sGetSomeText = ctl.Value
  If Err = 0 Then Exit Function
  sGetSomeText = "" 'Nothing worked '
End Function 

Another approach would be to check the type of the control at runtime. You can use

• If TypeName(ctl) = "whatever" or
• If TypeOf ctl Is whatever.

Then you could switch to code for specific control types that definitely have the Text property, etc.

回答3:

I'm not sure what you're hoping to accomplish, but I'm pretty sure VB6 does not support what you're talking about. You could try something like this:

If control.Value Is Not Nothing Then
   msgbox "I Have Value Property"
Else If control.Caption Is Not Nothing Then
   msgbox "I Have Caption Property"

See if that accomplishes what you're looking to do.