This sub is on a form to catch the previous control and works correctly if the control is a command button.
If the control is a textbox "Ctl" holds the contents of the box as a string.
Code:
Private Sub btnAbout_Click()
Dim ctl As Control
Set ctl = Screen.PreviousControl
' getHelp (Screen.PreviousControl)
End Sub
That is not possible, as the variable ctl is declared as control.
I assume you arrived at this incorrect conclusion by looking at or handling ctl in some way that caused it to return its default property's value, the Value property.
Show or explain how you arrived at your conclusion, and we'll probably be able to explain where it went wrong.
will pass what is in parentheses by value. It will evaluate Screen.PreviousControl.DefaultProperty or in a case of a textbox it will evaluate the expression to the value of the textbox.
However this will pass by reference
Code:
Call GetHelp (Screen.previousControl)
Yes it is confusing and dumb, but that is the way it is.
Why?
In Summary
Call GetHelp (Screen.previousControl) ... By ref (assume procedure argument by ref)
GetHelp Screen.previousControl .. By ref (assume procedure argument by ref)
GetHelp (Screen.previuosControl) .. By val
In Summary
Call GetHelp (Screen.previousControl) ... By ref (assume procedure argument by ref)
GetHelp Screen.previousControl .. By ref (assume procedure argument by ref)
GetHelp (Screen.previuosControl) .. By val
Thank you for that, it answers my question, but confused I am. What about the 'Set ctl =" returning a string?
Is there a more confusing way around that.
I commented some lines in your BtnStart_Click procedure:
Rich (BB code):
Private Sub BtnStart_Click()
Dim Ctl As Control
' On Error GoTo error
Set Ctl = Screen.PreviousControl
Stop' If InStr(Ctl, "Now") > 0 Then
' MsgBox "now Ctl is a string ---- " & Ctl
' End If
' Exit Sub
'error:
' MsgBox "now Ctl is an object ---- " & Ctl.Name
End Sub
I added the Stop to check what Ctl is at that point. The debugger says the type is Control/TextBox when the textbox is previous:
And when the button is previous, the type is Control/CommandButton
If you go into the object browser looking for the default value of the Control class, you will see that it has no default property. If you look for the CommandButton class, it also has no default property. However, if you look for the TextBox class, you'll see it does have a default property, look:
Predeterminado means Default. That Cyan icon helps see what the default member is. So, since the TextBox class does have a Default property, which is Value, when you use Set Ctl = Screen.PreviousControl, VBA will determine you need txt1.Valuewhen you try to use the MsgBox function. Since the CommandButton class has no such thing, it refers to the CommandButton itself, and it throws an error because it needs a string for the MsgBox.
By the way, what are you planning to do with the reference to the control? Set its color?
It's all part of a context sensitive help system.
I have written a system that controls a number of tables with scientific data in them. The major forms have some 90 text/ combo boxes on a single form with up to 20 buttons in the header and more in the footer.
There are some 60 different forms in the system and, as you can imagine, working your way through this lot can be intimidating. Hence the context sensitive help.
Basically one can access the help files, a word document with many bookmarks and hyperlinks, by either clicking a "Help"
button which looks at the previous control or the "F1" key that looks at the current control.
I only started writing this a couple of days ago so it is in it's infancy and I am in a steep learning curve.
This is the guts of it. I just have to add a whole bunch more "IF" and "Case" statements plus a lot more writing in the word doc.
There is a trap for "F1" in each form and code for the "Help" button. Lots of cut and paste.
John
Code:
Public Sub getHelp(Ctl As Control)
Dim str As String
Dim sName As String
Dim num As Integer
Dim sSect As String
sSect = IIf(Ctl.Section = 0, "Detail", "Header")
num = Ctl.TabIndex
If sSect = "Header" Then
Select Case Ctl.Parent.Name
Case "Herbarium Collection"
Select Case Ctl.TabIndex
Case 0 To 5: str = "Recordcontrol"
Case 6: str = "Copy"
Case 7 To 9: str = "Recordlocate"
Case 10 To 12: str = "Labelsgroup"
Case 13 To 20: str = "User"
End Select
Case "National Parks Collection"
Select Case Ctl.TabIndex
Case 0 To 3: str = "Recordcontrol"
Case 4 To 6: str = "Recordlocate"
Case 7 To 9: str = "Usere"
End Select
End Select
End If
If Nz(str, "") = "" Then
strMessage = "This is a work in progress"
strImage = "i"
bOK = True
Messenger
Exit Sub
End If
Application.FollowHyperlink TempVars!LYN & "The Don McNair Herbarium Data Set.docx", str
End Sub
In that particular code, I see you're using the Ctl variable to get the section, tabindex and parent members.
However, in the example db you posted, you're looking for the condition that your PreviousControl's something has the word "Now" in it. But that something can be many things depending on the control. If it's a combo box bound to a foreign key, you'll likely get a number, not a string, if it's a button, you'll get the button object itself (maybe you need its caption?), if it's a subform, you'll get its Controls collection, and you probably need something else, its name perhaps? So you'll have to write a condition for each type of control.
You can use the TypeName function like If TypeName(ctl) = acTextBox Then or a select case for that.
In that particular code, I see you're using the Ctl variable to get the section, tabindex and parent members.
However, in the example db you posted, you're looking for the condition that your PreviousControl's something has the word "Now" in it. But that something can be many things depending on the control. If it's a combo box bound to a foreign key, you'll likely get a number, not a string, if it's a button, you'll get the button object itself (maybe you need its caption?), if it's a subform, you'll get its Controls collection, and you probably need something else, its name perhaps? So you'll have to write a condition for each type of control.
You can use the TypeName function like If TypeName(ctl) = acTextBox Then or a select case for that.
The code sample was just to demonstrate the way "Ctl" reacted to the text box or button. It had nothing to do with the help function.
Had you left the code as it was, the message boxes had the results in them.
The type of control is irrelevant for my purpose. The help function relies in the tabindex, the form name and "Header"/ "Detail".
It does involve a lot of extra work sorting out the tab order. The default is across then down. I need down then across.
I guess the system is only as good as the time one put's into it.
John
That is definitely not what is happening.
What is happening is the VBA will do its best to Cast/evaluate values to the proper type.
The instr function takes a string
Code:
Private Sub BtnStart_Click()
Dim Ctl As Control
On Error GoTo error
Set Ctl = Screen.PreviousControl
msgbox TypeName(ctl)
If InStr(Ctl, "Now") > 0 Then
MsgBox "now Ctl is a string ---- " & Ctl
End If
Exit Sub
error:
MsgBox "now Ctl is an object ---- " & Ctl.Name
End Sub
Since a textbox has a default Value property, CTL does not become a string but it gets evaluated in the function.
msgbox TypeName(ctl)
Proves it is set as an object as we would expect.
A cmd button does not have a value or even a default property (which is strange) so it cannot evaluate it to a string.
InStr(Ctl, "Now")
You will see this in VBA where you would think the code would fail but VBA guesses what you are trying to do and evaluates or casts it to a correct format.
I have no idea why this is failing, I simply want to make the background red if the Date is before Today. The results I am getting are all over the place.
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Seems the more one gets clarity, the more confused one gets.
If you look at Ctl directly after the "set" It has a string enclosed in inverted commas so it would appear to be getting "Ctl.value".
I've oft said that Access is consistently inconsistent, I'll stick with that.
Thank you for casting some light on this. it's very helpful.
John
In your original upload, the "error" you are reporting is incorrect.
Try the error handler below
If you just click help, you get error 2483, as there is no previous control.
If you click the text box, then help it works
if you click the other button then click help, you get a different error.
Thank you Gemma.
The information from MajP solved my problem.
I was calling the "GetHelp" function incorrectly.
In Summary
Call GetHelp (Screen.previousControl) ... By ref (assume procedure argument by ref)
GetHelp Screen.previousControl .. By ref (assume procedure argument by ref)
GetHelp (Screen.previuosControl) .. By val
