Obtaining textbox value in change event handler

问题:

I've written a form that performs queries asynchronously as text is typed into a textbox, however I somewhat arbitrarily seem to get the following error thrown: "You can't reference a property or method for a control unless the control has focus."

The immediately relevant code is:

Dim UpdateRequested As Boolean
Dim qryText As String

.
.
.

Private Sub txtBox_Change()
    qryText = txtBox.Text
    UpdateRequested = true
End Sub

Some place in the ellipses is the code that handles dynamically loading an ADODB record set, populating a local table, and refreshing a sub form. However, even when I disable this code, the problem persists: Sometimes I get the error. Sometimes I do not.

This seems to be persistent through closing the database and reopening it. Every time it starts working again, it's because I've been fooling around with code in the debugger, but I'm not sure what exactly is causing it to magically "just work" or what is causing it to not work at all.

Update

Just to make things more puzzling, I added a couple of simple event handlers:

Private Sub txtBox_GotFocus()
    MsgBox "Got focus"
End Sub

Private Sub txtBox_LostFocus()
    MsgBox "Lost focus"
End Sub

I run the form. I click in the test box. I receive the "Got focus" message. As soon as I type I see the error as described above. If I re-open the form, I can click between the text box in question (which itself is unbound) and a bound text box in the sub form and see both "Got focus" and "lost focus" messages as one would expect. Furthermore, showing a message box with the current value of "Screen.ActiveControl.Name" shows the expected name just before the Text property is accessed.

回答1:

I know this is an old thread but it's the first I found when I had the same problem. None of the answers helped except Kaganar's own solution, which pointed me in the right direction. I'm guessing the reason people had trouble reproducing the error is there are some important details missing from Kaganar's description:

1. The Textbox was in the form header (or footer).
2. The form did not allow additions.

Because I believe the full answer is...

The Text property of any control is inaccessible when the form has a record source with no records to edit

I think there is part of Access that does not realise the textbox exists :) To understand how that might come about...

• Put the unbound TextBox in the detail of the form
• Do not allow additions
• Set the recordsource to return no records
• Open the form.

Hey presto! No Textbox.

Return a record, or allow additions, or delete the recordsource, et Voila! There is your Textbox with it's Text.

回答2:

I added a text box named txtFoo to my form. Here is the procedure for its change event.

Private Sub txtFoo_Change()
    Debug.Print "Value: " & Nz(Me.txtFoo.value, "*Null*") & _
        "; Text: " & Nz(Me.txtFoo.Text, "*Null*")
End Sub

Then, with nothing in txtFoo (IOW its value is Null) when I type "abc" into txtFoo, here is what I see in the Immediate window.

Value: *Null*; Text: a
Value: *Null*; Text: ab
Value: *Null*; Text: abc

Basically, each character I add to the text box triggers its change event and prints the text box's current contents to the Immediate window.

As far as I understand, you want to do something similar ... except you want a different action in place of Debug.Print. Take another look at your change event procedure and compare it to mine.

Private Sub txtBox_Change()
    qryText = txtVendorName.Text
    UpdateRequested = true
End Sub

That is the change event for a control named txtBox. Within that procedure you reference the .Text property of a control named txtVendorName. However txtBox is the active control at the time its change event code runs ... so you can not access the .Text property of txtVendorName because it is not the active control.

Given that this problem surfaces for only the one form, but not on other new forms, I would suspect the problem form has become corrupted. Read the 2 answers to this SO question and try decompile to cure the corruption: HOW TO decompile and recompile. Decompile is often recommended as a routine practice during development.

You could also use the undocumented Application.SaveAsText method to save your form as a text file. Delete the bad form, and use Application.LoadFromText to import the saved text copy.

Make sure you have a backup copy of your db file in case anything goes wrong.

回答3:

To set or return a control's Text property, the control must have the focus, or an error occurs.
To move the focus to a control, you can use txtBox.SetFocus or DoCmd.GoToControl "txtBox".

Also, the Text property is not always available:
While the control has the focus, the Text property contains the text data currently in the control; the Value property contains the last saved data for the control. When you move the focus to another control, the control's data is updated, and the Value property is set to this new value. The Text property setting is then unavailable until the control gets the focus again.

回答4:

The form had a lingering data source. I'm not sure why this would cause to the behavior described above, especially considering the text box controls are unbound, however since removing the data source the text boxes are behaving as expected.

回答5:

You said "somewhat arbitrarily" I think if everything is fine you must get the error when your form's recordset is empty.

In fact it's a know bug in Access and this error can occur if these conditions are met: a) The control is in the Form Header or Form footer section b) The form is filtered such that no records match (or there are no records) c) No new record can be added.

In this case, the Detail section of the form goes blank. The controlis still visible, but Access gets really confused and can throw the error you describe.

More info: http://allenbrowne.com/bug-06.html

回答6:

I know my answer is out of date. Yet you just can set focus three times. On TextBox in header, on any texbox in detail space and On TextBox in header again. I use access 2003.