I have a ComboBox bound to a table field and I want to validate the selection, since only certain selections are valid depending on context. When in the On Validating Event how can I get the Value before or what it is in the table.field before selection changed?
The WinForms ComboBox control doesn't provide the functionality of being able to intercept a value change and cancel it. You can use the Validating event (or, as you describe, subclass the ComboBox and override OnValidating), but these only allow you to keep the focus on the control. You can't actually "cancel" a value change through the validating events.
There are several third-party (DevExpress, for example) packages that provide ComboBoxes that allow you to inspect both the initial and the new values when the value changes and cancel the change if desired, but the ComboBox provided in System.Windows.Forms does not.
Related
I have an application whereby I have the behaviour of 2 groupboxes enable/disable based on the value in a combobox.
This combobox however the behaviour for the group boxes only works when I leave the field by tab or click, not when the text changes.
I have tried using the Leave, TextChanged, Validated Events and everytime I have to actually "Leave" the field for it to perform the enabled/disabled of the groupboxes and their subsequent controls.
I need it so that when they choose 1 of the 3 options it immediately changes and doesn't work when they leave the field but when they choose the correct word.
Any assistance would be great I'm tearing my hair out here.
I think you are looking for the event on your combo boxes
SelectedIndexChanged
To stop the user from leaving an invalid field use the event
Validating
set the e.cancel to True if the validation fails
I have searched several forums but did not find answer for checking whether ComboBox is already DroppedDown via VBA code.
I have other code on Form_KeyDown events due to which anytime I press vbKeyDown it moves to next record. I need to check if ComboBox is DroppedDown then don't use other code and instead treat the default functionality of access where vbKeyDown will start scrolling through the items of ComboBox displayed in DropDown.
There is no such property, neither an event for OnDropDown or similar.
If the combobox has focus, you can force a dropdown using the DropDown method, but that's as close you can get.
I have a custom user form in Excel where the number of option buttons is dynamic, depending on what a user selects from a combo box. I have written a script that will add and format those option buttons with appropriate captions, groupname, etc. However, I would like it so that after those buttons are added dynamically, if a user clicks a button from a group just added, then more code will be executed. I am aware that one can create a custom class so that multiple userform controls are handled with one event handler, but I can't figure out how to get this to work with controls that were added dynamically to a form, after the form initialized. I am hoping this question makes sense. Thanks in advance for any help you can offer.
Is this possible to do or are you only allowed to .focus one textbox on each form? I'm looking to highlight more than one textbox at one time if data is empty.
Only one control can have the focus every time (and thus what you request is not possible). In any case, note that the focus is meant for actions (not for visuals) and that only one control can perform actions every time in the GUI thread (e.g., text written in a TextBox or Button being clicked). On the other hand, you might provoke situations similar-enough to various controls getting the focus simultaneously (e.g., text written in various textboxes, coordinated via TextChanged Events: the actions are not performed simultaneously but the user will not realise about it).
If your intention is just highlighting the given control, you shouldn't rely on the focus. The focused control does get somehow highlighted, although this visual effect is not too relevant and, some times, not even perceptible. The best thing you can do is provoking the highlighting effect "manually". For example: Panel surrounding the TextBox, whose dimensions/visibility are affected; or just simply changing the BackColor property of the TextBox.
I have a combobox where the SelectedValue on the combo is bound to a property on a business object.
Everything works fine, but the property that's bound to the SelectedValue on the combo only gets updated when the focus leaves the control. I understand that the property doesn't get updated until the control is validated (loses focus), but I need it to update the datasource as soon as the dropdown is closed.
I know I could probably leave focus from the control on the DropDownClosed event but I'd prefer something a little less kludgy.
What's the best way to immediately update my datasource when the dropdown is closed?
Set the DataSourceUpdateMode to OnPropertyChanged. Here is similar problem:
[http://social.msdn.microsoft.com/Forums/en/winformsdatacontrols/thread/bc39342b-d9b5-4ad0-bd35-073869ccf8be][1]
The way I'd do it is to set (in the events) the OnUpdate of the combo box and put in the VB.net
Me.<business object>.Requery