Problems with ComboBox.OnChange triggering too often and with weird timing.

[SaWu]

Hello

Please be so kind as to read my full post before responding.
Thank you for your consideration.

In my PowerApp I often use the pattern of having something like

UpdateContext({
    unsaved: true
})

in my input controls, and only show things like Save or Reset buttons depending on unsaved.
In my MyForm.OnReset event I have

UpdateContext({
    unsaved: false
})

and my Save and Cancel buttons both use

ResetForm(MyForm)

However, I am having trouble using this together with ComboBoxes used with LookUp fields when using Save, or when entering the Screen.
It appears that the ComboBox.OnChange event gets triggered with a "weird timing" and more often than, say, TextInput.OnChange.
Hence, whenever I enter the screen or Save anything (Save triggers ResetForm in my case), ComboBox.OnChange gets triggered.
In contrast, for example TextInput.OnChange only gets triggered with an actual text change.

As an example to better highlight my problem, I have slightly modified one of my PowerApps that uses ComboBoxes in an EditForm.
I added a text context Variable logTxt with Screen.OnVisible

UpdateContext({
    logTxt: ""
})

and changed ComboBox.OnChange to, and note the "safeguard" resetting

UpdateContext({
    logTxt: logTxt & "
ComboBox.OnChange"});
If(!resetting,
    UpdateContext({deliveryUnsaved: true})
)

all my TextInput.OnChange to

UpdateContext({
    deliveryUnsaved: true,
    logTxt: logTxt & "
TextInput.OnChange"
});

and Form.OnReset

UpdateContext({
    deliveryUnsaved: false,
    logTxt: logTxt & "
Form.OnReset"
})

I also added a big Label with Label.Text set

"logTxt:
" & logTxt

and at the end of my Cancel/ResetForm and my Save buttons I have

UpdateContext({
    resetting: true
});
ResetForm(LieferungForm);
UpdateContext({
    resetting: false
})

Using, this, upon entry to the screen, with nonempty default record selected, I already see this:

That is, by "virtue" of ComboBox.OnChange triggering, I have already entered my PowerApp Mode of having unsaved changes without actually having done anything.

Changing the Text in one TextInput yields:

Saving via SaveButton.OnSelect and thus triggering ResetForm yields:

which causes an unexpected triggering on ComboBox.OnChange after Form.OnReset ignoring the resetting safeguard and the order of functions inside my SaveButton.OnSelect event.

Trying to afterwards change the ComboBox itself triggers another ComboBox.OnChange:

Saving and triggering ResetForm again yields:

which again causes an unexpected triggering of ComboBox.OnChange after Form.OnReset ignoring the resetting safeguard and the order of functions inside my Save buttons OnSelect event.

My questions:

1. How do I get this setup to work even with that ComboBox.OnChange nonsense?
2. Why is ComboBox.OnChange triggering so often, and completely inconsistent with the way OnChange gets triggered for TextInput controls?
3. Why is ComboBox.OnChange triggering at all from using ResetForm? No other controls seem to do this.
4. Shouldn't Form.OnReset trigger after all controls inside the form have already been reset, i.e. shouldn't Form.OnReset be in my logs after ComboBox.OnChange?

Last tested with:

App ID: 8200a3f3-30fd-44f9-b3b7-0c9e0f803c50
Session ID: 21a66c2e-a2f6-472c-bffc-a84600ce0745
PowerApps 3.19081.26

If you have read all of this properly, thank you!
If you have a solution for me or know documented answers, thank you and kudos!
    Sa.

[KeithV1]

In addition to this thread, when using a combobox in a gallery, the onchange function of the combobox is also triggered by scrolling down and filling up the gallery with records.  In this instance, the onset solution won't work because the variable that is set, is set for the complete column of the gallery.  To overcome this problem I first compare the value of the combobox with the defaultselecteditems, whenever they are different, the onchange function gets triggered

[krishangopi]

I was surprised to notice that this issue with combo box OnChange property still exist as of today. Looks like Microsoft is not listening to the community at all. 

[bthomas89]

Good report.  I've also noticed that the datepicker control has similar behavior which is inconsistent with other input controls.  Beware...

[HelpfulBit]

Hi guys.  Call it a bug or call it bad documentation.  I think I can shed a little light on this.

According to current the documentation, the OnChange fires when the user changes the selection.  This would be consistent with the Model Driven App Client Side Object Model, where OnChange does not fire if code updates the value. There, the code has to explicitly fire the onchange event.  Documentation Here.

Unfortunately, the onChange is fired whenever the value changes, whether by user or not.  And, it is likely in an async event loop, which is why some are reporting odd timing. 

The short answer around this is to use the OnSelect property instead, and perform a check to see if the current value(s) match whatever your DefaultSelectedValues property is set to.  If they match, do nothing. If not, perform whatever update is appropriate, and refresh the data that your DefaultSelectedValues is pointed at.

I'm submitting feedback to MSFT and may write up a more in-depth article on my blog at https://helpfulbit.com, but for now, hope this helps.  Ping me with any questions.

Ryan Perry

[james_hathaway]

Hi @hjaf 

The problem with using the OnSelect on the ComboBox is that this event fires when the User first Clicks on the control (either drop-down chevron or clicking on the text itself) - so This event fires BEFORE the User has actually changed the value in the Combo-Box...

... not really very useful!

As others have commented, the best workaround is for the onSelect to set a variable "changingComboBoxSelection" to true, and then check this variable in your OnChange event:

OnSelect:
UpdateContext({changingComboBoxSelection:true});

OnChange:
If(changingComboBoxSelection,
     [Do your Actions]
     UpdateContext({changingComboBoxSelection:false});
)

James.