Combobox OnChange fires & loops unexpectedly when selecting

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Posted on by brownietitan

Hello

This topic has come up quite a bit, but any of the solutions haven't worked.

I have a gallery with a combobox, the user can selected a value, and I want to save the ID from the selected value to a local collection. When I do that, it patches shortly, before the combobox triggers the onchange again and removes the value.

Here's the code I'm using:

OnChange:

If(
 locAllowEdit = true,
 Patch(
 colNewProjectMeasurepoints1,
 ThisItem,
 {MeasurepointIDPatched: Self.Selected.ID}
 );
 Trace("OnChange")
)

OnSelect:

UpdateContext({
 locAllowEdit: !locAllowEdit
})

DefaultSelectedItems:

LookUp(Measurepoints, ThisItem.MeasurepointID = ID)

The onSelect code prevents the combobox from starting a loop, but technically it should ignore the Patch statement, yet it doesn't. Anyone got any ideas?

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Building Power Apps

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Adrian_Celis 1,652 Moderator on at

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Hi @brownietitan
You should reset the locAllowEdit variable to false in your OnChange.
So can you change your code to:
OnSelect
UpdateContext({locAllowEdit: true})
OnChange
If( locAllowEdit = true, Patch( colNewProjectMeasurepoints1, ThisItem, {MeasurepointIDPatched: Self.Selected.ID} ); UpdateContext({locAllowEdit: false}) Trace("OnChange") )

This is similar to the use-case below. See the step 6 OnChange and OnSelect property of this tutorial. As you can see they are resetting the IsSelected variable:
Power Apps – Rearrange gallery items using dropdown

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brownietitan 2 on at

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That doesn't seem to work, it patches the data to the collection for a brief second, and then it gets reset again.

It seems that the internal component still fires the onChange completely, even though it shouldn't.

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Suggested answer

DF-27021330-0 6 on at

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I hope this is able to bless someone's day! It was nerve racking for me! hahah. 😂

After the entire week of just sitting here playing with the ONE combo box, with no help from online, I think it would be good for me to post my solution here for the next person.

I am working with items = Office365Users combobox with onchange patch and a conflict with defaultselecteditems. It was entering a never ending circular loop.

my application screenshot:

FULL EXPLANATION BELOW!

my application screenshot:

APP ONSTART CODE (be sure to "run" onstart):

// ~~~~~~~~~~~~~~~~~ SET VARIABLES TO ALLOW DEFAULT VALUES ~~~~~~~~~~~~~~~~~ ||

// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ||

Set(varPatch, 0); // ~~~~~~~~~ IS THE PATCH PERMITTED ON STARUP? NO! ~~~~~~~ ||

Set(varRunning, 0); // ~~~~~~~ IS THE PATCH RUNNING ON STARTUP? NO! ~~~~~~~~ ||

Set(varStartup, 1); // ~~~~~~~ DID THE APP JUST STARTUP? YES! ~~~~~~~~~~~~~~ ||

// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ||

Set(varSpinner, false);

COMBO BOX ITEMS:

Filter(

Office365Users.SearchUserV2({searchTerm:Trim(Self.SearchText), isSearchTermRequired:(false)}).value,

!IsBlank(Mail) && EndsWith(Mail, "@youremail.com")

)

COMBO BOX DEFAULTSELECTEDITEMS:

IfError(Split(ThisItem.manager_name, ","), [])

COMBO BOX DISPLAYMODE:

If(varRunning = 1 && varStartup = 0, DisplayMode.Disabled, DisplayMode.Edit)

// ~~~~~~~ IF "RUNNING", BUT APP NOT ON "STARTUP" THEN "DISPLAYMODE" = DISABLED WHILE "RUNNING".

// ~~~~~~~ IF APP IS ON "STARTUP", THEN BE SURE TO ALLOW "DISPLAYMODE" = EDIT.

COMBO BOX ONSELECT:

Set(varPatch, 1); // ~~~~~~~~~~~ IS ALLOWED TO ENTER "ONCHANGE" TO "PATCH" TO DATAVERSE? IF THEY SELECT, THEN YES!

Set(varStartup, 0); // ~~~~~~~~~ IF USER SELECTS THIS FIELD, THEN THE "STARTUP" DISPLAYMODE WILL BE TURNED OFF. SET VALUE TO ZERO (0).

// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ STARTUP = 1 IS ONLY ASSIGNED IN THE APP'S ONSTART FUNCTION TO ENSURE "DISPLAYMODE" IS NOT DISABLED ON "STARTUP".

COMBO BOX ONCHANGE:

/*****************************************************************************************************|

CMB DEFAULTSELECTEDITEMS *****************************************************************************|

• REVERSE THE "CONCAT" PATCH ("ONCHANGE") WITH "SPLIT" TO CONVERT STRING TO TABLE.

• THIS VALUE WILL BE ASSIGNED DURING "ONSTART" AND "ONCHANGE".

/*****************************************************************************************************|

APP ONSTART ******************************************************************************************|

• VARIABLES REQUIRED TO MITIGATE FOREVER ONCHANGE/DEFAULT VALUES IN CIRCLULAR REF LOOP.

• ON STARTUP, THE PATCH PROCESS IS NOT "RUNNING" (0) NOR ALLOWED TO RUN.

• ON STARTUP, THE APP IS NOT ALLOWED TO "PATCH" (0) VIA "ONCHANGE" FUNCTION.

• ON STARTUP, THE APP IS ON "STARTUP" (1) ALLOW "DISPLAYMODE" TO BE EDITED.

/*****************************************************************************************************|

CMB DISPLAYMODE **************************************************************************************|

• IF "RUNNING" (1) ANNNND NOT "STARTUP" (0) THEN "DISPLAYMODE" = DISABLED

• ELSE "DISPLAYMODE" = EDIT

• THEREFORE, IF PATCH IS "RUNNING", DO NOT ALLOW COMBOBOX INTERACTIONS, BUT

• DEFAULT THE "DISPLAYMODE" = EDIT ON "STARTUP" OF THE APPLICATION.

/*****************************************************************************************************|

CMB ONSELECT *****************************************************************************************|

• IF USER SELECTS THIS FIELD, THEN THIS IS EVIDENCE THAT "STARTUP" IS COMPLETE. SET TO ZERO (0).

• STARTUP VALUE WILL NOT BE SET TO ONE AGAIN UNTIL APPLICATION IS RESTARTED.

• WITH THE "ONSELECT" AND "DISPLAYMODE" LOGIC, THIS WILL ENSURE USERS CANNOT EDIT MULTIPLE ROWS SIMULTANEOUSLY.

• IF USER SELECTS THIS FIELD, THEN ALLOW "ONCHANGE" PATCH, THUS SETTING "PATCH" TO ONE (1).

/*****************************************************************************************************|

CMB ONCHANGE *****************************************************************************************|

• IF ALLOWED TO "PATCH" (1) THEN SET "RUNNING" TO ONE (1).

• "RUNNING" SET TO ONE (1) WILL PREVENT EDITING DURING PATCH UPDATE. "DISPLAYMODE" = DISABLE.

• IF ALLOWED TO "PATCH" (1) THEN EXECUTE "PATCH" AND WRITE TO DATAVERSE TABLE.

• AFTER PATCH FUNCTION IS COMPLETE, THEN RESET "PATCH" AND "RUNNING" TO ZERO (0) TO PREVENT FOREVER CIRCULAR REF LOOP.

• THIS WILL PREVENT THE "DEFAULTSELECTEDITEMS" FROM BEING REASSIGNED TO THE ENTIRE COLUMN (FOREVER CIRCULAR LOOP).

/*****************************************************************************************************|

******************************************************************************************************/

Notify(ThisItem.KEY_CST); // ~~~~~~~~~~~~~~~~~ TO TROUBLESHOOT CURRENT POINTER! YOU CAN SEE THE LOOP TRYING TO REENTER.

If(varPatch = 1, // ~~~~~~~~~~~~~~~ IS THE PROCESS PERMITTED TO PATCH THE ROW? ~~~~~~~~~~~~~ || YES, LET'S PROCESS THE PATCH.

Set(varRunning, 1); // ~~~~~~~~~~ IS THE PROCESS RUNNING? ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ || YES, THE PROCESS IS RUNNING. THEREFORE, LOCK THE APP (DISPLAY MODE).

Patch(_iat_config_customers, LookUp(_iat_config_customers, KEY_CST = ThisItem.KEY_CST), {manager_name: Concat(cst_table_cmb_manager_classic.SelectedItems, ThisRecord.DisplayName, ",")});

); // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ||

Set(varPatch, 0); // ~~~~~~~~~~~~~~ NO MORE PROCESSING IS PERMITTED. ~~~~~~~~~~~~~~~~~~~~~~~ ||

Set(varRunning, 0); // ~~~~~~~~~~~~~~ THE PROCESS HAS FINISHED RUNNING. ~~~~~~~~~~~~~~~~~~~~~~ ||

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DF-27021330-0 6 on at

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To complement my other suggested answer, I ended up having to take a different approach to speed up processing:

Dataflows to push data changes to dataverse (and bypass the infinite loop).

I found this resource explaining the infinite loop: https://github.com/MicrosoftDocs/powerapps-docs/blob/main/powerapps-docs/maker/canvas-apps/gallery-best-practice.md

the patch variables are sent to a timer (do while < 16hours) loop to verify that the data is pushed. I am refreshing the other screens through this timer loop since pushing to data verse does not automatically update the frontend (while the patch does update the cache).

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