Resetting Gallery Selection Formula - Why does this work?

[WillyD44]

I read a thread on this PowerApps user forum that helped me acheive my desired end state...but I DON'T KNOW WHY IT WORKS and it's killing me. 🙂  

I want to set the value of a Gallery to not have any items in the gallery selected...in essence, show ALL gallery items.  This in turn affects how my table displays data as my table control is set to show only the row of data that corresponds to the Gallery selection.  But...what if the user says, "I don't want to look at a single record in the table any longer.  I want to see all table records."  At this point, I need to clear the Gallery.Selected value so that nothing is selected, which in turn will drive my table to show all records. 

A picture is worth a thousand words.  This sould tie things together.  

In the below image, the user selects Hull (Gallery1) in the Facility list.  Hull then shows in the Facility Details Table (Table Control whose data source is a SharePoint list).  

But now, the user wants to reset the selection in the Facility to list to NONE...or BLANK.  The user wants all the facilities to show.  So, the user clicks the Reset Selection button and sure enough, the selection in Gallery1.Selection goes to BLANK and he is able to see all table records now.   See below screenshot, then see my question below that. 

Last detail...Gallery1 (Facility list, far left column)...Gallery1's Default property is set to: ResetButton.

What I don't understand is why the OnSelect property formula has to be the way it is.  I would have thought it should have been like this:

OnSelect = UpdateContext({ResetButton:{}})

If I use the property formula above, the Reset Selection Button works one time.  After that it does not work.  

Why does the property have to be set to what the screenshot above shows to work?  In the event the screenshot does not show the working property formula well, here it is:

OnSelect = UpdateContext({ResetButton:Gallery1.Selected});UpdateContext({ResetButton:{}})

Hopefully someone can help.  It won't do me much good to have a formula stashed away with no understanding of how to use it, change it, improve it for different scenarios, etc. 

Bill

[dinusc]

I don't know which thread you're referencing to so it would be helpfull to also know how your ResetButton is set. Is it like this?

Gallery1.OnSelect=UpdateContext({ResetButton: Gallery1.Selected})

And then your second gallery uses it for filtering the content?

[Mike8 · Accepted solution]

Hello,

OnSelect = UpdateContext({ResetButton:{}})
This works the first time because the default property of the gallery is set to an empty record ---> {}.
Before it wasn't an empty record and it changed to an empty record. 🙂
If you try to press it again, it will not work because the second time you set the ResetButton variable from {} to {}. So, it doesn't change. If the ResetButton doesn't change powerapps doesn't trigger the default property.

OnSelect = UpdateContext({ResetButton:Gallery1.Selected});UpdateContext({ResetButton:{}})
This works every time because in the same expression, you set the ResetButton to a value (Gallery1.Selected) and then you set it to an empty record. So, the ResetButton changes and powerapps triggers the default property.

To sum up, this is how powerapps works. You need to change the variable in the default property in order to trigger and apply the default value on the gallery.

[WillyD44]

Mike8...brilliant!  Great, clear and detailed explanation.  Thank you for taking time to answer my question. 

Best regards,

Bill

[RussW]

Hi,

Thanks for bringing this function up in the forums. 

May I suggest an alternative I've discovered that has less overhead?

I discovered it mainly out of your suggestion not quite working for my app's gallery.

Simply, I want to select a name from a gallery list and have this trigger the displaymode on a button from disabled to edit essentially not allowing the button to activate without first selecting a name from the list. In working through this, I found the below formulas work to deselect the name in the list and/or start with no name selected when you navigate to the screen.

Set the Gallery1.Default to {}        < an empty record

Set the ResetButton.OnSelect to Reset(Gallery1)        < resets the gallery to default

[DeeTronSEAM]

Thanks, @RussW  !

Using the Reset(NameOfMyGallery) method (aka formula) WORKS.  This is surprising since (currently) PApps galleries do not have a Reset property.  But hey, I'll take it.  It sure is easier than using the default property of the gallery via a toggled context variable.

[larry_nSightMgt]

Thanks and kudos to Mike8.  I've been working with PowerApps for the past 4 months and consider myself fairly knowledgeable.  In my application, users can make a selection from a drop-down and their selected value determines the contents of a Gallery.  The contents of the drop-down and the gallery come from SharePoint lists.  This is a very common scenario where the parent-child relationship is represented via two SharePoint lists. You select the parent ID value from the drop-down and the list of dependent records are displayed in the Gallery.

I was completely unable to control the default value of the Gallery. PowerApps would get the Gallery default value correct on the first display of the screen. However, the "child" gallery would not move to the correct default record the next time the user selected a value from the drop-down. I was going crazy and was ready to give up completely on PowerApps and look for some other solution. But Mike8 made a simple statement that woke me up.  His statement "To sum up, this is how powerapps works. You need to change the variable in the default property in order to trigger and apply the default value on the gallery."  I suddenly got it. There are probably many ways to accommodate PowerApps to trigger the updated default value on the Gallery. I switched to using a collection for the Gallery items property instead of using Filter directly from the SharePoint list. The collection is created/re-created using the drop-down control on-change event. Very simple. This pernicious problem is now solved. I'm going to continue to use PowerApps.

[Mike8]

I am glad I could help @larry_nSightMgt.
The community is really helpful and active and if you have more questions I am sure someone can also help you next time. 🙂

[ananda]

Hi

Any update on the same.

Thank you

[CtrlAF]

Few years removed but I still found this post very helpful to reset my gallery to not just be deselected, but also scroll to the top (maybe there's a better way?).

Thought I would share my variation to get both:

OnSelect = UpdateContext({cvResetGallery:Blank()}); Reset(Gallery1); UpdateContext({cvResetGallery:{}})

Key for me was to change the Gallery Default to nothing using Blank() (aka. Null) so that it auto selects the first entry and would force the reset to bring it back to the top of the long list if the user has scrolled down.

Then it updates the context variable back to an empty record so that there is nothing selected.