How to show only pre-selected items from local database in dataviewer-list/-grid?

to every row of my database i have a “datafield” named “seleced” - with this “flag =0/1)” i want to “select” or “deselect” each item before showing it in a dataviewer-list / -grid.


how do i have to code this with blocks, that only items with flag = 1 are shown in dataviewer-list / - grid?

many thanks in advance for every proposal!

1 Like

Data Viewer Lists can only show the entire contents of a data source. So in order to filter them, you have to duplicate the data source and filter it. You can have a second data source where you delete all rows and then create rows and populate them from the data in your original data source but only if a condition is true (selected = 1). You’ll need to loop through the original data source to do this.

1 Like

many thanks for your advice - it saves me very much time!

1 Like

Check this

I do this, but it is quite slow as I have 40 rows.

1 Like

Yes @codeswept
This would be slow for two obvious reasons.

  • You are evaluating the list of values block with every iteration of your loop which means you are reading the database 40 times in your example.
  • You are retrieving the value of a cell in every iteration which again means reading the database 40 times.

See my version of your code which should run much faster.


Thank you so much for this! No wonder it was taking 2 minutes to filter my DB each time.

1 Like

Yep, switching from a stored variable to an app variable is also going to be faster. If you need to use a stored variable, assign its value to an app variable before using the app variable in the loop.


Great, thanks for the suggestions!

1 Like

Thank you very much for your version - i tried to test it out but could not succeed,
i build an item_list with 5 datasets (see screenshot)

with blocks i want to “deselect” one dataset (= “duck”) ot my itemList …

but it shows me all datasets of my item_list

many thank in advance for your help!

1 Like

Have you tested it on your mobile?

yes, i test it with thunkableApp on my iphone 12 and on android tablet, same result - all 5 items are dsplayed …

1 Like

here is link to project …

1 Like

check this

I made it highlight the line but the logic is the same.

i replace your

“higlight the line”


"set Data_Viewer_List1`s LayoutWrapper for … “s Visible to false”

and now it works fine …

thank you so much!

1 Like