Issue with grid selection when storing objects

Thank you Shikha, but I still have this error.

Finally, I've gave up (as a colleague just confirmed me, that he has exactly the same error few months ago)...

I've decided to deal with the selectedIds selection ony (array of identifiers)... and then, all I need to do works like a charm now :-)

I will wait for the next Appian versions and will re-test in the future (as I have a good workaround)...

I tried the same code , except using one of the CDT's  that I have . It works fine for me . I am able to select/deselect the rows. 

may I see the whole code please (the saveinto part) ?

a!localVariables(
  local!selection,
  local!selectedVehicles: ri!selectedVehicles,
  /* cast(
    'type!{urn:com:appian:types:cjt2}CJT2_Vehicles', ri!selectedVehicles),
  */
  a!sectionLayout(
    contents: {
      a!columnsLayout(
        columns: {
          a!columnLayout(
            contents: {
              a!cardLayout(
                contents: {
                  a!gridField(
                    label: "Read-only Grid",
                    labelPosition: "ABOVE",
                    data: ri!projectDetails,
                    columns: {
                      a!gridColumn(
                        label: "Name",
                        value: fv!row.name
                      ),
                      a!gridColumn(
                        label: "Manager",
                        value: fv!row.manager
                      ),
                      
                    },
                    selectable: true,
                    selectionStyle: "CHECKBOX",
                    selectionValue: local!selection,
                    selectionSaveInto: {
                      local!selection,
                      a!save(
                        local!selectedVehicles,
                        append(
                          local!selectedVehicles,
                          fv!selectedRows
                        )
                      ),
                      a!save(
                        local!selectedVehicles,
                        difference(
                          /*cast(typeof('type!{urn:com:appian:types:AMT}projectDetails?list'),local!selectedVehicles),*/
                         local!selectedVehicles, fv!deselectedRows
                        )
                      ),
                      a!save(
                      ri!test,
                        local!selectedVehicles
                      ),
                      
                    },
                    validations: {}
                  )
                },
                height: "AUTO",
                style: "NONE",
                marginBelow: "STANDARD"
              ),
              
            }
          ),
          a!columnLayout(
            contents: {}
          )
        }
      ),
      a!paragraphField(
        label:"local!selectedVehicle",
        value: local!selectedVehicles
      )
    },
    showWhen: true
  )
)

I created Ri test of same table type (Array type). Giving some dummy values to Ri!projectDetails. 

Yes, it works because your ri!test can not be used from a parent interface as an input.

(your ri!test shows the current Objects selection only but it can not be set)

With this code if I set the ri!test to null from my parent interface, it does not apply any modification in the selected objects of the grid. It just set the ri!test in the parent interface.

Can somebody explain me why I can not use a rule input for the grid mecanism selection (to save objects), without having the "Invalid types" error above please?

(The Shikha example is a very simple example to test this error)
 

a!localVariables(
  local!selection,
  a!sectionLayout(
    contents: {
      a!columnsLayout(
        columns: {
          a!columnLayout(
            contents: {
              a!cardLayout(
                contents: {
                  a!gridField(
                    label: "Read-only Grid",
                    labelPosition: "ABOVE",
                    data: ri!projectDetails,
                    columns: {
                      a!gridColumn(
                        label: "Name",
                        value: fv!row.name
                      ),
                      a!gridColumn(
                        label: "Manager",
                        value: fv!row.manager
                      ),
                      
                    },
                    selectable: true,
                    selectionStyle: "CHECKBOX",
                    selectionValue: local!selection,
                    selectionSaveInto: {
                      local!selection,
                      a!save(
                        ri!selectedVehicles,
                        append(
                          ri!selectedVehicles,
                          fv!selectedRows
                        )
                      ),
                      a!save(
                        ri!selectedVehicles,
                        difference(
                         ri!selectedVehicles, fv!deselectedRows
                        )
                      ),
                    },
                    validations: {}
                  )
                },
                height: "AUTO",
                style: "NONE",
                marginBelow: "STANDARD"
              ),
              
            }
          ),
          a!columnLayout(
            contents: {}
          )
        }
      ),
      a!paragraphField(
        label:"ri!selectedVehicle",
        value: ri!selectedVehicles
      )
    },
    showWhen: true
  )
)

Thank you everybody for your help.
It works fine now, the only thing missing was to add "?list" why doing the cast (Thanks Peter)