link showwhen in grid

You probably have a local variable you use to store the selected rows. You just have to check whether the list of selected rows contains that row.

at same time when i select other row both links are disappeared 

Then you condition is wrong. Wanna share some code?

a!gridLayout(
              headerCells: {
                a!gridLayoutHeaderCell(label: cons!CR_SF_ALL_LABELS[10]),
                a!gridLayoutHeaderCell(label: "")
              },
              columnConfigs: {
                a!gridLayoutColumnConfig(width: "DISTRIBUTE", weight: 2),
                a!gridLayoutColumnConfig(width: "DISTRIBUTE", weight: 2)
              },
              selectionValue: ri!selected_txt,
              selectionSaveInto: ri!selected_txt,
              selectable: true(),
              rows: a!forEach(
                items: local!limitsList,
                expression: a!gridRowLayout(
                  id: fv!item,
                  contents: {
                    a!textField(value: fv!item, readOnly: true()),
                    if(
                      rule!APN_isEmpty(ri!selected_txt),
                      a!textField(readOnly: true()),
                      a!richTextDisplayField(
                        value: a!richTextItem(
                          showWhen: index(ri!selected_txt, fv!item, {}),
                          text: if(
                            local!showLimitData,
                            "Hide Data",
                            "Show Data"
                          ),
                          link: a!dynamicLink(
                            value: not(local!showLimitData),
                            saveInto: if(
                              local!showLimitData = true(),
                              a!save(local!showLimitData, false()),
                              a!save(local!showLimitData, true())
                            )
                          ),
                          color: if(
                            local!showLimitData,
                            "#ff0000",
                            "#00ff00"
                          )
                        )
                      )
                    )
                  }
                )
              )
            )

a!gridLayout(
              headerCells: {
                a!gridLayoutHeaderCell(label: cons!CR_SF_ALL_LABELS[10]),
                a!gridLayoutHeaderCell(label: "")
              },
              columnConfigs: {
                a!gridLayoutColumnConfig(width: "DISTRIBUTE", weight: 2),
                a!gridLayoutColumnConfig(width: "DISTRIBUTE", weight: 2)
              },
              selectionValue: ri!selected_txt,
              selectionSaveInto: ri!selected_txt,
              selectable: true(),
              rows: a!forEach(
                items: local!limitsList,
                expression: a!gridRowLayout(
                  id: fv!item,
                  contents: {
                    a!textField(value: fv!item, readOnly: true()),
                    if(
                      rule!APN_isEmpty(ri!selected_txt),
                      a!textField(readOnly: true()),
                      a!richTextDisplayField(
                        value: a!richTextItem(
                          showWhen: index(ri!selected_txt, fv!item, {}),
                          text: if(
                            local!showLimitData,
                            "Hide Data",
                            "Show Data"
                          ),
                          link: a!dynamicLink(
                            value: not(local!showLimitData),
                            saveInto: if(
                              local!showLimitData = true(),
                              a!save(local!showLimitData, false()),
                              a!save(local!showLimitData, true())
                            )
                          ),
                          color: if(
                            local!showLimitData,
                            "#ff0000",
                            "#00ff00"
                          )
                        )
                      )
                    )
                  }
                )
              )
            )

This is not how the index() function works.  This is a very powerful and useful function but, i'm afraid, it doesn't do what you seemed to want here.

The good news is the real solution here is probably simpler - you can probably just replace that code with, "ri!selected_txt = fv!item" or something similar to that.