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.

To achieve this, save the selection in a local variable, and then in the showWhen parameter of the link, check if the row is selected or not. You can check this by using the contains() function.
Just give it a try ;)

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"
                          )
                        )
                      )
                    )
                  }
                )
              )
            )

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.