How to add a custom action to the list ribbon?

Question

How to add a custom action to the list ribbon?

The custom action should open a sitepage in modal popup.

Answer 1

<?xml version="1.0" encoding="utf-8"?>
    <Elements xmlns="http://schemas.microsoft.com/sharepoint/">
    <CustomAction Id="9b3d1a59-78ca-45da-aa2c-4964e3f68c58.AppHost-RCA"
    RegistrationType="List"
    RegistrationId="100"
    Location="CommandUI.Ribbon"
    Sequence="10001"
    Title="Invoke &apos;AppHost_RCA&apos; action">
    <CommandUIExtension>
    <!--
    Update the UI definitions below with the controls and the command actions
    that you want to enable for the custom action.
    -->
    <CommandUIDefinitions>
    <CommandUIDefinition Location="Ribbon.ListItem.Actions.Controls._children">
    <Button Id="Ribbon.ListItem.Actions.AppHost-RCAButton"
    Alt="Request App"
    Sequence="100"
    Command="Invoke_AppHost-RCAButtonRequest"
    LabelText="Request App"
    TemplateAlias="o1"
    Image32by32="_layouts/15/images/placeholder32x32.png"
    Image16by16="_layouts/15/images/placeholder16x16.png" />
    </CommandUIDefinition>
    </CommandUIDefinitions>
    <CommandUIHandlers>
    <CommandUIHandler Command="Invoke_AppHost-RCAButtonRequest"
    CommandAction="~appWebUrl/Pages/Default.aspx"/>
    </CommandUIHandlers>
    </CommandUIExtension >
    </CustomAction>
    </Elements>

• See more at: http://www.sharepoint-journey.com/custom-actions-in-sharepoint-2013.html#sthash.Ic1fEx3A.dpuf

Answer 2

You can associate your custom action to a specific list by using the RegistrationId property.

Check this post, already have answer.

Show custom action in ribbon for only one list