Create custom ribbon button in list view for Sharepoint Online using client object model

In this post I will show how to create custom ribbon button in specific list for Sharepoint Online. Suppose that we have the following xml file with declaration of the ribbon button:

   1: <UserCustomAction Location="CommandUI.Ribbon"

   2:     Sequence="5" Title="Get tasks">

   3: <![CDATA[<CommandUIExtension>

   4:   <CommandUIDefinitions>

   5:     <CommandUIDefinition Location="Ribbon.Documents.Manage.Controls._children">

   6:       <Button Id="Ribbon.ListItem.Manage.GetTasks"

   7:         Alt="Get tasks"

   8:         Sequence="10001"

   9:         Command="Get tasks_Button"

  10:         Image32by32="/_layouts/images/rtrsendtoicon.png"

  11:         Image16by16="/_layouts/images/copy16.gif"

  12:         LabelText="Get tasks"

  13:         TemplateAlias="o1" />

  14:     </CommandUIDefinition>

  15:   </CommandUIDefinitions>

  16:   <CommandUIHandlers>

  17:    <CommandUIHandler Command="Get tasks_Button" CommandAction="javascript: GetTasks();" />

  18:   </CommandUIHandlers>

  19: </CommandUIExtension>]]>

  20: </UserCustomAction>

For more convenient work we create own class for that in order to be able to deserialize it from xml:

   1: public class UserCustomActionEntity

   2: {

   3:     [XmlAttribute("Location")]

   4:     public string Location;

   5:     [XmlAttribute("Sequence")]

   6:     public int Sequence;

   7:     [XmlAttribute("Title")]

   8:     public string Title;

   9:     [XmlText]

  10:     public string CommandUIExtension;

  11: }

With these preparations ribbon button can be created using the following code:

   1: var web = ...;

   2: var list = ...;

   3: var existingActions = list.UserCustomActions;

   4: web.Context.Load(existingActions);

   5: web.Context.ExecuteQueryRetry();

   6:  

   7: bool exists = false;

   8: foreach (var a in existingActions)

   9: {

  10:     if (string.Compare(a.Title, ac.Title, false) == 0)

  11:     {

  12:         exists = true;

  13:         break;

  14:     }

  15: }

  16:  

  17: if (exists)

  18: {

  19:     return;

  20: }

  21:  

  22: var action = existingActions.Add();

  23: action.Location = ac.Location;

  24: action.Sequence = ac.Sequence;

  25: action.Title = ac.Title;

  26: action.CommandUIExtension = ac.CommandUIExtension;

  27: action.Update();

  28: web.Context.ExecuteQuery();

Here we first check that same ribbon button is not added already by comparing titles (lines 7-20) and if not, add new custom ribbon button using data from xml declaration (lines 22-28).