public class RibbonizedWebPart : WebPart {
  private string POSTBACK_EVENT = "RibbonizedWebPartPostback";

  protected override void CreateChildControls() {
    this.Controls.Add(
      new LiteralControl(
        "<em>Ribbonized Web Part contents go here</em>"
      )
    );

    // Handle postback from ribbon. 
    HandleRibbonPostback();
  }
}

private void HandleRibbonPostback() {
  if (this.Page.Request["__EVENTTARGET"] == POSTBACK_EVENT) {
    this.Controls.Add(
      new LiteralControl(
        "<p>Responding to postback event from ribbon.</p>"
      )
    );
  }
}

protected override void OnPreRender(EventArgs e) {
  LoadAndActivateRibbonContextualTab();
  base.OnPreRender(e);
}

private void LoadAndActivateRibbonContextualTab() {
  SPRibbon ribbon = SPRibbon.GetCurrent(this.Page);
  // Ensure ribbon exists.
  if (ribbon != null) {
    // Load dependencies if not already on the page.
    ScriptLink.RegisterScriptAfterUI(this.Page, 
      "SP.Ribbon.js", false, true);

    // Load and activate contextual tab.
    ribbon.MakeTabAvailable("Ribbon.PropertyChangerTab");
    ribbon.MakeContextualGroupInitiallyVisible(
      "Ribbon.WebPartContextualTabGroup", string.Empty);
  }
}

<?xml version="1.0" encoding="utf-8"?>
<Elements xmlns="http://schemas.microsoft.com/sharepoint/">
  <CustomAction Id="WebPartContextualTabs" Location="CommandUI.Ribbon">
    <CommandUIExtension>
      <CommandUIDefinitions>
        ...
      </CommandUIDefinitions>
      <CommandUIHandlers>
        <CommandUIHandler Command="WebPartContextualTab.OnEnableContextualTab"
          CommandAction=""
          EnabledScript="return true;" />
        <CommandUIHandler Command="WebPartContextualTabs.OnPostback"
          CommandAction="javascript:__doPostBack('RibbonizedWebPartPostback','');" />
      </CommandUIHandlers>
    </CommandUIExtension>
  </CustomAction>
</Elements>

// Register the page component object.
Type.registerNamespace('ApplyDocumentPrefix');

// Helper methods to set up and initialize the page component.
ApplyDocumentPrefix.ApplyDocumentPrefixPageComponent = function ApplyDocumentPrefix_PageComponent() {
  ApplyDocumentPrefix.ApplyDocumentPrefixPageComponent.initializeBase(this);
}

ApplyDocumentPrefix.ApplyDocumentPrefixPageComponent.initialize = function () {
  ExecuteOrDelayUntilScriptLoaded(Function.createDelegate(null, 
  ApplyDocumentPrefix.ApplyDocumentPrefixPageComponent.initializePageComponent), 'SP.Ribbon.js');
}

ApplyDocumentPrefix.ApplyDocumentPrefixPageComponent.initializePageComponent = function () {
  var ribbonPageManager = SP.Ribbon.PageManager.get_instance();
  if (ribbonPageManager !== null) {
    ribbonPageManager.addPageComponent(ApplyDocumentPrefix.ApplyDocumentPrefixPageComponent.instance);
  }
}

// Page component object.
ApplyDocumentPrefix.ApplyDocumentPrefixPageComponent.prototype = {

  init: function ApplyDocumentPrefix_PageComponento$init() {
    // Array of commands that can be handled that are associated with handler methods.
    this.handledCommands = new Object;
    this.handledCommands['ApplyDocumentPrefix.OnApplyDocPrefixPageComponent'] = 
    this.onApplyDocPrefixPageComponent;

    // Array of commands that can be handled that are associated with canHandler methods.
    this.canHandledCommands = new Object;
    this.canHandledCommands['ApplyDocumentPrefix.OnApplyDocPrefixPageComponent'] = 
    this.onApplyDocPrefixPageComponent_canExecute;

    // Array of commands.
    this.commandList = ['ApplyDocumentPrefix.OnApplyDocPrefixPageComponent'];
  },
  getId: function ApplyDocumentPrefixPageComponent_PageComponent$getId() {
    return "ApplyDocumentPrefixPageComponent";
  },  ...
}

ApplyDocumentPrefix.ApplyDocumentPrefixPageComponent.prototype = {
  ...
  getFocusedCommands: function ApplyDocumentPrefixPageComponent_PageComponent$getFocusedCommands() {
    return [];
  },

  getGlobalCommands: function ApplyDocumentPrefixPageComponent_PageComponent$getGlobalCommands() {
    return this.commandList;
  },

  canHandleCommand: function 
  ApplyDocumentPrefixPageComponent_PageComponent$canHandleCommand(commandID) {
    var canHandle = this.handledCommands[commandID];
    if (canHandle)
      return this.canHandledCommands[commandID]();
    else
      return false;
  },

  handleCommand: function 
  ApplyDocumentPrefixPageComponent_PageComponent$handleCommand(commandID, 
  properties, sequence) {
    return this.handledCommands[commandID](commandID, properties, sequence);
  },
  ...
}

ApplyDocumentPrefix.ApplyDocumentPrefixPageComponent.prototype = {
  ...
  onApplyDocPrefixPageComponent: function () {
    var selectedItems = SP.ListOperation.Selection.getSelectedItems();
    var selectedItemIds = '';
    var selectedItemIndex;
    for (selectedItemIndex in selectedItems) {
      selectedItemIds += '|' + selectedItems[selectedItemIndex].id;
    }

    var dialogOptions = {
      url: '/_layouts/ApplyDocumentPrefixRibbon/DocPrefixPrompt.aspx?selectedItems=' + 
      selectedItemIds + '&ListId=' + SP.ListOperation.Selection.getSelectedList(),
      title: 'Set Document Prefix',
      allowMaximize: false,
      showClose: false,
      width: 500,
      height: 400,
      dialogReturnValueCallback: PageComponentCallback
    };

    SP.UI.ModalDialog.showModalDialog(dialogOptions);
  },

  onApplyDocPrefixPageComponent_canExecute: function () {
    var selectedItems = SP.ListOperation.Selection.getSelectedItems();
    var count = CountDictionary(selectedItems);
    return (count > 0);
  }
  ...
}
function PageComponentCallback(dialogResult, returnValue) {
  SP.UI.Notify.addNotification(returnValue);
  SP.UI.ModalDialog.RefreshPage(SP.UI.DialogResult.OK);
}

ApplyDocumentPrefix.ApplyDocumentPrefixPageComponent.prototype = {
  ...
}
ApplyDocumentPrefix.ApplyDocumentPrefixPageComponent.registerClass
('ApplyDocumentPrefix.ApplyDocumentPrefixPageComponent', 
CUI.Page.PageComponent);
ApplyDocumentPrefix.ApplyDocumentPrefixPageComponent.instance = 
new ApplyDocumentPrefix.ApplyDocumentPrefixPageComponent();
ApplyDocumentPrefix.ApplyDocumentPrefixPageComponent.initialize();
SP.SOD.notifyScriptLoadedAndExecuteWaitingJobs("ApplyDocumentPrefix.UI.js");

<%@ Register TagPrefix="wssuc" TagName="InputFormSection" 
Src="~/_controltemplates/InputFormSection.ascx" %>
<%@ Register TagPrefix="wssuc" TagName="InputFormControl" 
src="~/_controltemplates/InputFormControl.ascx" %>
<%@ Register TagPrefix="wssuc" TagName="ButtonSection" 
Src="~/_controltemplates/ButtonSection.ascx" %>

<asp:Content ID="Main" ContentPlaceHolderID="PlaceHolderMain" runat="server">
  <table border="0" cellspacing="0" cellpadding="0" width="100%">
    <tr>
      <td>
        <wssuc:InputFormSection runat="server" 
                                Title="Selected Documents" 
                                Description="The following documents have been selected 
                                to have the specified prefix added to their titles.">
          <Template_InputFormControls>
                        <tr>
                          <td>
                            <asp:DataList ID="SelectedDocumentsDataList" runat="server"
                            RepeatColumns="2" CellPadding="2" CellSpacing="5">
                  <ItemTemplate><li><%# DataBinder.Eval(Container.DataItem, 
                  "File.Name").ToString()%></li></ItemTemplate>
                </asp:DataList>
                          </td>
                        </tr>
                  </Template_InputFormControls>
        </wssuc:InputFormSection>

        <wssuc:InputFormSection runat="server" 
                                Title="Document Prefix" 
                                Description="Prefix to add to the selected document 
                                titles.">
          <Template_InputFormControls>
            <wssuc:InputFormControl LabelText="Prefix to add to the selected documents:"
            runat="server">
              <Template_control>
                <asp:TextBox ID="DocumentPrefixTextBox" runat="server" />
              </Template_control>
            </wssuc:InputFormControl>
                  </Template_InputFormControls>
        </wssuc:InputFormSection>

        <wssuc:ButtonSection runat="server" ShowStandardCancelButton="FALSE" 
        TopButtons="TRUE">
          <Template_Buttons>
            <asp:Button ID="SetPrefixButton" class="ms-ButtonHeightWidth" runat="server" 
            Text="Set Prefix" OnClick="OnClickSetPrefixButton" />
            <asp:Button ID="CancelButton" class="ms-ButtonHeightWidth" runat="server" 
            Text="Cancel" OnClientClick=
            "SP.UI.ModalDialog.commonModalDialogClose(SP.UI.DialogResult.cancel,
            'Assignment of prefix cancelled.'); return false;" />
          </Template_Buttons>
        </wssuc:ButtonSection>
      </td>
    </tr>
  </table>
</asp:Content>

public partial class DocPrefixPrompt : LayoutsPageBase {
  List<SPListItem> _selectedListItems = new List<SPListItem>();

  protected override void OnLoad(EventArgs e) {
    // Get all the selected documents.
    SPList selectedDocumentLibrary = 
        SPContext.Current.Web.Lists[new Guid(
                  Request.QueryString["ListId"]
        )];
    string[] selectedItems = 
      Request.QueryString["selectedItems"].ToString().Split('|');

    for (int index = 1; index < selectedItems.Length; index++) {
      _selectedListItems.Add(
        selectedDocumentLibrary.GetItemById(
          int.Parse(selectedItems[index]))
      );
    }

    // Bind to the repeater.
    SelectedDocumentsDataList.DataSource = _selectedListItems;
    SelectedDocumentsDataList.DataBind();
  }

  protected void OnClickSetPrefixButton(object sender, EventArgs e) {
    foreach (SPListItem listItem in _selectedListItems) {
      listItem["Name"] = 
        DocumentPrefixTextBox.Text + " " + listItem.File.Name;
      listItem.Update();
    }

    CloseDialogOnSuccess();
  }
  private void CloseDialogOnSuccess() {
    ContentPlaceHolder pageHead = this.Master.FindControl("PlaceHolderAdditionalPageHead") as ContentPlaceHolder;
    if (pageHead != null)
      pageHead.Controls.Add(
        new LiteralControl("
<script language='javascript'>
ExecuteOrDelayUntilScriptLoaded(closeDialog,'sp.js');
function closeDialog(){
  SP.UI.ModalDialog.commonModalDialogClose(SP.UI.DialogResult.OK, 'Prefix assigned to selected documents.');
}
</script>"));
  }
}