Creating a zoom factor extension that works with a ToolbarControl
Application\ToolbarControlExtension.cs
// Copyright 2010 ESRI
// 
// All rights reserved under the copyright laws of the United States
// and applicable international laws, treaties, and conventions.
// 
// You may freely redistribute and use this sample code, with or
// without modification, provided you include the original copyright
// notice and use restrictions.
// 
// See the use restrictions.
// 

using System;
using System.Windows.Forms;
using ESRI.ArcGIS.SystemUI;
using ESRI.ArcGIS.esriSystem;
using ESRI.ArcGIS;
using Microsoft.Win32;


namespace ToolbarControlExtension
{
  public class Form1 : System.Windows.Forms.Form
  {
    private System.ComponentModel.Container components = null;
    public System.Windows.Forms.CheckBox chkExtension;
    public System.Windows.Forms.Label Label3;
    public System.Windows.Forms.Label Label1;
    public System.Windows.Forms.Label Label2;
    private ESRI.ArcGIS.Controls.AxToolbarControl axToolbarControl1;
    private ESRI.ArcGIS.Controls.AxMapControl axMapControl1;
    private ESRI.ArcGIS.Controls.AxLicenseControl axLicenseControl1;
    private IExtensionManagerAdmin m_ExtensionManagerAdmin;

    public Form1()
    {
      //
      // Required for Windows Form Designer support
      //
      InitializeComponent();

      //
      // TODO: Add any constructor code after InitializeComponent call
      //
    }

    protected override void Dispose( bool disposing )
    {

      if( disposing )
      {
        if (components != null) 
        {
          components.Dispose();
        }
      }
      base.Dispose( disposing );
    }

    #region Windows Form Designer generated code

    private void InitializeComponent()
    {
            System.ComponentModel.ComponentResourceManager resources = new System.ComponentModel.ComponentResourceManager(typeof(Form1));
            this.chkExtension = new System.Windows.Forms.CheckBox();
            this.Label3 = new System.Windows.Forms.Label();
            this.Label1 = new System.Windows.Forms.Label();
            this.Label2 = new System.Windows.Forms.Label();
            this.axToolbarControl1 = new ESRI.ArcGIS.Controls.AxToolbarControl();
            this.axMapControl1 = new ESRI.ArcGIS.Controls.AxMapControl();
            this.axLicenseControl1 = new ESRI.ArcGIS.Controls.AxLicenseControl();
            ((System.ComponentModel.ISupportInitialize)(this.axToolbarControl1)).BeginInit();
            ((System.ComponentModel.ISupportInitialize)(this.axMapControl1)).BeginInit();
            ((System.ComponentModel.ISupportInitialize)(this.axLicenseControl1)).BeginInit();
            this.SuspendLayout();
            // 
            // chkExtension
            // 
            this.chkExtension.BackColor = System.Drawing.SystemColors.Control;
            this.chkExtension.Cursor = System.Windows.Forms.Cursors.Default;
            this.chkExtension.Font = new System.Drawing.Font("Arial", 8F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((byte)(0)));
            this.chkExtension.ForeColor = System.Drawing.SystemColors.ControlText;
            this.chkExtension.Location = new System.Drawing.Point(592, 8);
            this.chkExtension.Name = "chkExtension";
            this.chkExtension.RightToLeft = System.Windows.Forms.RightToLeft.No;
            this.chkExtension.Size = new System.Drawing.Size(113, 25);
            this.chkExtension.TabIndex = 6;
            this.chkExtension.Text = "Enable Extension";
            this.chkExtension.UseVisualStyleBackColor = false;
            this.chkExtension.CheckedChanged += new System.EventHandler(this.chkExtension_CheckedChanged);
            // 
            // Label3
            // 
            this.Label3.BackColor = System.Drawing.SystemColors.Control;
            this.Label3.Cursor = System.Windows.Forms.Cursors.Default;
            this.Label3.Font = new System.Drawing.Font("Arial", 8F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((byte)(0)));
            this.Label3.ForeColor = System.Drawing.SystemColors.ControlText;
            this.Label3.Location = new System.Drawing.Point(592, 136);
            this.Label3.Name = "Label3";
            this.Label3.RightToLeft = System.Windows.Forms.RightToLeft.No;
            this.Label3.Size = new System.Drawing.Size(137, 65);
            this.Label3.TabIndex = 9;
            this.Label3.Text = "Enable the extension and navigate around the data using the commands from the ext" +
                "ension.";
            // 
            // Label1
            // 
            this.Label1.BackColor = System.Drawing.SystemColors.Control;
            this.Label1.Cursor = System.Windows.Forms.Cursors.Default;
            this.Label1.Font = new System.Drawing.Font("Arial", 8F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((byte)(0)));
            this.Label1.ForeColor = System.Drawing.SystemColors.ControlText;
            this.Label1.Location = new System.Drawing.Point(592, 88);
            this.Label1.Name = "Label1";
            this.Label1.RightToLeft = System.Windows.Forms.RightToLeft.No;
            this.Label1.Size = new System.Drawing.Size(137, 41);
            this.Label1.TabIndex = 8;
            this.Label1.Text = "Navigate around the data using the commands on the ToolbarControl.";
            // 
            // Label2
            // 
            this.Label2.BackColor = System.Drawing.SystemColors.Control;
            this.Label2.Cursor = System.Windows.Forms.Cursors.Default;
            this.Label2.Font = new System.Drawing.Font("Arial", 8F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((byte)(0)));
            this.Label2.ForeColor = System.Drawing.SystemColors.ControlText;
            this.Label2.Location = new System.Drawing.Point(592, 40);
            this.Label2.Name = "Label2";
            this.Label2.RightToLeft = System.Windows.Forms.RightToLeft.No;
            this.Label2.Size = new System.Drawing.Size(137, 40);
            this.Label2.TabIndex = 7;
            this.Label2.Text = "Browse to a map document to load into the MapControl.";
            // 
            // axToolbarControl1
            // 
            this.axToolbarControl1.Location = new System.Drawing.Point(8, 8);
            this.axToolbarControl1.Name = "axToolbarControl1";
            this.axToolbarControl1.OcxState = ((System.Windows.Forms.AxHost.State)(resources.GetObject("axToolbarControl1.OcxState")));
            this.axToolbarControl1.Size = new System.Drawing.Size(576, 28);
            this.axToolbarControl1.TabIndex = 10;
            // 
            // axMapControl1
            // 
            this.axMapControl1.Location = new System.Drawing.Point(8, 40);
            this.axMapControl1.Name = "axMapControl1";
            this.axMapControl1.OcxState = ((System.Windows.Forms.AxHost.State)(resources.GetObject("axMapControl1.OcxState")));
            this.axMapControl1.Size = new System.Drawing.Size(576, 432);
            this.axMapControl1.TabIndex = 11;
            // 
            // axLicenseControl1
            // 
            this.axLicenseControl1.Enabled = true;
            this.axLicenseControl1.Location = new System.Drawing.Point(595, 204);
            this.axLicenseControl1.Name = "axLicenseControl1";
            this.axLicenseControl1.OcxState = ((System.Windows.Forms.AxHost.State)(resources.GetObject("axLicenseControl1.OcxState")));
            this.axLicenseControl1.Size = new System.Drawing.Size(32, 32);
            this.axLicenseControl1.TabIndex = 12;
            // 
            // Form1
            // 
            this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
            this.ClientSize = new System.Drawing.Size(736, 478);
            this.Controls.Add(this.axLicenseControl1);
            this.Controls.Add(this.axMapControl1);
            this.Controls.Add(this.axToolbarControl1);
            this.Controls.Add(this.chkExtension);
            this.Controls.Add(this.Label3);
            this.Controls.Add(this.Label1);
            this.Controls.Add(this.Label2);
            this.Name = "Form1";
            this.Text = "MenuTracking";
            this.Load += new System.EventHandler(this.Form1_Load);
            ((System.ComponentModel.ISupportInitialize)(this.axToolbarControl1)).EndInit();
            ((System.ComponentModel.ISupportInitialize)(this.axMapControl1)).EndInit();
            ((System.ComponentModel.ISupportInitialize)(this.axLicenseControl1)).EndInit();
            this.ResumeLayout(false);

    }
    #endregion

    [STAThread]
    static void Main() 
    {
            
            if (!RuntimeManager.Bind(ProductCode.Engine))
            {
                if (!RuntimeManager.Bind(ProductCode.Desktop))
                {
                    MessageBox.Show("Unable to bind to ArcGIS runtime. Application will be shut down.");
                    return;
                }
            }

      Application.Run(new Form1());
    }

    private void Form1_Load(object sender, System.EventArgs e)
    {
      //Set buddy control
      axToolbarControl1.SetBuddyControl(axMapControl1.Object);

      //Add control command items to the ToolbarControl
      axToolbarControl1.AddItem("esriControls.ControlsOpenDocCommand",-1,-1,false,0,esriCommandStyles.esriCommandStyleIconOnly);
      axToolbarControl1.AddItem("esriControls.ControlsMapZoomInTool",-1,-1,true,0,esriCommandStyles.esriCommandStyleIconOnly);
      axToolbarControl1.AddItem("esriControls.ControlsMapZoomOutTool",-1,-1,false,0,esriCommandStyles.esriCommandStyleIconOnly);
      axToolbarControl1.AddItem("esriControls.ControlsMapPanTool",-1,-1,false,0,esriCommandStyles.esriCommandStyleIconOnly);
      //Add extension command items to the ToolbarControl
      axToolbarControl1.AddItem("ZoomFactorExtensionCSharp.SetZoomFactor",-1,-1,true,0,esriCommandStyles.esriCommandStyleIconAndText);
      axToolbarControl1.AddItem("ZoomFactorExtensionCSharp.ZoomIn",-1,-1,true,0,esriCommandStyles.esriCommandStyleIconAndText);
      axToolbarControl1.AddItem("ZoomFactorExtensionCSharp.ZoomOut",-1,-1,true,0,esriCommandStyles.esriCommandStyleIconAndText);

      //Get the extension manager admin
      m_ExtensionManagerAdmin = (IExtensionManagerAdmin) new ExtensionManagerClass();

      //Add the extension to the extension manager
      UID uID = new UIDClass();
      uID.Value = "ZoomFactorExtensionCSharp.ZoomExtension";
      object obj = new object();
      m_ExtensionManagerAdmin.AddExtension(uID, ref obj);
    }

    private void chkExtension_CheckedChanged(object sender, System.EventArgs e)
    {
      //Get the extension manager
      IExtensionManager extensionManager = (IExtensionManager) m_ExtensionManagerAdmin;
      //Get the extension from the extension manager
      IExtensionConfig extensionConfig = (IExtensionConfig) extensionManager.FindExtension("Zoom Factor Extension");
      //Set the enabled state
      if (chkExtension.CheckState == CheckState.Checked) extensionConfig.State = esriExtensionState.esriESEnabled;
      else extensionConfig.State = esriExtensionState.esriESDisabled;
    }

  }
}