ButtonMod.cs

using ColossalFramework.UI;
using ICities;
using UnityEngine;

namespace ButtonMod
{
  public class ButtonMod : IUserMod
  {
    public string Name { get { return "Button"; } }
    public string Description { get { return "Shows a button"; } }
  }

  public class LoadingExtension : LoadingExtensionBase
  {
    public override void OnLevelLoaded(LoadMode mode)
    {
      // Get the UIView object. This seems to be the top-level object for most
      // of the UI.
      var uiView = UIView.GetAView();

      // Add a new button to the view.
      var button = (UIButton)uiView.AddUIComponent(typeof(UIButton));

      // Set the text to show on the button.
      button.text = "Click Me!";

      // Set the button dimensions.
      button.width = 100;
      button.height = 30;

      // Style the button to look like a menu button.
      button.normalBgSprite = "ButtonMenu";
      button.disabledBgSprite = "ButtonMenuDisabled";
      button.hoveredBgSprite = "ButtonMenuHovered";
      button.focusedBgSprite = "ButtonMenuFocused";
      button.pressedBgSprite = "ButtonMenuPressed";
      button.textColor = new Color32(255, 255, 255, 255);
      button.disabledTextColor = new Color32(7, 7, 7, 255);
      button.hoveredTextColor = new Color32(7, 132, 255, 255);
      button.focusedTextColor = new Color32(255, 255, 255, 255);
      button.pressedTextColor = new Color32(30, 30, 44, 255);

      // Enable button sounds.
      button.playAudioEvents = true;

      // Place the button.
      button.transformPosition = new Vector3(-1.65f, 0.97f);

      // Respond to button click.
      button.eventClick += ButtonClick;
    }

    private void ButtonClick(UIComponent component, UIMouseEventParameter eventParam)
    {
      // Do something
    }
  }
}