Component and ISupportInitialize: A Quick Guide

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Introduction

Ever wanted to create a control like ErrorProvider that sits in the non-UI portion of the UI designer and does stuff? It's fairly easy. I'll show an example here of how to derive from Component and another helpful interface, ISupportInitialize.

Component

The reason ErrorProvider sits in the non-UI part of the designer is because it is a Component. A Component is the base class for all MarshalByRefObjects in the CLR. Other things that derive from Component are ToolTip, Control, HelpProvider, ImageList, and Menu.

The Component also exposes the site to a container and allows them to communicate. A Component can be placed "in any object that implements the IContainer interface, and can query and get services from its container".

Let's say, I wanted to write a component that would sit in the non-UI part of the designer (does anyone know what the heck that's called?) and after all the initialization is complete at run-time, it would fix the tab ordering automatically. Now, here the tab ordering algorithm is trivial, so let's assume it works. (Thanks to Scott McMaster, who wrote this article and was the inspiration for this article. Sorry about hacking up your TabOrderManager so bad.)

using System;
using System.Collections;
using System.Diagnostics;
using System.Windows.Forms;
using System.ComponentModel;
using System.Collections.Specialized;

namespace ComponentTest
{
    public class TabOrderManager : Component, ISupportInitialize
    {
        public void SetTabOrder()
        {
            ...
        }

        // ISupportInitialize members
        public void BeginInit()
        {
        }

        public void EndInit()
        {
            this.SetTabOrder();
        }
    }
}

Once you slap this on your form (and assign your form to the ContainerControl property), you should notice that something funny has happened in InitializeComponent():

private void InitializeComponent()
{
    this.tabOrderManager = new ComponentTest.TabOrderManager();
    ...
    ((System.ComponentModel.ISupportInitialize)(this.tabOrderManager)).BeginInit();
    this.SuspendLayout();
    ...
    this.Controls.Add(...);
    ((System.ComponentModel.ISupportInitialize)(this.tabOrderManager)).EndInit();
    this.ResumeLayout(false);
}

ISupportInitialize adds these things in InitializeComponent automatically. Normally, they are for transacted notification of when batch initialization has started and finished. Now, when the TabOrderManager.EndInit() is called, it sets the tab index of all the components on the form.