WinForms ListView Performance - Initializing checked states

CheckBoxes in a WinForms ListView are of course a bit simpler to use than dealing the underlying Win32 control directly. WinForms deals with the ListView structures and the WM_NOTIFY messages. Of course this comes at a cost. Here's a simple demonstration of how to tweak things for better performance. This is a simple example so the gains aren't monumental but when you add real world complexities to the Checked event handler and the computation of the Checked state of an item. There are real noticeable improvements by paying attention to some simple things.

When you are populating a ListView that has CheckBoxes, you really want to set the Checked property of the ListViewItem before you add it to the list. The reason is that once you have added the item to the ListView.Items collection, WinForms will always defer to the underlying Win32 control to query and set the Checked state of the item. Before it's added to the ListView the ListViewItem maintains the state itself. Calling down into the Win32 control is very expensive since it involved PInvoking SendMessage.

There are 5 examples with steady gains in improvement.

 using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
 
namespace ListViewPerf
{
    public partial class Form1 : Form
    {
        const int ListEntryCount = 5000;
        static int seed = 7919;         //  use a constant for repeatable results
 
        String[] strings;
        bool[] checksInit;
        DateTime start;
        int checkedEvents;
 
        public Form1()
        {
            Random rand = new Random(seed);
            strings = new String[ListEntryCount];
            checksInit = new bool[ListEntryCount];
 
            for (int i = 0; i < ListEntryCount; i++)
            {
                strings[i] = rand.Next().ToString();
                checksInit[i] = (rand.Next() % 2) == 0;
            }
 
            InitializeComponent();
        }
 
        void PreCall()
        {
            listView1.Items.Clear();
            checkedEvents = 0;
            start = DateTime.Now;
        }
 
        void PostCall(string s)
        {
            TimeSpan ts = DateTime.Now - start;
 
            MessageBox.Show(s + " took " + ts.TotalMilliseconds.ToString() + " milliseconds\nAnd generated " + checkedEvents.ToString() + " Checked events");
        }
 
        enum CheckMode { Before, After, AfterWithTest }
 
        void FillListViewWithStrings(CheckMode checkMode)
        {
            for (int i = 0; i < ListEntryCount; i++)
            {
                ListViewItem lvi = new ListViewItem(strings[i]);
                bool check = checksInit[i];
 
                switch (checkMode)
                {
                    case CheckMode.After:
                        listView1.Items.Add(lvi);
                        lvi.Checked = check;
                        break;
 
                    case CheckMode.Before:
                        lvi.Checked = check;
                        listView1.Items.Add(lvi);
                        break;
 
                    case CheckMode.AfterWithTest:
                        listView1.Items.Add(lvi);
                        if (check)
                        {
                            lvi.Checked = check;
                        }
                        break;
                }
            }
        }
 
        private void checkAfter_Click(object sender, EventArgs e)
        {
            PreCall();
 
            FillListViewWithStrings(CheckMode.After);
 
            PostCall("Check After");
        }
 
        private void checkAfterTest_Click(object sender, EventArgs e)
        {
            PreCall();
 
            FillListViewWithStrings(CheckMode.AfterWithTest);
 
            PostCall("Check After With Test");
        }
 
        private void checkBefore_Click(object sender, EventArgs e)
        {
            PreCall();
 
            FillListViewWithStrings(CheckMode.Before);
 
            PostCall("Check Before");
        }
 
        ListViewItem[] BuildListViewItems(bool setChecks)
        {
            ListViewItem[] items = new ListViewItem[ListEntryCount];
 
            if (setChecks)
            {
                for (int i = 0; i < ListEntryCount; i++)
                {
                    items[i] = new ListViewItem(strings[i]);
                    items[i].Checked = checksInit[i];
                }
            }
            else
            {
                for (int i = 0; i < ListEntryCount; i++)
                {
                    items[i] = new ListViewItem(strings[i]);
                }
            }                
 
            return items;
        }
 
        private void addRangeAfter_Click(object sender, EventArgs e)
        {
            PreCall();
 
            ListViewItem[] items = BuildListViewItems(false);
            listView1.Items.AddRange(items);
            
            for (int i = 0; i < ListEntryCount; i++)
            {
                listView1.Items[i].Checked = checksInit[i];
            }
 
            PostCall("AddRange After");
        }
 
        private void addRangeBefore_Click(object sender, EventArgs e)
        {
            PreCall();
 
            ListViewItem[] items = BuildListViewItems(true);
            listView1.Items.AddRange(items);
 
            PostCall("AddRange Before");
        }
 
        private void listView1_ItemChecked(object sender, ItemCheckedEventArgs e)
        {
            checkedEvents++;
        }
 
    }
}