var form = new CheckedListBoxFormLibrary().GetForm();

form.Text = "new title";
form.label1.Text = "new name";
form.button1.Text = "Ok";
form.button2.Text = "Cancel";
form.button3.Text = "Toggle Selection";
form.checkedListBox1.Items.Add("A");
form.checkedListBox1.Items.Add("B");
form.checkedListBox1.Items.Add("C");

// Changes the selection mode from single click to double-click (default is single click)
//form.checkedListBox1.CheckOnClick = false;

var result = form.ShowDialog();

if(result.ToString() == "Cancel") {
    sp.MessageBox("You clicked Cancel", "Cancel");

} else if(result.ToString() == "OK") {

    var allItemsCount = form.checkedListBox1.Items.Count; // how many items is in checkedListBox1
    var selItemsCount = form.checkedListBox1.CheckedItems.Count; // how many items are selected

    sp.MessageBox("All items: " + allItemsCount + "\nAll selected items: " + selItemsCount, "OK");

    // SHOW INDEX, TITLE AND STATE OF ONLY SELECTED ITEMS
    var itemChecked = form.checkedListBox1.CheckedItems;
    var indexChecked = form.checkedListBox1.CheckedIndices;
    for (i = 0; i < itemChecked.Count; i++) {
        sp.MessageBox("Index: " + indexChecked[i] + "\nTitle: " + itemChecked[i] + "\nState: " + form.checkedListBox1.GetItemCheckState(indexChecked[i]).ToString(), "SEL ITEMS i=" + i);
    }

    // SHOW INDEX, TITLE AND STATE OF ALL ITEMS
    var item = form.checkedListBox1.Items;
    for (i = 0; i < form.checkedListBox1.Items.Count; i++) {
        // index number is the same as "i"
        sp.MessageBox("Index: " + i + "\nTitle: " + item[i] + "\nState: " + form.checkedListBox1.GetItemCheckState(i).ToString(), "ALL ITEMS i=" + i);
    }
}