C# 5.0 Programmer's Reference

324 ❘ CHAPTER 14 Collection Classes
A single ArrayList object can hold objects of many different kinds. For example, the following
code creates an ArrayList, adds several items of different types to it, and then loops through the
list displaying the values.
ArrayList list = new ArrayList();
list.Add("What");
list.Add(this);
list.Add(7331);
list.Add(new Bitmap(32, 32));
foreach (object obj in list)
Console.WriteLine(obj.ToString());
The following text shows the result.
What
WindowsFormsApplication1.Form1, Text: Form1
7331
System.Drawing.Bitmap
StringCollection
The System.Collections.Specialized namespace’s StringCollection class is similar to
ArrayList, except that it can hold only strings. Because it works only with strings, this class provides
some extra type checking that the ArrayList does not. For example, if your program tries to add an
Employee object or Bitmap to a StringCollection, the collection throws an exception.
A StringCollection can hold duplicate values and null values.
The following code shows how the UseStringCollection example program, which is available for
download on the book’s website, demonstrates a StringCollection.
// The values.
private StringCollection Values = new StringCollection();
// Add a value to the collection.
private void addButton_Click(object sender, EventArgs e)
{
Values.Add(valueTextBox.Text);
valueTextBox.Clear();
valueTextBox.Focus();
ListValues();
}
// Display the name/values groups.
private void ListValues()
{
valueListBox.Items.Clear();
foreach (string value in Values)
{
valueListBox.Items.Add(value);
}
}
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