The DateTimePicker Class The GroupBox Class The ImageList Class

188 The CheckBox classs Checked property can be set to True to make the checkbox checked or False to uncheck it.

5.1.3 The ComboBox Class

Both the ComboBox and ListBox classes derive from the ListControl class; therefore, the ComboBox class is very similar to the ListBox class and has properties and methods similar to those of the ListBox class. Refer to Sect ion 5.1.9 for information on these common properties and methods. The following properties are specific to the ComboBox class: DropDownStyle Defines the drop-down style of the ComboBox. It can take any value of the ComboBoxStyle enumeration: DropDown the default value, DropDownList , and Simple . Both DropDown and DropDownList require the user to click the arrow button to display the drop-down portion of the ComboBox; however, DropDown allows the user to edit the text portion of the ComboBox. Simple makes a ComboBoxs text portion editable and its drop-down portion always visible. DroppedDown Specifies whether the drop-down portion of a ComboBox is visible.

5.1.4 The DateTimePicker Class

The DateTimePicker class represents a control that allows users to select a date in the calendar, just like the MonthCalendar control. Unlike MonthCalendar, however, the DateTimePicker control only displays a box, which looks like a combo box, containing the selected date. When the user clicks the arrow, the control displays a drop-down calendar similar to the MonthCalendar control, from which the user can select a date. This drop-down portion closes as soon as the user selects a date. The user can also click on the day, date, month, or year portion of the control for editing. The DateTimePicker class has MinDate and MaxDate properties that are similar to the ones in the MonthCalendar class. To set the current date or to obtain the selected date, use the Value property of the DateTimePicker class. The selected date is readily available as a DateTime data type.

5.1.5 The GroupBox Class

As the name implies, a GroupBox control is used for grouping other controls, such as radio buttons or checkboxes; it corresponds to the Frame control in Visual Basic 6.0. A GroupBox grouping two radio buttons is shown in Figur e 5- 2 . Figure 5-2. A GroupBox grouping two radio buttons The Controls property of GroupBox represents a Control.ControlCollection class. It has methods such as Add, AddRange, Clear, GetEnumerator, and Remove, which behave exactly as do the same 189 methods in Form.ControlCollection. For example, you can add several controls at once to a GroupBox using its AddRange method, as demonstrated by the following code that adds two radio buttons to a GroupBox named groupBox1: groupBox1.Controls.AddRangeNew Control {radioButton1, radioButton2}

5.1.6 The ImageList Class

The ImageList class allows you to manage a collection of images. The most important property of this class is Images, which returns an ImageList.ImageCollection object. The ImageList.ImageCollection class has methods to add and remove images from the collection. The Add method of the ImageList.ImageCollection class adds a bitmap image or an icon to the ImageLists image collection. The Add method has three overloads, whose signatures are given as follows: Overloads Public Sub Add ByVal value As System.Drawing.Icon Overloads Public Sub Add ByVal value As System.Drawing.Image Overloads Public Sub Add ByVal value As System.Drawing.Image, _ ByVal transparentColor as System.Drawing.Color The first overload allows you to add an icon, and the second overload is used to add an object of type System.Drawing.Image. The third overload is used to add an image and make a color of that image transparent. For example, if you have an image with a blue background color, you can make the added image transparent by passing a blue color as the second argument to the third overload of the Add method. The RemoveAt method of the ImageList.ImageCollection class allows you to remove an image. Once you instantiate an ImageList object, you can start adding images or icons. The following code, for example, adds three images and icons using three different overloads of the Add method: Imports System.Drawing Dim imageList1 As ImageList1 = New ImageList ImageList1.Images.AddNew IconC:\Palm.ico ImageList1.Images.AddNew BitmapC:\TV.bmp ImageList1.Images.AddNew BitmapC:\Dog.bmp, Color.White Important properties of the ImageList class include ColorDepth and ImageSize. The ColorDepth property determines the number of colors available for the ImageList. For example, a value of 4 means that 24 = 16 colors are available. The ImageSize property determines the sizes of all images in the list. By default, the value is System.Drawing.Size16, 16. You can assign an ImageList object to the ImageList property of controls such as Label, Button, and ListView. You can then select an image from the ImageList to be displayed on the control using the controls ImageIndex property. For example, the following code uses an ImageList for a button and selects the first image as the background image for the button: button1.ImageList = imageList1 button1.ImageIndex = 0

5.1.7 The Label Class