Visual Basic intrinsic controls

The Pointer isn't a control; click this icon when you want to select controls already on the form rather than create new ones.

The PictureBox control is used to display images in any of the following formats: BMP, DIB (bitmap), ICO (icon), CUR (cursor), WMF (metafile), EMF (enhanced metafile), GIF, and JPEG.

The Label control serves to display static text or text that shouldn't be edited by the user; it's often used to label other controls, such as TextBox controls.

The TextBox control is a field that contains a string of characters that can be edited by the user. It can be single-line (for entering simple values) or multiline (for memos and longer notes). This is probably the most widely used control of any Windows application and is also one of the richest controls in terms of properties and events.

The Frame control is typically used as a container for other controls. You rarely write code that reacts to events raised by this control.

The CommandButton control is present in almost every form, often in the guise of the OK and Cancel buttons. You usually write code in the Click event procedure of this control.

The CheckBox control is used when the user has to make a yes/no, true/false selection.

OptionButton controls are always used in groups, and you can select only one control in the group at a time. When the user selects a control in the group, all other controls in the group are automatically deselected. OptionButton controls are useful for offering to the user a number of mutually exclusive selections. If you want to create two or more groups of OptionButton controls on a form, you must place each group inside another container control (most often a Frame control). Otherwise, Visual Basic can't understand which control belongs to which group.

The ListBox control contains a number of items, and the user can select one or more of them (depending on the value of the control's MultiSelect property).

The ComboBox control is a combination of a TextBox and a ListBox control, with the difference that the list portion is visible only if the user clicks on the down arrow to the right of the edit area. ComboBox controls don't support multiple selections.

The HScrollBar and VScrollBar controls let you create stand-alone scroll bars. These controls are used infrequently because the majority of other controls display their own scroll bars if necessary. Stand-alone scroll bars are sometimes used as sliders, but in this case you'd better use other, more eye-catching controls, such as the Slider control, which is covered in Chapter 10.

The Timer control is peculiar in that it isn't visible at run time. Its only purpose is to regularly raise an event in its parent form. By writing code in the corresponding event procedure, you can perform a task in the background—for instance, updating a clock or checking the status of a peripheral device.

The DriveListBox, DirListBox, and FileListBox controls are often used together to create file-oriented dialog boxes. DriveListBox is a ComboBox-like control filled automatically with the names of all the drives in the system. DirListBox is a variant of the ListBox control; it shows all the subdirectories of a given directory. FileListBox is another special ListBox control; this control fills automatically with names of the files in a specified directory. While these three controls offer a lot of functionality, in a sense they have been superseded by the Common Dialog control, which displays a more modern user interface (to be covered in Chapter 12). If you want to write applications that closely conform to the Windows 9x look, you should avoid using these controls.

The Shape and Line controls are mostly cosmetic controls that never raise any events and are used only to display lines, rectangles, circles, and ovals on forms or on other designers.

The Image control is similar to the PictureBox control, but it can't act as a container for other controls and has other limitations as well. Nevertheless, you should use an Image control in place of a PictureBox control whenever possible because Image controls consume fewer system resources.

The Data control is the key to data binding, a Visual Basic feature that lets you connect one or more controls on a form to fields in a database table. The Data control works with Jet databases even though you can also use attached tables to connect to data stored in databases stored in other formats. But it can't work with ActiveX Data Objects (ADO) sources and is therefore not suitable for exploiting the most interesting database-oriented Visual Basic 6 features.

The OLE control can host windows belonging to external programs, such as a spreadsheet window generated by Microsoft Excel. In other words, you can make a window provided by another program appear as if it belongs to your Visual Basic application.