Chapter 6

Basic Windows Controls

In the previous chapters, we explored the environment of Visual Basic and the principles of event-driven programming, which is the core of VB’s programming model. In the process, we briefly explored a few basic controls through the examples. The .NET Framework provides many more controls, and all of them have a multitude of properties. Most of the properties have obvious names, and you can set them either from the Properties window or from within your code.

This chapter explores several of the basic Windows controls in depth. These are the controls you’ll be using most often in your applications because they are the basic building blocks of the Windows user interface.

Rather than look at controls’ background and foreground color, font, and other trivial properties, we’ll look at the properties unique to each control and how these properties are used in building a user interface.

Note This chapter doesn’t present every property and every method of the basic Windows controls. That would take another book, and its value would be questionable. Most properties are quite simple to use and easy to understand (and then there are some you’ll never use). This chapter focuses on the unique properties, methods, and events of each control you need to know, in order to use them in your user interface.

The TextBox Control

The TextBox control is the primary mechanism for displaying and entering text and is one of the most common elements of the Windows user interface. The TextBox control is a small text editor that provides all the basic text-editing facilities: inserting and selecting text, scrolling if the text doesn’t fit in the control’s area, and even exchanging text with other applications through the Clipboard.

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VB6 VB.NET

The VB.NET TextBox control is very similar to the one in VB6, with a major improvement. The old TextBox control couldn’t handle large chunks of text. It could handle up to 32K characters, and this was a serious limitation. The new TextBox control can hold more than 2 billion characters, which is more than you care to read in a single session.

The WordWrap property allows you to specify whether the control will wrap text lines as they approach the width of the control. In the old version of the control, the ScrollBars property determined whether the control wraps the text. Without a horizontal ScrollBar, the text was wrapped automatically. Now, you can enter long lines of text even if no horizontal scroll bar is present.

Another feature of the new TextBox control is that it allows you to access individual lines of text through the Lines property. The Lines property is a string array, and each element of the array holds a text line. Lines(0) is the first line, Lines(1) is the second line, and so on. The number of text lines on the control is given by the expression Lines.Length.

Finally, the properties that let you select or manipulate text—the SelStart, SelLength, and SelText proper- ties—have changed names. They’re now called SelectionStart, SelectionLength, and SelectedText. The Alignment property, which specifies the alignment of the text on the control, is now called TextAlignment. The AppendText method lets you add text to the control, and it’s much faster than the equivalent statement

TextBox1.Text = TextBox1.Text & newLine

The text box is an extremely versatile data-entry tool that can be used for entering a single line of text, such as a number or a password, or for entering simple text files. Figure 6.1 shows a few typical examples created with the TextBox control. All the boxes in Figure 6.1 contain text—some a single line, some several lines. The scroll bars you see in some text boxes are part of the control. You can specify which scroll bars (vertical and/or horizontal) will appear on the control, and the appropriate scroll bars are attached to the control automatically whenever the control’s contents exceed the visible area of the control.

With the exception of graphics applications, the TextBox control is the bread and butter of any Windows application. By examining its properties and designing a text editor based on the TextBox control, you’ll see that most of the application’s functionality is already built into the control.

Figure 6.1

Typical uses of the

TextBox control

THE TEXTBOX CONTROL 243

Basic Properties

Let’s start with the properties that determine the appearance and, to some degree, the functionality of the TextBox control; these can be set through the Properties window. Then, we’ll look at the properties that allow you to manipulate the control’s contents. Let me mention quickly the TextAlign property, which sets (or returns) the alignment of the text on the control and can be Left, Right, or Center. The TextBox control doesn’t allow you to format text, but you can set the font in which the text will be displayed with the Font property, as well as the control’s background color with the BackColor property. If you want to display a background image, use the BackImage property and assign to it the path of the file with the desired image.

MultiLine

This property determines whether the TextBox control will hold a single line or multiple lines of text. By default, the control holds a single line of text. To change this behavior, set the MultiLine property to True.

ScrollBars

This property controls the attachment of scroll bars to the TextBox control if the text exceeds the control’s dimensions. Single-line text boxes can’t have a scroll bar attached, even if the text exceeds the width of the control. Multiline text boxes can have a horizontal or a vertical scroll bar, or both.

Scroll bars can appear in multiline text boxes even if they aren’t needed or the text doesn’t exceed the dimensions of the control.

If you attach a horizontal scroll bar to the TextBox control, the text won’t wrap automatically as the user types. To start a new line, the user must press Enter. This arrangement is useful in implementing editors for programs in which lines must break explicitly. If the horizontal scroll bar is missing, the control inserts soft line breaks when the text reaches the end of a line, and the text is wrapped automatically. You can change the default behavior by setting the WordWrap property.

WordWrap

This property determines whether the text is wrapped automatically when it reaches the right edge of the control. The default value of this property is True. If the control has a horizontal scroll bar, however, you can enter very long lines of text. The contents of the control will scroll to the left, so that the insertion point is always visible as you type. You can turn off the horizontal

scroll bar and still enter long lines of text; just use the left/right arrows to bring any part of the text into view.

This feature may seem dubious at first, but you’ll find it useful when you resize the control. By the way, it’s very easy to resize the control so that it always fills the form, with the Dock property (see section “Anchoring and Docking” in Chapter 5). If the text is a program listing, like the one shown in Figure 6.2, or a list of numbered items, you don’t want the text to wrap at any point.

You’d rather force users to open up the form so that the entire width of the text is visible across the control. You can experiment with the WordWrap and ScrollBars properties in the TextPad application, which is described later in this chapter.

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Figure 6.2

Turn off the WordWrap property to display program listings or other lines that shouldn’t break arbitrarily.

Notice that the WordWrap property has no effect on the actual line breaks. The lines are wrapped automatically, and there are no hard breaks (returns) at the end of each line. Open the TextPad project, enter a long paragraph, and resize the window. The text will be automatically adjusted to the new width of the control. Then select it and copy it by pressing Ctrl+C. Switch to Word, or another word processor, and paste it. You will see that the text is copied as a single paragraph, without additional hard breaks. The lines will break according to the size of the container and will be re-broken when the control is resized.

As you can understand, when WordWrap is set to True, there’s no reason to attach a horizontal scroll bar to the control. Even if you set the ScrollBars property to Horizontal, this setting will be ignored.

AcceptsReturn, AcceptsTab

These two properties specify how the TextBox control reacts to the Return (Enter) and Tab keys. The Enter key activates the default button on the form, if there is one. The default button is usually an OK button that can be activated with the Enter key, even if it doesn’t have the focus. In a multiline TextBox control, however, we want to be able to use the Enter key to change lines. The default value of this property is True, so that pressing Enter creates a new line on the control. If you set it to False, users can still create new lines in the TextBox control, but they’ll have to press Ctrl+Enter. If the form contains no default button, then the Enter key creates a new line regardless of the AcceptsReturn setting.

Most forms that contain text boxes have also a default button, so users can work with the keyboard. Otherwise, they’d be forced to take their hands off the keyboard, use the mouse to click a button, and then return to the keyboard—or press the Tab button repeatedly to move the focus to one of the buttons.

Tip This is a very important issue in designing practical user interfaces. You shouldn’t force your users to switch between the keyboard and the mouse all the time. Follow the Windows standards (the Enter key for the default button, the Tab key to move from one control to the next, and shortcuts) to make sure that your application can be used without the mouse. Data-entry operators would rather work without the mouse at all.