were added to make the program capable of responding to events. The following line was added to the InitializeComponent() method:

this.btnDont.Click += new System.EventHandler(this.btnDont_Click);

The code tells the computer to call the btnDont_Click method as soon as the user clicks the button. This process is sometimes referred to as registering an event handler. C# requires the programmer to register all events that might occur in your program. Although this seems like a lot of extra work (Visual Basic 6 automatically recognizes every event of every component in your program), registering event handlers is a sound practice. First, it is usually done for you in C#. Second, only those events that contain code are registered. When the computer is running your program, it does not have to waste any time looking for events that have no code in them.

1In the Real World

The += operator might seem strange in this context because you are accustomed to seeing it used to add to some numeric value. C# has a feature called operator overloading, which allows an object creator to assign meaning to the ordinary mathematical operators when applied to this class.

Programmers have had passionate debates about the wisdom and utility of operator overloading. I don’t use it often because the meaning of mathematical operators can be vague if the class doesn’t represent a number. In this particular case, it is not very intuitive to note that the += operator is adding an event handler to the click member of the button. However, this is a useful trick, and it is how event handlers are assigned in C#. Fortunately, you don’t usually have to come up with this code from memory because it is created for you in the editor.

Allowing for Multiple Selections

In many situations, you want to have the user choose a value from a series of possible choices. The

.NET framework supplies several controls that make it quite easy to add such features to your programs.

Choosing a Font with Selection Controls

The Font Chooser program, featured in Figures 6.16 and 6.17, demonstrates potentially useful selection tools. As a user, you’ve encountered radio buttons, check boxes, and list boxes. They are frequently used to allow the user to choose from a limited set of options. The Font Chooser program uses all these types of components to set the characteristics of a Font.

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Figure 6.16: The user has used familiar interface tools to specify a 10−point Arial font with italic style.

Figure 6.17: The user has selected a different font. Notice that the font can be both bold and italic but can have only one size.

Although more selection components are available to you, you will have no problems creating your own after you learn how the ones in this program work.

Creating the User Interface

Creating the visual interface is a logical starting point for any visual program, so that’s where I began. Figure 6.18 illustrates the controls I used in this program. The form contains the following components:

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Figure 6.18: Sketch out the types and names of objects in your form.

∙myForm. A form object

∙lblOutput. A label that will show the output font

∙lstFontName. A list box holding a series of font names

∙rad10, rad20. Radio buttons to set the font size

∙chkBold, chkItalic. Check boxes to set the font style

Start your programs by drawing up the forms and naming all the components. This step is often done best on paper when you aren’t near a computer; then you can concentrate on the design itself. Give names to each element on the form, including the form itself. Also, the object names begin with a three−character abbreviation indicating the kind of control the object is. This is Hungarian notation and is widely used in GUI programming. Hungarian notation helps you remember what kind of control a variable name refers to. This eliminates the possibility of mistakes.

Hint Try to create your entire form before you begin adding code. Most importantly, change the names of all your components before you begin to write event handlers. If you change an object’s name after you have written the event handler for that object, the event logic will no longer be associated with that control.

Trap The Visual Designer writes sloppy code for you if you let it. Be sure to name all objects before you write event handlers. Also, the Visual Designer sometimes crashes if you change the main form’s name. It fails to change the Application.Run() line to the new form name, so you must make this change manually. Also, the file name of the form retains the old name, so you’ll probably want to use the Save Form1.cs As option from the File menu to rename the actual file on the disk. I hope that these issues are simply problems with the beta version of C# that I had as I wrote this book and that Microsoft has corrected these errors by the time you write the programs. Still, this situation illustrates why you shouldn’t trust the Visual Designer to build correct code for you. You need to know how the underlying code works because the Designer will make mistakes.

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Examining Selection Tools

The .NET environment provides great interface tools for allowing multiple selections. I used three distinct tools—the list box, radio buttons, and checkboxes—that allow the user to select from a list of choices. Each has slightly different characteristics.

The List Box

A list box is a box that shows a list of strings. The list box is terrific when you have a large number of strings that you want the user to choose from. The list box is closely related to the combo box, which allows you to make a drop−down menu, instead of a list, where all elements are visible. Both the list box and the combo box feature the items property, which holds all the strings in the list box. If you highlight the items property in the Properties window when a list box or combo box is visible, a small button with an ellipsis (...) appears inside the Properties window. You can select this button to bring up an editor that allows you to enter the elements you want stored in the list box. Figure 6.18 illustrates editing the contents of a list box.

Radio Buttons

Radio buttons get their name from the old car radios that had pushbuttons. When you pushed one button to select a radio station, no other button could be pressed at the same time. (A radio can be tuned to only one station at a time.) In GUI designs, you use a set of radio buttons when you want to allow only one element from a set of elements to be active at a time. In the Font Chooser program, it makes sense for a font to have only one size at a time, so the font size is a perfect choice for a radio button group. All the radio buttons that live in the same container are considered part of a group. If you want to have more than one group of radio buttons on a form, you create a panel for each set of radio buttons and place the radio buttons on the panel.

In the Real World

Entire books have been written about effective user interface design. The design of interfaces is a complex field that touches on the disciplines of computer science, human factors engineering, cognitive psychology, design, and art. There is some debate about what goes into a good user interface design, but a few questions are clearly important in any design:

∙Does the user interface help the user?

∙Does the interface prevent illegal input?

∙How well does the interface utilize the available space?

∙Does the interface add to the theme and spirit of the software?

If you keep these questions in mind as you choose the types of components you put in your forms, you will build an appropriate interface for your program. If you are working on professional software, you can consult an expert on user interface design and usability testing. This ensures that the user interface of your software will help your program communicate clearly with your users.

Check Boxes

The font style is controlled by check boxes. You can set as many check boxes to true as you like. Check boxes are a good choice for the font style because a font can have any combination of bold and italic (or neither).

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