private void mnuFr1_Click(object sender, System.EventArgs e) { lblNumber.Text = "un";

}

private void mnuFr2_Click(object sender, System.EventArgs e) { lblNumber.Text = "deux";

}

private void mnuFr3_Click(object sender, System.EventArgs e) { lblNumber.Text = "trois";

}

private void mnuExit_Click(object sender, System.EventArgs e) { Application.Exit();

} // end setupMenu

Using Dialog Boxes to Enhance Your Programs

As programmers started developing GUI software, it quickly became apparent that certain kinds of complex tasks are needed again and again. For example, allowing the user to choose a file is a potentially risky operation because the programmer doesn’t know anything about the user’s file structure (how many drives are on the computer, what the drive names are, and so on). Also, allowing the user to type in a file name is simple to program but leads to many errors. Soon standards began to appear. If you think about most programs you use, a standard form appears when you start to save or load a program. This form takes control of the program until the user makes a choice. Forms like this are called dialog boxes because they facilitate a dialog with the user. As a user, the dialog box that appears when you save or load files seems to be much the same no matter what program you are using. This leads to shorter learning time (because the dialog box is already familiar to you) and fewer mistakes (because you already know how to get around in the dialog box). In the early days of GUI programming, developers had to be able to build file dialog boxes by hand. The same thing was true of color−choosing dialogs, print dialogs, and font selection dialogs. These dialog boxes were tedious to create by hand, and ensuring that they work exactly as users expect was challenging.

Fortunately, the .NET framework offers prebuilt, standard dialog boxes to help you include the more common dialogs used by programmers. Each of these dialogs is a class with properties, methods, and events. You can use the dialogs to greatly simplify your interactions with the user.

Exploring the Dialog Demo Program

The Dialog Demo program extends the text editor built in the File IO program. It replaces the command buttons with menus and adds access to several standard dialog boxes to change the program's appearance and behavior. Figure 9.14 shows the Dialog Demo.

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Figure 9.14: When the user chooses Open from the File menu, a familiar−looking dialog appears. The file dialog makes your job as a programmer much easier because you don’t have to worry much about how it works (isn’t encapsulation grand?). All you have to do is drop it on the form, set a few properties, and respond to its events.

Notice that the dialog box is preset to display only text files (the file names end with .txt). You can set up a filter to display any kind of file you want. You can also determine a default directory, a default file name, and other interesting characteristics.

You can also change the font visible in the text editor with another custom editor. Figure 9.15 shows the font dialog.

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Figure 9.15: The font dialog allows the user to set the font, including typeface, size, and style.

The font dialog is an especially welcome tool because fonts have a long history of causing trouble for programmers. Each user can install whatever fonts he or she wants on his own computer. However, the programmer has no way of knowing directly which fonts are on the client machines because each user’s machine has a different set of fonts installed. The font dialog sidesteps this problem by letting the user choose directly from the fonts installed on the user’s computer.

The Dialog Demo program also allows the user to change the foreground and background colors of the text editor. Figure 9.16 shows this process. Like files and fonts, color can be a challenging attribute for the programmer to control. The color dialog gives a simple mechanism for allowing the user to choose a color. The color dialog is more sophisticated than it seems at first glance. The Custom Colors option allows the user to generate a color using RGB and HSL (hue, saturation, luminance) models.

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Figure 9.16: The user can independently set the foreground and background colors of the text editor.

Adding Standard Dialogs to Your Form

Although the standard dialogs seem to be a very diverse group of objects, they all work the same way from the programmer’s point of view. Each dialog is a control you can drop on the form. All are available in the Toolbox to the left of the IDE window. As you drop the dialogs on your form, you see them added in the off−screen space at the bottom of the form, where timers and image lists go. Like these other controls, the dialog boxes don’t have a physical presence on the screen; they appear at opportune moments under program control. Figure 9.17 shows the text editor with the dialog boxes added.

Figure 9.17: The dialogs are added to the bottom of the form. Notice the menu structure as well. Trick The dialog controls usually appear towards the bottom of the Toolbox list, so they aren’t immediately apparent in the IDE. You have to scroll down the Toolbox to see the dialog

controls.

Like any other control, a dialog has properties that affect its appearance and behavior. Also, each dialog has at least one event it can trigger. The properties and events are associated with specific types of dialogs, so they are described separately in the sections that follow.

Using the File Dialog Controls

The OpenFileDialog and SaveFileDialog controls are almost identical. It’s important to understand that the dialogs don’t actually save and load files! As a user, you expect these dialogs to save and load files, but that isn’t the case from the programmer’s point of view. The real purpose of the file dialogs is to let the user choose a file name. It’s up to the programmer to save or load the file. Although this might seem like a burden, it isn’t, because the hardest part of saving and loading files is usually getting the file name from the user. Many other tools (such as the StreamReader and StreamWriter classes you learned about earlier in this chapter) help with the actual file manipulation. Dialogs are all about communication with the user. The file dialog controls have properties that simplify and direct this communication.

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