CREATE A PASSWORD DIALOG

We will use this dialog to request a password when an album is opened. The point here is to illustrate the PasswordChar property, and not to create a secure mechanism for handling passwords.

ENFORCE (INSECURE) PASSWORD MECHANISM

ENFORCE (INSECURE) PASSWORD MECHANISM (continued)

Our PhotoAlbum class is now ready. Each PhotoAlbum instance supports the new title, password, and display option settings. These settings are saved in the album file, and in the Open method an album cannot be loaded unless the proper password is provided.3

Let’s get back to the matter at hand and create our Album Properties dialog.

9.3.3CREATING THE ALBUMEDITDLG PANEL AREA

With our new infrastructure in place, we are ready to create the AlbumEditDlg form. This section will inherit the new dialog from our base form, and add controls to the panel at the top of the form.

3 Of course, the password mechanism here is quite insecure. A user can examine the album file by hand in order to discern the password. We could make this scheme more secure by using the password as a scrambling mechanism on the file. For example, rather than storing the password string in the file, call GetHashCode on the password string and XOR each character in the file with this hash code and the byte-sum of the password characters. The scrambled result is then stored in the file. The validity of the password is checked by using it to unscramble the version number of the file to see if it makes sense. If so, then the password is presumed to be valid. Again, this is not a totally secure mechanism, but it is slightly better then that shown in the text. For more information on security in .NET in general and the System.Security namespace in particular, see the book .NET Security by Tom Cabanski from Manning Publications.

The Panel control inherited from the BaseEditDlg form will display the album file and the title in our new AlbumEditDlg form. The following steps create the new form class and the controls contained by the panel.

CREATE THE ALBUMEDITDLG FORM AND ITS PANEL CONTROLS

With these steps completed, we are ready to add our button controls.

9.3.4USING RADIO BUTTONS

The bottom part of our dialog will contain some radio and check box buttons. We will begin with the radio buttons in the middle of the form.

Radio buttons display a set of mutually exclusive options. In our case, they indicate which Photograph setting should be used to represent the photograph in a main window. Radio buttons in .NET work much the same as radio buttons in other graphical environments. An overview of this class appears in .NET Table 9.6.

In our code, three radio buttons will collectively set the _displayOption setting for the album. Since these are the only radio buttons on the form, it is not necessary to group them within a container control. We will anyway, since it improves the overall appearance of the form.

.NET Table 9.6 RadioButton class

The RadioButton class represents a button that displays one of a possible set of options. Radio buttons are usually grouped together, and only one button may be checked at any one time. By default, when a radio button is clicked, it is automatically selected and all radio buttons in the same group are deselected. This behavior can be disabled using the AutoCheck property.

The parent container for this control defines its group. So if four radio buttons are contained within a form, then only one of the four buttons may be checked at any one time. Use container classes such as GroupBox and Panel to provide multiple independent groups of radio buttons on a single form.

This control is part of the System.Windows.Forms namespace, and inherits from the ButtonBase class. See .NET Table 9.4 on page 292 for members inherited from this class.

A Panel control could be used here, of course, but this is a good opportunity to create a GroupBox control. The GroupBox class inherits directly from the Control class to