provide a collection of control objects with no scrolling capabilities. A group box includes a simple border, and the Text property for this control displays an optional label as part of the border. In general, use a group box control to provide simple containment of controls, especially when you wish to provide a label for the group.

The Panel and GroupBox controls are similar in that they are both used to contain controls. The Panel class provides some advanced features such as automated scrolling and configurable borders, while the GroupBox control provides a simple border with an optional label.

The steps to create the radio buttons on our form are provided in the following table. Note in particular how the Tag property inherited from the Control class is used to hold the enumeration value associated with the button.

CREATE THE GROUP BOX SECTION OF THE ALBUMEDITDLG FORM

CREATE THE GROUP BOX SECTION OF THE ALBUMEDITDLG FORM (continued)

Before we discuss the new code here, the tab behavior of RadioButton and GroupBox controls is worth a mention.

For radio button controls, all radio buttons in a group are treated as a single tab index. When you tab to a group of radio buttons, the selected button receives the focus, and then the left and right arrow keys alter the selected button.

The tab behavior for the GroupBox control is much like the Label class, in that it never receives the focus directly. Instead, the first control in the box receives the focus. In our form, when you tab to the group box, or use the access key Alt+O, the currently selected radio button receives the focus on behalf of the group. We will set the tab order for our controls shortly, after which we can see this behavior for ourselves.

As for the code changes here, let’s look at them in a bit more detail. Here is an excerpt of the AlbumEditDlg.cs source file after the previously mentioned code modifications have been made.

namespace Manning.MyPhotoAlbum

{

public class AlbumEditDlg : Manning.MyPhotoAlbum.BaseEditDlg

{

. . .

private PhotoAlbum.DisplayValEnum _selectedDisplayOption;

this.groupBox1.Location = new System.Drawing.Point(8, 104); this.groupBox1.Name = "groupBox1";

this.groupBox1.Size = new System.Drawing.Size(280, 56); this.groupBox1.TabIndex = 4;

this.groupBox1.TabStop = false; this.groupBox1.Text = "Phot&o Display Text";

//

// rbtnFileName

//

this.rbtnFileName.Location = new System.Drawing.Point(8, 24); this.rbtnFileName.Name = "rbtnFileName"; this.rbtnFileName.Size = new System.Drawing.Size(80, 24); this.rbtnFileName.TabIndex = 0;

. . .

this.Controls.AddRange(new System.Windows.Forms.Control[] { this.groupBox1, this.panel1});

. . .

private void DisplayOption_Click(object sender, System.EventArgs e)

{

RadioButton rb = sender as RadioButton;

if (rb != null)

this._selectedDisplayOption = (PhotoAlbum.DisplayValEnum)rb.Tag;

}

}

}

Let’s look at the numbered sections of this code in a little more detail.

bThe Tag property contains an object to associate with the control. This provides a general mechanism for associating any data with any control. In our case, we use this property to hold the DisplayValEnum enumeration value corresponding to the individual buttons.

cVisual Studio suspends the layout logic for all container controls during initialization, including our group box. This ensures that the controls do not perform any layout of their contained objects during initialization.

dAs we saw for our Panel control previously, the contained controls, in this case the three radio buttons, are added directly to the GroupBox control. This means that layout-related values, such as the Anchor and Dock properties, apply within the GroupBox container, and not within the Form.

eThe Click handler for our three radio buttons is set using the standard += notation for events.

fIt is interesting to note that the form itself only contains two controls so far. These are the Panel control and the GroupBox control.

gThe shared click handler, DisplayOption_Click, receives a radio button object and records its Tag value as the currently selected radio button. We will use this selected value to save the settings for our dialog box when the user clicks OK.

Also note the use of the C# as keyword in our shared click handler. An as statement works much like a cast, except that the value null is assigned if the provided variable is not of the given type, as opposed to the InvalidCastException that is thrown when a cast operation fails. This handler could also be written as follows, although the following code is slightly less efficient since the sender parameter is checked twice—once for the is statement and once for the cast.

private void DisplayOption_Click(object sender, System.EventArgs e)

{

// Our click handler using the is statement – not our approach if (sender is RadioButton)

{

RadioButton rb = (RadioButton) sender; this._selectedDisplayOption = (PhotoAlbum.DisplayValEnum)rb.Tag;

}

}

Before we hook up this new form to our application, let’s create the check box control on our form as well.

9.3.5USING CHECK BOX BUTTONS

The CheckBox control is similar to a radio button. While a radio button is used for a set of mutually exclusive options, a check box is used for a single option that can be turned on or off. A check box normally appears as a small square followed by a textual

description of the option. The settings for this control are rather similar to those provided for RadioButton objects, and are summarized in .NET Table 9.7.

.NET Table 9.7 CheckBox class

The CheckBox class represents a button that displays an option to the user. Typically, a check box represents one of two states, either checked or unchecked. A three-state check box can also be established, with an additional intermediate state. This third state is useful when used with a set of objects, where some objects have the option checked and some unchecked.

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 the ButtonBase class.

Check boxes are normally used in one of two ways. The first is as a simple on or off state. For example, we could have elected to add a check box indicating whether the album can be modified. If yes, then photographs could be added to and removed from the album. If no, then any attempt to modify the album could throw an InvalidOperationException object. In a Windows dialog box, this option could be represented as a check box, which the user would click to turn modifications on or off.

Another common usage for a check box is to enable or disable a set of controls related to a specific option. This is the type of check box we will create here. In our case, the check box relates to whether the photo album has a password associated with it or not. If it does, then controls to set this password will be enabled on our form. If it does not, then these controls will be disabled.

Let’s begin by adding the CheckBox and related controls to our AlbumEditDlg form. These steps also add some logic for processing the check box and associated controls. We discuss the events used here following the table.