TRY IT! You may have noticed that our interface is not very friendly for albums that happen to contain a password. Since each album is opened in the OnLoad method, before the MainForm window is displayed, any passwords required must be entered before the user even sees the application window.

As an alternative approach, modify the PhotoAlbum class to provide a static GetInfo method, and use this new method in the MainForm.OpenAlbum method of our application. This method should simply return the required statistics for a given album and ignore any password required. While this alters the meaning of the existing password mechanism slightly, it does not provide access to the photographs contained in the album.

In your implementation of the GetInfo method, return a new AlbumInfo structure that provides access to the statistics for the album. This structure can use the same property names as the PhotoAlbum class. In order to accommodate changes made in the remainder of this chapter, you should implement properties to provide the title of the album, whether or not a password is required, and the number of photographs stored in the album. Make certain you close the album regardless of whether or not an exception occurs.

14.3LISTVIEW COLUMNS

The MyAlbumExplorer application displays three out of four possible View settings just fine. Not the best percentage we could hope for, so let’s see what it takes to add a Details view to our application. This is the only view that displays the collection of subitems associated with each item. The subitems display in columns to the right of the item label, as shown in figure 14.3.

Figure 14.3

The size of a column in the Details view can be changed by clicking on the line at the end of the column.

The columns in a list view are contained in the control’s Columns property. This property contains a collection of ColumnHeader components. The order of objects in this collection reflects the order in which columns are displayed in the control. As a result, the order of subitems in each ListViewItem object must match the order of

objects contained in the Columns collection. An overview of the ColumnHeader class is given in .NET Table 14.4. Note that the contents of the Columns property are cleared whenever the Clear method is called on the associated ListView control.

In order to fill in the Details view for our list control, we will first create the columns for the list, and then add the required subitems to each item as we populate the list. This section will finish with a discussion of how sorting can be performed in the Details view.

.NET Table 14.4 ColumnHeader class

The ColumnHeader class represents a single column in a ListView control. These columns appear when the View property for the control is set to Details, and they display the subitems associated with each item in the view. The ColumnHeader class is part of the System.Windows.Forms namespace. It is derived from the System.ComponentModel.Component class, and supports the IClonable interface.

14.3.1CREATING THE COLUMNS

We will create four columns in our application. Each column will represent a setting associated with our PhotoAlbum object. In this section, we will create our columns in the Forms Designer Window, and allow Visual Studio to generate them as part of the InitializeComponent method. Since columns are cleared whenever the list view is cleared, in many cases it is better to create the ColumnHeader objects programmatically. This also permits alternate columns to be used for different types of items displayed in the list. We will see this later in the chapter when we display both

Photograph and PhotoAlbum objects in our list.

The following table summarizes the columns for our application, providing the variable name we will use and the text to appear at the top of the column. A description of the contents of each column is given as well.

Columns for displaying the albums

So let’s see how this is done. The following steps create these four columns and initialize their settings.

Set the version number of the MyAlbumExplorer application to 14.3.

CREATE THE COLUMNS HEADERS FOR THE LIST

1In the MainForm.cs [Design] window, display the ColumnHeader Collection Editor for the ListView control.

How-to

Click the … button associated with the Columns property item in the Properties window.

2Add four ColumnHeader objects and assign their properties.

A quick excerpt of the InitializeComponent method follows. As the code generated here is similar to other collections we have created in earlier chapters, we will not discuss this code any further.

private void InitializeComponent()

{

. . .

this.columnTitle = new System.Windows.Forms.ColumnHeader();

this.columnSize = new System.Windows.Forms.ColumnHeader();

. . .

//

// columnTitle

//

this.columnTitle.Text = "Title"; this.columnTitle.Width = 100;

//

//columnSize

this.columnSize.Text = "Size"; this.columnSize.TextAlign

=System.Windows.Forms.HorizontalAlignment.Center; this.columnSize.Width = 40;

. . .

//listViewMain

//

this.listViewMain.Columns.AddRange(

new System.Windows.Forms.ColumnHeader[] { this.columnName, this.columnTitle, this.columnPassword, this.columnSize});

. . .

}

Note that the order in which the ColumnHeader objects are added to the Columns collection is significant here as this determines the order in which the columns appear in the control. You can alter the order of a column in the ColumnHeader Collection Editor dialog using the up and down arrow buttons.

Feel free to run the application if you wish. You should now see the albums appear in the first column. The next section will populate these columns with the properties of each album.

14.3.2POPULATING THE COLUMNS

The columns in a Details listing contain both the item label and the text associated with each subitem. The first column always contains the item label, and the subsequent columns contain the contents of the list item’s SubItems property. The SubItems property contains a collection of ListViewSubItem objects. The ListViewSubItem class is only valid within the ListViewItem class, so the fully qualified class

name within the Windows Forms namespace is ListViewItem.ListViewSubItem. This class is typically created implicitly while initializing an existing

Item object or ListView control. A summary of this object appears in .NET Table 14.5.

.NET Table 14.5 ListViewSubItem class

The ListViewSubItem class is an object that represents a property or other value associated with a ListViewItem object. A ListViewSubItem appears in a ListView control when the control’s View property is set to Details and a column is configured for the subitem. The set of ListViewSubItem objects associated with an item is defined by the SubItems property in the ListViewItem object.

This class is often written as ListViewItem.ListViewSubItem. It is defined within the ListViewItem class and is therefore part of the System.Windows.Forms namespace.

There are a number of methods provided by the framework for adding subitems to items and items to list views. Some of the constructors available are shown here, and you can look through the online documentation to examine these and also the Add method overloads provided for each collection object. In our code we will use a fairly straightforward method to expose the individual steps along the way. In your own applications you can use the methods employed here or whatever other means works best for your situation.

Since the columns and items are already defined for our control, the only change required is to update the LoadAlbumData method to add the required subitems. The following steps outline the actions required to add the three required subitems, namely the password flag, the album size, and the album file name.