LIST CONTROLS in C#.NET

Printing Data Matrix 2d barcode in C#.NET LIST CONTROLS

Set the version number of the MyAlbumEditor application to 10.5. ADD A CONTEXT MENU Action 1 Add a ContextMenu control named ctxtPhotoList to the form in the MainForm.cs [Design] window. Add a single menu item to this context menu.

Set the ContextMenu property for the ListBox control to this new menu. Add a Click handler for the new menu item to reverse the Checked state of this menu. When checking the menu, set the DrawMode for the Photographs list to be ownerdrawn. When unchecking the menu, set the DrawMode to its default setting. Also reset the default item height.

} private void menuThumbs_Click (object sender, System.EventArgs e) { menuThumbs.Checked = ! menuThumbs.Checked; if (menuThumbs.Checked) { lstPhotos.DrawMode = DrawMode.OwnerDrawVariable; } else { lstPhotos.DrawMode = DrawMode.Normal; lstPhotos.ItemHeight = lstPhotos.Font.Height + 2; }

The Click handler for our new menu simply toggles its Checked flag and sets the drawing mode based on the new value. The DrawMode property is used for both the ListBox and ComboBox controls to indicate how each item in the list will be drawn. The possible values for this property are shown in .NET Table 10.6. Since the size of our photographs in an album may vary, we allow the size of each element in the list to vary as well. As a result, we use the DrawMode.OwnerDrawVariable setting in our code. The ItemHeight property contains the default height for each item in the list. When the DrawMode property is set to Normal, we set this property to the height of the current font plus 2 pixels. For our owner-drawn list, the item height depends on the size of the photograph we wish to draw. This requires that we assign the item height dynamically, and this is our next topic.

The DrawMode enumeration specifies the drawing behavior for the elements of a control. This enumeration is part of the System.Windows.Forms namespace. Controls that use this enumeration include the ListBox, CheckedListBox, and ComboBox classes, although the CheckedListBox class only supports the Normal setting. Normal Enumeration Values OwnerDrawFixed OwnerDrawVariable All elements in the control are drawn by the .NET Framework and are the same size. Elements in the control are drawn manually and are the same size. Elements in the control are drawn manually and may vary in size.

SETTING THE ITEM HEIGHT Since a ListBox normally holds text in a specific font, the default height of each list box item is just large enough to accommodate this font. In our case, we want to draw an image in each item, so the height of the default font is likely a bit on the small side. We can assign a more appropriate item height by handling the MeasureItem event. This event occurs whenever the framework requires the size of an owner-drawn item. Note that this event does not occur with the setting DrawMode.OwnerDrawFixed, since the items are by definition all the same size. For this setting, the ItemHeight property should be assigned to the common height of the items. Since we are using the DrawMode.OwnerDrawVariable setting, this event will occur each time a list item must be custom drawn.

The MeasureItemEventArgs class provides the event data necessary to determine the size of an owner-drawn item. This class is part of the System.Windows.Forms namespace, and inherits from the System.EventArgs class. Graphics Index ItemHeight ItemWidth Gets the graphics object to use when calculating measurements. Gets the index of the item to measure. Gets or sets the height of the specified item. Gets or sets the width of the specified item.

A MeasureItem event handler receives a MeasureItemEventArgs class instance to permit an application to set the width and height of a given item. Specifics of this class are shown in .NET Table 10.7. In our case, we are drawing an image followed by a string. We will fit the image into a 45 45 pixel box, and use the Caption property as the string portion.