How to Use Advanced Windows Forms | 3

How to Use Advanced Windows Forms

18.2.2 The TreeView class

The SplitContainer class is great for dividing a form or other container into two parts. The next question, of course, is what to place in each part. One of the more common controls for the left side of a split form is the TreeView control.

One of the better-known examples of the TreeView control is the Windows Explorer interface, where the Folders view provides a tree of the devices, folders, network locations, and other information about the local computer environment. The Windows Forms TreeView class supports this functionality, and is summarized in .NET Table 18.2.

Each item in a tree view is called a tree node, or just a node. Tree nodes can contain additional nodes, called child nodes, to arbitrary levels in order to represent a hierarchy of objects in a single tree. Tree nodes at the top level of a tree view control are called root nodes. Figure 18.5 shows some of concepts and classes used with the Windows Forms TreeView control.

The members in .NET Table 18.2 are just some of the members defined by the TreeView class explicitly. As you can see, members are provided to manage the nodes in the tree, including the selection, drawing, and contents of each node. We use many of these members as we build our sample explorer application.

A short summary of some members not mentioned in .NET Table 18.2 is probably worthwhile. The nodes in the tree can be sorted alphabetically by setting the Sorted property to true, or a custom IComparer interface can be assigned to the TreeViewNodeSorter property to specify a custom sort for the nodes.

An additional set of properties defines how the nodes in the tree are laid out. The Indent property indicates how many pixels to indent each level in the tree, while the color, existence, and appearance of lines between nodes are affected by the Line- Color, ShowLines, ShowPlusMinus, and ShowRootLines properties.

As shown in figure 17.5, each node in a tree view can display an icon next to the node label. The ImageList property defines the images to use for this purpose.

Other image properties include the ImageIndex property to indicate the index of the default image and the SelectedImageIndex property to indicate the index of the default image for a selected node. The default images can alternately be specified by image name, using the ImageKey and SelectedImageKey properties, which we demonstrate in the next section.

A second set of images can also be displayed to represent the state of each node. The images for the state icons are defined by the StateImageList property. When the CheckBoxes property is true and state images are defined, the first two images in the StateImageList collection are used to indicate the unchecked and checked state, respectively.

One other set of members we should probably highlight consists of the After and Before events. A few of these are shown in .NET Table 18.2, but be aware that before and after events occur when a user clicks on node check boxes, expands or collapses nodes, edits node labels, or selects nodes.

Created: March 27, 2003
Revised: May 1, 2006

URL: https://webreference.com/programming/winforms/1