These changes implement the correct functionality for the button. When the button is pushed, a Click event for the menuPixelData menu is performed, which displays the dialog. When the button is unpushed,1 the dialog is hidden using the Hide method. In this later case we ensure that the dialog exists and is shown before trying to hide it. The AssignPixelToggle method adjusts the image and the tool tip to reflect the new state of the button.

You can run the program to see the button in action. If you do, you may notice that there are two problems we still need to address:

•The button is not pushed when the pixel data dialog is displayed using the View menu item.

•The button is not unpushed when the dialog is closed manually.

For the first problem, we simply need to adjust the button in the Click event handler for this menu. Let’s do this before we discuss the second problem.

UPDATE THE TOGGLE BUTTON WHEN THE PIXEL DATA MENU IS SELECTED

Our second problem, that of the user closing the pixel data dialog by hand, is more problematic. Since this dialog is a nonmodal window, this dialog can be closed at any time. So we need a mechanism for notifying our main window whenever the dialog is closed.

If you recall, and as shown in step 5 in the previous table, the MainForm form is defined as the owner of the PixelDlg form. This ensures that both windows are

1I know, I know. There is no such word as “unpushed.” You know what I mean. I thought about the word “released,” but unpushed seems much more packed with meaning.

shown when either window is displayed or minimized. We can take advantage of this relationship to ensure that our main window is notified when the pixel dialog is closed.

The trick is to force the MainForm window to activate whenever the PixelDlg dialog is closed. Our main form will then receive an Activated event, at which time we can update our button. Since the MainForm class derives directly from Form, we can handle this event by overriding the protected OnActivated method.

The following steps implement this mechanism.

UPDATE THE TOGGLE BUTTON WHEN THE PIXELDLG FORM IS CLOSED

This code ensures that whenever the user closes the PixelDlg form, the main form is activated and the toggle toolbar button immediately updated. Compile and run the application to ensure that it works as expected.

TRY IT! Add two new menus to the top of the View menu called menuToolBar and menuStatusBar. Implement these menus to show and hide the corresponding controls in the application. Use the Visible property inherited from the Control class to identify the control’s current state and set it to the opposite one. If you are careful, you can implement a single Click

handler for both menus by using the sender parameter and observing that both objects are Control instances. When you run the program with these changes, note how the control shows or hides their contained buttons or panels as well.

This completes our discussion of toolbars. We now move on to the mostly unrelated but similarly named ToolTip class.

13.4TOOL TIPS

You never know when a good tip might come in handy. In Windows applications, tool tips provide short and quick explanations of the purpose of a control or other object. A number of classes provide their own tool tip mechanism through a ToolTipText property, in particular the StatusBarPanel, TabPage, and ToolBarButton classes. For classes derived from the Control object, the ToolTip class handles this logic in a general fashion.

.NET Table 13.5 ToolTip class

The ToolTip class is a component that provides a small popup window for a control. This window normally contains a short phrase describing the purpose of the control, and appears whenever the mouse hovers over the control for a configurable amount of time. This class is part of the System.Windows.Forms namespace, and supports the IExtenderProvider interface. The ToolTip class derives from the

System.ComponentModel.Component class.