MAP THE PAGE DOWN AND PAGE UP KEYS TO THE NEXT AND PREVIOUS MENUS

Run the program to see how this code works. Open an album and make sure all four keys we handled work as expected.

TRY IT! Modify the OnKeyDown method to recognize the Home and End keys as well. Have the Home key display the first photograph in the album, and the End key display the last.

As an alternate approach, modify this method so that Shift+PageDown will display the last photograph, and Shift+PageUp the first photograph in the album. To implement this change, you will need to modify the method to check the Shift property within the PageUp and PageDown case blocks.

That’s probably enough for our quick look at keyboard events. Let’s also take a look at mouse events.

12.2MOUSE EVENTS

The mouse device has gone through its own little evolution since it was invented by Xerox Corporation almost 30 years ago. The number of buttons have varied from one to three, and the shape has evolved from a rather uncomfortable rectangle to the hand-fitting contours found in most modern versions. The mouse wheel is a rather recent addition, permitting automated scrolling from the comfort of your mouse. An even newer addition is a five-button mouse, with the extra buttons intended for backward/forward navigation in applications such as web browsers.

Regardless of the type mouse you own, the possible events in .NET are the same. In chapter 8 we used the MouseMove event to update the PixelDlg form as the

mouse pointer changed position. In the previous chapter we used the MouseDown event in our MonthCalendar control to pop up a context menu when the user clicked on a date. Here, we look at mouse events in general.

Mouse events are somewhat similar to keyboard events. Mouse buttons go down and up just like keyboard keys, and the events MouseDown and MouseUp occur accordingly. Since the mouse also controls the mouse pointer, there are events related to pointer movement as well. The complete list of mouse events is shown in the following table. These events occur with respect to a specific control.

Mouse events

12.2.1THE MOUSEEVENTARGS CLASS

As you can see from the table, all mouse event handlers received an instance of the MouseEventArgs class as their event parameters. A summary of this class appears in

.NET Table 12.3. We will illustrate mouse events a few different ways in this chapter. Our first example will combine the keyboard support we examined in the previous chapter with mouse events.

12.2.2HANDLING MOUSE EVENTS

Since we have seen a couple of mouse events before, let’s make a change that involves both keyboard and mouse events. Keeping with our theme of the Previous and Next menus, let’s modify the mouse button behavior in our Panel control so that the left and right buttons invoke the Previous and Next menus, respectively, when the Ctrl key is pressed.

.NET Table 12.3 MouseEventArgs class

The MouseEventArgs class is the event argument class associated with the mouse events. This class represents information about the mouse device and the mouse pointer position when the event occurs. It is part of the System.Windows.Forms namespace, and inherits from the System.EventArgs class.

This requires handling both the KeyDown and KeyUp events to track when the Ctrl key is held down, and the MouseDown event to map a mouse click to the appropriate menu. Once we have done this, we will discover some additional changes that will improve our interface. First, let’s take a look at how to track the Ctrl key.

Set the version number of the MyPhotos application to 12.2.

TRACK WHEN THE CTRL KEY IS HELD DOWN

TRACK WHEN THE CTRL KEY IS HELD DOWN (continued)

Note that we use the ControlKey value from the Keys enumeration in our switch statement. There is also a Control value for the Keys enumeration that is used for the Modifiers property of the KeyEventArgs class which will not work here.

With this in place, we can now use the MouseDown event to invoke the Next and Previous menus when the Ctrl key is held. Continuing the previous steps:

MODIFY THE MOUSE BEHAVIOR WHEN THE CTRL KEY IS HELD

This looks good, right? Well, not exactly. If you run the program, you’ll find that this code mostly works as long as you do nothing else while the Ctrl key is pressed. When you press the right mouse button, the next photo is displayed but the context menu also pops up. In addition, if you use a keyboard accelerator such as Ctrl+O, or you