Set the version number of the MyPhotoAlbum library to 7.2.

IMPLEMENT A SCALETOFIT METHOD IN THE PHOTOGRAPH CLASS

Since this algorithm is a bit off-topic from Windows Forms development, we will not discuss it in much detail. This gives us a mechanism for scaling our image to the proper display size, and accounts for both horizontal and vertical images. The method returns a Rectangle object containing both a location and a size for the new image. That is, this method does not just provide the final size for our displayed image; it also provides the location where it should appear within the target rectangle.

With this in hand, let’s turn back to our MyPhotos application. To implement our Scale to Fit menu, we need to add the menu item itself, the menu-handling logic, and the appropriate drawing code. We will begin with the menu option.

The code generated by these steps is similar to the menu code generated in chapter 3 and elsewhere. In particular, note that the Index property settings for these menus are adjusted in the InitializeComponent method to reflect the insertion of the new item at the first location.

menuScale.Index = 0;

menuStretch.Index = 1;

menuActual.Index = 2;

Since the DisplayMode enumeration must match our menu, we need to update the values appropriately.

UPDATE DISPLAYMODE ENUMERATION

We also need to check each place in the code where this enumerator is used. If you do a search, you will discover the _selectedMode field in menuImage_Popup, menuImage_ChildClick, and OnPaint. The popup event is not affected by this change, but the click handler requires a change to its switch block.

UPDATE MENUIMAGE_CHILDCLICK EVENT HANDLER

The final change required to properly scale our image is in the OnPaint method. Here we simply draw the image into the Rectangle determined by our Photograph.ScaleToFit method.

There you have it. The Scale to Fit display mode is very similar to the Stretch to Fit display mode. Both fit the image into the display area, and both draw the image into a rectangle. The difference is the rectangle into which they draw. Compile your application to verify that the image scales properly. It may be a bit hard to determine if this is working properly since a window resize does not cause the image to be redrawn. Let’s address this problem next.

7.2.5REPAINTING WHEN THE FORM IS RESIZED

Now that we are drawing directly on the form, we need to redraw our image whenever the form is resized. The PictureBox control used in prior chapters handled this issue automatically for us.

There is in fact a Resize event associated with controls. This event occurs when

a control, including a Form object, is resized. Handling this event would allow us to invalidate the window whenever the display mode is ScaleToFit or StretchToFit. Since our MainForm class is derived from Form, we could even go directly to the protected OnResize method that raises this event. This would force our OnPaint method to be called and the window would update appropriately. A fine idea, but there is another way.

.NET Table 7.4 ControlStyles enumeration

The ControlStyles enumeration specifies a set of values related to the interaction of a control with the Windows desktop. These styles define how low-level Windows messages are processed by the control when a user interacts with it in various ways. This enumeration is part of the System.Windows.Forms namespace.

The values in this enumeration can be combined using the bitwise “or” operator. The protected GetStyle and SetStyle methods in the Control class can be used to modify these settings for a control.

a. Actually, the messages here are not passed to the underlying NativeWindow object, but you can think of it as the control itself. For UserMouse, this affects the WM_MOUSEDOWN, WM_MOUSEMOVE, and WM_MOUSEUP messages. For UserPaint, this affects the WM_PAINT and WM_ERASEBKGND messages.