IMPLEMENT A CLICK HANDLER FOR THE CAPTION MENU

If you are familiar with the MFC library, this code will be reminiscent of how you might use the CDialog class to perform a similar task. One major difference is how the object is created and destroyed. In MFC you would create the dialog on the stack and rely on C++ to destroy the object by calling its destructor when the stack is cleaned up. In C#, of course, the memory for our dialog is cleaned up by the garbage collector. To ensure that its nonmemory resources are cleaned up immediately, we create the dialog within a using statement.

The dialog does not appear to the user until the ShowDialog method is called, at which point the entire application waits until the user clicks the OK or the Cancel button.

if (dlg.ShowDialog() == DialogResult.OK)

{

photo.Caption = dlg.Caption; this._bAlbumChanged = true; sbpnlFileName.Text = photo.Caption; statusBar1.Invalidate();

}

If the user clicks the OK button, DialogResult.OK is returned and any new caption he or she entered is stored in the photograph and propagated to the status bar. Note how we set _bAlbumChanged to true to indicate the album has changed. If the user clicks the Cancel button, DialogResult.Cancel is returned and the photograph’s caption will not be altered.

Our dialog is now complete. It is displayed via the Caption menu and initialized with the current image file and caption settings. The user can modify the caption and click OK to save it. The new caption appears on the status bar and is stored in the album file when the album is saved.

We will see more modal dialogs as we continue our trip through Windows Forms. Before we end the chapter, let’s also discuss modeless dialogs.

8.4MODELESS DIALOGS

In the previous section we created a dialog box to allow the user to edit the caption for a photograph. Modal dialog boxes tend to be in and out. You open it, you do something, you close it. Modeless dialog boxes tend to show some information relevant to the program. In a stock analysis program, for example, you might have a stock ticker window that runs independently of the program. This would be a modeless, or nonmodal, dialog and would update continuously with stock information, perhaps related to a displayed portfolio or to what the user is viewing in the main application window.

In this section we will create a modeless dialog to display the location of the mouse pointer within the image window, and the color of the image at this location. This information will update continuously as the location of the mouse pointer changes, using the dialog in figure 8.6. As you can see in the figure, the pixel position of the mouse pointer within the image is shown as an X and Y coordinate, along with the color in RGB or red, blue, and green, coordinates. This par-

ticular figure indicates that the mouse pointer is over the image at pixel (100, 100) of the image, and the current color at that pixel has an RGB value of (203, 183, 185).

As for our caption dialog, we will need to make sure our three layers can support this dialog.

•Data layer. The position and color of the current pixel is based on the location of the mouse pointer within the displayed bitmap. Since this information is already available, no changes are necessary here.

•Presentation layer. As before, we will need a Form-based class to display the dialog. Since we are showing information about the current pixel, we will call this class PixelDlg and store it in the file PixelDlg.cs.

•Application layer. Our application will again tie the data and presentation together. To do this, we will create a new menu item under the View menu called “Pixel Data.”

Since no changes are required to the data layer in this case, we will begin with the presentation layer

8.4.1CREATING THE PIXELDLG FORM

The creation of a dialog is much the same whether it is a modal or modeless dialog. First you create a new Form class for the dialog, update the property settings, lay out the controls on the form, and finally add code to set or process the controls as required.

So let’s begin by creating the dialog.

Set the version number of the MyPhotos application to 8.4.

CREATE THE PIXELDLG CLASS