AUTOMATED SCROLLING in C#.NET

Paint Data Matrix 2d barcode in C#.NET AUTOMATED SCROLLING

When the user clicks the ActualSize display mode, we need to adjust not just the Actual Size display mode, but also our Scale to Fit and Stretch to Fit menus to ensure that scrolling is disabled when these modes are set. The following steps detail the changes required.

Set the version number of the MyPhotos application to 7 .3. MODIFY MENUIMAGE_CHILDCLICK FOR ACTUALSIZE DISPLAY MODE Action 1 Locate the menuImage_ChildClick method in the MainForm.cs source window. Turn scrolling off for the ScaleToFit and StretchToFit display modes. Result

protected void menuImage_ChildClick (object sender, System.EventArgs e) { . . . switch (_selectedMode) { default: case DisplayMode.ScaleToFit: case DisplayMode.StretchToFit: // Display entire image in window AutoScroll = false; SetStyle(ControlStyles.ResizeRedraw, true); . . . case DisplayMode.ActualSize: // Display image at actual size AutoScroll = true; SetStyle(ControlStyles.ResizeRedraw, false); Invalidate(); break; } . . . }

Turn scrolling on for the ActualSize display mode. How-to a. Set AutoScroll to true. b. Turn off the ResizeRedraw style for the form.

Note here that we did not set AutoScrollMinSize to the size of the current image. Since different images may have different sizes, we will need to adjust this setting whenever the current image changes. One way to do this would be to modify this setting in all the places where the current image changes. This would include the Next, Previous, and Remove menu handlers, and possibly other locations in the future as well. That s a lot to keep track off. Instead, we will set this property when the image is painted so that it is updated by default whenever the image changes. For the Paint operation itself, another version of the Graphics.DrawImage method is used to account for drawing the image into a space larger than the client area. The DrawImage method has a number of overloads to handle various types of drawing. See the documentation for the complete list.

MODIFY ONPAINT METHOD FOR ACTUALSIZE DISPLAY MODE Action 4 Locate the OnPaint method in the MainForm.cs source window. When the display mode is

protected override void OnPaint(PaintEventArgs e) { . . . case DisplayMode.ActualSize: // Draw appropriate portion of image g.DrawImage(photo.Image, AutoScrollPosition.X, AutoScrollPosition.Y, photo.Image.Width, photo.Image.Height); AutoScrollMinSize = photo.Image.Size; break; . . . }

That s it! Your application will now handle all three display modes. Note how the AutoScrollPosition property is used for the location to appear in the upper left corner of the client area. As the window scrolls, this value is updated automatically so we can use it future Paint operations. Crank it up and display your favorite set of images stretched to fit, scaled to fit, and at the actual size. Make sure you try some images of alternate sizes to ensure that the scroll bars adjust appropriately as you move through the album. Also note how the scroll bars disappear when the window is expanded to be larger than the image. Too bad about our status bar. It really should not be part of the scrolled area here. The problem is that we are drawing and scrolling the form itself, and both the image and the status bar are part of the form. As a result, as goes the image, so goes the status bar. To fix this, we need to isolate the image portion of the form and have our image appear only in this area. The PictureBox control isolated the image without the ability to scroll. The Panel class will provide both isolation and scrolling.

If you have prior experience with MFC, then you must know how frustrating the MFC group box control can be. A fine control, I would submit, except when you have to adjust its position, or worse, add controls inside of it. The problem, for those not familiar with this construct, is that it is just a box, with no relationship to the inside of the box. If you move the box, you have to adjust the contents separately, and vice versa. Very frustrating. In the .NET Framework, controls can act as containers for other controls. When you move the container, the controls inside move with it. Two such containers in the System.Windows.Forms namespace are the GroupBox and Panel classes. When you move a .NET container, the contents move with it. The position of the inner controls are defined in relationship to the container, and the Anchor and Dock properties are used to set their resize behavior within the container just like within a form.