UPDATE THE MENUIMAGE_CHILDCLICK METHOD TO USE THE NEW PANEL

That’s it for our menu handlers. The SetStyle method is a protected member and cannot be modified for our Panel class, so we just force the redraw to happen at the Form level as we did before. This will redraw the entire form and not just our panel, but it gets the job done. In this case, the drawing required outside of our panel is not overly complex, so this extra drawing should not be a problem.

On a more complex form, it would make sense to handle the Resize event for the pnlPhoto object instead of setting a form-level style as we do here. Handling the Resize event would allow us to only redraw the panel itself, and not the other parts of the Form.

The AutoScroll property is a public member of the ScrollableControl class, so we can set its value for the pnlPhoto object directly.

As you can see, because the Panel and Form classes are based on a similar class hierarchy, design changes like this are very easy to make in .NET. Let’s move on to our owner-drawn status bar.

7.4.3DRAWING THE STATUS BAR PANEL

Our status bar is drawn in the statusBar1_DrawItem method. This method must calculate the percentage of the image shown in the window. Since the image will now be displayed inside the Panel object, we must modify this routine to use the Panel client area rather than the MainForm one.

UPDATE THE STATUSBAR1_DRAWITEM METHOD TO USE THE PANEL

UPDATE THE STATUSBAR1_DRAWITEM METHOD TO USE THE PANEL (continued)

Once again this change simply uses our private Panel field rather than the this keyword. Our last change is to draw the image inside the panel rather than on the form itself.

7.4.4DRAWING THE IMAGE

When drawing the image on the form, we were able to override the protected

OnPaint method that raises the Paint event. For the Panel object, we do not have access to protected members, so we must use the public Paint event to update the panel. Internally in the Windows Forms library, of course, the Panel control will use its own version of the OnPaint method to invoke our event handler.

ADD A PAINT HANDLER FOR THE PNLPHOTO OBJECT

Note that the Paint event handler receives a PaintEventArgs instance containing the event data. As we saw earlier in the chapter, this class contains the Graphics object for drawing inside the panel. Our code uses this object in the same way as when the image was drawn in the form. Continuing our previous steps:

TRANSFER THE DRAWING CODE INTO THE NEW PAINT HANDLER

TRANSFER THE DRAWING CODE INTO THE NEW PAINT HANDLER (continued)

It may look like a lot of code, but the number of changes is actually quite small, as indicated by the few number of bolded lines. The program is all set now. Verify that your code compiles and runs properly. Change display modes, use different-sized images, and resize the form to observe the effect.

TRY IT! If you are feeling brave, try adding a Fit to Width menu item to the Image submenu. This should preserve the aspect ratio of the image by scaling the image to match the width of the panel window. You will need to add a FitToWidth enumeration value to the DisplayMode enumeration. Calculate the height using code similar to the Photograph.ScaleToFit method where the width is preserved. The tricky part is setting the pnlPhoto.AutoScrollMinSize property appropriately and drawing the image into this same rectangle.

7.5RECAP

This chapter has looked at some drawing and scrolling aspects of the Form class. In particular, we removed the PictureBox control from our application and learned

how to draw our image directly onto the form. We used the protected OnPaint method and made use of the automated scroll bars inherited by the Form class to scroll our image. This did not work exactly as we wanted, so we modified our code to use the Panel class instead as a way to draw the image independent of the rest of the form.

The next chapter will continue our investigation of the Form class by looking at dialog boxes.