MODIFY ONPAINT METHOD FOR ACTUALSIZE DISPLAY MODE

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.

7.4PANELS

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.

Our focus in this section will be the Panel class. This class can contain and position controls just like the Form class, and supports automated scrolling since it inherits from the ScrollableControl class.2 We will not position controls within a panel in this chapter, but we will use this class to fix some of the problems we have seen when drawing directly on the form. We will draw our photo directly in a Panel, and solve the following problems we noticed when drawing directly on the form:

•Our image was off-center vertically for the Scale to Fit display option. The DisplayRectangle property included the vertical space occupied by the

scroll bar, which threw our calculations off. Here, we will use the panel’s playRectangle property, so that the image will be centered exactly inside the panel.

•The 3-D border we used for the PictureBox control was gone. We could have attempted to draw a border inside the form using the ControlPaint.DrawBorder3D method, but a Panel provides a much easier solution. The Panel class provides a BorderStyle property much like the corresponding PictureBox property, so the .NET framework will draw the border for us.

•The status bar was part of the scrollable area. Since the Form object managed the scrolling, the StatusBar control on the form was caught up in the scrolling logic. In this section, the scrolling will be managed by the Panel class independent of the form and status bar. As a result, our status bar will return to and remain at its natural position at the base of the form.

Before we get into the required changes, figure 7.5 shows how our three display modes will appear by the end of this section. As you can see, the application looks much more polished here than when we drew directly on the form. Note especially the excellent centering, the fine border, and the well-behaved scroll bars.

Figure 7.5 This shows an image drawn inside a panel with the Scale to Fit, Stretch to Fit, and Actual Size display modes.

2 For the curious, the GroupBox control inherits from the Control class and does not support scrolling.

As you will see, the code to draw the image inside a panel is very similar to drawing the image directly on the form. We will need to add a new panel, update some of our menu handlers and the drawing of the status bar, and finally draw the image into the panel.

7.4.1ADDING A PANEL

Adding a Panel object in Visual Studio is much like adding any other control. You open the Toolbox and drag a Panel onto the form. In the source code, the panel is added using the Control property of the parent form. We will look at both of these, beginning with the use of Visual Studio.

Set the version number of the MyPhotos application to 7.4.

ADD A PANEL TO THE FORM

Take a look at the MainForm.cs source file to see how the panel is created. As you can see, this code looks very similar to the code for other controls from prior chapters. A private instance is created in the MainForm class, initialized in the InitializeComponent method, and added to the form using the Form.Controls property.

private System.Windows.Forms.Panel pnlPhoto;

. . .

private void InitializeComponent()

{

. . .

this.pnlPhoto = new System.Windows.Forms.Panel ();

. . .

//

// pnlPhoto

//

this.pnlPhoto.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D; this.pnlPhoto.Dock = System.Windows.Forms.DockStyle.Fill; this.pnlPhoto.Name = "pnlPhoto";

this.pnlPhoto.Size = new System.Drawing.Size(292, 233); this.pnlPhoto.TabIndex = 3;

. . .

this.Controls.AddRange(new System.Windows.Forms.Control[] { this.pnlPhoto, this.statusBar1});

The Panel class depends largely on its base classes for exported functionality, with the BorderStyle property just about the only new member added by the class. An overview of the Panel class appears in .NET Table 7.5.

.NET Table 7.5 Panel class

The Panel class represents a scrollable control that acts as a container for other controls. This class is often used to define a region of controls within a Form. This class is part of the System.Windows.Forms namespace and inherits from the ScrollableControl class. See .NET Table 7.1 on page 196 for a list of members inherited from the ScrollableControl class.

7.4.2UPDATING THE MENU HANDLERS

With our panel on the form, we need to update the code for drawing our image to use the new panel rather than interacting with the form itself. We will begin with the menu handlers for the Image submenu.

The menuImage_Popup method simply sets the Enabled and Checked menu properties as required for the current display mode. This behavior does not change, so no modifications are required. The menuImage_ChildClick method sets scrolling properties for the form. Since our scrolling will be managed from the Panel object now, we need to use the corresponding Panel members rather than those in the Form itself.

UPDATE THE MENUIMAGE_CHILDCLICK METHOD TO USE THE NEW PANEL