1.4Resizing forms

The final topic we touch on in this chapter is resizing forms. For readers familiar with MFC programming in Visual C++, you will know that it can take some work to properly resize a complicated form. The folks at Microsoft were likely aware of this and sought to simplify this task in .NET.

Before looking at our new code listing, try resizing our existing program to see what happens. The position of each control is fixed relative to the top-left corner of the form, as shown in figure 1.5.

Figure 1.5

Version 1.3 of our application uses the default resize behavior, with both controls anchored to the top and left of the window.

We would prefer the PictureBox control to resize automatically along with the window, as is shown in figure 1.6. Fortunately, Windows Forms controls provide a couple of properties to achieve this effect, namely the Anchor and Dock properties.

Figure 1.6

Version 1.4 of our application anchors the picture box control to all sides of the window, so that it resizes automatically whenever the window is resized.

Revise your code so that it matches listing 1.4. This new code sets the Anchor property for each control, and uses the version number 1.4. As before, the changes to our code from section 1.3 are shown in bold.

Listing 1.4 The PictureBox resizes based on the Anchor property setting

[assembly: System.Reflection.AssemblyVersion("1.4")]

namespace MyNamespace

{

using System;

using System.Drawing;

using System.Windows.Forms;

public class MyForm : System.Windows.Forms.Form

{

private Button btnLoad; private PictureBox pboxPhoto;

public MyForm()

{

// Constructor

this.Text = "Hello Form 1.4";

this.MinimumSize = new Size(200,200);

// Create and configure the Button btnLoad = new Button(); btnLoad.Text = "&Load"; btnLoad.Left = 10;

btnLoad.Top = 10;

btnLoad.Click += new System.EventHandler(this.OnLoadClick); btnLoad.Anchor = AnchorStyles.Top | AnchorStyles.Left;

// Create and configure the PictureBox pboxPhoto = new PictureBox();

pboxPhoto.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D; pboxPhoto.Width = this.Width / 2;

pboxPhoto.Height = this.Height / 2;

pboxPhoto.Left = (this.Width - pboxPhoto.Width) / 2; pboxPhoto.Top = (this.Height - pboxPhoto.Height) / 2; pboxPhoto.SizeMode = PictureBoxSizeMode.StretchImage;

pboxPhoto.Anchor = AnchorStyles.Top | AnchorStyles.Bottom

| AnchorStyles.Left | AnchorStyles.Right;

// Add our new controls to the Form this.Controls.Add(btnLoad); this.Controls.Add(pboxPhoto);

}

protected void OnLoadClick(object sender, System.EventArgs e)

{

OpenFileDialog dlg = new OpenFileDialog();

dlg.Title = "Open Photo";

dlg.Filter = "jpg files (*.jpg)|*.jpg|All files (*.*)|*.*" ;

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

{

pboxPhoto.Image = new Bitmap(dlg.OpenFile());

}

dlg.Dispose();

}

public static void Main()

{

Application.Run(new MyForm());

}

}

}

As an aside, figure 1.6 exposes a problem with our application that will need to be fixed. Since the image scales along with our PictureBox control, the aspect ratio changes as well. The aspect ratio is the ratio of the height of an image to its width. A standard 4-inch by 6-inch photograph, for example, has an aspect ratio of two-thirds (4 divided by 6). As the form is resized the image is distorted to fit the control, which affects the aspect ratio. We will fix this in chapter 7. In the meantime, keep in mind that our program exhibits what can only be called a bug.

While we have only added three lines here, they lead us to some interesting discussion points.

1.4.1Desktop layout properties

The first change in our program sets the MinimumSize property to define the minimum possible size for the form. This ensures that the form never becomes so small that the PictureBox disappears and our image cannot be seen.

The MinimumSize property is a Size structure representing the minimum width and height of the form. As you may recall, structures are value types and store their data directly, either on the stack or as part of the containing type. As we discussed in section 1.1.3, the new keyword is used to create a new value type. When one value type is assigned to another, as we do here, the contents of the original type are copied into the target type. As a result, the fact that the newly allocated Size structure is destroyed when the MyForm constructor is finished has no effect on the value stored within the MyForm class.

public MyForm()

{

. . .

this.MinimumSize = new Size(200,200);

. . .

}

Note that the System.Drawing namespace defines a number of structures that are used in a similar manner, including the Size, Point, and Rectangle structures. We will encounter these types repeatedly throughout the book.

The MinimumSize property is one of a number of properties that control how a form behaves on the Windows Desktop. While not directly related to our discussion, this is a good place to introduce these properties as a set. Figure 1.7 illustrates how these properties relate to the desktop.

A brief explanation of each property shown in figure 1.7 is provided in the following table:

1.4.2The Anchor property

The remaining two lines added to our program use the Anchor property to fix the control on the form in relation to the form’s edges.

//Create and configure the Button

. . .

btnLoad.Anchor = AnchorStyles.Top | AnchorStyles.Left;

//Create and configure the PictureBox

. . .

pboxPhoto.Anchor = AnchorStyles.Top | AnchorStyles.Bottom | AnchorStyles.Left | AnchorStyles.Right;

d

e

h

f

g

Figure 1.7 The properties for the Form class that relate to the Windows desktop define the size, appearance, and position of the form on the desktop.

All controls in the .NET Framework support the Anchor property for this purpose. The property is set using the AnchorStyles enumeration, discussed in .NET Table 1.3..

.NET Table 1.3 AnchorStyles enumeration

The AnchorStyles enumeration specifies the settings available for the Anchor property in the Control class, and by inheritance all controls in the .NET Framework. The enumeration is part of the System.Windows.Forms namespace. An Anchor property is set for a control object using a bitwise or (with the vertical bar ‘|’ operator) of the desired values.