CHAPTER 6: Windows
The basic element of most GUI programming in Windows Forms is the window. Essentially, everything on a GUI screen—buttons, text boxes, and icons—are windows. Because of this, most of the windows and controls in the Windows Forms package have the same characteristics. For instance, they all have a Text property. How they use the property is up to the specific type of window.
Building a Windows Forms application is easy once a few basic concepts are understood. This section covers some of these concepts and provides a starting point from which to proceed. Listing 16.1 shows a relatively simple Windows Forms application. To compile the code in Listing 16.1, use the command line in Listing 16.2.
Listing 16.1 A Simple Windows Forms Application
using System;
using System.Windows.Forms;
using System.ComponentModel;
using System.Drawing;
public class FirstForm : Form
{
private Container components;
private Label howdyLabel;
public FirstForm()
{
InitializeComponent();
}
private void InitializeComponent()
{
components = new Container ();
howdyLabel = new Label ();
howdyLabel.Location = new Point (12, 116);
howdyLabel.Text = "Howdy, Partner!";
howdyLabel.Size = new Size (267, 40);
howdyLabel.AutoSize = true;
howdyLabel.Font = new Font (
"Microsoft Sans Serif",
26, System.
Drawing.FontStyle.Bold);
howdyLabel.TabIndex = 0;
howdyLabel.Anchor = AnchorStyles.None;
howdyLabel.TextAlign = ContentAlignment.MiddleCenter;
Text = "First Form";
Controls.Add (howdyLabel);
}
public static void Main()
{
Application.Run(new FirstForm());
}
}
Listing 16.2 Command Line for Listing 16.1
csc /r:System.Windows.Forms.DLL
_/r:System.Drawing.DLL FirstForm.cs
Listing 16.2 contains a command line that can be used to compile the code from Listing 16.1. The command line references a few dynamic link libraries by using the /r: <dllname> option. The System.Windows.Forms.DLL and System.Drawing.DLL libraries contain all the routines required to present graphical components, such as forms and controls, on the screen.
At the top of the file are a few new namespaces to be familiar with. The most familiar is the Systemnamespace, holding all the basic class libraries. The System.Windows.Forms namespace holds definitions of all the Windows Forms windows and controls. It also has other supporting types including interfaces, structs, delegates, and enumerations supporting the window types. TheSystem.ComponentModel namespace contains several classes and interfaces (language as opposed to graphical interfaces) for providing generalized support of components. The System.Drawingnamespace provides access to the operating system graphics functionality.
The first two class members of the FirstForm class are components and howdyLabel. Thecomponents field is a Container object from the System.ComponentModel namespace. This object doesn't participate in the graphical presentation of the program. However, it does do a lot of behind-the-scenes work to support timers, multithreading, and cleanup when the program ends. Its declaration and instantiation are mandatory. The other field, howdyLabel, is a Windows Forms Label Control. It is used in this program to display the "Howdy, Partner!" message in the window that is created.
The FirstForm constructor calls the InitializeComponent() method. TheInitializeComponent() method creates and instantiates the Windows Forms Controls and Forms that make up the graphical interface of this program. It begins by instantiating the components andhowdyLabel fields as objects. The following paragraphs explain the rest of this method.
The first group of statements initializes the howdyLabel label. Labels are well suited to presenting static text. That's exactly what howdyLabel does.
Labels have a Location property, keeping track of where the Label is placed on the screen. TheLocation property accepts a Point structure, which is a member of the System.Drawing namespace. The Point struct is used frequently in Windows Forms applications to specify X and Y screen coordinates. In the example, the Location of the howdyLabel is 12 pixels from the left and 116 pixels from the top of the main form. Here's how the Location property of the howdyLabel label is set:
howdyLabel.Location = new Point (12, 116);
The static text of a Label is set through the Text property. The following statement sets the text of theLabel to the string "Howdy, Partner!:
howdyLabel.Text = "Howdy, Partner!";
A Label also has a Size property that takes a Size structure. In Listing 16.1, the size of howdyLabelis set to 267 pixels wide by 40 pixels high:
howdyLabel.Size = new Size (267, 40);
The AutoSize property accepts a Boolean value, which tells whether a Label can automatically resize itself to accommodate its contents. For instance, in this program the actual size of the howdyLabelcontents exceeds its set size from the previous statement, so the label must grow to fully show the entirety of its text. Here's how the AutoSize property of the howdyLabel label is set.
howdyLabel.AutoSize = true;
A Label can change its typeface through the Font property. It accepts a Font object. The constructor for the Font object in the following statement accepts three parameters: the font name, the font size, and a font style. The font style is from the FontStyle enum in the System.Drawing namespace.
howdyLabel.Font = new Font (
"Microsoft Sans Serif",
26,
System.Drawing.FontStyle.Bold);
When there are multiple controls on a form, each control that can accept input can have its TabIndexproperty set. This permits the user to press the Tab key to move to the next control on the form, based on TabIndex. In this example, the TabIndex of howdyLabel is set to 0. This is for illustrative reasons only. The fact is that a Label can never be a tab stop because it doesn't normally accept user input. Furthermore, for this program, this is the only control on the form. There isn't any other control to tab to. Here's how the TabIndex property of the howdyLabel label is set:
howdyLabel.TabIndex = 0;
Window layout in Windows Forms is done with the techniques of anchoring and docking. Docking specifies the location of the form that a control will reside in. Anchoring tells which side of a control will be attached to another control. These two techniques permit any type of layout a window design would need. The following code line states that howdyLabel will not be anchored. It uses the AnchorStylesenumeration to set the Anchor property.
howdyLabel.Anchor = AnchorStyles.None;
The horizontal alignment of a Label may be set with the TextAlign property, which accepts aContentAlignment enumeration. The following statement sets the horizontal alignment ofhowdyLabel to be centered between its left and right margins.
howdyLabel.TextAlign = ContentAlignment.MiddleCenter;
The next few statements perform initialization on the main form. Since FirstForm is a Form object, it is considered the main form.
Text = "First Form";
All forms and controls have Text properties. What they do with them is unique to each form or control. A Form object sets its title bar with the value of the Text property. This example sets the program's title bar to say "First Form."
Controls.Add (howdyLabel);
A form's Controls object holds a collection of all of its controls. When the form has to redraw itself, it iterates through this collection and sets itself up according to several factors, including the anchoring and docking properties of each control. This example adds howdyLabel to the FirstForm Controlscollection object.
public static void Main()
{
Application.Run(new FirstForm());
}
The Main() method simply gets the program running. It calls the static Run() method of theApplication class. Its parameter is a new instance of the FirstForm class. When the HowdyPartnerprogram runs, it looks like the window shown in Figure 16.1.
Figure 16.1** The HowdyPartner Windows Forms**