Writing Windows C# Programs

3. Writing Windows C# Programs The C# language has its roots in C++, Visual Basic and Java. Both C# and VB.Net utilize the same libraries and compile to the same underlying code. Both are managed languages with garbage collection of unused variable space and both can be used interchangeably. Both also use classes with method names that are very similar to those in Java, so if you are familiar with Java, you will have no trouble with C#. Objects in C# In C#, everything is treated as an object. Objects contain data and have methods that operate on them. For example, strings are now objects. They have methods such as Substring ToLowerCase ToUpperCase IndexOf Insert and so forth. Integers, float and double variables are also objects, and have methods. string s; float x; x = 12.3; s = x.ToString(); Note that conversion from numerical types is done using these methods rather than external functions. If you want to format a number as a particular kind of string, each numeric type has a Format method. Managed Languages and Garbage Collection C# and VB.Net are both managed languages. This has two major implications. First, both are compiled to an intermediate low-level language, and a common language runtime (CLR) is used to execute this compiled code, perhaps compiling it further first. So, not only do C# and VB.Net share the same runtime libraries, they are to a large degree two sides of the same coin and two aspects of the same language system. The differences are that VB7 is more Visual Basic like and a bit easier for VB programmers to learn and use. C# on the other hand is more C++ and Java- like, and may appeal more to programmers already experienced in those languages. The other major implication is that managed languages are garbagecollected. Garbage collected languages take care of releasing unused memory: you never have to be concerned with this. As soon as the garbage collection system detects that there are no more active references to a variable, array or object, the memory is released back to the system. So you no longer need to worry as much about running out of memory because you allocated memory and never released it. Of course, it is still possible to write memory-eating code, but for the most part you do not have to worry about memory allocation and release problems. Classes and Namespaces in C# All C# programs are composed entirely of classes. Visual windows forms are a type of class, as we will see that all the program features we’ll write are composed of classes. Since everything is a class, the number of names of class objects can get to be pretty overwhelming. They have therefore been grouped into various functional libraries that you must specifically mention in order to use the functions in these libraries. Under the covers these libraries are each individual DLLs. However, you need only refer to them by their base names using the using statement, and the functions in that library are available to you. using System; using System.Drawing; using System.Collections; Logically, each of these libraries represents a different namespace. Each namespace is a separate group of class and method names which the compiler will recognize after you declare that name space. You can use namespaces that contain identically named classes or methods, but you will only be notified of a conflict if you try to use a class or method that is duplicated in more than one namespace. The most common namespace is the System namespace, and it is imported by default without your needing to declare it. It contains many of the most fundamental classes and methods that C# uses for access to basic classes such as Application, Array, Console, Exceptions, Objects, and standard objects such as byte, bool, string. In the simplest C# program we can simply write a message out to the console without ever bringing up a window or form: class Hello { static void Main(string[] args) { Console.WriteLine ("Hello C# World"); } } This program just writes the text “Hello C# World” to a command (DOS) window. The entry point of any program must be a Main method, and it must be declared as static. Building a C# Application Let’s start by creating a simple console application: that is, one without any windows, that just runs from the command line. Start the Visual Studio.NET program, and select File |New Project. From the selection box, choose C# Console application as shown in Figure 3-1. Figure 3-1 – The New Project selection window. Selecting a console application. This will bring up a module, with Main already filled in. You can type in the rest of the code as follows: Console.WriteLine ("Hello C# World"); You can compile this and run it by pressing F5. When you compile and run the program by pressing F5, a DOS window will appear and print out the message “Hello C# World” and exit. The Simplest Window Program in C# C# makes it very easy to create Windows GUI programs. In fact, you can create most of it using the Windows Designer. To do this, start Visual Studio.NET and select File|New project, and select C# Windows Application. The default name (and filename) is WindowsApplication1, but you can change this before you close the New dialog box. This brings up a single form project, initially called Form1.cs. You can then use the Toolbox to insert controls, just as you can in Visual Basic. The Windows Designer for a simple form with one text field and one button is shown in Figure 3-2. Figure 3-2 – The Windows designer in Visual Studio.NET You can draw the controls on the form by selecting the TextBox from the Toolbox and dragging it onto the form, and then doing the same with the button. Then to create program code, we need only double click on the controls. In this simple form, we want to click on the “Hello” button and it copies the text from the text field to the textbox we called txHi, and clears the text field. So, in the designer, we double click on that button and the code below is automatically generated: private void btHello_Click(object sender, EventArgs e) { txHi.Text ="Hello there"; } Note that the Click routine passes in a sender object and an event object that you can query for further information. Under the covers, it also connects the event to this method. The running program is shown in Figure 3-3. Figure 3-3 – The SimpleHello form after clicking the Say Hello button. While we only had to write one line of code inside the above subroutine, it is instructive to see how different the rest of the code is for this program. We first see that several libraries of classes are imported so the program can use them: using using using using using using System; System.Drawing; System.Collections; System.ComponentModel; System.Windows.Forms; System.Data; Most significant is the Windows.Forms library, which is common to all the .Net languages. The code the designer generates for the controls is illuminating. And it is right there in the open for you to change if you want. Essentially, each control is declared as a variable and added to a container. Here are the control declarations. Note the event handler added to the btHello.Click event. private System.Windows.Forms.TextBox txHi; private System.Windows.Forms.Button btHello; private void InitializeComponent() { this.btHello = new System.Windows.Forms.Button(); this.txHi = new System.Windows.Forms.TextBox(); this.SuspendLayout(); // // btHello // this.btHello.Location = new System.Drawing.Point(80, 112); this.btHello.Name = "btHello"; this.btHello.Size = new System.Drawing.Size(64, 24); this.btHello.TabIndex = 1; this.btHello.Text = "Hello"; this.btHello.Click += new EventHandler(this.btHello_Click); // // txHi // this.txHi.Location = new System.Drawing.Point(64, 48); this.txHi.Name = "txHi"; this.txHi.Size = new System.Drawing.Size(104, 20); this.txHi.TabIndex = 0; this.txHi.Text = ""; // // Form1 // this.AutoScaleBaseSize = new System.Drawing.Size(5, 13); this.ClientSize = new System.Drawing.Size(240, 213); this.Controls.AddRange( new System.Windows.Forms.Control[] { this.btHello, this.txHi}); this.Name = "Form1"; this.Text = "Hello window"; this.ResumeLayout(false); } If you change this code manually instead of using the property page, the window designer may not work any more. We’ll look more at the power of this system after we discuss objects and classes in the following chapter. Windows Controls All of the basic Windows controls work in much the same way as the TextBox and Button we have used so far. Many of the more common ones are shown in the Windows Controls program in Figure 3-4. Figure 3-4 – A selection of basic Windows controls. Each of these controls has properties such as Name, Text, Font, Forecolor and Borderstyle that you can change most conveniently using the properties window shown at the right of Figure 3-2. You can also change these properties in your program code as well. The Windows Form class that the designer generates always creates a Form1 constructor that calls an InitializeComponent method like the one above. One that method has been called, the rest of the controls have been created and you can change their properties in code. Generally, we will create a private init() method that is called right after the InitializeComponent method, in which we add any such additional initialization code. Labels A label is a field on the window form that simply displays text. Usually programmers use this to label the purpose of text boxes next to them. You can’t click on a label or tab to it so it obtains the focus. However, if you want, you can change the major properties in Table 3-1 either in the designer or at runtime. Property Value Name BackColor BorderStyle Enabled Font ForeColor Image ImageAlign Text Visible At design time only A Color object None, FixedSingle or Fixed3D true or false. If false , grayed out. Set to a new Font object A Color object An image to be displayed within the label Where in the label to place the image Text of the label true or false Table 3-1 –Properties for the Label Control TextBox The TextBox is a single line or multiline editable control. You can set or get the contents of that box using its Text property: TextBox tbox = new TextBox(); tbox.Text = "Hello there"; In addition to the properties in Table 3-1, the TextBox also supports the properties in Table 3-2. Property Lines Locked Multiline ReadOnly Value An array of strings, one per line If true, you can’t type into the text box true or false Same as locked. If true, you can still select the text and copy it, or set values from within code. WordWrap from within code. true or false Table 3-2 – TextBox properties CheckBox A CheckBox can either be checked or not, depending on the value of the Checked property. You can set or interrogate this property in code as well as in the designer. You can create an event handler to catch the event when the box is checked or unchecked, by double clicking on the checkbox in the design mode. CheckBoxes have a Appearance property which can be set to Appearance.Normal or Appearance.Button. When the appearance is set to the Button value, the control appears acts like a toggle button that stays depressed when you click on it and becomes raised when you click on it again. All the properties in Table 3-1 apply as well. Buttons A Button is usually used to send a command to a program. When you click on it, it causes an event that you usually catch with an event handler. Like the CheckBox, you create this event handler by double clicking on the button in the designer. All of the properties in Table 3-1 can be used as well. Buttons are also frequently shown with images on them. You can set the button image in the designer or at run time. The images can be in bmp, gif, jpeg or icon files. Radio buttons Radio buttons or option buttons are round buttons that can be selected by clicking on them. Only one of a group of radio buttons can be selected at a time. If there is more than one group of radio buttons on a window form, you should put each set of buttons inside a Group box as we did in the program in Figure 3-1. As with checkboxes and buttons, you can attach events to clicking on these buttons by double clicking on them in the designer. Radio buttons do not always have events associated with them. Instead, programmers check the Checked property of radio buttons when some other event, like an OK button click occurs. Listboxes and Combo Boxes Both list boxes and Combo boxes contain an Items array of the elements in that list. A ComboBox is a single line drop-down, that programmers use to save space when selections are changed less frequently. ListBoxes allow you to ser properties that allow multiple selections, but ComboBoxes do not. Some of their properties include those in Table 3-3. Property Items MultiColumn SelectionMode SelectedIndex SelectedIndices SelectedItem Value A collection of items in the list If true, the ColumnWidth property describes the width of each column. One, MultiSimple or MultiExtended. If set to MultiSimple, you can select or deselect multiple items with a mouse click. If set to MultiExtended, you can select groups of adjacent items with a mouse. Index of selected item Returns collection of selections when list box selection mode is multiple. Returns the item selected Table 3-3 – The ListBox and ComboBox properties. SelectionMode and MultiColumn do not apply to combo boxes. The Items Collection You use the Items collection in the ListBox and ComboBox to add and remove elements in the displayed list. It is essentially an ArrayList, as we discuss in Chapter 8. The basic methods are shown in Table 3-4. Method Value Add Count Item[i] RemoveAt(i) Add object to list Number in list Element in collection Remove element i Table 3-4 – Methods for the Items Collection If you set a ListBox to a multiple selection mode, you can obtain a collection of the selected items or the selected indexes by ListBox.SelectedIndexCollection it = new ListBox.SelectedIndexCollection (lsCommands); ListBox.SelectedObjectCollection so = new ListBox.SelectedObjectCollection (lsCommands); where lsCommands is the list box name. Menus You add menus to a window by adding a MainMenu controls to the window form. Then, you can the menu control and edit its drop-down names and new main item entries as you see in Figure 3-5. Figure 3-5 – Adding a menu to a form. As with other clickable controls, double clicking on one in the designer creates an event whose code you can fill in. ToolTips A ToolTip is a box that appears when your mouse pointer hovers over a control in a window. This feature is activated by adding an (invisible) ToolTip control to the form, and then adding specific tool tips control and text combinations to the control. In our example in Figure 3-4, we add tooltips text to the button and list box using the tips control we have added to the window. tips.SetToolTip (btPush, "Press to add text to list box"); tips.SetToolTip (lsCommands, "Click to copy to text box"); This is illustrated in Figure 3-6. Figure 3-6 – A ToolTip over a button. Other Windows Controls We discuss how to use the Datagr id and TreeList in the Adapter and Bridge pattern chapters, and the Toolbar in the State and Strategey pattern chapters. The Windows Controls Program This program, shown in Figure 3-4, has the following features. The text in the label changes whenever you change the • Font size from the combo box • Font color from the radio buttons • Font bold from the check box. For the check box, we create a new font which is either bold or not depending on the state of the check box: private void ckBold_CheckedChanged(object sender, EventArgs e) { if (ckBold.Checked ) { lbText.Font =new Font ("Arial", fontSize,FontStyle.Bold ); } else { lbText.Font = new Font ("Arial", fontSize); } } When we create the form, we add the list of font sizes to the combo box: private void init() { fontSize = 12; cbFont.Items.Add ("8"); cbFont.Items.Add ("10"); cbFont.Items.Add ("12"); cbFont.Items.Add ("14"); cbFont.Items.Add ("18"); lbText.Text ="Greetings"; tips.SetToolTip (btPush, "Press to add text to list box"); tips.SetToolTip (lsCommands, "Click to copy to text box"); } When someone clicks on a font size in the combo box, we convert that text to a number and create a font of that size. Note that we just call the check box changing code so we don’t have to duplicate anything. private void cbFont_SelectedIndexChanged( object sender, EventArgs e) { fontSize= Convert.ToInt16 (cbFont.SelectedItem ); ckBold_CheckedChanged(null, null); } For each radio button, we click on it and insert color-changing code: private void opGreen_CheckedChanged(object sender, EventArgs e) { lbText.ForeColor =Color.Green; } private void opRed_CheckedChanged(object sender, EventArgs e) { lbText.ForeColor =Color.Red ; } private void opBlack_CheckedChanged(object sender, EventArgs e) { lbText.ForeColor =Color.Black ; } When you click on the ListBox, it copies that text into the text box, by getting the selected item as an object and converting it to a string. private void lsCommands_SelectedIndexChanged( object sender, EventArgs e) { txBox.Text = lsCommands.SelectedItem.ToString () ; } Finally, when you click on the File | Exit menu item, it closes the form, and hence the program: private void menuItem2_Click(object sender, EventArgs e) { this.Close (); } Summary Now that we’ve seen the basics of how you write programs in C#, we are ready to talk more about objects and OO programming in the chapters that follow. Programs on the CD-ROM Console Hello \IntroCSharp\Hello Windows hello \IntroCSharp\SayHello Windows controls \IntroCSharp\WinControls