Classes in C# namespace classtest { public class myclass { public myclass() { } } }

Transcription

1 Classes in C# A class is of similar function to our previously used Active X components. The difference between the two is the components are registered with windows and can be shared by different applications, whereas the class is accessible only by that specific application. This would tend to indicate that the component is the way to go, however, if your application has to be run on several machines you must have a setup or manually install and register that component on each machine and your class is compiled directly into your application. Being as the component and class are similar in functionality they are comprised of properties, methods, and events. In the following we discuss how to write each of the affore mentioned, as well as, creating and invoking your class within your application. Firstly, let us create the class within our application. Within the Solution Explorer you will see at the top of the list the name or namespace of your application. Right click on the name and select Add -> Add Class. A dialog box will appear so you can name your class and once you have done this your newly named and created class should appear in the solution listing as well the class framework code should pop up in the main window. The things we can see are that the class is created within the namespace as your application. We also see the class declaration as well as the class constructor. The constructor always has the same name as the class and can be left null and void, or you can add initializing code for things that need to be done when you first invoke your class. You may also notice that is almost stand alone code where if you require additional resources you must call those up with separate using statements from your main application. namespace classtest public class myclass public myclass() Our project/application name is classtest, which is the name you gave your application when you first started.net. The class added was named myclass.

2 We are now ready to start writing code for use in the class and to be by the main application. We will start by adding a property. A property is simply a data variable that is contained within the class. I prefer to place my properties at the beginning of the class. There are two parts to the definition, the local variable for use within the class and the actual property definition for use by the main application. Private int Myvar; Public int myvar Get Return this.myvar; Set Myvar = value; The first declare variable Myvar is the local class variable for use only within the class and it was declared as an integer. The variable myvar will be the variable name accessible to our main application. If you were to only use the get portion of the declaration you would be creating a read only variable for the main application. The set portion allows the main application to set the value. Let us now look at the main application to see how we use these properties. We first have to create a new instance of our class to be used in the main application. After you see the listing of components you have drawn on your form there is a comment filed that says designer variables and after that you would declare your class variable. myclass classvar; A little bit further down in your main applications code after InitializeComponent() you will see a comment filed asking for constructors. Now you call your constructor. classvar = new myclass(); Declaring these where I have stated makes this class accessible throughout your main application. If you wished the class accessible only within a certain subroutine you can take these two lines and place them at the beginning of a button_click event or something else and they will be available locally.

3 That takes car of properties, so on to methods. I will write a simple method to multiply Myvar by two. To declare the method it is just like writing a subroutine, you can suppy data to the method or retrieve a value back from the method. My method will be simple, no data to be passed back or forth. public void timestwo() Myvar = Myvar *2; Hence, in the main application we would say. classvar.timestwo(); There are other ways to achieve the same results and depending on how you want your method to function you may choose one the these other methods. public int ttagain(int newvar) return newvar * 2; In this case we pass the value to the class method and return the newly calculated value. Our main application call to this method would look like this. int i; i = classvar.ttagain(int32.parse(mytext.text); Your locally declared variable i will end up with the result of the operation and we are taking the text from mytext textbox and converting it to an integer and passing that value to the method.

4 public void t2again(int i, out int newvar) newvar = 0; newvar = i * 2; In this case we have two variable passing to the method and newvar is passed with the out keyword in front allowing us to modify that variables content and have the new value passed back from the method without returning the value. Hence, our main application call looks like this. int i,newvar; i = Int32.Parse(mytext.Text); classvar.t2again(i, out newvar); newvar will contain the value of i times 2. The other topic to be covered in writing classes is event handling and generation. This topic will follow in the next article. So, lets finish this. This is the form layout, where mytext is the textbox. Get and Set are the two buttons used with changing the property values. The two two times buttons are used to invoke the methods.

5 The following is the main application code. using System; using System.Drawing; using System.Collections; using System.ComponentModel; using System.Windows.Forms; using System.Data; namespace classtest / <summary> / Summary description for Form1. / </summary> public class Form1 : System.Windows.Forms.Form private System.Windows.Forms.TextBox mytext; private System.Windows.Forms.Button setbut; private System.Windows.Forms.Button getbut; / <summary> / Required designer variable. / </summary> myclass classvar; private System.Windows.Forms.Button ttagainbut; private System.Windows.Forms.Button ttoutbut; private System.ComponentModel.Container components = null; public Form1() Required for Windows Form Designer support InitializeComponent(); TODO: Add any constructor code after InitializeComponent call myclass classvar; classvar = new myclass(); / <summary> / Clean up any resources being used. / </summary> protected override void Dispose( bool disposing ) if( disposing ) if (components!= null) components.dispose(); base.dispose( disposing ); #region Windows Form Designer generated code / <summary> / Required method for Designer support - do not modify / the contents of this method with the code editor. / </summary> private void InitializeComponent() this.mytext = new System.Windows.Forms.TextBox(); this.setbut = new System.Windows.Forms.Button(); this.getbut = new System.Windows.Forms.Button(); this.ttagainbut = new System.Windows.Forms.Button(); this.ttoutbut = new System.Windows.Forms.Button();

6 #endregion this.suspendlayout(); mytext this.mytext.location = new System.Drawing.Point(32, 24); this.mytext.name = "mytext"; this.mytext.size = new System.Drawing.Size(144, 20); this.mytext.tabindex = 0; this.mytext.text = "100"; setbut this.setbut.location = new System.Drawing.Point(16, 80); this.setbut.name = "setbut"; this.setbut.size = new System.Drawing.Size(88, 40); this.setbut.tabindex = 1; this.setbut.text = "Set"; this.setbut.click += new System.EventHandler(this.setbut_Click); getbut this.getbut.location = new System.Drawing.Point(152, 80); this.getbut.name = "getbut"; this.getbut.size = new System.Drawing.Size(80, 40); this.getbut.tabindex = 2; this.getbut.text = "Get"; this.getbut.click += new System.EventHandler(this.getbut_Click); ttagainbut this.ttagainbut.location = new System.Drawing.Point(24, 152); this.ttagainbut.name = "ttagainbut"; this.ttagainbut.size = new System.Drawing.Size(96, 32); this.ttagainbut.tabindex = 3; this.ttagainbut.text = "X2"; this.ttagainbut.click += new System.EventHandler(this.ttagainbut_Click); ttoutbut this.ttoutbut.location = new System.Drawing.Point(160, 152); this.ttoutbut.name = "ttoutbut"; this.ttoutbut.size = new System.Drawing.Size(96, 32); this.ttoutbut.tabindex = 4; this.ttoutbut.text = "X2 Out"; this.ttoutbut.click += new System.EventHandler(this.ttoutbut_Click); Form1 this.autoscalebasesize = new System.Drawing.Size(5, 13); this.clientsize = new System.Drawing.Size(292, 266); this.controls.addrange(new System.Windows.Forms.Control[] this.ttoutbut, this.ttagainbut, this.getbut, this.setbut, this.mytext); this.name = "Form1"; this.text = "Form1"; this.resumelayout(false); / <summary> / The main entry point for the application. / </summary>

7 [STAThread] static void Main() Application.Run(new Form1()); private void setbut_click(object sender, System.EventArgs e) classvar.myvar = Int32.Parse(mytext.Text); classvar.timestwo(); private void getbut_click(object sender, System.EventArgs e) mytext.text = classvar.myvar.tostring(); private void ttagainbut_click(object sender, System.EventArgs e) int i; i = classvar.ttagain(int32.parse(mytext.text)); mytext.text = i.tostring(); private void ttoutbut_click(object sender, System.EventArgs e) int i,newvar; i = Int32.Parse(mytext.Text); classvar.t2again(i, out newvar); mytext.text = newvar.tostring(); Next is the class code. using System; namespace classtest public class myclass private int Myvar; public int myvar get return this.myvar; set

8 Myvar = value; public myclass() public void timestwo() Myvar = Myvar * 2; public int ttagain(int newvar) return newvar * 2; public void t2again(int i, out int newvar) newvar = 0; newvar = i * 2; public event myeventhandler myevent; protected virtual void Onmyevent(myeventargs e) myevent(this, e); end of myclass class And there we have it, we have tackled classes and after reading this you should be ready to write your own. So have fun. Bruce Misner 2005