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Event Driven Programming Notes

Review Questions

1. What do these symbols mean in C#? Some have more than one meaning.
   +   &   /   %   ^   #   @   ( )   { }   [ ]

2. What are the values of these expressions?
   "1" + 2 + 3     18 / 4 * 2.0

3. What does 328.76M mean?

4. Which operators use short circuit evaluation?

5. How do you know if & denotes logical or bitwise and?

6. What is the difference between the C# keywords ref and out?

7. When is the keyword params used?

8. For what are base-64 strings used?

9. What does "{3,8:#.00}" mean as a format string?

10. Give three methods in which a format string can be used.

11. Show how to use a WinForms PictureBox control to display an image embedded into an XML resource file (.resx file).

Examples

Part A: Topics from C#-1 Notes

1. Enum Declarations   C#-1.WeekDaysEnum Example

2. Flow of Control

3. One-Dimensional Arrays
   • Defining and Using Arrays   C#-1.Array Example

4. Scope
   • Local variables, instance variables, static variables.

5. Methods
   • Subroutines   C#-1.RepeatSentence Example

   • Functions   C#-1.Square Example

6. System.Math   C#-1.MathMethods Example

Part B:   Winforms Controls.

1. Controls as Classes   Intro.Controls1, WinformsEvents Examples
   • Every control WinForms Control is defined by a .Net class.

   • Control properties can be set
     1. Using the properties window (at design time) or

     2. In the source code (at run time).

   • Every class defining a control inherits the class Control. Here is the complete inheritance hierarchy:
     object (System.Object)   (Any C# object)
         System.MarshalByRefObject   (Objects that can be managed remotely)
            System.ComponentModel.Component  (Primarily handles containment and cleanup)
               System.Windows.Forms.Control   (Any Windows control)
                  Derived classes of Control  (Specific Windows controls and base classes for a group of controls, like ButtonBase, TextBoxBase)

   • This online chapter from the Troelsen text explains how MarshalByRefObject objects can be used for remoting.

   • Control objects have constructors, properties, methods, and events.

   • Some events that are unique to the Form class:
     
     FormLoad  FormActivated  FormDeactivate
     FormClosing  FormClosed

   • Names of .Net controls are traditionally specified using Hungarian notation. Here are some common Hungarian notation prefixes:

      

     Class Name	Prefix		Class Name	Prefix
     Label	lbl		ListBox	lsb or lst
     TextBox	txt		ComboBox	cbo
     Button	btn		GroupBox	grb
     CheckBox	chk		Panel	pnl
     RadioButton	rad		ImageList	iml
     TrackBar	trk		ListView	lvw
     HScrollBar	hsb		VScrollBar	vsb
     TreeView	tvw		Form	frm

2. Form Instantiation
   • The primary form for a project is instantiated in the Main method of the startup class.

   • Secondary forms are instantiated using the new operator as needed.

3. Event Handlers   MonthlyPayment Example
   • An event handler has the following form:
     private void button1_Click(object sender, EventArgs e)
     {
         ...
     }

   • sender and e that are passed in as parameters when an event occurs.
     sender is the control that caused the event.
     e supplies addition information about the event.

   • To register the event handler button1_Click with the Button.Click event:
     button1.Click += new EventHandler(button1_Click);

   • The code
     new EventHandler(button1_Click);
     creates a delegate that contains a reference to the button1_Click method.

   • The MonthlyPayment Example uses the Enter and Leave events with corresponding event handlers that fire when a control gains or loses focus.

Part C: ASP.Net Controls

1. The WebControl Class   ToUpper1 Example
   • Like WinForms controls, every ASP.Net web control is defined by a .Net class.

   • The complete inheritance hierarchy of the WebControl class is
     object (System.Object)   (Any C# object)
         System.Web.UI.Control   (Any control on an ASP.Net web page. Two common possibilities are HtmlControl and WebControl.)
            System.Web.UI.Control.WebControls.WebControl  (Any ASP.Net control)
              
   • WebControl objects also have constructors, properties, methods, and events.

2. Web Pages
   • An ASP.Net web page consists of
     1. an .aspx page that contains items such as HTML markup and web controls,

     2. a code-behind page that contains C# or Visual Basic source code.

     3. An ASP.Net control such as a textbox is defined on an .aspx page using an XML tag like this:
        <asp:TextBox ID="TextBox1" Width="200px"
           runat="server">0</asp:TextBox>

   • An .aspx page also contains a header:
     <%@ Page Language="C#" AutoEventWireup="true"
         CodeBehind="WebForm1.aspx.cs"
         Inherits="WebApplication1.WebForm1" %>

   • Visual Studio, by default, creates a web project with a page that uses a master page. Since master pages are discussed later, we first create an empty web project, and then add a single web page (WebPage1.aspx) to the project with associated code-behind file WebPage1.aspx.cs.

3. Event Handlers and Wireup
   • An event handler is specified in a code-behind file, for example, WebForm1.aspx.cs:
     protected void Button1_Click(object sender, EventArgs e)
     {
         // body of event handler
     }

   • An event handler is connected (wired) to a control using an attribute in the web control definition:
     <asp:Button ID="Button1" Text="Button"
         OnClick="Button1_Click" runat="server" />

   • The .aspx page header contains the specification
     AutoEventWireup="true"
     This avoids the need to define explicit delegates to connect events to event handlers.

4. Viewing an ASP.Net Page in a Browser   ToUpper1, ToUpper2 Examples
   • During development, web applications can be viewed in the lightweight ASP.Net Development webserver that displays pages with a localhost URL.

   • For uploading an ASP.Net project to a server hosting ASP.Net, two options are possible:
     1. (ToUpper1 Example) Upload all the .aspx pages the server. In addition upload the compiled DLL for the project into the home folder.

     2. (ToUpper2 Example) Before uploading, move the page event handlers from the code-behind file to the top of the .aspx page within script tags like this:
        <script runat="header">
        // event handlers go here.
        </script>
        This script goes immediately under the .aspx page header. Then delete the code-behind source code files and the CodeBehind and Inherits specifications in the .aspx page header.

Part D: Some Specific Web Controls

1. Standard Control Members
   • Properties:   AppRelativeTemplateSourceDirectory BindingContainer CLientID Controls EnableTheming EnableViewStateID NamingContainer Page Parent Site TemplateControl TemplateSourceDirectory UniqueID Visible

2. Standard WebControl Members
   • Properties:   AccessKey AutoPostBack BackColor BorderColor BorderStyle BorderWidth CausesValidation CssClass Enabled EnableTheming Font ForeColor Height IsEnabled SkinID Style TabIndex ToolTip ValidationGroup ViewStateMode Width

   • Methods:   ApplyStyle ApplyStyleSheetSkin DataBind Dispose Focus ToString

   • Events:   DataBinding Disposed Init Load PreRender Unload

3. TextBox
   • Properties:   AutoComplete Columns MaxLength ReadOnly Rows Text TextMode

   • Event:   TextChanged

4. Button   ToUpper1 Example
   • Properties:   PostBackUrl Text

   • Event:   Click Command

5. Label
   • Properties:   Text

   • The Label control is usually used for labeling the function of other controls.

6. Literal   ShowPoem Example
   • Properties:   Text

   • The Literal control is more lightweight than the Label control. It is used for displaying literal HTML text on a web page.

   • The Literal control inherits directly from the Control class.

7. RadioButton   Quiz1 Example
   • Properties:   AutoPostBack Checked

   • Events:   CheckedChanged

8. ListItem   Animals Example
   • Properties: Enabled Selected Text Value

   • Methods: (S) FromString

   • ListItem objects inherit directly from the Object class.

   • ListItem objects are used in the RadioButtonList and DropDownMenuList controls.

   • The complete inheritance hierarchy for these controls:
     System.Object
         System.Web.UI.Control  
            System.Web.UI.WebControls.WebControl  
               System.Web.UI.WebControls.BaseDataBoundControl  
                  System.Web.UI.WebControls.ListControl  
                     System.Web.UI.WebControls.RadioButtonList or
                     System.Web.UI.WebControls.DropDownMenuList
     

9. RadioButtonList   Quiz2 Example
   • Properties:   SelectedIndex SelectedItem SelectedValue

   • Events: OnSelectedIndexChanged

10. CheckBox   Beverage Example
    • Properties:   AutoPostBack Checked

    • Events:   CheckedChanged

11. DropDownMenuList   ChineseZodiac
    • Properties:   SelectedIndex SelectedItem SelectedValue

    • Events: OnSelectedIndexChanged

12. Image   Greeter3 Example
    • Properties:   AlternateText DescriptionUrl ImageAlign ImageUrl

    • Images must be added to the Visual Studio project to be accessible to the image control.

Part E:   HTML Controls

1. Client-side vs. Server-side Controls
   • ASP.Net Web controls are server-side controls. They generate events that trigger event handlers, written in C# or Visual Basic that are executed by the server.

   • Client-side controls generate events that trigger event handlers that are executed by the browser.

   • ASP.Net also provides traditional HTML controls, which execute JavaScript event handlers.

2. Examples of HTML Controls   HtmlControls Example
   • HTML Controls available in Visual Studio:
     Button Reset Submit Text File Password Checkbox Radio

     Hidden TextArea Table Image Select Horizontal Rule Div

Part F:   CurrencyConverter Project

• Discuss the CurrencyConverter Project.

• Look at the Misc.CurrRateFromWeb Example.