- •Microsoft C# Programming for the Absolute Beginner
- •Table of Contents
- •Microsoft C# Programming for the Absolute Beginner
- •Introduction
- •Overview
- •Chapter 1: Basic Input and Output: A Mini Adventure
- •Project: The Mini Adventure
- •Reviewing Basic C# Concepts
- •Namespaces
- •Classes
- •Methods
- •Statements
- •The Console Object
- •.NET Documentation
- •Getting into the Visual Studio .Net Environment
- •Examining the Default Code
- •Creating a Custom Namespace
- •Adding Summary Comments
- •Creating the Class
- •Moving from Code to a Program
- •Compiling Your Program
- •Looking for Bugs
- •Getting Input from the User
- •Creating a String Variable
- •Getting a Value with the Console.ReadLine() Method
- •Incorporating a Variable in Output
- •Combining String Values
- •Combining Strings with Concatenation
- •Adding a Tab Character
- •Using the Newline Sequence
- •Displaying a Backslash
- •Displaying Quotation Marks
- •Launching the Mini Adventure
- •Planning the Story
- •Creating the Variables
- •Getting Values from the User
- •Writing the Output
- •Finishing the Program
- •Summary
- •Chapter 2: Branching and Operators: The Math Game
- •The Math Game
- •Using Numeric Variables
- •The Simple Math Game
- •Numeric Variable Types
- •Integer Variables
- •Long Integers
- •Data Type Problems
- •Math Operators
- •Converting Variables
- •Explicit Casting
- •The Convert Object
- •Creating a Branch in Program Logic
- •The Hi Bill Game
- •Condition Testing
- •The If Statement
- •The Else Clause
- •Multiple Conditions
- •Working with The Switch Statement
- •The Switch Demo Program
- •Examining How Switch Statements Work
- •Creating a Random Number
- •Introducing the Die Roller
- •Exploring the Random Object
- •Creating a Random Double with the .NextDouble() Method
- •Getting the Values of Dice
- •Creating the Math Game
- •Designing the Game
- •Creating the Variables
- •Managing Addition
- •Managing Subtraction
- •Managing Multiplication and Division
- •Checking the Answers
- •Waiting for the Carriage Return
- •Summary
- •Chapter 3: Loops and Strings: The Pig Latin Program
- •Project: The Pig Latin Program
- •Investigating The String Object
- •The String Mangler Program
- •A Closer Look at Strings
- •Using the Object Browser
- •Experimenting with String Methods
- •Performing Common String Manipulations
- •Using a For Loop
- •Examining The Bean Counter Program
- •Creating a Sentry Variable
- •Checking for an Upper Limit
- •Incrementing the Variable
- •Examining the Behavior of the For Loop
- •The Fancy Beans Program
- •Skipping Numbers
- •Counting Backwards
- •Using a Foreach Loop to Break Up a Sentence
- •Using a While Loop
- •The Magic Word Program
- •Writing an Effective While Loop
- •Planning Your Program with the STAIR Process
- •S: State the Problem
- •T: Tool Identification
- •A: Algorithm
- •I: Implementation
- •R: Refinement
- •Applying STAIR to the Pig Latin Program
- •Stating the Problem
- •Identifying the Tools
- •Creating the Algorithm
- •Implementing and Refining
- •Writing the Pig Latin Program
- •Setting Up the Variables
- •Creating the Outside Loop
- •Dividing the Phrase into Words
- •Extracting the First Character
- •Checking for a Vowel
- •Adding Debugging Code
- •Closing Up the code
- •Summary
- •Introducing the Critter Program
- •Creating Methods to Reuse Code
- •The Song Program
- •Building the Main() Method
- •Creating a Simple Method
- •Adding a Parameter
- •Returning a Value
- •Creating a Menu
- •Creating a Main Loop
- •Creating the Sentry Variable
- •Calling a Method
- •Working with the Results
- •Writing the showMenu() Method
- •Getting Input from the User
- •Handling Exceptions
- •Returning a Value
- •Creating a New Object with the CritterName Program
- •Creating the Basic Critter
- •Using Scope Modifiers
- •Using a Public Instance Variable
- •Creating an Instance of the Critter
- •Adding a Method
- •Creating the talk() Method for the CritterTalk Program
- •Changing the Menu to Use the talk() Method
- •Creating a Property in the CritterProp Program
- •Examining the Critter Prop Program
- •Creating the Critter with a Name Property
- •Using Properties as Filters
- •Making the Critter More Lifelike
- •Adding More Private Variables
- •Adding the Age() Method
- •Adding the Eat() Method
- •Adding the Play() Method
- •Modifying the Talk() Method
- •Making Changes in the Main Class
- •Summary
- •Introducing the Snowball Fight
- •Inheritance and Encapsulation
- •Creating a Constructor
- •Adding a Constructor to the Critter Class
- •Creating the CritViewer Class
- •Reviewing the Static Keyword
- •Calling a Constructor from the Main() Method
- •Working with Multiple Files
- •Overloading Constructors
- •Viewing the Improved Critter Class
- •Adding Polymorphism to Your Objects
- •Modifying the Critter Viewer in CritOver to Demonstrate Overloaded Constructors
- •Using Inheritance to Make New Classes
- •Creating a Class to View the Clone
- •Creating the Critter Class
- •Improving an Existing Class
- •Introducing the Glitter Critter
- •Adding Methods to a New Class
- •Changing the Critter Viewer Again
- •Creating the Snowball Fight
- •Building the Fighter
- •Building the Robot Fighter
- •Creating the Main Menu Class
- •Summary
- •Overview
- •Introducing the Visual Critter
- •Thinking Like a GUI Programmer
- •Creating a Graphical User Interface (GUI)
- •Examining the Code of a Windows Program
- •Adding New Namespaces
- •Creating the Form Object
- •Creating a Destructor
- •Creating the Components
- •Setting Component Properties
- •Setting Up the Form
- •Writing the Main() Method
- •Creating an Interactive Program
- •Responding to a Simple Event
- •Creating and Adding the Components
- •Adding an Event to the Program
- •Creating an Event Handler
- •Allowing for Multiple Selections
- •Choosing a Font with Selection Controls
- •Creating the User Interface
- •Examining Selection Tools
- •Creating Instance Variables in the Font Chooser
- •Writing the AssignFont() Method
- •Writing the Event Handlers
- •Working with Images and Scroll Bars
- •Setting Up the Picture Box
- •Adding a Scroll Bar
- •Revisiting the Visual Critter
- •Designing the Program
- •Determining the Necessary Tools
- •Designing the Form
- •Writing the Code
- •Summary
- •Chapter 7: Timers and Animation: The Lunar Lander
- •Introducing the Lunar Lander
- •Reading Values from the Keyboard
- •Introducing the Key Reader Program
- •Setting Up the Key Reader Program
- •Coding the KeyPress Event
- •Coding the KeyDown Event
- •Determining Which Key Was Pressed
- •Animating Images
- •Introducing the ImageList Control
- •Setting Up an Image List
- •Looking at the Image Collection
- •Displaying an Image from the Image List
- •Using a Timer to Automate Animation
- •Introducing the Timer Control
- •Configuring the Timer
- •Adding Motion
- •Checking for Keyboard Input
- •Working with the Location Property
- •Detecting Collisions between Objects
- •Coding the Crasher Program
- •Getting Values for newX and newY
- •Bouncing the Ball off the Sides
- •Checking for Collisions
- •Extracting a Rectangle from a Component
- •Getting More from the MessageBox Object
- •Introducing the MsgDemo Program
- •Retrieving Values from the MessageBox
- •Coding the Lunar Lander
- •The Visual Design
- •The Constructor
- •The timer1_Tick() Method
- •The moveShip() Method
- •The checkLanding() Method
- •The theForm_KeyDown() Method
- •The showStats() Method
- •The killShip() Method
- •The initGame() Method
- •Summary
- •Chapter 8: Arrays: The Soccer Game
- •The Soccer Game
- •Introducing Arrays
- •Exploring the Counter Program
- •Creating an Array of Strings
- •Referring to Elements in an Array
- •Working with Arrays
- •Using the Array Demo Program to Explore Arrays
- •Building the Languages Array
- •Sorting the Array
- •Designing the Soccer Game
- •Solving a Subset of the Problem
- •Adding Percentages for the Other Players
- •Setting Up the Shot Demo Program
- •Setting Up the List Boxes
- •Using a Custom Event Handler
- •Writing the changeStatus() Method
- •Kicking the Ball
- •Designing Programs by Hand
- •Examining the Form by Hand Program
- •Adding Components in the Constructor
- •Responding to the Button Event
- •Building the Soccer Program
- •Setting Up the Variables
- •Examining the Constructor
- •Setting Up the Players
- •Setting Up the Opponents
- •Setting Up the Goalies
- •Responding to Player Clicks
- •Handling Good Shots
- •Handling Bad Shots
- •Setting a New Current Player
- •Handling the Passage of Time
- •Updating the Score
- •Summary
- •Chapter 9: File Handling: The Adventure Kit
- •Introducing the Adventure Kit
- •Viewing the Main Screen
- •Loading an Adventure
- •Playing an Adventure
- •Creating an Adventure
- •Reading and Writing Text Files
- •Exploring the File IO Program
- •Importing the IO Namespace
- •Writing to a Stream
- •Reading from a Stream
- •Creating Menus
- •Exploring the Menu Demo Program
- •Adding a MainMenu Object
- •Adding a Submenu
- •Setting Up the Properties of Menu Items
- •Writing Event Code for Menus
- •Using Dialog Boxes to Enhance Your Programs
- •Exploring the Dialog Demo Program
- •Adding Standard Dialogs to Your Form
- •Using the File Dialog Controls
- •Responding to File Dialog Events
- •Using the Font Dialog Control
- •Using the Color Dialog Control
- •Storing Entire Objects with Serialization
- •Exploring the Serialization Demo Program
- •Creating the Contact Class
- •Referencing the Serializable Namespace
- •Storing a Class
- •Retrieving a Class
- •Returning to the Adventure Kit Program
- •Examining the Room Class
- •Creating the Dungeon Class
- •Writing the Game Class
- •Writing the Editor Class
- •Writing the MainForm Class
- •Summary
- •Chapter 10: Chapter Basic XML: The Quiz Maker
- •Introducing the Quiz Maker Game
- •Taking a Quiz
- •Creating and Editing Quizzes
- •Investigating XML
- •Defining XML
- •Creating an XML Document in .NET
- •Creating an XML Schema for Your Language
- •Investigating the .NET View of XML
- •Exploring the XmlNode Class
- •Exploring the XmlDocument Class
- •Reading an Existing XML Document
- •Creating the XML Viewer Program
- •Writing New Values to an XML Document
- •Building the Document Structure
- •Adding an Element to the Document
- •Displaying the XML Code
- •Examining the Quizzer Program
- •Building the Main Form
- •Writing the Quiz Form
- •Writing the Editor Form
- •Summary
- •Overview
- •Introducing the SpyMaster Program
- •Creating a Simple Database
- •Accessing the Data Server
- •Accessing the Data in a Program
- •Using Queries to Modify Data Results
- •Limiting Data with the SELECT Statement
- •Using an Existing Database
- •Adding the Capability to Display Queries
- •Creating a Visual Query Builder
- •Working with Relational Databases
- •Improving Your Data with Normalization
- •Using a Join to Connect Two Tables
- •Creating a View
- •Referring to a View in a Program
- •Incorporating the Agent Specialty Attribute
- •Working with Other Databases
- •Creating a New Connection
- •Converting a Data Set to XML
- •Reading from XML to a Data Source
- •Creating the SpyMaster Database
- •Building the Main Form
- •Editing the Assignments
- •Editing the Specialties
- •Viewing the Agents
- •Editing the Agent Data
- •Summary
- •List of Figures
- •List of Tables
- •List of Sidebars
It’s okay if you’re still a little confused, because the various characteristics of a node can be very confusing. If you’re still hazy, run the XML Viewer and watch what happens as you move around in a document. Look at the XML source code of your XML document so that you can see how it relates to the various properties of the node object. The best way to make sure that you understand this is to build a quick XML document in the XML editor, load it into the XML Viewer, and see whether you understand how everything fits together. The XML Viewer is really just a window into the XmlNode class, so if you understand how it works, you are well on your way to understanding XML in .NET.
Creating the XML Viewer Program
The design of the XML Viewer program is more transparent than in many programs in this book because the XML Viewer is meant primarily as a programmer’s tool. Most of the form’s visual elements map directly to a specific property of the XmlNode class.
Building the Visual Layout
The XML Viewer provides a window to a document by providing details about one node at a time. Several properties of the current node are shown, including the Name, Value, InnerText, and InnerXml properties. The values of each of these properties are displayed in an appropriately named label (see Figure 10.13).
Figure 10.13: Most of the visual interface is composed of labels, with a few buttons and a list box added for navigation.
In addition to the mentioned properties of the node, the XML Viewer displays the name of the parent node in the Parent button. The name and description of each of the current node’s child nodes are listed in a text box.
The user can maneuver through the document by clicking the Parent button, double−clicking a child in the list box, clicking the Root button (which takes the user directly to the document’s root), or clicking the Next Sibling button, which displays the current node’s next sibling, if it has one.
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I made the lblInnerText and lblInnerXml labels taller than a typical label because I knew that they would sometimes include large amounts of text. I placed these labels and their descriptors inside panels to break up the screen and make the purpose of the large labels apparent.
I used a list box to display child nodes because it seemed like a natural fit. The children can be any number of elements and can easily be described by string values. The list box seemed like the simplest way to handle the display and selection of child nodes.
Creating Instance Variables
The XML Viewer program has only two form−level variables, and both are classes from the System.Xml namespace. The viewer code begins with a reference to that namespace:
using System.Xml;
The two instance variables are an XmlDocument object named doc and an XmlNode object named theNode:
private XmlNode theNode; private XmlDocument doc;
The doc variable will contain a reference to the entire XML document. It will remain the same until the user requests another document with the Open Document button. The theNode variable will change to reflect whichever node is currently being described on the screen.
Initializing the Program
As usual, I did much of my initialization in the form’s load event. The main objectives of the xmlReader_Load() method are to load the document from a file, set theNode to the root document of the file, and display the root node:
private void xmlReader_Load(object sender, System.EventArgs e) {
doc = new XmlDocument(); doc.Load("c#Test.xml"); theNode = doc.FirstChild; displayNode();
} // end form load
The doc = new XmlDocument() code assigns a new instance of the XmlDocument class to doc. The next line uses doc’s Load() method to load a pre−existing file name. The FirstChild property of doc will call the first tag in the document, which is usually the <xml> tag. displayNode() is a method of the XML Reader class that I’ll describe in the next section.
Displaying a Node
The code to display a node is the centerpiece of the XML Viewer program. It is involved, so I’ll explain the displayMode() method in smaller pieces: (look on the CD−ROM to see the function in its complete form.)
The displayNode() method begins by creating a local XmlNode named childNode. This variable will be used to populate the child list box.
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Working with the Plain Text Properties
The first series of statements deals with the properties of a node that return plain text:
//handle all the straight text properties lblCurName.Text = theNode.Name; lblCurValue.Text = theNode.Value; lblInnerXml.Text = theNode.InnerXml; lblInnerText.Text = theNode.InnerText;
There isn’t anything at all challenging about this code because all the properties return a text value, which is easily mapped to the Text property of the labels.
Displaying and Enabling the Parent Button
The more interesting work comes when dealing with the parent, child, and sibling properties because they do not simply return a string value, but an actual node. You must take more care when dealing with these properties:
//handle the parent button btnParent.Text = theNode.ParentNode.Name; //enable btnParent only when appropriate
if (theNode.ParentNode.NodeType == XmlNodeType.Element){ btnParent.Enabled = true;
}else {
btnParent.Enabled = false;
}// end if
The ParentNode property returns an XmlNode. I mapped the name of this node to a button because I want the user to be able to view the parent by clicking the button. This is easily accomplished, but there’s a potential problem. If the user is already at the document’s root, the parent is listed as #document, which cannot be traversed. The easiest way to prevent this problem is to check the parent node’s type as soon as a node is loaded and to disable the Parent button when displaying the parent node is inappropriate. I used an if statement to compare the NodeType of the parent node to a built−in value called Xml.NodeType.Element. I allowed the Parent button to be displayed only if the parent is an element type. This will be true in all nodes of an XML document but the root, so it prevents moving above the root node.
Trick The code for moving to the parent class belongs in the Parent button’s click event. You might think that it would make more sense to put code that traps for an error in the event method where the error will occur (which is in the button click, in this instance). However, sometimes the best kind of error handling is error prevention. Rather than trap for an error after it has occurred (which would happen if you put the code in the button press method), you can prevent the button from being pressed when you know that it will cause an error. Often this type of preventive programming saves you grief in the long run. You will see the practice used in a couple other places in the XML Viewer program.
Enabling the Next Sibling Button
Like the Parent button, the Next Sibling button is enabled only if the program has determined that the current node has a next sibling. If it does not, the NextSibling property returns the value null. Using an else clause is important because it’s possible that the button has been disabled by a previous node. Therefore, you must always explicitly set it disabled or enabled, based on the NextSibling property of the current node.
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Populating the Children List Box
The child nodes require a different display technique because you cannot predict how many children a node will have. The list box control is a very convenient way to work with child nodes because it is designed to hold lists. Whenever the user wants to display a new node, the list box must be repopulated, based on the current node’s children:
//populate the list box with children XmlNode childNode; lstChildren.Items.Clear();
if (theNode.HasChildNodes){ childNode = theNode.FirstChild; while (childNode != null){
lstChildren.Items.Add(childNode.Name + " − " + childNode.InnerText);
childNode = childNode.NextSibling;
} // end while
}// end if statement
The first task is to clear the list box so that any residual items are removed. Then the program checks whether the current node has any child nodes. If not, there is no need to proceed. If so, the local childNode variable is assigned the first child of the parent node. As long as the child node exists (in other words, isn’t null), the name and inner text of the child node are added to the ListBox, and the next sibling is assigned to childNode. If there isn’t a next sibling, childNode will get a null value, which ends the loop.
Moving to the Other Nodes
Three buttons on the XML Viewer form are used to move to a new place within the XML document and display the resulting node. The code for these three methods is very similar, so I will present them together:
private void btnNextSib_Click(object sender, System.EventArgs e) {
theNode = theNode.NextSibling; displayNode();
} // end btnNextSib
private void btnParent_Click(object sender, System.EventArgs e) {
theNode = theNode.ParentNode; displayNode();
} // end btnParent
private void btnRoot_Click(object sender, System.EventArgs e) {
theNode = doc.FirstChild; displayNode();
} // end btnRoot
All three of these buttons set theNode to a new node and then call the displayNode() method to display the new node. The only thing different about the various methods is which node is displayed. The btnNextSib_Click() method sets the button to the current node’s next sibling. It isn’t necessary to ensure that there is a next sibling here because the displayNode() method disables this button if there are no more siblings. The code can be called only when theNode has a next sibling.
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The btnParent_Click() method sets theNode to the current node’s parent node. As with the sibling, the showNode() method prevents the Parent button from being active if the current node’s parent is not an element.
The btnRoot_Click() method always goes to the root element of the XML document, which is always the first child of the document. There’s no need for error checking here because any valid XML document has at least one child element. The first child of the document is commonly referred to as the root of the document.
Moving to a Child Node
The child nodes of the current node are stored in the lstChildren list box. The general approach to selecting a child is much like that for the buttons. However, ensuring that the viewer moves to the appropriate node requires attention. First, I did not use the default event of the list box because it seemed more appropriate to move to a new child after the user double−clicks a child in the list box. (Usually, if a list box has any direct events, they are related to double clicks. A single click is usually used to change which element in the list box currently has the focus.) The double−click event code uses the selectedIndex property to determine which child the user wants to see and to set theNode appropriately:
private void lstChildren_DoubleClick(object sender, System.EventArgs e) {
if (lstChildren.Items.Count > 0){
theNode = theNode.ChildNodes[lstChildren.SelectedIndex]; displayNode();
} // end if
}// end lstChildren
Upon testing the program, I discovered that the user could double−click the list box even if the current node has no children, causing an exception. I used an if statement to prevent this situation from occurring.
Opening a New Document
The XML Viewer program works with any valid XML document, not just the one I used as a default. To take advantage of this, I added a button to open a new file. The code for this button displays a File dialog, opens the requested file, and sets the node to the new file’s root node:
private void btnOpen_Click(object sender, System.EventArgs e) {
if (opener.ShowDialog() != DialogResult.Cancel){ doc.Load(opener.FileName);
theNode = doc.FirstChild;
}// end if
}// end btnOpen
Trick You might want to use the Open button to examine a version of the test XML that might be considered a better design. TestComplex.xml (included on the CD−ROM) has an <answer> element that contains a group of elements. Use the XML Viewer to explore this document and see how it changes things. You might also want to open the XML document in Visual Studio and see how it changes the data mode.
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