ProgramGood.Net - Beginning C# OOP

Ch15 Inheritance and Polymorphism

Dave Mateer — Wed, 23 Dec 2009 16:13:03 GMT

Symbolic constants vs Enumerated Types'

These constants are handy when cheking on the setter (as can use an int range)

    public const int APARTMENT
= 1;

    public const int COMMERCIAL
= 2;

    public const int HOME
= 3;

    public int BuildingType

        get { return buildingType;
}

set

            if (value >=
APARTMENT && value <= HOME)

                buildingType = value;

This keyword

public clsBuilding()

        address = "Not
closed yet";

    public clsBuilding(string addr, decimal price, decimal payment, decimal tax, decimal insur,
DateTime date, int type)

        : this() //
good practise to call initial constructor first..second constructor will overwrite
address = "Not closed yet"

        if (addr.Equals("")
== false)

            address = addr;

        purchasePrice = price;

        monthlyPayment = payment;

        taxes = tax;

        insurance = insur;

        datePurchased = date;

        buildingType = type;

Base keyword

    public clsCommercial(string addr, decimal price, decimal payment,

                        decimal tax, decimal insur,
DateTime date, int type) :

                        base(addr,
price, payment, tax, insur, date, type)

        buildingType = type;   //
Commercial type from base

this is calling the bases’ constructor.

can also call base methods from the derived (child) class.

Polymorphism

essentially this means we can send the same message to a group of different classes and each class will know how to respond correctly. eg

        lstMessages.Items.Add(myApt.RemoveSnow());

        lstMessages.Items.Add(myComm.RemoveSnow());

        lstMessages.Items.Add(myHome.RemoveSnow());

clsApt and clsComm have overridden methods and respond with different phone numbers. clsHome doesn’t have a RemoveSnow method and responds as above.

Abstract Classes

To prevent instantiation of the base class ie if it makes no sense.

public abstract class clsDeciduous

Virtual and Override

The method may be overridden in a derived class.

    public virtual string RemoveSnow()

        return whichType[buildingType]
+ ": No snow removal service available.";

And in the derived class:

public override string RemoveSnow()

        return "Commercial:
Call Acme Snow Plowing: 803.234.5566";

To prevent further inheritence use public sealed class.

Implicitly Typed Local Variables and Anonymous Types

Dave Mateer — Wed, 23 Dec 2009 16:12:38 GMT

From msdn.

        //
i is compiled as an int

        var i = 5;

        //
s is compiled as a string

        var s = "Hello";

        //
a is compiled as int[]

        var a = new[]
{ 0, 1, 2 };

        //
person is compiled as an anonymous type

        var person = new {
Name = "Terry", Age = 34 };

Anonymous types:

var v = new {
Amount = 108, Message = "Hello" };

Anonymous types provide a convenient way to encapsulate a set of read-only properties into a single object without having to first explicitly define a type

Ch14 Databases

Dave Mateer — Wed, 23 Dec 2009 10:51:11 GMT

See: http://www.programgood.net/2009/10/20/TestDrivenDevelopmentInNETDALCh5.aspx

ADO.NET (ActiveX Data Objects) consists of two primary parts:

Data provider

These classes provide access to a data source, such as a Microsoft SQL Server. Each data source has its own set of provider objects, but they each have a common set of utility classes:

Connection: Provides a connection used to communicate with the data source.
Command: Used to perform some action on the data source, such as reading, updating, or deleting relational data.
Parameter: Describes a single parameter to a command. A common example is a parameter to a stored procedure.
DataAdapter: A bridge used to transfer data between a Data source and a DataSet object (see below).
DataReader: Used to efficiently process a large list of results one record at a time. It allows records to be accessed in a read-only, forward-only mode, i.e., records have to be accessed in sequential order; they can neither be randomly accessed nor can a record which has been processed previously be accessed again.

DataSets

DataSet objects, a group of classes describing a simple in-memory relational database,

A DataSet object represents a schema (either an entire database or a subset of one). It can contain tables and relationships between those tables.
- A DataTable object represents a single table in the database. It has a name, rows, and columns.
  - A DataView object overlays a DataTable and sorts the data (much like an SQL "order by" clause) and filters the records (much like an SQL "where" clause) if a filter is set. An in-memory index is used to facilitate these operations. All DataTables have a default filter, while any number of additional DataViews can be defined, reducing interaction with the underlying database and thus improving performance.
    - A DataColumn represents a column of the table, including its name and type.
    - A DataRow object represents a single row in the table; it allows reading and updating of values in that row, likewise retrieving any rows that are related to it through a primary-key foreign-key relationship.

OLE-DB is a replacement for ODBC.

When adding in a reference (a COM – Component Object Model).. I had to restart VS to get Resharper/VS to recognize and give me intellisense.

The reference was an ADOX reference – ADO ext 2.8 for DDL and Security. We have to use this as the OLE DB features do not give create new database functionality.

int index;

        string newDB;

        string dbName
= txtDatabaseName.Text;

try

            if (dbName.Length
== 0)

                return;

            index = dbName.LastIndexOf('.');

            if (index
== -1) // no secondary filename

                dbName += ".mdb";

            string pathName
= Application.StartupPath.ToString();

            string combinedName
= Path.Combine(pathName, dbName);

            ADOX.CatalogClass myCat = new ADOX.CatalogClass();

            newDB = CONNECTSTRING + combinedName + ";" +
CONNECTSTRINGPART2;

            myCat.Create(newDB);

            myCat = null;

CreateDatabase_website

Good bit of functionality, if you double click on an element in the list, it deletes it.

void lstFieldsToAdd_DoubleClick(object sender,
EventArgs e)

        ListView.SelectedIndexCollection indexes = lstFieldsToAdd.SelectedIndices;

        foreach (int index in indexes)

            lstFieldsToAdd.Items[index].Remove();

Writing to the database he uses a class in clsDB called ProcessCommand

However to read data he does this from a form object. So only using the clsDB to get the connection string.

OleDbConnection myDB = new OleDbConnection();

OleDbDataReader myReader;

OleDbCommand myCommand;

clsDB myData = new clsDB("Friend");

try

    myDB.ConnectionString = myData.getConnectString + dbName;

    myDB.Open();

    if (txtLastName.Text.Length
!= 0)

        sql = "SELECT
* FROM Friend WHERE LastName = '" +

              txtLastName.Text + "'";

    else

        sql = "SELECT
* FROM Friend WHERE ID = " + txtRecordID.Text;

    ClearFields();

    myCommand = new OleDbCommand(sql,
myDB);

    myReader = myCommand.ExecuteReader();

    if (myReader.Read()
== true)

        record = (int)myReader[0];

        txtRecordID.Text = record.ToString();

Querying and DataGrid

Changing properties on the grid, such as docking to allow window resizing, colour schemes, formatting of cells.

Double click on the database table automatically runs the execute query. User can drag column headers around, and sort each column. User can add/edit/del data (code not implemented in this example).

LINQ

var query = from p in numbers //
the linq query

                    where p
> lo && p < hi

                    select p;

        foreach (var
val in query) //
display results

            lstOutput.Items.Add(val.ToString());

This is an interesting construct, using anonymous types. What this is actually saying

var friends = new[]

                          new {name
= "Tom", state = "IN"},

                          new {name
= "Alice", state = "VA"},

                          new {name
= "Tammy", state = "IN"},

                          new {name
= "Ann", state = "KY"},

};

var query = from p in friends

                        where p.state
== txtLow.Text

                        select p;

            foreach (var
val in query)

                lstOutput.Items.Add(val.name.ToString() + ",
" + val.state.ToString());

Beginning C# 3.0 – An Introduction to Object Oriented Programming

Dave Mateer — Wed, 09 Dec 2009 17:57:59 GMT

This book looked interesting as it seemed to be written by someone with a lot of experience teaching. Sometimes it is great to go back to basics, as there is always something new to learn, and I was so right! Here are my notes, source code, screenshots.

Chapter 1 – Getting Started

setting up the IDE.. VS2008 Express. And installing the MSDN library.. 2GB download here: http://www.microsoft.com/downloads/details.aspx?FamilyID=7BBE5EDA-5062-4EBB-83C7-D3C5FF92A373&displaylang=en

Also a tool to take msdn into a chm help file: http://www.codeplex.com/packagethis

Chapter 2 - Understanding Objects

Class eg Person.. a template used to describe an object
properties..that describe the object
methods.. or actions that we associate with the object

Object eg the Person Object for Jack

naming convention
cls - class
txt - textbob
btn - button

good for selecting in the ide

making a blank project
putting in references for winform:

System, System.Drawing, System.Windows.Forms

putting in bootstrapper
change output to winform and tell which startup object asdf

using System;
using System.Windows.Forms;

public class frmMain : Form
{
#region Windows code
private void InitializeComponent()
{
}
#endregion

public frmMain()
{
InitializeComponent();
}

public static void Main()
{
frmMain main = new frmMain();
Application.Run(main);
}

}

3d on labels cool
making a default enter button (acceptbutton)
ctrl x and ctrl d shortcut keys with the ampersand on Text
True Type vs non fonts.. good to make things line up properly.

**screenshot mailing label program

**source code here too … c:\code\oopbook

Part II – Understand C# Syntax

Chapter 3 – Understanding Data Types

Integer Division
.Focus property when coming back from an error
Int.TryParse method to see if it really is an integer
.Visible proerty of a textbox

Floating Point
AcceptButton
StartPosition - CenterScreen

int
float - 32 bit.. F,f
double - 64 bit... this is the usual one.. D,d
Decimal - 128bit (28 digit precision).. M,m

eg int i = 0.5M

**insert source code c:\code\oopbook\ch3IntegerDivision\

Also Fahrehiegh converter:

** put in source code link… c:\code\oopbook\ch3TempConvert

Interesting here was the use of consts…

how a division takes up more cycles, so better not to do 5/9 but to put in the decimal equivalent. The out.. focus when coming back from an error. And unhiding the results box when it needs to be.

bool flag;
double operand1;
double answer;
const double FIVENINTHS = 0.55555555;
const double ZEROFAHRENHEIGHT = 32;

flag = double.TryParse(txtOperand1.Text, out operand1);
if (flag == false)
{
MessageBox.Show("Enter a whole number", "Input Error");
txtOperand1.Focus();
return;
}

answer = FIVENINTHS *(operand1 - ZEROFAHRENHEIGHT);

txtResult.Text = operand1.ToString() + " degressF " + " equals " + answer.ToString() + " degreesC";
txtResult.Visible = true;

Ch4 – Understanding C# Statements

operand eg 10
operator eg +, -, *, /, % these are binary operators
unary
binary
ternary

expression
one or more operands and their associated operator

statements
one or more expressions terminated by a semicolon.

lvalue - location value.. memory address
rvalue - register value..actual value

eg int i
this is defining a variable to be at address 900,000 ie lvalue
i = 10
this is declaring a variable to have an rvalue of 10

if narly bug, hardcode data into the textboxes to make it easy!
10 / 6

avoid magic numbers
use const

Ch5 - Reference Data Types

If you're not going to manipulate data with Maths, store it as a string.

intellisense (expect in Resharper which is clearer)
hand is a property
diamond is a method

Pass by reference vs Pass by Value

Ctrl spacebar to give help on methods/props near current selection.

**insert source…c:\code\oopbook\ch5StringTester

Escape characters eg string message = “this is a \\ backlash, and this is a quote \””;

String literals eg string message = @”Go the the c:\program files\ directory and”;

DateTime reference Objects

**upload source code** c:\code\oopbook\ch5DateTime

Interesting code here is:

txtLongDate.Text = myTime.ToString("D");

Starting the app (everything gets populated automatically without having to press Test)

public frmMain()
{
// 2) place all the label, textbox and button objects in correct positions on the form and set their properties
InitializeComponent();
UpdateTimeInfo(); // 3) set the properties of the objects just created
}

public static void Main()
{
// 1) start here then this goes to constructor now everything is in memory ready to go
frmMain main = new frmMain();
Application.Run(main); // 4) run the app
MessageBox.Show("hello"); // 5) this would only be displayed when Close() is called.
}

Ch6 – Making Decisions In Code

20% of a programs time is spent in initial development

80% of a programs time is spent in testing, debugging, and maintenance

flag = int.TryParse(txtOperand1.Text, out operand1);

don’t need to initialise operand1 to any value.. int operand1 is fine.

**upload code ** c:\code\oopbook\ch6OddOrEven

Interesting here is the .Clear method after the check.

MessageBox.Show("Enter a whole number", "Input Error");
txtOperand1.Clear();
txtOperand1.Focus();
return;

Brackets Style:

K&R (Kernighan and Ritchie… 1978 book on C)

if (x == 2) {

//do something

}

Other style:

if (x == 2)

{

//do something

}

if (x == 2)

// do something

the danger of the above is it’s easier to make a mistake like:

if (x == 2); // notice the semicolon!

//do something

Nested If Statements / Cascading if statements

Switch

statements are better

switch (expression1)

{

case 1:

// do stuff here

break;

case 2:

// do other stuff

break;

default:

// do the default stuff.

break;

}

Ch7 Statement Repetition Using Loops

<= end; i++)
for (i = start; i {
// {0, 5} first argument and right-justify it in a field of five characters
// {1,20} second argument and right-justify in a field of twenty characters
buff = string.Format("{0, 5}{1, 20}", i, i*i);
lstOutput.Items.Add(buff);
}

for loops – ideally suited for counting operations

while loops are good for searching for a particular value in a set

bucket = 1;
for (int i = num; i > 1; i--)
{
bucket *= i;
}

Don’t need to do the last factorial as it multiplies by 1, so leave i > 1.

Keyboard shortcut – F7 to view designer / view code

Notice the currency here:

buff = string.Format("{0,4}, {1,15:C}", i, assetIsWorth);
lblResults.Items.Add(buff);

http://www.programgood.net/2009/12/14/ParameterPassingInCValueAndReferenceTypes.aspx