HOW CAN OBJECT ORIENTED PROGRAMMING AND PC# WORK TOGETHER
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Object Oriented Programming is considered to be essential for business. Some believe that
using Personal C Sharp and object oriented programming cannot go together. This is incorrect.
The fact that the classes which we have used for all of the illustrative examples extend
class (pcs) does not mean that you need to extend (pcs) by all your classes. You like to
create hundreds of classes which extend some ".NET" classes, extend one another, implement
interfaces and instanciate one another. How could that be done while they are able to access
Personal C Sharp class methods? To use an instance of class (pcs) into every class you have,
will probably be a waste of resources.
One answer is internal classes. Divide your classes into groups. Create a container class for
each group which extends class (pcs), then create a static object of the container class and
use it to access PC# methods by all the classes inside the container class.
Let us see an example. In the first example of "Networking" we have showed how to obtain the
stock price of one stock using Yahoo's financial website. Let us make it general. We need to
write a group of classes which work to gether to allow the user to get the stock price for any
stock symbol which he provides. The classes will be accessing PC# methods to do their job
without extending (pcs)
This little project requires two types of classes:
(1) Library classes to do all the important operations.
(2) One executable class which will be very simple.
The executable class will use the other classes to do most of the job then will display the
results to the user. This class will be good to extend PC# if you like to have a nice looking
display without much of work. However, you can also do it all by yourself.
The job will be shared by 3 library classes which will be contained into a class named "Library"
which extends (pcs) Class "Library" will be compiled to a "dll" file with the tool "pcl".
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Example 1: Write a library of classes to get a stock symbol from the user then obtain the
latest stock price for the symbol. Write also an executable class to display the results
to the user.
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The Library Class:
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public class Library:pcs { // The class extends (pcs)
static new Library l=new Library(); // (l) is a static object of the Library
// class. The "new" word is to prevent
// conflict with the int (l)
public override void init() {
l=this; // This makes (l) = the same instance which
base.init(); // the container class is running
}
public class GetSymbol { // First class
public string getSymbol () { // Method of first class
l.os="Enter Stock Symbol ";l.tm("i"); // Get symbol using PC# method tm()
return l.os; // and return it to caller.
}
}
public class GetPage { // Second class
public string getPage(string sy) { // Method of 2nd class, receives the symbol
l.urs="http://finance.yahoo.com/q?d=s&s="+sy; // It adds it to the URL
l.jb=true;l.kb=true;l.nm("hg"); // and retrieves the web page using PC#
return l.os; // method nm() then returns the page body
}
}
public class GetPrice { // Third class
public string getPrice(string pg) { // Method of 3rd class, receives the page
l.txs=pg; // Assigns it to searchable string (txs)
l.js="Last Trade:";l.ks="Trade Time:";l.tm("s");
// Calls PC#'s method tm("s") to find the
char[] CC=l.os.ToCharArray(); // price.
string price=""; // Now it's removing the "|" char's
for (int n=0;n< CC.Length;n++) { // around the price.
if (CC[n]!='|') price+=CC[n];
}
return price; // and returning the price.
}
}
}
The Executable Class:
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//assembly Library.dll; // Where to find refrenced objects of the
// class. (See PC# Reference) Notice that
// "Library.dll" is all we need to list here
public class a:pcs { // Class a extends (pcs)
public override void run() {
cm("fe"); // Eliminate form
Library.GetSymbol gs=new Library.GetSymbol(); // Creating object of GetSymbol class
Library.GetPage gp=new Library.GetPage(); // Creating object of GetPage class
Library.GetPrice gpr=new Library.GetPrice(); // Creating object of GetPrice class
os="When finished Push [ENTER]";tm();os="";tm();// Display instruction
while (true) { // Start of endless loop:
ss=gs.getSymbol(); // Call method of 1st class to get symbol
if (ss.Length<1) break; // Exit if [ENTER] pushed without entry
ps=gp.getPage(ss); // Call method of 2nd class to get page
os=gpr.getPrice(ps); // Call method of 3rd class to get price
os="Latest stock price: $"+os;tm(); // Display price.
}
}
}
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Can we make use of the Container Class: (This requires version 1.6 or higher)
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Since the container class running instance is the same instance which all inner classes use to
access PC# methods, the inner classes can for example, draw any object on the container's
Graphical Output device or display any text on the container's Text Screen.
This is a great advantage which makes it more convenient to eliminate class (a) and use the
library class to interface with the user.
In the next example, we are going to see how to do this. Additionally class "GetSymbol" will
be eliminated and class "GetPrice" will extend class "GetPage" and access its method by itself
to get the page before it searches it to obtain the price.
Class "GetPrice" will also display the stock price directly on it's container's Text Screen
which will make the container's class simpler. For this reason method getPrice() will be of
"void" type since no return value will be necessary.
The container's class's name is going to be changed from "Library" to "Quotes" and will be an
executable class compiled with the tool "pcp".
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Example 2: Modify example 1 in order to make the container class replace class (a) Also make
class "GetPrice" extends class "GetPage". Use Text Screen for display and show how it could
be accessed from the inner classes.
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public class Quotes:pcs { // Class Quotes extends (pcs)
static new Quotes l; // (l) is a static object of the Quotes
// class. The "new" keyword is to prevent
// conflict with the int (l) of class (pcs)
GetPrice gpr=new GetPrice(); // Creating object of GetPrice class
public override void init() {
l=this; // This makes (l) = Running Quotes instance
tia=toa="t"; // Text output device=TextScreen
bli=0; // Start at block number 0
base.init(); // Initialize parent class.
}
public override void run() {
if (bli==0) { // Starting block
cls="r0"; // Set color to red
os=" STOCK QUOTES";
tm();os="";tm(); // Display title then skip one line
cls="G4";os="When finished, push the [ENTER] key.";
tm(); // Display exit instructions in green
bli=1;um("b");return; // Jump to block 1.
}
else if (bli==1) { // Start of the continuous operation
cls="S9"; // Change to black color. Get stock symbol
os="Enter Stock Symbol: ";bli=2;tm("i");return;
} // from user then move to block 2.
else if (bli==2) {
if (os.Length<1) sm("e"); // Exit if [ENTER] pushed without data
gpr.getPrice(os); // Call method getPrice() with the symbol
bli=1;um("b"); // then jump to block 1.
}
}
public class GetPage { // This class is used internally by GetPrice
public string getPage(string sy) { // Method receives the symbol
l.urs="http://finance.yahoo.com/q?d=s&s="+sy; // It adds it to the URL
l.jb=true;l.kb=true;l.nm("hg"); // and retrieves the web page using PC#
return l.os; // method nm() then returns the page body
}
}
public class GetPrice:Quotes.GetPage { // This class extends class "GetPage"
public void getPrice(string sy) { // Method is now "void". It receives symbol
l.txs=getPage(sy); // sends it to getPage() and assigned the
// page received to searchable string (l.txs)
l.js="Last Trade:";l.ks="Trade Time:";l.tm("s");
// Search page using l.tm("s")
char[] CC=l.os.ToCharArray(); // Convert (os) to Char array to scan it
string price=""; // Reset (price)
for (int n=0;n< CC.Length;n++) { // Scan all char's
if (CC[n]!='|') price+=CC[n]; // Add all chars to (price) except |'s
}
l.cls="b0"; // Change color to blue
l.os="Latest stock price: $"+price;l.tm(); // Display price on container's TextScreen
}
}
}
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