The IComparable interface (defined in the System namespace) specifies a behavior that allows an object

Apress © 2003 (1200 pages)

to be sorted based on some internal key. Here is the formal definition:

This comprehensive text starts with a brief overview of the C# language and then quickly moves to key technical and

architectural issues for .NET developers.

// This interface allows an object to specify its

// relationship between other like objects.

interfaceIComparable

Table of Contents

{

C# and the .NET Platform, Second Edition int CompareTo(object o);

Introduction

}

Part One - Introducing C# and the .NET Platform

Chapter 1 - The Philosophy of .NET

ChapterLet's assume2 - Buildingyou haveC# Aupdatedplicationsthe Car class to maintain an internal ID number. Object users might

PacreateTwoan- ThearrayC#ofProgCarammingtypes asLanguagefollows:

Chapter 3 - C# Language Fundamentals

Chapter 4 - Object-Oriented Programming with C#

// Make an array of Car types.

ChCar[]pter 5 - Exceptions and Object Lifetime

myAutos = new Car[5];

ChaptermyAutos[0]6 - Interfac= news andCar(123,Collections"Rusty");

ChaptermyAutos[1]7 - Callback= newInterfaces,Car(6,Delegates,"Mary");and Events

ChaptermyAutos[2]8 - Advanced= newC#Car(83,Type Construction"Viper");Techniques

PartmyAutos[3]Three - Programming= new Car(13,with .NET "NoName");Assemblies

myAutos[4] = new Car(9873, "Chucky");

Chapter 9 - Understanding .NET Assemblies

Chapter 10 - Processes, AppDomains, Contexts, and Threads

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

As you recall, the System.Array class defines a static method named Sort(). When you invoke this method on an array of intrinsic types (e.g., int, short), you are able to sort the items in the array from lowest to

highest, as these intrinsic data types implement IComparable. However, what if you were to send an array

Chapter 13 - Building a Better Window (Introducing Windows Forms) of Car types into the Sort() method as follows:

Chapter 14 - A Better Painting Framework (GDI+)

following message: "At least one object must implement IComparable." Therefore, when you build custom

Chaptertypes, you20 -canXMLimplementWeb S rvicesIComparable to allow arrays of your types to be sorted. When you flesh out the

Indexdetails of CompareTo(), it will be up to you to decide what the baseline of the ordering operation will be. ListForoftheFiguresCar type, the internal ID seems to be the most logical candidate:

List of Tables

//The iteration of the Car can be ordered

//based on the CarID.

public class Car : IComparable

{

...

// IComparable implementation.

int IComparable.CompareTo(object o)

{

Car temp = (Car)o; if(this.CarID > temp.CarID)

return 1; if(this.CarID < temp.CarID)

return -1;

else

return 0;

}

C# and the .NET Platform, Second Edition

}

Apress © 2003 (1200 pages)

As you can see, theThislogiccomprehensivebehind CompareTo()text starts withis toatestbrieftheoverviewincomingof typehe against the current instance. The return valueC#of CompareTo()langu ge and thenis usedquicklyto discovermoves toif thiskeytypetechnicalis lessandthan, greater than, or equal to the

architectural issues for .NET developers. object it is being compared with (Table 6-1).

Table 6-1: CompareTo() Return Values

Chapter 3 - C# Language Fundamentals

Now that your Car type understands how to compare itself to like objects, you can write the following user

Chapter 4 - Object-Oriented Programming with C# code:

Chapter 5 - Exceptions and Object Lifetime Chapter 6 - Interfaces and Collections

// Exercise the IComparable interface.

Chapter 7 - Callback Interfaces, Delegates, and Events

public class CarApp

Chapter 8 - Advanced C# Type Construction Techniques

{

Part Three - Programming with .NET Assemblies

public static int Main(string[] args)

Console.WriteLine("{0} {1}", c.ID, c.PetName); return 0;

}

}

Figure 6-9 illustrates a test run.

Array.Sort(myAutos,new SortByPetName());

C# and the .NET Platform, Second Edition

// Dump sorted array.

This comprehensive text starts with a brief overview of the

Console.WriteLine("{0} {1}", c.ID, c.PetName);

C# language and then quickly moves to key technical and architectural issues for .NET developers.

Table

C# and

Part

Chapter

Chapter

Part

Chapter 6 - Interfaces and Collections

Figure 6-10: Sorting automobiles by pet name

Chapter 7 - Callback Interfaces, Delegates, and Events

Chapter 8 - Advanced C# Type Construction Techniques

Part Three - ProgProperties,amming with .NETCustomA semblies

Custom Sort Types

Chapter 9 - Understanding .NET Assemblies

ChapterIt is worth10 pointing- Processes,out thatAppDyoumains,can makeContextuse, andof aThreadscustom static property in order to help the object user

Chapteralong when11 - TypesortingReflection,your CarLatetypesBinding,by petanamed Attribute. Assume-BasedtheProgrammingCar class has added a static read-only

PapropertyFour -namedLev ragingSortByPetName()the .NET Librariesthat returns the correct IComparer interface:

Chapter 12 - Object Serialization and the .NET Remoting Layer

Chapter 13 - Building a Better Window (Introducing Windows Forms)

// We now support a custom property to return

Chapter 14correct- A B tter PaintingIComparerF amework (GDI+)

// the interface.

Chapterpublic15class- ProgrammingCar : withIComparableWindows Forms Controls

Chapter{ 16 - The System.IO Namespace

Chapter ...17 - Data Access with ADO.NET

Part Five//- WebPropertyApplicationsto andreturnXML WebtheServicesSortByPetName comparer.

public static IComparer SortByPetName

Chapter 18 - ASP.NET Web Pages and Web Con rols

{ get { return (IComparer)new SortByPetName(); } }

Chapter 19 - ASP.NET Web Applications

}

Chapter 20 - XML Web Services

Index

List of Figures

The object user code can now be modified as follows:

List of Tables

//This was a bit cumbersome.

//Array.Sort(myAutos, new SortByPetName());

//Cleaner! Just ask the car for the correct sort object.

Array.Sort(myAutos,Car.SortByPetName);

SOURCE The ObjComp project is located under the Chapter 6 subdirectory.

CODE

for(int i = 0; i < arrayOfCars.Length; i++)

C# and the .NET Platform, Second Edition

{

}This comprehensive text starts with a brief overview of the C# language and then quickly moves to key technical and architectural issues for .NET developers.

Here you are making use of the AddRange() method to populate your ArrayList with a set of Car types (as

you can tell, this is basically a shorthand notation for calling Add() n number of times). Once you print out

Table of Contents

the number of items in the collection (as well as enumerate over each item to obtain the pet name), check

C# and the .NET Platform, Second Edition

out the call to Insert(). As you can see, Insert() allows you to plug a new item into the ArrayList at a

Introduction

specified index. Next, notice the call to the ToArray() method, which returns a generic array of

Part One - Introducing C# and the .NET Platform

System.Object types based on the contents of the original ArrayList. Figure 6-12 shows the output.

Chapter 1 - The Philosophy of .NET

Chapter 2 - Building C# Applications

Part

Chapter

Chapter

Chapter

Chapter

Chapter

Chapter

Part

Chapter 13 - Building a Better Window (Introducing Windows Forms)

Chapter 14 - A Better Painting Framework (GDI+)

Working with the Queue Type

Chapter 15 - Programming with Windows Forms Controls

Chapter 16 - The System.IO Namespace

Queues are containers that ensure that items are accessed using a first-in, first-out manner. Sadly, we

Chumansapter 17are- DatasubjectA cessto queueswith ADOall.NETday long: lines at the bank, lines at the movie theater, and lines at the

PartmorningFive -coffeeWeb Applicationshouse. Whena dyouXMLareWebmodelingServicesa scenario in which items are handled on a first-come,

To illustrate these methods, we will leverage our automobile theme once again and build a Queue object that simulates a line of cars waiting to enter a car wash. First, assume the following static helper method:

public static void WashCar(Car c)

{

Console.WriteLine("Cleaning {0}", c.PetName);

}

C# and the .NET Platform, Second Edition

Apress © 2003 (1200 pages)

// Make a Q withThis compthreehensiveitemstext. starts with a brief overview of the

C# language and then quickly moves to key technical and

Queue carWashQ = new Queue();

architectural issues for .NET developers. carWashQ.Enqueue(new Car("FirstCar", 0, 0));

carWashQ.Enqueue(new Car("SecondCar", 0, 0));

carWashQ.Enqueue(new Car("ThirdCar", 0, 0));

Table of Contents

// Peek at first car in Q.

C# and the .NET Platform, Second Edition

Console.WriteLine("First in Q is {0}",

Introduction

((Car)carWashQ.Peek()).PetName);

Part One - Introducing C# and the .NET Platform

// Remove each item from Q.

Chapter 1 - The Philosophy of .NET

WashCar((Car)carWashQ.Dequeue());

Chapter 2 - Building C# Applications

WashCar((Car)carWashQ.Dequeue());

Part Two - The C# Programming Language

WashCar((Car)carWashQ.Dequeue());

Chapter 3 - C# Language Fundamentals

// Try to de-Q again?

Chapter 4 - Object-Oriented Programming with C# try

Chapter 5 - Exceptions and Object Lifetime

{

Chapter WashCar((Car)carWashQ6 - Inte faces and Collections.Dequeue());

Chapter} 7 - Callback Interfaces, Delegates, and Events

Chcatch(Exceptionpter 8 - Advanced C#e) Type Construction Techniques

Part{ ConsoleThree - Prog.WriteLine("Error!!amming with .NET Assemblies{0}", e.Message);}

Chapter 9 - Understanding .NET Assemblies

Chapter 10 - Processes, AppDomains, Contexts, and Threads

Here, you insert three items into the Queue type via its Enqueue() method. The call to Peek() allows you to view (but not remove) the first item currently in the Queue, which in this case is the car named FirstCar. Finally, the called to Dequeue() removes the item off the line and sends it into the WashCar() helper

function for processing. Do note that if you attempt to remove items from an empty queue, a runtime

Chapter 13 - Building a Better Window (Introducing Windows Forms) exception is thrown. Figure 6-13 shows the output of the queue example.

Chapter 14 - A Better Painting Framework (GDI+)

Chapter 15 - Programming with Windows Forms Controls

Chapter

Chapter

Part

Chapter

Chapter

Chapter

Index

List of

List of Tables

Figure 6-13: System.Collections.Queue at work

Working with the Stack Type

The System.Collections.Stack type represents a collection that maintains items using a last-in, first-out manner. As you would expect, Stack defines a member named Push() and Pop() (to place items onto or remove items from the stack), as well as a Peek() method. Due to the fact that I am hard-pressed to come up with a car-centric stack example (perhaps a junkyard automobile crusher?), the following stack example makes use of the standard System.String:

Stack stringStack = new Stack();

stringStack.Push("One");

stringStack.Push("Two");

stringStack.Push("Three");

// Now look at the top item, pop it and look again.

Console.WriteLine("Top item is: {0}", stringStack.Peek());

C# and the .NET Platform, Second Edition

Console.WriteLine("Popped off {0}", stringStack.Pop());

by Andrew Troelsen ISBN:1590590554

Console.WriteLine("Top item is: {0}", stringStack.Peek());

Apress © 2003 (1200 pages)

Console.WriteLine("Popped off {0}", stringStack.Pop());

WriteLine("TopTh s comprehensiveitemtext starts with a brief overview of the

Console. is: {0}", stringStack.Peek());

C# language and then quickly moves to key technical and

Console.WriteLine("Popped off {0}", stringStack.Pop()); architectural issues for .NET developers.

try

{

Console.WriteLine("Top item is: {0}", stringStack.Peek());

Table of Contents

Console.WriteLine("Popped off {0}", stringStack.Pop());

C# and the .NET Platform, Second Edition

}

Introduction catch(Exception e)

Part One - Introducing C# and the .NET Platform

{ Console.WriteLine("Error!! {0}", e.Message);}

Chapter 1 - The Philosophy of .NET

Chapter 2 - Building C# Applications

PartHere,Twoyou- ThebuildC#aProgrammingstack that containsLanguagethree string types (named according to their order of insertion). As Chapteryou peek3 onto- C#theLanguagestack, youFundamentalswill always see the item at the very top, and therefore the first call to Peek()

Chapterreveals4the- thirdObjectstring-Oriented. AfterProgrammingseries of Pop()with C#and Peek() calls, the stack is eventually empty, at which

Chaptertime additional5 - ExceptionsPeek()/Pop()and ObjectcallsLifetimeraise a system exception. The output can be seen in Figure 6-14.

Chapter

Figure 6-14: System.Collections.Stack type at work

Chapter 17 - Data Access with ADO.NET

Part Five - Web Applications and XML Web Services

Chapter 18 - ASP.NET Web Pages and Web Controls

System.Collections.Specialized Namespace

Chapter 19 - ASP.NET Web Applications

Chapter 20 - XML Web Services

In addition to the types defined within the System.Collections namespace, you should also be aware that

Index

the .NET base class libraries provide the System.Collections.Specialized namespace that defines another

set of types that are more (pardon the redundancy) specialized. For example, the StringDictionary and

List of Tables

ListDictionary types each provide a stylized implementation of the IDictionary interface. Table 6-5 documents the key types.

Table 6-5: Types of the System.Collections.Specialized Namespace

ChapterCODE16 - The System.IO Namespace

Chapter 17 - Data Access with ADO.NET

Part Five - Web Applications and XML Web Services

Chapter 18 - ASP.NET Web Pages and Web Controls

Chapter 19 - ASP.NET Web Applications

Chapter 20 - XML Web Services

Index

List of Figures

List of Tables

Building a Custom# and the .ContainerNET Pl tform, Second(RetrofittingEdition the Cars Type)

To conclude this chapter, let's examine one possible way to build a stylized custom collection. As

Apress © 2003 (1200 pages)

mentioned, the System.Collections namespace supplies some abstract base types that allow you to build

This comprehensive text starts with a brief overview of the

strongly typed collectionsC# language. However,and thenratherquicklythanmovesdealingto keywithtechnicalthe implementationand of various abstract members, you arearchitablecturalto buildissuescustomfor .collectionsNET developersusing. simple containment/delegation techniques.

Previously in this chapter, you created the Cars type that was responsible for holding a number of Car

Tableobjectsof Conte. Internally,ts the set of Car objects was represented with an instance of System.Array, and because C#of andthis thefact,.NETyouPlatform,needed toSecondwrite aEditigoodn deal of extra code to allow the outside world to interact with your

subobjects. Furthermore, the Car array is defined with a fixed upper limit.

Introduction

Part One - Introducing C# and the .NET Platform

A more intelligent design would be to represent the internal set of Car objects as an instance of System.Collections.ArrayList. Given that this class already has a number of methods to insert, remove, and enumerate its contents, the only duty of the Cars type is to supply a set of public functions that

delegate to the inner ArrayList (in other words, the Cars type "has-a" ArrayList). As with any

Chapter 3 - C# Language Fundamentals

containment/delegation scenario, it is up to you to decide how much functionality of the inner object to

Chapter 4 - Object-Oriented Programming with C#

expose to the object user. Here, then, is one possible implementation of the updated Cars type:

Chapter 5 - Exceptions and Object Lifetime

Chapter 6 - Interfaces and Collections

// This time use an ArrayList, not System.Array.

Chapter 7 - Callback Interfaces, Delegates, and Events public class Cars : IEnumerable

Chapter 8 - Advanced C# Type Construction Techniques

{

Part Three - Programming with .NET Assemblies

// This class maintains an array of cars.

Chapter 9 - Understanding .NET Assemblies private ArrayList carList;

Chapter 10 - Processes, AppDomains, Contexts, and Threads

// Make the ArrayList.

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming public Cars() { carList = new ArrayList ();}

Chapter public13 - Buildingvoida BetterAddCar(CarWindow (Introducingc) Windows Forms)

Chapter {14 -carListA Better Painting.Add(c);}Framework (GDI+)

Chapter //15 -RemoveProgrammingcarwith. Windows Forms Controls

public void RemoveCar(int carToRemove)

Chapter 16 - The System.IO Namespace

{ carList.RemoveAt(carToRemove);}

Chapter 17 - Data Access with ADO.NET

// Return number of cars.

Part Five - Web Applications and XML Web Services

public int CarCount

Chapter 18 - ASP.NET Web Pages and Web Controls

{ get{ return carList.Count;} }

Chapter 19 - ASP.NET Web Applications

// Kill all cars.

Chapter 20 - XML Web Services

public void ClearAllCars()

Index

{carList.Clear(); }

List of Figures

// Determine if the incoming car is already in the list.

List of Tables

public bool CarIsPresent(Car c)

{return carList.Contains(c); }

// Simply return the IEnumerator of the ArrayList.

public IEnumerator GetEnumerator()

{ return carList.GetEnumerator();}

}

This new implementation also makes using the Cars type a bit less of a burden for the object user:

// Use the new Cars container class.

public static void Main()

{

Cars carLot = new Cars();

// Add some cars.

carLot.AddCar(new Car("Jasper", 200, 80));

carLot.AddCar(new Car("Mandy", 140, 0));

C# and the .NET Platform, Second Edition carLot.AddCar(new Car("Porker", 90, 90));

Apress © 2003 (1200 pages)

// Get each one and print out some stats.

This comprehensive text starts with a brief overview of the

Console.WriteLine("You have {0} in the lot:\n", carLot.CarCount);

C# language and then quickly moves to key technical and foreach (Car c in carLot)

architectural issues for .NET developers.

{

Console.WriteLine("Name: {0} ", c.PetName);

Console.WriteLine("Max speed: {0} \n", c.MaxSpeed);

Table of Contents

}

C# and the .NET Platform, Second Edition

// Kill the third car.

Introduction carLot.RemoveCar(3);

Part One - Introducing C# and the .NET Platform

Console.WriteLine("You have {0} in the lot.\n", carLot.CarCount);

Chapter 1 - The Philosophy of .NET

// Add another car and verify it is in the collection.

Chapter 2 - Building C# Applications

Car temp = new Car("Zippy", 90, 90);

Part Two - The C# Programming Language

carLot.AddCar(temp);

Chapter 3 - C# Language Fundamentals

if(carLot.CarIsPresent(temp))

Chapter 4 - Object-Oriented Programming with C#

Console.WriteLine("{0} is already in the lot.", temp.PetName);

Chapter 5 - Exceptions and Object Lifetime

// Kill 'em all.

Chapter carLot6 - In erfacClearAllCars();and Collections

.

Chapter Console7 - Ca lback.WriteLine("YouIn erfaces, Delegates,haveand{0}Eventsin the lot.\n", carLot.CarCount);

Chapter} 8 - Advanced C# Type Construction Techniques

Part Three - Programming with .NET Assemblies

Chapter 9 - Understanding .NET Assemblies

The output is shown in Figure 6-15.

Chapter 10 - Processes, AppDomains, Contexts, and Threads

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

Chapter

IndexFigure 6-15: The updated Cars container

List of Figures

ListYouofmayT blesbe wondering why you bothered to make the custom Cars type at all, given that the object user could create an ArrayList type directly. The reason is that ArrayList can contain any object reference. If you did not create a custom wrapper class such as Cars, the ArrayList instance could contain Cars, Boats, Airplanes, Strings, or any other type!

ArrayList ar = new ArrayList();

ar.Add(carLot);

ar.Add("Hello");

ar.Add(new JamesBondCar());

ar.Add(23);

Using the containment/delegation model, you are able to leverage the functionality of the ArrayList type, while maintaining control over what can be inserted into the container.

Note Also beC#awarend thatthe .manyNET Plaof theform,typesSecondof theEditionSystem.Collections namespace can function as base classesby Andrewto derivedTro lsentypes. Thus, as an alternative,ISBN:1590590554you are able to build strongly typed collectionsApressby©deriving2003 (1200frompages)the collection type of interest and overriding various virtual members.

This concludes our formal investigation of interface-based programming techniques. Be painfully aware, Tablehowever,of Contentsthat you will encounter numerous .NET interfaces through the remainder of this text. As you will

see, interfaces are used during ASP .NET development, Windows Forms development, multithreaded

C# and the .NET Platform, Second Edition

applications, and so forth. Unlike other development frameworks (such as MFC), interfaces are

Introduction

unavoidable when exploring the .NET universe.

Part One - Introducing C# and the .NET Platform

Chapter 1 - The Philosophy of .NET

Chapter 2 - Building C# Applications

Part Two - The C# Programming Language

Chapter 3 - C# Language Fundamentals

Chapter 4 - Object-Oriented Programming with C#

Chapter 5 - Exceptions and Object Lifetime

Chapter 6 - Interfaces and Collections

Chapter 7 - Callback Interfaces, Delegates, and Events

Chapter 8 - Advanced C# Type Construction Techniques

Part Three - Programming with .NET Assemblies

Chapter 9 - Understanding .NET Assemblies

Chapter 10 - Processes, AppDomains, Contexts, and Threads

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

Part Four - Leveraging the .NET Libraries

Chapter 12 - Object Serialization and the .NET Remoting Layer

Chapter 13 - Building a Better Window (Introducing Windows Forms)

Chapter 14 - A Better Painting Framework (GDI+)

Chapter 15 - Programming with Windows Forms Controls

Chapter 16 - The System.IO Namespace

Chapter 17 - Data Access with ADO.NET

Part Five - Web Applications and XML Web Services

Chapter 18 - ASP.NET Web Pages and Web Controls

Chapter 19 - ASP.NET Web Applications

Chapter 20 - XML Web Services

Index

List of Figures

List of Tables