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Introduction to .Net/C#
By Oliver
Feb 23, 2011
Outline
Introduction to .NET
Introduction to C#
Data Type
Array
Property
Flow control
Exception handler
Hello world and debug
Microsoft .NET
.NET initiative
Introduced by Microsoft (June 2000)
• Vision for embracing the Internet in software development
Independence from specific language or platform
• Applications developed in any .NET-compatible language
• Visual Basic.NET, Visual C++.NET, C# and more
• Supports portability and interoperability
Architecture capable of existing on multiple
platforms
• Supports portability
Microsoft .NET
Key components of .NET
Web services
• Applications used over the Internet
Software reusability
• Web services provide solutions for variety of companies
• Cheaper than one-time solutions that can’t be reused
• Single applications perform all operations for a company
via various Web services
• Manage taxes, bills, investments and more
• Pre-packaged components using Visual Programming
• (buttons, text boxes, scroll bars)
• Make application development quicker and easier
Microsoft .NET
Keys to interaction
XML (Extreme Markup Language) and
SOAP (Simple Object Access Protocol)
• “Glue” that combines various Web services
to form applications
• XML gives meaning to data
• SOAP allows communication to occur easily
Microsoft .NET
RTM:
2002(v1.0)
2003 (v1.1)
2005 (v2.0)
2006 (v3.0)
2007 (v3.5)
2010 (v4.0)
…
.NET Framework
.NET Framework
Heart of .NET strategy
• Manages and executes applications and Web services
• Provides security, memory management and other
programming capabilities
Includes Framework Class Library (FCL)
• Pre-packaged classes ready for reuse
• Used by any .NET language
Details contained in Common Language Specification (CLS)
• Submitted to European Computer Manufacturers Association
to make the framework easily converted to other platforms
Executes programs by Common Language Runtime (CLR)
Common Language
Runtime (CLR)
Managed Executable
Legacy Reusable
Managed Components
Software
(unmanaged code)
Common Language Runtime
(JIT compilation, memory management, etc.)
Windows
(or other operating oystem)
Common Language
Runtime (CLR)
Why two compilations?
Platform independence
• .NET Framework can be installed on different platforms
• Execute .NET programs without any modifications to code
• .NET compliant program translated into platform independent
MSIL
Language independence
• MSIL form of .NET programs not tied to particular language
• Programs may consist of several .NET-compliant languages
• Old and new components can be integrated
• MSIL translated into platform-specific code
Other advantages of CLR
Execution-management features
• Manages memory, security and other features
• Relieves programmer of many responsibilities
• More concentration on program logic
Compilation And Execution
Compilation
Source Language Code (IL)
Code Compiler Assembly
Metadata
Native JIT Compiler At installation or
Code the first time each
method is called
Execution
JIT
All managed code runs in native machine
language
However, all managed code is made up of IL
and metadata
The CLR JIT-compiles the IL and metadata
At execution time
Executed directly by CPU
Allows for the best of both worlds
Code management features
Performance of full-speed execution
Garbage Collector
GC is a most important part of CLR
It manages many objects lifetime.
Instead of allocate/delete keywords in C++, objects
are automatically deleted when the application no
longer needs them.
It’s Important to build a efficiently application.
Garbage Collector
string s;
StraighLine line;
s = "dog";
line = new StraightLine(0.5, 2.5);
0.5
"dog" 2.5
line
s
Stack
Heap
Garbage Collector
CLR will run GC automatically to
free all unreachable objects in heap
memory which no references
remained.
Garbage Collector
Free space
object6
object5
object4
object3
x a
… b
…
… banana
object2
…
object1
Stack
…
allocated
Managed Heap
Garbage Collector
Free space
object6
object5
x
… object3
… a
… b
…
object1
Stack
…
allocated
Managed Heap
Garbage Collector
GC demo, show GC collect and
different result in debug and release
mode.
Garbage Collector
GC manages all objects in Heap, but
not any objects been allocated on
Heap, like: Unmanaged resource,
windows handler, DB connection, file
handler…therefore, we need use the
Dispose pattern to clean up the
memory.
Garbage Collector
FileStream fs = new FileStream("Temp.dat",
FileMode.Create);
try
{
fs.Write(bytesToWrite, 0, bytesToWrite.Length);
}
finally
{
if (fs != null)
((IDisposable)fs).Dispose();
}
Garbage Collector
GC events notification have been
added in .Net 4.0.
Summary
CLR will run GC automatically to free all unreachable
objects in heap memory which no references remained.
The GC is only called by the CLR when heap memory
becomes scarce.
The GC only can collect manage resources, all
unmanaged resources need to be collected by
programmer.
The GC will reduce memory leak, but not disappeared.
The .NET Framework Library
Sit on top of the CLR
Reusable types that tightly integrate with the
CLR
Object oriented – inheritance, polymorphism,
etc.
Provide functionality for ASP.NET, XML Web
Services, ADO.NET, Windows Forms, basic
system functionality (IO, XML, etc.)
The .NET Framework Library
System.Web System.Windows.Forms
Services UI Design ComponentModel
Description
HtmlControls
Discovery
Protocols WebControls System.Drawing
Caching Security Drawing2D Printing
Configuration SessionState Imaging Text
System.Data System.Xml
OleDb SqlClient XSLT Serialization
Common SQLTypes XPath
System
Collections IO Security Runtime
Configuration Net ServiceProcess InteropServices
Diagnostics Reflection Text Remoting
Globalization Resources Threading Serialization
Base Framework
Collections Security
Configuration ServiceProcess
Diagnostics Text
Globalization Threading
IO
Runtime
Net InteropServices
Reflection Remoting
Resources Serialization
Summary
.NET Framework is a code execution platform
.NET Framework consists of two primary parts: .NET
Class Libraries, Common Language Runtime
All CLR-compliant compilers support the common
type system
Managed code is object oriented
Managed code is compiled to and assembly (MSIL)
by language specific compiler
Assemblies are compiled to native code by JIT
compiler
.NET and C#
.NET platform
Web-based applications can be distributed to variety of
devices and desktops
C#
Developed specifically for .NET
Enable programmers to migrate from C/C++ and Java easily
Event-driven, fully OO, visual programming language
Has IDE
Process of rapidly creating an application using an IDE is
called Rapid Application Development (RAD)
C#
Language interoperability
Can interact with software components written in
different languages or with old packaged software
written in C/C++
Can interact via internet, using industry
standards (SOAP and XML)
Simple Object Access Protocol - Helps to share
program “chunks” over the internet
Accommodates a new style of reusable
programming in which applications are created
from building blocks
Data Types/Arrays
System-defined types
Object
User-defined types
String Array ValueType Exception Delegate Class1
Primitive types Multicast
Enum Structure1 Class2
Delegate
Boolean Single
Byte Double
Int16 Decimal Enum1 Delegate1 Class3
Int32 DateTime
Int64 TimeSpan
Char Guid
Mapping C# to CTS
Keyword Description Special format for literals
bool Boolean true false
char 16 bit Unicode character 'A' '\x0041' '\u0041'
sbyte 8 bit signed integer none
byte 8 bit unsigned integer none
short 16 bit signed integer none
ushort 16 bit unsigned integer none
int 32 bit signed integer none
uint 32 bit unsigned integer U suffix
long 64 bit signed integer L or l suffix
ulong 64 bit unsigned integer U/u and L/l suffix
float 32 bit floating point F or f suffix
double 64 bit floating point no suffix
decimal 128 bit high precision M or m suffix
string character sequence "hello",
@"C:\dir\file.txt"
Value & Reference Types
ctor
Value type always have a default value
Reference type can be null
x =0 int x;
obj is null MyClass obj;
Value & Reference Types
Memory allocation
Reference type always allocate in heap
Value type always be allocated in a place
where its been declared
Allocate a variable on stack int x;
Allocate a variable on stack MyClass obj;
Allocate the object on heap obj = new MyClass();
Value & Reference Types
0.5
2.5
obj
x
Stack
Heap
Value & Reference Types
Copy
int x;
MyClass obj;
obj = new MyClass();
deep copy Int y = x;
shallow copy MyClass objCopy = obj;
Value & Reference Types
Memory Disposal
Once the method has finished running, its local stack-allocated
variable, x, obj, will disappear from scope and be “popped” off the
stack.
GC will automatically deallocate it from the heap some times later.
GC will know to delete it, because the object has no valid referee
(one whose chain of reference originates back to a stack-allocated
object).
C++ programmers may be a bit uncomfortable with this and may
want to delete the object anyway (just to be sure!) but in fact there
is no way to delete the object explicitly. We have to rely on the
CLR for memory disposal—and indeed, the whole .NET framework
does just that!
Type Example
An example of using types in C#
declare before you use (compiler enforced)
initialize before you use (compiler enforced)
public class App
{
public static void Main()
{
declarations int width, height;
width = 2;
decl + initializer height = 4;
int area = width * height;
error, x not set int x;
int y = x * 2;
...
}
}
Type conversion
Some automatic type conversions available
from smaller to larger types
Otherwise you need a cast or an explicit conversion…
typecast syntax is type name inside parentheses
conversion based on System.Convert class
Type conversion
int i = 5;
double d = 3.2;
string s = "496";
implicit conversion d = i;
typecast required i = (int) d;
conversion required i = System.Convert.ToInt32(s);
Boxing and Unboxing
Boxing
Automatic conversion of a value-type in a
reference-type
Like: Object o = 25;
Unboxing
Conversion of a reference-type into a value-
type
int i= (int)o;
Like:
Boxing and Unboxing
Boxing
Memory is allocated from the
managed heap.
The value type’s fields are copied to
the newly allocated heap memory
The address of the object is returned.
This address is now a reference to an
object
Boxing and Unboxing
Performance
If boxing occurs frequently, it will
wastes memory and hurts
performance.
Because many small objects will be
created on heap, and waiting be clean
up by GC
Instead, we often use generics
method or delegate.
String
How to create a string object.
String’s performance
StringBuilder object
String encoding
String
Create string s = "496";
String ss = “adasdc”;
String object is immutable. That is, once created, a string
can never get longer, get shorter, or have any of its
characters changed.
String
string s = "496";
String ss = “adasdc”;
Bad performance String text = s + ” and ” +
ss + “ and …”;
because it creates multiple string objects on the garbage-
collected heap.
String
StringBuilder sbText= new stringBuilder();
sbText.append(s);
sbText.append(“ and ”);
sbText.append(ss);
sbText.append(“ and… ”);
string text = sbText.ToString();
String
OR:
string text = String.Format(“{0} and {1}
and…”, s, ss);
Because String.Format() method be implemented by
StringBuilder operations.
String
Encoding
Demo
Collections
Array
Queue
Stack
HashTable
List<T>
Dictionary<Tkey,Tvalue>
…
Arrays
Arrays are reference types
assigned default values (0 for numeric, null for
references, etc.)
int[] a;
create a = new int[5];
element access a[0] = 17;
a[1] = 32;
int x = a[0] + a[1] + a[4];
number of elements int l = a.Length;
Queue
Use Queue to implement a First-In, First-Out type (FIFO)
type of collection:
create Queue myQ = new Queue();
insert an element myQ.Enqueue( new Robin( 8 ) );
myQ.Enqueue( new BlueJay( 14 ) );
pop an element ((Bird)myQ.Dequeue()).Speak();
((Bird)myQ.Dequeue()).Speak();
Stack
Use Stack to implement a Last-In, First-Out type (LIFO) type
of collection:
create Stack myStack = new Stack();
insert an element myStack.Push( new Robin( 8 ) );
myStack.Push( new BlueJay( 14 ) );
pop an element ((Bird)myStack.Pop()).Speak();
((Bird)myStack.Pop()).Speak();
HashTable
Use Hashtable to implement a dictionary type of collection:
create Hashtable myHT = new Hashtable();
insert an element myHT["Robin"] = new Robin( 8 );
myHT["BlueJay"] = new BlueJay( 14 );
use an element ((Bird)myHT["BlueJay"]).Speak();
List<T>
It’s the most commonly collection type, use List<T> to
implement a Robin collection :
create List<Robin> myList= new List<Robin> ();
myList.Add( new Robin ( 8 );
insert an element
myList.Add( new Robin ( 10 );
foreach (Robin obj in myList)
{
obj.Speak();
use an element
}
Dictionary<Tkey,Tvalue>
It’s the most commonly collection type, use List<T> to
implement a Robin Dictionary:
create Dictionary<string,Robin> myDic= new
Dictionary<string,Robin>();
string sarah = " Sarah ";
string harold= " harold ";
insert an element myDic.Add(sarah , new Robin ( 8 );
myDic.Add(harold , new Robin ( 10 );
if (myDic.ContainsKey(sarah))
{
use an element myDic[sarah].Speak();
}
Dictionary VS Hashtable
Dictionary<K,V> is used in signal threaded application.
Hashtable is a thread safe type, it also can be used in
multi-threaded application.
Hashtable table=Hashtable.Synchronized(new
Hashtable());
Properties
Instead expose a field, in C#, we usually use get/set to
expose a property of class. Like:
using System;
class MyClassk
{
int _integer;
public int Integer
Define a Property
{
get {return _integer;}
Get method block
set {_integer = value;}
Set method block }
}
Properties
After compilation, we can got the following code from IL
class MyClassk
{
int _integer;
public int get_Integer()
Get method
{
return _integer;
}
public void set_Integer( int value)
Set method
{
_integer = value;
}
}
Properties
To avoid the data be destroyed, we can make a read only
property :
using System;
class MyClassk
{
int _integer;
public int Integer
Define a Property
{
get {return _integer;}
Get method block
}
}
Properties
Property has all features of method
using System;
class MyClassk
{
int _integer;
define a virtual Property public virtual int Integer
{
get method block get {return _integer;}
protected set {_integer = value;}
access modifiers
}
}
Properties
Enhanced features of Interface, more component-
oriented
using System;
define an interface Interface INameValuePair
{
string Name
{
get;
}
define a Property Object Value
{
get;
set;
}
}
Properties Summary
More component-oriented
Accommodate the changes of the feature
JIT often use code inline to speed up application
Code snippet let coding properties more easy.
Iteration & Flow Control
Iteration Constructs
Flow Control
Iteration Constructs
Loop over data
for
foreach
while
do while
Iteration Constructs: for
for (int index = 0; index < int.MaxValue; index++)
{
//just do it...
}
Iteration Constructs: foreach
List<Robin> myList= new List<Robin> ();
myList.Add( new Robin ( 8 );
myList.Add( new Robin ( 10 );
foreach (Robin obj in myList)
{
obj.Speak();
}
Iteration Constructs: while
int index = 0;
check first before running while (index < int.MaxValue)
{
//just do it...
index++;
}
Iteration Constructs: do while
int index = 0;
check after the running Do
{
//just do it...
first pass always executed index++;
} while (index < int.MaxValue);
Flow Control
Flow control statements
if
switch
Flow Control: IF
if ("" == string.Empty)
{
Console.WriteLine("equal");
}
else
{
Console.WriteLine(“not equal");
}
Flow Control: IF
if (string.Empty == “”)
{
Console.WriteLine("equal");
}
else if (string.Empty == null)
{
Console.WriteLine(“equal N");
}
else
{
Console.WriteLine(“not equal");
}
Flow Control: switch
Numeric and string types are allowed
Switch(variable)
{
case a:
//code
break;
case b:
//code
break;
default:
//default code or exception
}
Exception Handling
No matter which kind of programming
languages, exception handling is
always a necessary features.
Try-catch
Finally
Coding practice
Performance
Exception Handling
Try-catch
Place the sections of code that might throw exceptions in a
try block and place code that handles exceptions in a catch
block
try
{
//remote access.
}
catch catch (InvalidOperationException )
{
throw;
}
Exception Handling
It throws the same exception object that it caught and
causes the CLR to reset its starting point for the
exception:
try
{
//InvalidOperationException
}
catch (InvalidOperationException ex)
{
Incorrect throw ex;
}
Exception Handling
finally
When an exception occurs, execution stops and control is
given to the closest exception handler. This often means
that lines of code you expect to always be called are not
executed. Some resource cleanup, such as closing a file,
must always be executed even if an exception is thrown. To
accomplish this, you can use a finally block. A finally block
is always executed, regardless of whether an exception is
thrown.
Exception Handling
FileStream fs = null;
try {
fs = new FileStream(@"C:\temp\data.txt", FileMode.Open);
try StreamReader sr = new StreamReader(fs);
string line;
line = sr.ReadLine();
Console.WriteLine(line);
}
catch (FileNotFoundException e)
catch
{
throw new NameNotFoundException(@"[data.txt not in
c:\temp directory]",e); }
catch (IOException e)
catch
{
throw new NameNotFoundException(@"[data.txt not in
finally c:\temp directory]",e); }
finally
{
if (fs != null) fs.Close();
}
Exception Handling
User-defined exception
public class EmployeeListNotFoundException: Exception
{
public EmployeeListNotFoundException() { }
public EmployeeListNotFoundException(string message)
: base(message) { }
public EmployeeListNotFoundException(string message,
Exception inner) : base(message, inner) { }
}
Exception Handling
Best Practice
add more friendly information to an
exception when thrown, like parameters…
Never throw an Exception type error, use a
more meaningful exception type instead.
Don’t catch everything
Never ignore any exception
Exception Handling
try {
// try to execute code that the programmer
knows might fail...
}
Incorrect catch (Exception) {
...
}
This code indicates that it was expecting any and all
exceptions and knows how to recover
from any and all situations. How can this possibly be?
Exception Handling
FileStream fs = new FileStream("Temp.dat", FileMode.Create);
try
{
fs.Write(bytesToWrite, 0, bytesToWrite.Length);
}
finally
{
if (fs != null)
((IDisposable)fs).Dispose();
}
Exception Handling
using (FileStream fs = new FileStream("Temp.dat", FileMode.Create))
{
fs.Write(bytesToWrite, 0, bytesToWrite.Length);
}
Exception Handling
Performance
If an exception occurs frequently,
performance hit of throwing and
catching the exceptions was taking a
large toll on the application’s overall
performance.
Exception Handling
Debugging
Run the DEMO and show how to
debugging exception in Visual studio
2010.
Exception Handling
static void Main(string[] args)
{
try
{
InternalMethod();
}
catch (InvalidOperationException ex)
{
Console.WriteLine(ex.Message);
What’s the result? }
}
static void InternalMethod()
{
try
{
throw new InvalidOperationException ("try");
}
finally
{
Console.WriteLine("exception finally");
}
}
Hello world
Create a DEMO and debug
