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[ASP.net教程]VB.NET and C# 差异


VB.NETProgram StructureC#
Imports System
Namespace Hello    Class HelloWorld       Overloads Shared Sub Main(ByVal args() As String)          Dim name As String = "VB.NET"
         'See if an argument was passed from the command line           If args.Length = 1 Then name = args(0)
          Console.WriteLine("Hello, " & name & "!")       End Sub    End Class End Namespace
using System;
namespace Hello {    public class HelloWorld {       public static void Main(string[] args) {          string name = "C#";
         // See if an argument was passed from the command line          if (args.Length == 1)             name = args[0];
         Console.WriteLine("Hello, " + name + "!");       }    } }
VB.NETCommentsC#
' Single line only Rem Single line only

// Single line /* Multiple     line  */ ///

VB.NETData TypesC#

Value Types Boolean Byte Char   (example: "A"c) Short, Integer, Long Single, Double Decimal Date

Reference Types Object String

Dim x As Integer Console.WriteLine(x.GetType())     ' Prints System.Int32 Console.WriteLine(TypeName(x))  ' Prints Integer

' Type conversion Dim d As Single = 3.5 Dim i As Integer = CType(d, Integer)   ' set to 4 (Banker's rounding) i = CInt(d)  ' same result as CType i = Int(d)    ' set to 3 (Int function truncates the decimal)

Value Types bool byte, sbyte char   (example: 'A') short, ushort, int, uint, long, ulong float, double decimal DateTime   (not a built-in C# type)

Reference Types object string

int x; Console.WriteLine(x.GetType());    // Prints System.Int32 Console.WriteLine(typeof(int));      // Prints System.Int32

// Type conversion float d = 3.5f; int i = (int)d;   // set to 3  (truncates decimal)

VB.NETConstantsC#
Const MAX_STUDENTS As Integer = 25 

' Can set to a const or var; may be initialized in a constructor ReadOnly MIN_DIAMETER As Single = 4.93

const int MAX_STUDENTS = 25; 

// Can set to a const or var; may be initialized in a constructor readonly float MIN_DIAMETER = 4.93f;

VB.NETEnumerationsC#
Enum Action   Start    [Stop]   ' Stop is a reserved word   Rewind   Forward End Enum
Enum Status   Flunk = 50   Pass = 70   Excel = 90 End Enum Dim a As Action = Action.Stop If a <> Action.Start Then _    Console.WriteLine(a.ToString & " is " & a)     ' Prints "Stop is 1"
Console.WriteLine(Status.Pass)     ' Prints 70 Console.WriteLine(Status.Pass.ToString())     ' Prints Pass
enum Action {Start, Stop, Rewind, Forward}; enum Status {Flunk = 50, Pass = 70, Excel = 90};
Action a = Action.Stop; if (a != Action.Start)   Console.WriteLine(a + " is " + (int) a);    // Prints "Stop is 1"
Console.WriteLine((int) Status.Pass);    // Prints 70 Console.WriteLine(Status.Pass);      // Prints Pass
VB.NETOperatorsC#

Comparison =  <  >  <=  >=  <>

Arithmetic +  -  *  / Mod \  (integer division) (raise to a power)

Assignment =  +=  -=  *=  /=  \=  ^=  <<=  >>=  &=

Bitwise And   Or   Not   <<   >>

Logical AndAlso   OrElse   And   Or   Xor   Not

Note: AndAlso and OrElse perform short-circuit logical evaluations

String Concatenation &   +

Comparison ==  <  >  <=  >=  !=

Arithmetic +  -  *  / %  (mod) (integer division if both operands are ints) Math.Pow(x, y)

Assignment =  +=  -=  *=  /=   %=  &=  |=  ^=  <<=  >>=  ++  --

Bitwise &   |   ^   ~   <<   >>

Logical &&   ||   &   |   ^   !

Note: && and || perform short-circuit logical evaluations

String Concatenation +

VB.NETChoicesC#

greeting = IIf(age < 20, "What's up?", "Hello")

' One line doesn't require "End If", no "Else" If language = "VB.NET" Then langType = "verbose"

' Use : to put two commands on same line If x <> 100 And y < 5 Then x *= 5 : y *= 2  

' Preferred If x <> 100 And y < 5 Then   x *= 5   y *= 2 End If

' or to break up any long single command use _ If whenYouHaveAReally < longLine And itNeedsToBeBrokenInto2 > Lines Then _   UseTheUnderscore(charToBreakItUp)

' If x > 5 Then   x *= y ElseIf x = 5 Then   x += y ElseIf x < 10 Then   x -= y Else   x /= y End If

Select Case color   ' Must be a primitive data type   Case "pink", "red"     r += 1   Case "blue"     b += 1   Case "green"     g += 1   Case Else     other += 1 End Select

greeting = age < 20 ? "What's up?" : "Hello";

if (x != 100 && y < 5) {    // Multiple statements must be enclosed in {}   x *= 5;   y *= 2; }

No need for _ or : since ; is used to terminate each statement.

if (x > 5)   x *= y; else if (x == 5)   x += y; else if (x < 10)   x -= y; else   x /= y;

switch (color) {                          // Must be integer or string   case "pink":   case "red":    r++;    break;        // break is mandatory; no fall-through   case "blue":   b++;   break;   case "green": g++;   break;   default:    other++;   break;       // break necessary on default }

VB.NETLoopsC#
Pre-test Loops:
While c < 10   c += 1 End While

Do Until c = 10    c += 1 Loop

Do While c < 10   c += 1 Loop

For c = 2 To 10 Step 2   Console.WriteLine(c) Next

Post-test Loops:
Do    c += 1 Loop While c < 10 Do    c += 1 Loop Until c = 10

'  Array or collection looping Dim names As String() = {"Fred", "Sue", "Barney"} For Each s As String In names   Console.WriteLine(s) Next

' Breaking out of loops Dim i As Integer = 0 While (True)   If (i = 5) Then Exit While   i += 1 End While

Pre-test Loops:   

// no "until" keyword while (c < 10)   c++;
for (c = 2; c < = 10; c += 2)   Console.WriteLine(c);

Post-test Loop:
do   c++; while (c < 10);

// Array or collection looping string[] names = {"Fred", "Sue", "Barney"}; foreach (string s in names)   Console.WriteLine(s);

// Breaking out of loops int i = 0; while (true) {   if (i == 5)     break;   i++; }

VB.NETArraysC#

Dim nums() As Integer = {1, 2, 3}  For i As Integer = 0 To nums.Length - 1   Console.WriteLine(nums(i)) Next
' 4 is the index of the last element, so it holds 5 elements Dim names(4) As String names(0) = "David" names(5) = "Bobby"  ' Throws System.IndexOutOfRangeException
' Resize the array, keeping the existing values (Preserve is optional) ReDim Preserve names(6)

Dim twoD(rows-1, cols-1) As Single twoD(2, 0) = 4.5
Dim jagged()() As Integer = { _   New Integer(4) {}, New Integer(1) {}, New Integer(2) {} } jagged(0)(4) = 5

int[] nums = {1, 2, 3}; for (int i = 0; i < nums.Length; i++)   Console.WriteLine(nums[i]);
// 5 is the size of the array string[] names = new string[5]; names[0] = "David"; names[5] = "Bobby";   // Throws System.IndexOutOfRangeException
// C# can't dynamically resize an array.  Just copy into new array. string[] names2 = new string[7]; Array.Copy(names, names2, names.Length);   // or names.CopyTo(names2, 0); 

float[,] twoD = new float[rows, cols]; twoD[2,0] = 4.5f;  

int[][] jagged = new int[3][] {   new int[5], new int[2], new int[3] }; jagged[0][4] = 5;

VB.NETFunctionsC#

' Pass by value (in, default), reference (in/out), and reference (out)   Sub TestFunc(ByVal x As Integer, ByRef y As Integer, ByRef z As Integer)   x += 1   y += 1   z = 5 End Sub

Dim a = 1, b = 1, c As Integer   ' c set to zero by default  TestFunc(a, b, c) Console.WriteLine("{0} {1} {2}", a, b, c)   ' 1 2 5

' Accept variable number of arguments Function Sum(ByVal ParamArray nums As Integer()) As Integer   Sum = 0    For Each i As Integer In nums     Sum += i   Next End Function   ' Or use Return statement like C#
Dim total As Integer = Sum(4, 3, 2, 1)   ' returns 10

' Optional parameters must be listed last and must have a default value Sub SayHello(ByVal name As String, Optional ByVal prefix As String = "")   Console.WriteLine("Greetings, " & prefix & " " & name) End Sub
SayHello("Strangelove", "Dr.") SayHello("Madonna")

// Pass by value (in, default), reference (in/out), and reference (out) void TestFunc(int x, ref int y, out int z) {   x++;     y++;   z = 5; } 

int a = 1, b = 1, c;  // c doesn't need initializing TestFunc(a, ref b, out c); Console.WriteLine("{0} {1} {2}", a, b, c);  // 1 2 5

// Accept variable number of arguments int Sum(params int[] nums) {   int sum = 0;   foreach (int i in nums)     sum += i;   return sum; }

int total = Sum(4, 3, 2, 1);   // returns 10

/* C# doesn't support optional arguments/parameters.  Just create two different versions of the same function. */  void SayHello(string name, string prefix) {   Console.WriteLine("Greetings, " + prefix + " " + name); } 
void SayHello(string name) {   SayHello(name, ""); }

VB.NETStringsC#

Special character constants vbCrLf, vbCr, vbLf, vbNewLine vbNullString vbTab vbBack vbFormFeed vbVerticalTab ""

' String concatenation (use & or +) Dim school As String = "Harding" & vbTab school = school & "University" ' school is "Harding (tab) University"

' Chars Dim letter As Char = school.Chars(0)   ' letter is H letter = Convert.ToChar(65)                ' letter is A letter = Chr(65)                                 ' same thing Dim word() As Char = school.ToCharArray() ' word holds Harding

' No string literal operator   Dim msg As String = "File is c:\temp\x.dat" 

' String comparison Dim mascot As String = "Bisons" If (mascot = "Bisons") Then   ' true If (mascot.Equals("Bisons")) Then   ' true If (mascot.ToUpper().Equals("BISONS")) Then  ' true If (mascot.CompareTo("Bisons") = 0) Then   ' true

Console.WriteLine(mascot.Substring(2, 3)) ' Prints "son"

' String matching If ("John 3:16" Like "Jo[Hh]? #:*") Then   'true
Imports System.Text.RegularExpressions   ' More powerful than Like Dim r As New Regex("Jo[hH]. \d:*") If (r.Match("John 3:16").Success) Then   'true

' My birthday: Oct 12, 1973 Dim dt As New DateTime(1973, 10, 12) Dim s As String = "My birthday: " & dt.ToString("MMM dd, yyyy") Console.WriteLine(s)

' Mutable string Dim buffer As New System.Text.StringBuilder("two ") buffer.Append("three ") buffer.Insert(0, "one ") buffer.Replace("two", "TWO") Console.WriteLine(buffer)         ' Prints "one TWO three"

Escape sequences \n, \r \t \\ \"

// String concatenation string school = "Harding\t"; school = school + "University";   // school is "Harding (tab) University"

// Chars char letter = school[0];            // letter is H letter = Convert.ToChar(65);     // letter is A letter = (char)65;                    // same thing char[] word = school.ToCharArray();   // word holds Harding

// String literal string msg = @"File is c:\temp\x.dat"; // same as string msg = "File is c:\\temp\\x.dat";

// String comparison string mascot = "Bisons"; if (mascot == "Bisons")    // true if (mascot.Equals("Bisons"))   // true if (mascot.ToUpper().Equals("BISONS"))   // true if (mascot.CompareTo("Bisons") == 0)    // true

Console.WriteLine(mascot.Substring(2, 3));    // Prints "son"

// String matching // No Like equivalent - use regular expressions
using System.Text.RegularExpressions; Regex r = new Regex(@"Jo[hH]. \d:*"); if (r.Match("John 3:16").Success)   // true

// My birthday: Oct 12, 1973 DateTime dt = new DateTime(1973, 10, 12); string s = "My birthday: " + dt.ToString("MMM dd, yyyy");

// Mutable string System.Text.StringBuilder buffer = new System.Text.StringBuilder("two "); buffer.Append("three "); buffer.Insert(0, "one "); buffer.Replace("two", "TWO"); Console.WriteLine(buffer);     // Prints "one TWO three"

VB.NETException HandlingC#

' Throw an exception Dim ex As New Exception("Something is really wrong.") Throw  ex 

' Catch an exception Try    y = 0   x = 10 / y Catch ex As Exception When y = 0 ' Argument and When is optional   Console.WriteLine(ex.Message) Finally   Beep() End Try

' Deprecated unstructured error handling On Error GoTo MyErrorHandler ... MyErrorHandler: Console.WriteLine(Err.Description)

// Throw an exception Exception up = new Exception("Something is really wrong."); throw up;  // ha ha

// Catch an exception try {    y = 0;   x = 10 / y; } catch (Exception ex) {   // Argument is optional, no "When" keyword    Console.WriteLine(ex.Message); } finally {   // Requires reference to the Microsoft.VisualBasic.dll   // assembly (pre .NET Framework v2.0)   Microsoft.VisualBasic.Interaction.Beep(); }

VB.NETNamespacesC#

Namespace Harding.Compsci.Graphics    ... End Namespace

' or

Namespace Harding   Namespace Compsci     Namespace Graphics        ...     End Namespace   End Namespace End Namespace

Imports Harding.Compsci.Graphics

namespace Harding.Compsci.Graphics {   ... }

// or

namespace Harding {   namespace Compsci {     namespace Graphics {       ...     }   } }

using Harding.Compsci.Graphics;

VB.NETClasses / InterfacesC#

Accessibility keywords Public Private Friend                    Protected Protected Friend Shared

' Inheritance Class FootballGame   Inherits Competition   ... End Class 

' Interface definition Interface IAlarmClock    ... End Interface

// Extending an interface  Interface IAlarmClock   Inherits IClock   ... End Interface

// Interface implementation Class WristWatch    Implements IAlarmClock, ITimer     ... End Class 

Accessibility keywords public private internal protected protected internal static

// Inheritance class FootballGame : Competition {   ... }

// Interface definition interface IAlarmClock {   ... }

// Extending an interface  interface IAlarmClock : IClock {   ... }

// Interface implementation class WristWatch : IAlarmClock, ITimer {    ... }

VB.NETConstructors / DestructorsC#
Class SuperHero   Private _powerLevel As Integer
  Public Sub New()     _powerLevel = 0   End Sub
  Public Sub New(ByVal powerLevel As Integer)     Me._powerLevel = powerLevel   End Sub
  Protected Overrides Sub Finalize()     ' Desctructor code to free unmanaged resources     MyBase.Finalize()   End Sub End Class

class SuperHero {   private int _powerLevel;
  public SuperHero() {      _powerLevel = 0;   }
  public SuperHero(int powerLevel) {     this._powerLevel= powerLevel;    }
  ~SuperHero() {     // Destructor code to free unmanaged resources.     // Implicitly creates a Finalize method   } }

VB.NETObjectsC#

Dim hero As SuperHero = New SuperHero ' or Dim hero As New SuperHero With hero   .Name = "SpamMan"   .PowerLevel = 3 End With

hero.Defend("Laura Jones") hero.Rest()     ' Calling Shared method ' or SuperHero.Rest()

Dim hero2 As SuperHero = hero  ' Both reference the same object hero2.Name = "WormWoman" Console.WriteLine(hero.Name)   ' Prints WormWoman

hero = Nothing    ' Free the object

If hero IsNothing Then _   hero = New SuperHero

Dim obj As Object = New SuperHero If TypeOf obj Is SuperHero Then _   Console.WriteLine("Is a SuperHero object.")

SuperHero hero = new SuperHero();

// No "With" construct hero.Name = "SpamMan"; hero.PowerLevel = 3;

hero.Defend("Laura Jones"); SuperHero.Rest();   // Calling static method

SuperHero hero2 = hero;   // Both reference the same object hero2.Name = "WormWoman"; Console.WriteLine(hero.Name);   // Prints WormWoman

hero = null ;   // Free the object

if (hero == null)   hero = new SuperHero();

Object obj = new SuperHero();  if (obj is SuperHero)   Console.WriteLine("Is a SuperHero object.");

VB.NETStructsC#

Structure StudentRecord   Public name As String   Public gpa As Single
  Public Sub New(ByVal name As String, ByVal gpa As Single)     Me.name = name     Me.gpa = gpa   End Sub End Structure

Dim stu As StudentRecord = New StudentRecord("Bob", 3.5) Dim stu2 As StudentRecord = stu  
stu2.name = "Sue" Console.WriteLine(stu.name)    ' Prints Bob Console.WriteLine(stu2.name)  ' Prints Sue

struct StudentRecord {   public string name;   public float gpa;
  public StudentRecord(string name, float gpa) {     this.name = name;     this.gpa = gpa;   } }

StudentRecord stu = new StudentRecord("Bob", 3.5f); StudentRecord stu2 = stu;  
stu2.name = "Sue"; Console.WriteLine(stu.name);    // Prints Bob Console.WriteLine(stu2.name);   // Prints Sue

VB.NETPropertiesC#

Private _size As Integer
Public Property Size() As Integer   Get     Return _size   End Get   Set (ByVal Value As Integer)     If Value < 0 Then       _size = 0     Else       _size = Value     End If   End Set End Property

foo.Size += 1

private int _size;
public int Size {   get {     return _size;   }   set {     if (value < 0)       _size = 0;     else       _size = value;   } } 

foo.Size++;

VB.NETDelegates / EventsC#

Delegate Sub MsgArrivedEventHandler(ByVal message As String)

Event MsgArrivedEvent As MsgArrivedEventHandler

' or to define an event which declares a delegate implicitly Event MsgArrivedEvent(ByVal message As String)

AddHandler MsgArrivedEvent, AddressOf My_MsgArrivedCallback ' Won't throw an exception if obj is Nothing RaiseEvent MsgArrivedEvent("Test message") RemoveHandler MsgArrivedEvent, AddressOf My_MsgArrivedCallback

Imports System.Windows.Forms

Dim WithEvents MyButton As Button   ' WithEvents can't be used on local variable MyButton = New Button

Private Sub MyButton_Click(ByVal sender As System.Object, _   ByVal e As System.EventArgs) Handles MyButton.Click   MessageBox.Show(Me, "Button was clicked", "Info", _     MessageBoxButtons.OK, MessageBoxIcon.Information) End Sub

delegate void MsgArrivedEventHandler(string message);

event MsgArrivedEventHandler MsgArrivedEvent;

// Delegates must be used with events in C#
MsgArrivedEvent += new MsgArrivedEventHandler(My_MsgArrivedEventCallback); MsgArrivedEvent("Test message");    // Throws exception if obj is null MsgArrivedEvent -= new MsgArrivedEventHandler(My_MsgArrivedEventCallback);

using System.Windows.Forms;

Button MyButton = new Button();  MyButton.Click += new System.EventHandler(MyButton_Click);

private void MyButton_Click(object sender, System.EventArgs e) {   MessageBox.Show(this, "Button was clicked", "Info",     MessageBoxButtons.OK, MessageBoxIcon.Information); }

VB.NETConsole I/OC#

Console.Write("What's your name? ") Dim name As String = Console.ReadLine() Console.Write("How old are you? ") Dim age As Integer = Val(Console.ReadLine()) Console.WriteLine("{0} is {1} years old.", name, age)  ' or Console.WriteLine(name & " is " & age & " years old.")
Dim c As Integer c = Console.Read()    ' Read single char Console.WriteLine(c)   ' Prints 65 if user enters "A"

Console.Write("What's your name? "); string name = Console.ReadLine(); Console.Write("How old are you? "); int age = Convert.ToInt32(Console.ReadLine()); Console.WriteLine("{0} is {1} years old.", name, age); // or Console.WriteLine(name + " is " + age + " years old.");

int c = Console.Read();  // Read single char Console.WriteLine(c);    // Prints 65 if user enters "A"

VB.NETFile I/OC#

Imports System.IO

' Write out to text file Dim writer As StreamWriter = File.CreateText("c:\myfile.txt") writer.WriteLine("Out to file.") writer.Close()

' Read all lines from text file Dim reader As StreamReader = File.OpenText("c:\myfile.txt") Dim line As String = reader.ReadLine() While Not line Is Nothing   Console.WriteLine(line)   line = reader.ReadLine() End While reader.Close()

' Write out to binary file Dim str As String = "Text data" Dim num As Integer = 123 Dim binWriter As New BinaryWriter(File.OpenWrite("c:\myfile.dat"))  binWriter.Write(str)  binWriter.Write(num)  binWriter.Close()

' Read from binary file Dim binReader As New BinaryReader(File.OpenRead("c:\myfile.dat")) str = binReader.ReadString() num = binReader.ReadInt32() binReader.Close()

using System.IO;

// Write out to text file StreamWriter writer = File.CreateText("c:\\myfile.txt"); writer.WriteLine("Out to file."); writer.Close();

// Read all lines from text file StreamReader reader = File.OpenText("c:\\myfile.txt"); string line = reader.ReadLine(); while (line != null) {   Console.WriteLine(line);   line = reader.ReadLine(); } reader.Close();

// Write out to binary file string str = "Text data"; int num = 123; BinaryWriter binWriter = new BinaryWriter(File.OpenWrite("c:\\myfile.dat")); binWriter.Write(str); binWriter.Write(num); binWriter.Close();

// Read from binary file BinaryReader binReader = new BinaryReader(File.OpenRead("c:\\myfile.dat")); str = binReader.ReadString(); num = binReader.ReadInt32(); binReader.Close();




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