VB.NET

Program Structure

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 + "!");
}
}
}

Comments

' Single line only
Rem Single line only

// Single line
/* Multiple line *//// XML comments on single line/** XML comments on multiple lines */

Data Types

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(GetType(Integer))
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 CTypeInt' set to 3 (Int function truncates the decimal)

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

object
string

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

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

Constants

Const MAX_STUDENTS 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;

Enumerations

Enum Action
Start
[Stop] ' Stop is a reserved word
Rewind
Forward
End 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};
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

Operators

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
& +

== < > <= >= !=

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

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

& | ^ ~ << >>

&& || & | ^ !

&& and || perform short-circuit logical evaluations

+

Choices

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

' One line doesn't require "End If"
If age < 20 Then greeting = "What's up?"
greeting = "What's up?" Else greeting = "Hello"

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

' Preferred
x *= 5
y *= 2
End If

' To break up any long single line use _ whenYouHaveAReally < longLine And _
itNeedsToBeBrokenInto2 > Lines _
UseTheUnderscore(charToBreakItUp)

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

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

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

if (age < 20)
greeting = "What's up?";
else
greeting = "Hello";

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

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

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

x /= y;

// Every case must end with break or goto case
switch (color) { // Must be integer or string
case "pink":
"red": r++; break;
"blue": b++; break;
"green": g++; default: other++; // break necessary on default
}

Loops

Pre-test Loops:
While c < 10 c += 1 End While	Do Until c = 10 c += 1 Loop
Do WhileLoop	For c = 2 To 10 Step 2 Console.WriteLine(c) Next
Post-test Loops:
Do c += 1 Loop While c < 10	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

' Continue to next iteration
For i = 0 To 4
If i < 4 Then Continue For
Console.WriteLine(i) ' Only prints 4
Next

Pre-test Loops:

// no "until" keywordwhile (c < 10)
c++;

for (c = 2; c <= 10; c += 2)
Console.WriteLine(c);

Post-test Loop:

do
c++;
(c < 10);

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

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

// Continue to next iteration
for (i = 0; i < 5; i++) {
if (i < 4)
continue;
Console.WriteLine(i); // Only prints 4Arrays

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 = {1,3};
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;

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

Functions

' Pass by value (in,default),reference (in/out),and reference (out)Sub TestFunc(ByVal x As Integer,ByRef y As Integer,'sans-serif'; font-size:10pt"> 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,c) ' 1 2 5

' Accept variable number of argumentsFunction 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(4,3,1) ' returns 10

' Optional parameters must be listed last and must have a default value
Sub SayHello(ByVal name As String,'sans-serif'; font-size:10pt">Optional ByVal prefix As String = "")
Console.WriteLine("Greetings," & prefix & " " & name)
End Sub

SayHello("Strangelove","Dr.")
SayHello("Madonna")

// Pass by value (in,'sans-serif'; font-size:10pt">
void TestFunc(int x,'sans-serif'; font-size:10pt">ref int y,'sans-serif'; font-size:10pt">out int z) {
x++;
y++;
z = 5;
}

int a = 1,c; // c doesn't need initializing
TestFunc(a,'sans-serif'; font-size:10pt"> b,'sans-serif'; font-size:10pt"> c);
Console.WriteLine("{0} {1} {2}",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(4,1); // 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,"");
}

Strings

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 ToUpper().("BISONS")) Then 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")

' 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 concatenationstring school = "Harding"t";
school = school + "University"; // school is "Harding (tab) University"

// Charschar 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.("Bisons")) ("BISONS")) ("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,'sans-serif'; font-size:10pt">
DateTime dt = new DateTime(1973,12);
string s = "My birthday: " + dt.ToString("MMM dd,yyyy");

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

Exception Handling

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

' Catch an exceptionTry
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 handlingOn 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 exceptiontry {
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();
}

Namespaces

Namespace Harding.Compsci.Graphics
...
End Namespace

' or

Harding
Compsci
Graphics
...
End NamespaceEnd Namespace End Namespace

Imports Harding.Compsci.Graphics

namespace Harding.Compsci.Graphics {
...
}

// or

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

using Harding.Compsci.Graphics;

Classes / Interfaces

Accessibility keywords
Public
Private
Friend
Protected
Protected Friend
Shared

' InheritanceClass FootballGame
Inherits Competition
...
End Class

' Interface definitionInterface IAlarmClock
...
End Interface

// Extending an interface IAlarmClock
IClock
...
// Interface implementation WristWatch
Implements IAlarmClock,ITimer
...
End Class

public
private
internal
protected
protected internal
static

// Inheritanceclass FootballGame Competition {
...
}

// Interface definitioninterface IAlarmClock {
...
}

IAlarmClock IClock {
...
}

WristWatch
Constructors / Destructors

C#

SuperHero
Private _powerLevel As Integer

Public Sub New()
_powerLevel = 0
End Sub

Public Sub (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

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
}
}

Using Objects

@H_460_3014@ @H_906_3015@

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

@H_906_3015@

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

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

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 Is Then _
hero = New SuperHero

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

' Mark object for quick disposal
Using reader As StreamReader = File.OpenText("test.txt")
Dim line As String = reader.ReadLine()
While Not line Is Nothing
Console.WriteLine(line)
line = reader.ReadLine()
End While
End Using

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

null ; // Free the object

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

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

// Mark object for quick disposal
using (StreamReader reader = File.OpenText("test.txt")) {
string line;
while ((line = reader.ReadLine()) != null)
Console.WriteLine(line);
}

Structs

Properties

Private _size As Integer

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

foo.Size += 1

private int _size;

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

foo.Size++;

Delegates / Events

Delegate Sub MsgArrivedEventHandler(ByVal message As String)

Event MsgArrivedEvent As MsgArrivedEventHandler

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

AddHandler MsgArrivedEvent,'sans-serif'; font-size:10pt">AddressOf My_MsgArrivedCallback
' Won't throw an exception if obj is NothingRaiseEvent MsgArrivedEvent("Test message")
RemoveHandler 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,
MessageBoxButtons.OK,MessageBoxIcon.Information);
}

Console I/O

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)

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.",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"

File I/O

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 writer = File.CreateText("c:""myfile.txt");
writer.WriteLine("Out to file.");
writer.Close();

// Read all lines from text file 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;
binWriter = new BinaryWriter(File.OpenWrite("c:""myfile.dat"));
binWriter.Write(str);
binWriter.Write(num);
binWriter.Close();

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

分类: .NET技术学习