Chương 3- VB

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Chng 3. ASP.NET v VB.NETS lc v VB.NETVariables v Arrays

Operators

Cc iu kin (conditional), looping v branching logic

Functions v Subroutines

Event Handler

Classes

Ving dng ch li thng dng

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3.1 S lc v VB.NET

ASP.NET nm trong cu trc nn ca .NET framework v dng.NET programming language nh VB.NET (mt trong 25 NNLT .NEThin nay) pht trin trang Web => cn bit s lt v .NETframework cng VB.NET dng cho cc trang ASP.NET.

Nu thch, ta c th dng C# hay C++ thay v VB.NET, v s khcbit phn ln l v c php (syntax) ch nguyn tc v cu trclp trnh th nh nhau. D dng bt c NNLT no, khi bin dchvn phi qua ngn ng trung gian Intermediate Language (IL) vqun l bi CLR.

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3.2 Variables v Arrays

Variables dng lu tr d kin (data) trong b nh (memory) camy tnh. Taphi khai bo (declare) bin s trc khi dng vi keyword Dim VD: DimmyVariable As String

.Data Types chia ra lm 5 nhm vi 10 kiu c bn gi l primitive types:

Byte Integers 1 byte (c bit nh System.Int)

Short Integers 2 bytes (System.Int16)

Integer Integers 4 bytes (System.Int32)

Long Integers 8 bytes (System.Int64)

Single decimal 4 bytes (System.Single)

Double decimal 8 bytes (System.Doublel)

Decimal decimal 12 bytes (System.Decimal)

Char String single Unicode character (System.Char)

Date Dates ngy gi (System.DateTime)

Boolean Boolean True/False (System.Boolean)

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3.2 Variables v Arrays (tt)

Arrays l 1 tp hp cc bin s c lin h ring bit qua chs(index) ca Arrays.

Arrays dng trong VB.NET bt u vi index bng s 0.

Mi bin s trong Array phi cng kiu d liu (data type).

Array c khai bo nh v d sau :

DimmyArray(9) As Integer

Dim yourArray( ) As String = { "T", "Su", "Dn", "Mo",_ "Thn",

T", "Ng", "Mi", "Thn", "Du", "Tut", "Hi" }

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3.4 Operators

^ M

+, - Du

*, / Php nhn, chia

\ Php chia ly phn d

+, - Php cng, trBitNot, BitAnd, BitOr, BitXor Bitwise NOT, AND, OR v XOR

&, + Ghp ni xu

=, , , >=,

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3.5 Cc cu trc iu khin

If statements Tng cng 3 kiu c php nh sau: If (condition) Then

......

End If If (condition) Then

(your code for condition = True)...Else

(your code for condition = False)...

End If If (condition 1) Then

(your code for condition 1 = True)

...ElseIf (condition 2) Then

(your code for condition 2 = True)...

Else(ngoi ra, thi hnh code y)...

End If

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3.5 Cc cu trc iu khin (tt)

While Loops

Rt tin li trong trng hp ta khng bit trc phi lp i lp li cng vicbao nhiu ln. Thi hnh cho n khi iu kin nh trc tr thnh False. Cphp ca While loop nh sau:

While condition

Your Code

End While

Th d ta mun b tr 1 my m (counter) t 1 n 9 v hin th (display) ktqu bng s browser:

Dim intCounter As Integer = 1

While intCounter < 10

Response.Write(intCounter & "
")

intCounter += 1

End While

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Do Loops

Do loop cng tng t nh while loop, chkhc ch Do loop thihnh cng vic trc ri mi kim tra iu kin xem c ph hpkhng?


Do

")

intCounter += 1

Loop While intCounter < 10

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For Loops Ta dng For loop khi bit trc s lp i lp li vic thi hnh ngunm bao

nhiu ln. My m trong trng hp ny (t ng tng hay gim ty theocch b tr) s thng bo chnh loop ca n khi no chm dt. C php nhsau:

For intCounter = 1 to 10

")Next hoc l:

For intCounter = 10 to 1 Step -1Response.Write(intCounter & "
")

Next

For loop cn c 1 dng khc l For each ... loop, thng dng vn dng ccthnh phn (hay yu t - elements) trong 1 b su tp (collection) t nh Arraychng hn:

Dim arrayWeekDays( ) As String = {"Mon", "Tue", "Wed", "Thu", "Fri"} For eachstrDay in arrayWeekDays

Response.Write(strDay & "
")Next

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Nu tamun nhy ra khi loop trc khi loop chm dt, ta c th dngkeyword Exit Do (trong Do loop) hay Exit For (trong For loop), VD:


DoResponse.Write(intCounter & "
")

intCounter += 1If intCounter = 8 then

Exit DoEnd If

Loop While intCounter < 10

hay

For intCounter = 1 to 10Response.Write(intCounter & "
")If intCounter = 8 then

Exit ForEnd If

Next

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3.6 Functions

Functions

C php nh sau:

Function FunctionName (Parameter1 As Type, ... , ParameterN As

Type) As ReturnType

'you code here

Return ReturnValue

End Function

Vi VB.NET Function tin dng:

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3.6 Functions (tt)

Cc functions v Date v Time Function Phn din t cng dng

day(datetime) Tr li 1 s t 1 ti 31 biu th ngy trong thng.

dateDiff(dateinterval, date1,date2) Tr li 1 s din t khong thi gian cch bitgia 2 ngy: (date1) v (date2). S ny c th di dng yyyy (year), q (quarter),m

(m

onth ), y (year), d (day), h(hour), n (m

inute) hay s (second).hour(time) gi trong ngy.

isdate(datetime) datetime c phi l 1 ngy hp l khng?

minute(time) pht trong gi.

month(datetime) thng trong datetime.

now( ) Tr li ngy gi hin thi

second(time) 0 ti 59 biu th giy trong pht.

year(datetime) nm ca datetime (c gi tr t 1 ti 9999)

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3.6 Functions (tt)

Cc Functions v Ton HcFunction Phn din t cng dng

abs(value) Tr li gi tr tuyt i (absolute) ca value.

atan(value) Tr li s arctangent ca value.

cos(value) Tr li s cosin ca value.

exp(value) Tr li s exponent ca value.

fix(value) Tr li phn integer ca value :fix(5.8)=5, fix(-5.8)=-6

hex(value) Tr li s hexadecimal ca value (base 10 to base 16).

int(value) Tr li phn integer ca value : in(5.8)=5, int(-5.8)=5

log(value) Tr li s nature logarithm ca value.

oct(value) Tr li s octal ca value (base 10 to base 8).

rnd Tr li s ngu nhin.round(value [, dec]) Lm trn vi 0, hoc dec s thp phn ca value.

sin(value) Tr li s sin ca value.

sqrt(value) Tr li s cn 2 ca value.

tan(value) Tr li s tangent ca value

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3.6 Functions (tt)

Cc Functions StringsFunction Phn din t cng dng

instr([start, ]s1, s2[, compare]) Tr li s biu th v tr 1 ca s2 trong s1,ngoi ra tr li s 0. Compare c th di dng 0 (=BinaryCompare) hay 1(=TextCompare).

left(s, len) Tr li xu con vi di =len k t pha bn tri ca s.len(s | variable) Tr li chiu di ca string hay tng s bytesm variable chang.

mid(s, start[, len]) Tr li xu con vi di len, k t v tr th start cas.

replace(exp, find, replace[,start[, count[, compare]]]) Thay th gi tr find trongbiu thc expression bng gi tr replace bt u t v tr start vi s ln thayth count. Lu gi trmc nh ca count l -1 - ngha l thay th tt c g truytm c, compare dng di dng 0 hay 1 nh trong phn instr.

right(s, len) Tr li xu con 1 di = len bt u t pha bn phi s.

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3.7 Th tc : Subroutines

Subroutines Th tc C php nh sau:

Sub SubroutineName (Parameter1 As Type, ... ,ParameterN As Type)

'you code here

End Sub

V d subroutine Page_Load rt ph thng trong cc trang ASP.NET :

Sub Page_Load (Obj As object, e As eventargs)

'you code here

End Sub

Cc bin s (variables) trong ( ) gi l thng s (parameters hay arguments),dng truyn cc gi tr u vo cho th tc

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3.7 Th tc : Subroutines

Event Handler

Ny , ta thy 1 trong nhng thng s (parameters) s dng trong th tctrn l thng s v s c (EventArgs). Trong cc trang Web ca ASP.NET , sc c th xy ra bt c lc no, nh user nhpmi chut vo 1 nt no trnForm hoc nhp vo 1 hnh nh, do ta cn chun b v to ra ci gi l event

handler c th p ng li cc s c . C php ca event handler gingnh c php ca subroutine, s khc bit l nm parameters list vi thngs chring cho loi EventArgs. Khi 1 s c khi ng, s c s to ra ccbin s nhm din t vic g xy ra v event handler s da trn cc bins phn ng sao cho thch hp.

.NET t ng gip ta to khung cho cc th tc x l s kin ( vi tn th tc,ds tham s v dong end sub, phn thn th tc, ta phi t vit code )

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3.8 Classes

Classes l phn ta xc nh hay nh ngha cc i tng (Object) t nh nh ngha 1 ci ng h, ta din t kim gi, kim pht, kim giy cng cc con schgi, cch b tr gi gic hay ngy thng nm, ... Tng t nh th, classnh ngha i tng (Object) qua cc c tnh (properties) v cc phngphp (method) biu th c trng cho class.

Ta nn nh r 1 iu: 'Mi th trong .NET Framework hay VB.NET u i biucho classes'.

C php nh sau:

Class classname

properties

subroutines

functions

End Class

Trc khi dng, nh instantiate class ra 1 i tng (Object).

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3.8 Classes (tt)

C rt nhiu Base Classes trong .NET Framework, tng qut c th xp vonhng loi sau:

String Collections v Arrays: VD Arrays, Lists, Maps, Linked Lists, ...

WinFor ms: dng hin th (display) Windows v cc Controls VD Text Boxes,Combo Boxes, List Boxes, File Dialogs, ...

Web For ms: phc tho dng chomng, ta s nghin cu k sau.

File Handling: dng lt qua li (navigate) cc file system trong my hay trongmng, kim tra c tnh (properties) ca files, read, modify hay write cng nhchuyn (move) v sao chp (copy) cc tp tin hay folders.

Registrry Access: lt qua li, c hay vit ni dung ca registry.

Internet: ni vo mng, ti ln hay ti xung cc tp tin.

ADO.NET: ni vo cc c s d liu (database) v vn dng cc records vi 1khi nimmi v disconnected data cng nh s dng XML chuyn data ikhpmi nimi ch.

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3.9 Inheritance

Inheritance nm vai tr quan trng trong classes v OOP. Takhng cn phi to ra 1 class mi hon ton khi c 1 classtng t nh ci ta mun m chcn to ra 1 lp mi , k that lp c (base class). Tr li trng hp ci ng h, nu cth to 1 class gi l Clock, ri sau c th xy dng class mi ly

Clock class lm c s (base class) v thm vo nhng g ctrng n hay lin h n loi ca Clock l Analog hay Digital.

C php nh sau vi th d v AnalogClock:

Class AnalogClock: Inherit Clock

private ClockWound ASP.NET Boolean = FalseSub WindClock( )

ClockWound = TrueEnd Sub

End Class

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V d : XD trang web nh sau :

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Code view

Protected Sub Button1_Click(ByVal sender As Object, ByVal e AsSystem.EventArgs) Handles Button1.Click

kq.Text = "Php cng: " & so1.Text & " + " & so2.Text & " = " &CInt(so1.Text) + CInt(so2.Text)

End Sub

Protected Sub Button2_Click(ByVal sender As Object, ByVal e As

System.EventArgs) Handles Button2.Click

kq.Text = "Php tr: " & so1.Text & " - " & so2.Text & " = " &CInt(so1.Text) - CInt(so2.Text)

End Sub

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Chương 3- VB

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