platform technology unit 4.ppt

8/13/2019 PLATFORM TECHNOLOGY UNIT 4.ppt

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VB.NET

UNIT 4

For

III-CSE


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CONTENTS

DELEGATES AND EVENTS

ACCESSING DATA

ADO.NET OBJECT MODEL

.NET DATA PROVIDERS

DIRECT ACCESS TO DATA

ACESSING DATA WITH DATASETS

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1. Delegates

Delegates Classes that encapsulate a set of references to methods

A delegate object that contains method references can be

passed to another method

Singlecast delegates

Delegates containing a single method and they are created and

derived from class Delegate

Multicast delegates

Delegates containing multiple methods and they are derived

from class MulticastDelegate AddressOf

Creates a delegate instance enclosing a reference to that

method


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Outline4

DelegateBubbleSort.vb

1 ' Fig. 10.24: DelegateBubbleSort.vb2 ' Uses delegates to sort random numbers (ascending or descending).34 Public ClassCDelegateBubbleSort56 ' delegate definition7 Public Delegate FunctionComparator( _

8 ByValelement1As Integer, _9 ByValelement2As Integer)As Boolean1011 ' sort array depending on comparator12 Public SubSortArray(ByValarrayAs Integer(), _13 ByValCompareAsComparator)1415 Dimi, passAs Integer1617 Forpass = 0Toarray.GetUpperBound(0)1819 ' comparison inner loop20 Fori = 0Toarray.GetUpperBound(0) - 12122 IfCompare(array(i), array(i + 1)) Then23 Swap(array(i), array(i + 1))24 End If

2526 Next' inner loop2728 Next' outer loop2930 End Sub' SortArray3132 ' swap two elements33 Private SubSwap(ByReffirstElementAs Integer, _

34 ByRefsecondElementAs Integer)35

Declaration of a delegate Comparator

Returns value Boolean

Define method SortArray

Determines how to sort the array


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Outline5

DelegateBubbleSort.vb

36 DimholdAs Integer3738 hold = firstElement39 firstElement = secondElement40 secondElement = hold41 End Sub' Swap42

43 End Class' CDelegateBubbleSort


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Outline6

FrmBubbleSort.vb

1 ' Fig. 10.25: FrmBubbleSort.vb2 ' Create GUI that enables user to sort array.34 ImportsSystem.Windows.Forms56 Public ClassCFrmBubbleSort7 InheritsForm

89 ' TextBox that contains original list10 Friend WithEventstxtOriginalAsTextBox11 Friend WithEventslblOriginalAsLabel1213 ' TextBox that contains sorted list14 Friend WithEventstxtSortedAsTextBox15 Friend WithEventslblSortedAsLabel1617 ' Buttons for creating and sorting lists18 Friend WithEventscmdCreateAsButton19 Friend WithEventscmdSortAscendingAsButton20 Friend WithEventscmdSortDescendingAsButton2122 ' Windows Form Designer generate code2324 ' reference to object containing delegate

25 DimmBubbleSortAs NewCDelegateBubbleSort()2627 ' original array with unsorted elements28 DimmElementArrayAs Integer() =NewInteger(9){}2930 ' delegate implementation sorts in asending order31 Private FunctionSortAscending(ByValelement1As Integer, _32 ByValelement2As Integer)As Boolean33

34 Returnelement1 > element235 End Function' SortAscending

Displays a list of unsorted numbers

Displays a list of sorted sequence

Creates a list in either ascending or descending order

Defines method SortAscending


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Outline7

FrmBubbleSort.vb

3637 ' delegate implementation sorts in descending order38 Private FunctionSortDescending(ByValelement1As Integer, _39 ByValelement2As Integer)As Boolean4041 Returnelement1 < element242 End Function' SortDescending

4344 ' creates random generated numbers45 Private SubcmdCreate_Click(ByValsenderAsSystem.Object, _46 ByValeAsSystem.EventArgs) HandlescmdCreate.Click4748 txtSorted.Clear()4950 DimoutputAs String51 DimrandomNumberAsRandom =NewRandom()52 DimiAs Integer5354 ' create String with 10 random numbers55 Fori = 0TomElementArray.GetUpperBound(0)56 mElementArray(i) = randomNumber.Next(100)57 output &= mElementArray(i) & vbCrLf58 Next59

60 txtOriginal.Text = output ' display numbers6162 ' enable sort buttons63 cmdSortAscending.Enabled = True64 cmdSortDescending.Enabled = True65 End Sub' cmdCreate_Click66

Defines method SortDescending


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Outline8

FrmBubbleSort.vb

67 ' display array contents in specified TextBox68 Private SubDisplayResults()6970 DimoutputAs String71 DimiAs Integer7273 ' create string with sorted numbers

74 Fori = 0TomElementArray.GetUpperBound(0)75 output &= mElementArray(i) & vbCrLf76 Next7778 txtSorted.Text = output ' display numbers79 EndSub' DisplayResults8081 ' sorts randomly generated numbers in ascending manner82 Private SubcmdSortAscending_Click(ByValsenderAs_83 System.Object, ByValeAsSystem.EventArgs) _84 HandlescmdSortAscending.Click8586 ' sort array87 mBubbleSort.SortArray(mElementArray,AddressOfSortAscending)8889 DisplayResults() ' display results90

91 cmdSortAscending.Enabled = False92 cmdSortDescending.Enabled = True93 EndSub' cmdSortAscending_Click9495 ' sorts randomly generated numbers in descending manner96 PrivateSubcmdSortDescending_Click(ByValsenderAs_97 System.Object, ByValeAsSystem.EventArgs) _98 HandlescmdSortDescending.Click99

100 ' create sort object and sort array101 mBubbleSort.SortArray(mElementArray,AddressOfSortDescending)

Methods cmdSortAscending_Clickand

cmdSortDescending_Clickare invoked when the user clicks the

Sort Ascendingand Sort Descendingbuttons


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Outline9

FrmBubbleSort.vb

102103 DisplayResults() ' display results104105 cmdSortDescending.Enabled = False106 cmdSortAscending.Enabled = True107 End Sub' cmdSortDescending_Click108

109 End Class' CFrmBubbleSort


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Outline11

FrmBubbleSort.vb


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12.3 Event-Handling Model

Fig. 12.5 Event-handling model using delegates.

Object A raises event EDelegate for event E

Handler 1 for event E



calls

calls



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12.3 Event-Handling Model

Fig. 12.6 Events section of the Properties window.

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Outline15

SimpleEvenExample.vb

1 ' Fig. 12.7: SimpleEventExample.vb2 ' Program demonstrating simple event handler.34 PublicClassFrmSimple5 InheritsSystem.Windows.Forms.Form67 #Region " Windows Form Designer generated code "

89 PublicSubNew()10 MyBase.New()1112 ' This call is required by the Windows Form Designer.13 InitializeComponent()141516 ' Add any initialization after the17 ' InitializeComponent() call18 EndSub ' New1920 ' Form overrides dispose to clean up the component list.21 ProtectedOverloadsOverridesSubDispose( _22 ByValdisposingAsBoolean)2324 Ifdisposing Then

2526 IfNot(components IsNothing) Then27 components.Dispose()28 EndIf2930 EndIf3132 MyBase.Dispose(disposing)33 EndSub ' Dispose

3435 FriendWithEventslblOutputAsSystem.Windows.Forms.Label

Beginning of Visual Studio

generated code

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3637 ' Required by the Windows Form Designer38 PrivatecomponentsAsSystem.ComponentModel.Container3940 ' NOTE: The following procedure is required by41 ' the Windows Form Designer.42 ' It can be modified using the Windows Form Designer.

43 ' Do not modify it using the code editor.44 _45 PrivateSubInitializeComponent()46 Me.lblOutput =NewSystem.Windows.Forms.Label()47 Me.SuspendLayout()48 '49 'lblOutput50 '51 Me.lblOutput.Location =NewSystem.Drawing.Point(32, 48)

52 Me.lblOutput.Name = "lblOutput"53 Me.lblOutput.Size =NewSystem.Drawing.Size(168, 40)54 Me.lblOutput.TabIndex = 055 Me.lblOutput.Text = "Click Me!"56 '57 'FrmSimple58 '59 Me.AutoScaleBaseSize =NewSystem.Drawing.Size(5, 13)

60 Me.ClientSize =NewSystem.Drawing.Size(272, 237)61 Me.Controls.AddRange( _62 NewSystem.Windows.Forms.Control() {Me.lblOutput})6364 Me.Name = "FrmSimple"65 Me.Text = "SimpleEventExample"66 Me.ResumeLayout(False)67 EndSub68

69 #End Region70

End of Visual Studio

generated code

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Outline17


71 ' handler for click event on lblOutput72 PrivateSublblOutput_Click(ByValsenderAsObject, _73 ByValeAsSystem.EventArgs) HandleslblOutput.Click7475 MessageBox.Show("Label was pressed")76 EndSub ' lblOutput_Click77

78 EndClass' FrmSimpleExample

Name of the handler

lowed by an underscore

and the event name

Reference to the object

that generated the event

Event arguments object

Event-handling code

displays a message box


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Outline30

DisplayTable.vb

295296 Me.ResumeLayout(False)297298 EndSub' InitializeComponent299300 #EndRegion301

302 EndClass' FrmTableDisplay

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19.6.2 Querying the Books Database

Use SELECTstatements on database and displayresults

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Outline32

DisplayQueryResults.vb

1 ' Fig. 19.28: DisplayQueryResults.vb2 ' Displays the contents of the authors database.34 PublicClassFrmDisplayQueryResult5 InheritsSystem.Windows.Forms.Form67 FriendWithEventstxtQueryAsSystem.Windows.Forms.TextBox

8 FriendWithEventscmdSubmitAsSystem.Windows.Forms.Button9 FriendWithEventsdgdResultsAsSystem.Windows.Forms.DataGrid10 FriendWithEventsBooksConnectionAs_11 System.Data.OleDb.OleDbConnection1213 FriendWithEventsBooksDataAdapterAs_14 System.Data.OleDb.OleDbDataAdapter1516 FriendWithEventsBooksDataSetAsSystem.Data.DataSet

1718 ' Visual Studio .NET generated code1920 ' perform SQL query on data21 PrivateSubcmdSubmit_Click(ByValsenderAsSystem.Object, _22 ByValeAsSystem.EventArgs) HandlescmdSubmit.Click2324 Try2526 ' set the text of the SQL query to what the user typed27 ' in28 BooksDataAdapter.SelectCommand.CommandText = _29 txtQuery.Text3031 ' clear the DataSet from the previous operation32 BooksDataSet.Clear()33

FormFrmDisplayQueryResultcontainsTextBoxtxtQuery, in which users input SELECT

statements

After entering a query, the user clicks ButtoncmdSubmit,labeled SubmitQuery, to view the results of the query

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Outline33

DisplayQueryResults.vb

Program Output

34 ' Fill the data set with the information that results35 ' from the SQL query36 BooksDataAdapter.Fill(BooksDataSet, "Authors")3738 ' Bind the DataGrid to the contents of the DatSet39 dgdResults.SetDataBinding(BooksDataSet, "Authors")40

41 ' display database connection verbose message42 CatchexceptionAs System.Data.OleDb.OleDbException43 MessageBox.Show("Invalid Query")44 EndTry4546 EndSub' cmdSubmit_Click4748 EndClass' FrmDisplayQueryResults

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19.8 Reading and Writing XML Files

ADO.NET can convert data from data source intoXML files

Uses methods WriteXml, ReadXml andGetXml

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Outline35

XMLWriter.vb

1 ' Fig. 19.30 XMLWriter.vb2 ' Demonstrates generating XML from an ADO.NET DataSet34 PublicClassFrmXMLWriter5 InheritsSystem.Windows.Forms.Form67 ' constructor

8 PublicSubNew()9 MyBase.New()1011 ' This call is required by the Windows Form Designer.12 InitializeComponent()1314 ' Add any initialization after the15 ' InitializeComponent() call16

17 ' open database connection18 BaseballConnection.Open()1920 ' fill DataSet with data from OleDbDataAdapter21 BaseballDataAdapter.Fill(BaseballDataSet, "Players")2223 ' bind DataGrid to DataSet24 dgdPlayers.SetDataBinding(BaseballDataSet, "Players")25 End Sub2627 FriendWithEventscmdWriteAsSystem.Windows.Forms.Button28 FriendWithEventsdgdPlayersAsSystem.Windows.Forms.DataGrid29 FriendWithEventstxtOutputAsSystem.Windows.Forms.TextBox30 FriendWithEventsBaseballConnectionAs_31 System.Data.OleDb.OleDbConnection3233 FriendWithEventsBaseballDataAdapterAs_

34 System.Data.OleDb.OleDbDataAdapter35

Establishes a connection to the BaseballdatabaseMethod Fill of class OleDbDataAdapteris called topopulate BaseballDataSetwith data from thePlayerstable in the Baseballdatabase

Binds the dgdPlayersto BaseballDataSetto

display the information to the user

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Outline36

XMLWriter.vb

36 FriendWithEventsBaseballDataSetAsSystem.Data.DataSet3738 ' Visual Studio .NET generated code3940 ' write XML representation of DataSet when button clicked41 PrivateSubcmdWrite_Click(ByValsenderAsSystem.Object, _42 ByValeAsSystem.EventArgs) HandlescmdWrite.Click

4344 ' write XML representation of DataSet to file45 BaseballDataSet.WriteXml("Players.xml")4647 ' display XML in TextBox48 txtOutput.Text &= "Writing the following XML:"& _49 vbCrLf& BaseballDataSet.GetXml() & vbCrLf50 EndSub' cmWrite_Click51

52 EndClass' FrmXMLWriter

DataSetmethodWriteXmlis invoked to generate anXML representation of the data contained in the DataSet

and then writes the XML to the specified file

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19.8 Reading and Writing XML Documents

1

2

3

4 John

5 Doe

6 0.375

7 1

8

9

10

11 Jack

12 Smith

13 0.223

14 2

15

16

17

18 George

19 O'Malley

20 0.44421 3

22

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Fig. 19.31 XML document generated from DataSetin DatabaseXMLWriter.

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.NET DATA PROVIDERS

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