Tài liệu Make a Generic Search Form in a Visual Basic .NET docx

Properties can be specified on a form by adding the following syntax to your form: Public Property PropertyName As DataType Get PropertyName = ModuleLevelMemoryVariable End Get SetBy

8.4 Make a Generic Search Form in a Visual Basic NET Desktop Application

Another useful utility that takes advantage of being data driven is a standard search form that you can use for any number of tables, such as customers, employees, or products This How-To shows you how to create such a Windows Form so that all you need to use

it with different tables is to set four custom properties of the form in code

You like to be able to provide a usable search form for my users, without having the hassle of creating a custom form for every topic that the users are maintaining In this How-To, you will see how to create a form that provides a quick lookup for records and can be used with various topics, such as Customers and Employees, by setting up only a few custom properties on the search form

Technique

The forms package of Visual Basic has a class module behind it where you can add your own properties and methods The NET version of it is no exception

In this How-To, you will see a simple use for custom properties that are being added to a form Properties can be specified on a form by adding the following syntax to your form:

Public Property PropertyName() As DataType

Get

PropertyName = ModuleLevelMemoryVariable

End Get

Set(ByVal Value As DataType)

ModuleLevelMemoryVariable = Value

End Set

End Property

With the ModuleLevelMemoryVariable being declared in the module declaration area of the form's class module, you can see the properties created for the search form, called frmHowTo8_b.vb, in Listing 8.16

Listing 8.16 frmHowTo8_4b.vb: Creating Custom Properties for the Search Form

Private mstrDisplayName As String

Private mstrRecordSource As String

Private mstrSearchField As String

Private moResultValue As Object

Private mstrKeyField As String

Public Property DisplayName() As String

Get

DisplayName = mstrDisplayName

End Get

Set(ByVal Value As String)

mstrDisplayName = Value

End Set

End Property

Public Property SearchRecordSource() As String Get

SearchRecordSource = mstrRecordSource End Get

Set(ByVal Value As String)

mstrRecordSource = Value

End Set

End Property

Public Property SearchField() As String

Get

SearchField = mstrSearchField

End Get

Set(ByVal Value As String)

mstrSearchField = Value

End Set

End Property

Public Property KeyField() As String

Get

KeyField = mstrKeyField

End Get

Set(ByVal Value As String)

mstrKeyField = Value

End Set

End Property

Public Property ResultValue() As Object

Get

ResultValue = moResultValue

End Get

Set(ByVal Value As Object)

moResultValue = Value

End Set

End Property

By assigning values to these properties after initiating an instance of the form, you can utilize the properties and the data stored in those properties from within the forms

properties and methods, as well as the procedures assigned to the events within the form

For more information on creating custom classes, properties, and methods for use with your database application, see Chapter 9, "Using Classes with Databases to Make Life Easier."

Steps

Open and run the VB.NET -Chapter 8 solution From the main Windows Form, click on the command button with the caption How-To 8.4a This form is a simple one that

contains text boxes for the Customer table in Northwind Click on the Search button to open the search form Click on the button labeled B You will see the data grid displayed

in the bottom of the form filled with the CompanyName column of the Customer table, beginning with the letter B (see Figure 8.7)

Figure 8.7 This form can be used for searching within any of the tables in your

databases

Place the cursor in one of the customers displayed in the grid, and then click Accept The search form will be hidden, and the fields in the first form will be filled in with the data from the chosen record

1 Create a Windows Form Then place the controls on the form shown in Figure 8.7, with the properties set forth in Table 8.5

Table 8.5 Label, TextBox, and Command Button Controls Property Settings

for the Calling Form Object Property Setting

Label Caption Contact

Label Caption Address

Label Caption City

Label Caption Region

Label Caption Country

Label Caption Phone

Label Caption Fax

Button Name btnSearch

2 On btnSearch, add the code in Listing 8.17 to the Click event This routine shows the power of creating custom properties After instantiating an instance of the Search form-in this case, frmHowTo8_4b.vb-the four custom properties shown in Listing 8.17 are set before the form is displayed This is powerful in letting you get the form set up exactly the way you want to before the user even sees it After setting up the custom properties, the ShowDialog method is called off of

frmSearch By calling this method, code execution is halted until the form is closed or hidden This same line of code compares the DialogResult property of the form to the value; if it matches, the code calls the LoadIndividual routine, passing the ResultValue custom property of frmSearch Both the DialogResult and ResultValue properties are set in frmSearch and will be shown later in these steps

Listing 8.17 frmHowTo8_4a.vb: Executing a SQL Server-Supplied Stored Procedure That Lists the Tables in the Database

Private Sub btnSearch_Click(ByVal sender As System.Object, _

ByVal e As System.EventArgs) Handles btnSearch.Click

' Instantiate the search forms

Dim frmSearch As frmHowTo8_4b

frmSearch = New frmHowTo8_4b()

' Set the custom data properties on the search form

' This is what makes it so data driven

frmSearch.DisplayName = "Customers"

frmSearch.SearchRecordSource = "Customers"

frmSearch.SearchField = "CompanyName"

frmSearch.KeyField = "CustomerID"

' Open the search form as dialog

' Based on the DialogResult property, use the

' custom property ResultValue property and load

' the requested record

If frmSearch.ShowDialog() = DialogResult.OK Then

LoadIndividual(frmSearch.ResultValue)

End If

End Sub

3 Create the LoadIndividual routine by entering the code shown in Listing 8.18 into the form Taking the strKeyValue passed from the results of the search, a data adapter is created and a DataSet is filled Next, the individual data row is created Last, each of the TextBox controls is loaded with the value from the column with the corresponding name Notice the use of the Try…Catch…End Try to ignore controls that don't have a like column in the data row

Listing 8.18 frmHowTo8_4a.vb: Loading an Individual Record into Text Boxes on the Form

Private Sub LoadIndividual(ByVal strKeyValue As String)

Dim strSQL As String

Dim strName As String

Dim oCtl As Object

Dim dsCustIndiv As New DataSet()

Dim odaCustIndiv As OleDb.OleDbDataAdapter

Dim drCustIndiv As DataRow

Try

' Load the individual record into the dataset

strSQL = "Select * from Customers Where CustomerID = '" &

strKeyValue & "'"

odaCustIndiv = New OleDb.OleDbDataAdapter(strSQL, _

BuildCnnStr("(local)", "Northwind"))

' Fill the dataset

odaCustIndiv.Fill(dsCustIndiv, "Customers")

' Grab the individual data row

drCustIndiv = dsCustIndiv.Tables("Customers").Rows(0)

Catch oexpData As OleDb.OleDbException

MessageBox.Show("Error loading individual data: " & _

oexpData.Message)

Exit Sub

End Try

' Run through the text boxes on the form

' If they match up with a field from the record, load them

For Each oCtl In Me.Controls

If TypeOf oCtl Is TextBox Then

strName = Mid(oCtl.Name, 4)

' By trapping the exception this way, errors are ignored

Try

oCtl.text = drCustIndiv(strName).ToString

Catch oexp As Exception

End Try

End If

Next

End Sub

4 Create the next Windows Form and call it whatever name you referred to in the search form in step 2 Then place the controls shown in Figure 8.7 of the search form, with the properties set as in Table 8.6

Table 8.6 Label, TextBox, DataGrid, and Command Button Controls

Property Settings for the Calling Form

Button Name btnA

Button Name btnB

Button Name btnC

Caption C

Button Name btnZ

Button Name btnAll

DataGrid Name dgSearch

Button Name btnAccept

Button Name btnCancel

5 Create the custom properties discussed in the "Technique" section of this How-To and found in Listing 8.19 Each of the properties is self-explanatory

Listing 8.19 frmHowTo8_4b.vb: Creating Custom Properties for the Search Form

Private mstrDisplayName As String

Private mstrRecordSource As String

Private mstrSearchField As String

Private moResultValue As Object

Private mstrKeyField As String

Public Property DisplayName() As String

Get

DisplayName = mstrDisplayName

End Get

Set(ByVal Value As String)

mstrDisplayName = Value

End Set

End Property

Public Property SearchRecordSource() As String

Get

SearchRecordSource = mstrRecordSource

End Get

Set(ByVal Value As String)

mstrRecordSource = Value

End Set

End Property

Public Property SearchField() As String

Get

SearchField = mstrSearchField

End Get

Set(ByVal Value As String)

mstrSearchField = Value

End Set

End Property

Public Property KeyField() As String

Get

KeyField = mstrKeyField

End Get

Set(ByVal Value As String)

mstrKeyField = Value

End Set

End Property

Public Property ResultValue() As Object

Get

ResultValue = moResultValue

End Get

Set(ByVal Value As Object)

moResultValue = Value

End Set

End Property

6 On the form, add the code in Listing 8.20 to the Load event This routine ensures that the calling form set the DisplayName custom property; thus, this routine can assume that the others were set as well If not, a message box is displayed If so, the Text property of the form, which is displayed in the Title bar, is set to

DisplayName

Listing 8.20 frmHowTo8_4b.vb: Executing a SQL Server-Supplied Stored Procedure That Lists the Tables in the Database

Private Sub frmHowTo8_4b_Load(ByVal sender As Object, _

ByVal e As System.EventArgs) Handles MyBase.Load

If Len(Me.DisplayName) = 0 Then

MessageBox.Show("Form specific properties not set.")

Me.Close()

Else

Me.Text = Me.Text & " " & Me.DisplayName

End If

End Sub

7 For each of the command buttons that has a single letter, add the first subroutine displayed in Listing 8.21 to each of the Click events For the btnAll Button

control, add the second subroutine to the Click event Each Button control will pass the letter it represents to the subroutine called SetData, discussed in the next step The btnAll code simply passes the empty string

Listing 8.21 frmHowTo8_4b.vb: Click Events for Each of the Letter Button Controls

Private Sub btnA_Click(ByVal sender As System.Object,

ByVal e As System.EventArgs) Handles btnA.Click

SetData("A")

End Sub

Private Sub btnAll_Click(ByVal sender As System.Object,

ByVal e As System.EventArgs) Handles btnAll.Click

SetData("")

End Sub

8 Add the subroutine in Listing 8.22 to the class module of the form This routine takes the letter value passed in strFilterLetter as a parameter A SQL Select string

is created that takes the literal values Select, From, and Where and uses the custom properties KeyField, SearchField, and SearchRecordSource The SearchField property is used with the Like clause, also using the strFilterLetter and the % (wildcard) Note that if "" is passed to strFilterLetter, all the records will be listed Finally, odtSearch is filled and set as the data source for dgSearch, which is the DataGrid control

Listing 8.22 frmHowTo8_4a.vb: Filling the Results Set Based on the Letter Button That Was Pressed

Sub SetData(ByVal strFilterLetter As String)

Dim odaSearch As OleDb.OleDbDataAdapter

Dim dtSearch As DataTable = New DataTable()

odaSearch = New _

OleDb.OleDbDataAdapter("Select " & Me.KeyField & ", " &

Me.SearchField & " From " & Me.SearchRecordSource & " Where " & Me.SearchField & " Like '" & strFilterLetter & "%'",

(BuildCnnStr("(local)", "Northwind")))

odaSearch.Fill(dtSearch)

dgSearch.DataSource = dtSearch

End Sub

Note

This routine more than any in this How-To shows the flexibility of this technique You can use any table values for these properties Just think of how many places you can use this form without changing a line of code in the form

9 On the buttons called btnAccept and btnCancel, add the code in Listing 8.23 to the appropriate Click event of each The btnAccept_Click routine creates a DataTable object from the data grid's DataSource property Then it derives the data row that

is currently selected from that data table The KeyField property is used to store the individual column value of drCurr into the ResultValue custom property The DialogResult property is set to OK, and the form is hidden with the Hide method

By hiding the form, you can still read the properties of the form without the user seeing it

In the btnCancel_Click routine, the DialogResult is set to No, and the form is closed This action tells the calling form that the search was canceled

Listing 8.23 frmHowTo8_4b.vb: Storing the Resulting Key Value to the

ResultValue Custom Property and Setting the DialogResult

Private Sub btnAccept_Click(ByVal sender As System.Object, _

ByVal e As System.EventArgs) Handles btnAccept.Click

Dim dtFromGrid As DataTable

Dim drCurr As DataRow

Try

' Using the DataRow and DataTable objects of the DataGrid control, ' get the selected result and assign it to the custom property

' ResultValue Then set the DialogResult

' property to DialogResult.OK,

' and hide the form so that the calling form can still access it

dtFromGrid = CType(dgSearch.DataSource, DataTable)

drCurr = dtFromGrid.Rows(Me.dgSearch.CurrentRowIndex())

Me.ResultValue = drCurr(Me.KeyField).ToString

Me.DialogResult = DialogResult.OK

Me.Hide()

Catch exp As Exception

Me.DialogResult = DialogResult.No

Me.Close()

End Try

End Sub

Private Sub btnCancel_Click(ByVal sender As System.Object, _

ByVal e As System.EventArgs) Handles btnCancel.Click

Me.DialogResult = DialogResult.Cancel

Me.Close()

End Sub

How It Works

When the user clicks on the search button, the calling form sets the custom properties of the search form, telling it what record source to use, as well as other information used for searching for the specific record and domain desired-in this case:

• Customers for the property DisplayName