Tài liệu Edit and Update Using Data Bound Controls pdf

1.4 Edit and Update Data Using Bound Controls Although viewing data is fine in some situations, the real power comes in being able to edit the data in the text box and update the data in

1.4 Edit and Update Data Using Bound Controls

Although viewing data is fine in some situations, the real power comes in being able to edit the data in the text box and update the data in the server In this How-To, you learn just that, using some new methods and properties from the various data controls,

including autogenerated commands that create update, insert, and delete SQL statements for you This How-To also introduces you to the BinderContext class, which is used to perform updates with bound controls

The form as created in How-To 1.4 is great if you just want to view data for various records But what if you want to let users edit and update the data?

Technique

Continuing with the form you used in the previous How-Tos, you are going to add a few command buttons with code that will perform the following:

• Edit Toggle the look of the text boxes to let the user know that he can edit the

data in the controls by giving the controls a sunken look

• Save Save the changes made to the data back to the server Then toggle the look

of the text boxes back to flat so that the user knows he can't edit them

• Cancel Toggle the text boxes back to flat so that the user knows he can't edit them anymore, but don't save the data

It is important to let users know when they can edit and when they can't By toggling the style of the text boxes between flat and sunken and the color between gray and white, users have a definite clue that they can edit the data at certain times (see Figure 1.8)

Another useful item to note about this How-To is the introduction of the BindingContext class This class helps you work with data bound controls Each control on a Windows form has a BindingContext object as well as BindingContext objects for any controls that are contained within that control Each form also has a BindingContext object

BindingContext objects manage BindingManagerBase class object(s) for each control Through the BindingContext object, you can manage editing and updating data back to the server BindingManagerBase objects help with synchronization of datasets with controls You are going to use the BindingContext class throughout the rest of this

chapter, but only a couple of methods

Steps

Open the solution for the chapter called "VB NET How-To Chapter 1," and run the application From the main form, click the command button with the caption "How-To 1.4." Click the Load List button Along with the list being filled with customers whose

names start with A, you will see the detail How-To fill in on the right side of the form

with the first customer in the list Click Edit You will now be able to change the data in

the text boxes After you have changed a couple of fields, click Save If you select

another customer from the list box, select the one you changed You will see that your

changes have in fact been saved If you click Cancel instead of Save, your changes will

not be saved Note that if you change the name of the customer, you must load the list

again to see the changes in the list box

1 Add the three command buttons to your form as described in Table 1.6 and as

displayed in Figure 1.8

Table 1.6 Command Buttons to Edit, Save, and Cancel Changes to Data

2 Add the code shown in Listing 1.6 to the btnEdit Click event

Listing 1.6 frmHowTo1_4.vb: Calling the ActiveEditing Subroutine from the

btnEdit Command Button

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

ByVal e As System.EventArgs) Handles btnEdit.Click

'- Enable the editing of the form

ActivateEditing(True)

End Sub

This calls the routine called ActivateEditing, listed here This code iterates through

all the controls on the form and uses the TypeOf condition to check whether the

current control is a text box It also ensures that the control is not the txtCustLimit

text box If the control is a text box and the parameter called bEnable has been

passed in as True, then the sunken look is given to the text box using the

BorderStyle and the BackColor property is set to white Otherwise, the

BorderStyle is set to FixedSingle, which is flat, and the BackColor is set to the backcolor of the form The Enabled property of the text box is set to whatever bEnabled is: True or False

Listing 1.7 frmHowTo1_4.vb: Toggling the Enabled Property and Look of Text Boxes

Private Sub ActivateEditing(ByVal bEnable As Boolean)

Dim oCurr As Object

'- Loop through each of the controls on the form

For Each oCurr In Me.Controls()

'- Check to see if the control is a text box

If TypeOf oCurr Is TextBox And oCurr.Name <> "txtCustLimit" Then

'- If so, toggle the properties

If bEnable Then

oCurr.BorderStyle() = _

System.Windows.Forms.BorderStyle.Fixed3D

oCurr.BackColor() = System.Drawing.Color.White

Else

oCurr.BorderStyle() = _

System.Windows.Forms.BorderStyle.FixedSingle

oCurr.BackColor() = Me.BackColor

End If

oCurr.Enabled = bEnable

End If

Next

End Sub

3 Add the code to the Click event of the btnSave command button This code calls a new routine called SaveRecord, which performs the actual save The

ActivateEditing is then called, passing False to disable the controls because you are finished editing

Listing 1.8 frmHowTo1_4.vb: Calling the SaveRecord Routine and Disabling the Text Boxes by Calling ActivateEditing

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

ByVal e As System.EventArgs) Handles btnSave.Click

'- Save the information

SaveRecord()

'- Disable the text boxes

ActivateEditing(False)

End Sub

Following is the code for the subroutine called SaveRecord This routine calls the EndCurrentEdit method of the BindingContext class, passing in the dataset called dsCustomerIndividual, and specifying the Customers table Then the Update method is called off the data adapter called odaCustomerIndividual, passing the same parameters This updates the changes back to the dataset Finally, the dataset changes are sent backto the server

Listing 1.9 frmHowTo1_4.vb: Saving the Data Back to the Server

Private Sub SaveRecord()

'- Use the BindingContext class to end current editing

' so that we can update the server

Me.BindingContext(Me.dsCustomerIndividual,

"Customers").EndCurrentEdit()

'- Perform the requested task at the dataset

' level using the data adapter

Me.odaCustomerIndividual.Update(Me.dsCustomerIndividual, "Customers")

'- By accepting the changes, the data gets sent back to the server

Me.dsCustomerIndividual.AcceptChanges()

End Sub

Note

If you haven't read about ADO.NET yet, then you might be confused about doing an update to the dataset, accepting changes, and sending the changes back to the server ADO.NET works using disconnected data When you create a dataset by using a data adapter, the data is actually created using XML To see proof of this, take a look at dsCustomerIndividual.xsd, found in the Solutions Explorer

<xsd:schemaid="dsCustomerIndividual"targetNamespace="http://w ww.tempuri.org /

dsCustomerIndividual.xsd"xmlns="http://www.tempuri.org/ dsCustomerIndividual.xsd"xmlns:

xsd="http://www.w3.org/2001/XMLSchema"

xmlns:msdata="urn:schemas-microsoft-com:

xml-msdata"attributeFormDefault="qualified"

elementFormDefault="qualified">

<xsd:element name="dsCustomerIndividual"

msdata:IsDataSet="true">

<xsd:complexType>

<xsd:choice maxOccurs="unbounded">

<xsd:element name="Customers">

<xsd:complexType>

<xsd:sequence>

<xsd:element name="CustomerID" type="xsd:string" /> <xsd:element name="CompanyName" type="xsd:string" /> <xsd:element name="ContactName" type="xsd:string"

minOccurs="0" />

<xsd:element name="ContactTitle" type="xsd:string"

minOccurs="0" />

<xsd:element name="Address" type="xsd:string"

minOccurs="0" />

<xsd:element name="City" type="xsd:string" minOccurs="0" />

<xsd:element name="Region" type="xsd:string"

minOccurs="0" />

<xsd:element name="PostalCode" type="xsd:string"

minOccurs="0" />

<xsd:element name="Country" type="xsd:string"

minOccurs="0" />

<xsd:element name="Phone" type="xsd:string"

minOccurs="0" />

<xsd:element name="Fax" type="xsd:string" minOccurs="0" />

</xsd:sequence>

</xsd:complexType>

</xsd:element>

</xsd:choice>

</xsd:complexType>

<xsd:unique name="Constraint1" msdata:PrimaryKey="true"> <xsd:selector xpath=".//Customers" />

<xsd:field xpath="CustomerID" />

</xsd:unique>

</xsd:element>

</xsd:schema>

This is all performed under the covers, so the good news is that you don't have to know XML to work with datasets and ADO More information on this can be found in Chapter 3

4 The last task is to give you the capibility to cancel the edits You do this by

placing the following code in the Click event on btnCancel Calling the

CancelCurrentEdit method of the BindingContext object for the form, the current edits are cancelled Next, the text boxes are disabled using the routine

ActivateEditing

Listing 1.10 frmHowTo1_4.vb: Canceling Changes to Data and Disabling the Text Boxes Again

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

ByVal e As System.EventArgs) Handles btnCancel.Click

'- Use the BindingContext class to cancel the current editing

Me.BindingContext(Me.dsCustomerIndividual, _

"Customers").CancelCurrentEdit()

ActivateEditing(False)

End Sub

How It Works

When the user clicks the btnEdit button, the ActiveEditing routine alerts the user that he can edit the data in the text boxes The text boxes are enabled

If the user then clicks the btnSave button, the data is updated to the dataset and then back

to the server If the user clicks the btnCancel button, the edits are canceled In both cases, the ActivateEditing routine is called to disable the text boxes and let the user know that the text boxes cannot be edited

Comments

This How-To showed the bare bones for editing and updating data It presented a basic technique to get started As you continue, you will learn methods to add and delete records, as well as handle errors

Using ADO.NET, which you use for bound controls, takes some getting used to if you have worked with other data accessing methods such as ADO and DAO The

BindingContext and BindingManagerBase objects make working with bound objects in code much more manageable