Previous
Page Next
Page
Event for the Save Button
The event for the Save button reads
the values from the text boxes and stores them in the current record in
the data table. The event for the Save Button is:
Private Sub btnSave_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnSave.Click
lblLabel.Text = "Saving Changes..."
Me.Cursor = Cursors.WaitCursor
Dim row As DataRow = dataTable.Rows(currRec)
row.BeginEdit()
row("title") = txtArticleTitle.Text
row("topic") = txtArticleTopic.Text
row("authorId") = txtAuthorId.Text
row("lines") = txtNumOfLines.Text
row("dateOfPublishing") = txtDateOfPublishing.Text
row.EndEdit()
dataAdapter.Update(ds, "article")
ds.AcceptChanges()
ToggleControls(True)
insertSelected = False
Me.Cursor = Cursors.Default
lblLabel.Text = "Changes Saved"
End SubHere we first change the progress label (lblLabel) text
to show the current status and then change the cursor to a wait cursor.
lblLabel.Text = "Saving Changes...
"Me.Cursor = Cursors.WaitCursor Then we take a reference of the
current record's row and call its BeginEdit() method. An update on a row
is usually bound by a DataRow's BeginEdit() and EndEdit() methods. The
BeginEdit() method temporarily suspends the events for the validation of
row's data. Within the BeginEdit() and EndEdit() boundary, we stored the
changed values in the text boxes to the row.
Dim row As DataRow = dataTable.Rows(currRec)
row.BeginEdit()
row("title") = txtArticleTitle.Text
row("topic") = txtArticleTopic.Text
row("authorId") = txtAuthorId.Text
row("lines") = txtNumOfLines.Text
row("dateOfPublishing") = txtDateOfPublishing.Text
row.EndEdit()
After saving the changes in the row, we update the DataSet and table by
calling the Update method of the Data Adapter. This saves the changes in
the local repository of data: DataSet. To save the changed rows and tables
to the physical database, we called the AcceptChanges() method of the
DataSet class.
dataAdapter.Update(ds, "article")
ds.AcceptChanges() Finally we brought the controls to the normal mode
by calling the ToggleControls() method and passing it the true value. We
set the insertSelected variable to false, changed the cursor back to
normal and updated the progress label. (The use of the insertSelected
variable is discussed later in the Cancel button event )
ToggleControls(True)
insertSelected = False
Me.Cursor = Cursors.Defaultlbl
Label.Text = "Changes Saved" It is important to note here that the
Save button is used to save the changes in the current record. It may be
selected after either the Edit Record or Insert Record buttons. In the
case of the Edit Record button, the pointer is already on the current
record, while in the case of the Insert Record button, as we will see
shortly in the Inserting Record section, the program inserts a new empty
row. Then moves the current record pointer to it and presents it to the
user to insert the values. Hence, the job of the Save button in both cases
is to save the changes in the current record from the text boxes to the
data table, updating the Data Set and finally updating the database.
Event for the Cancel Button
The Cancel button's event handler
is:
Private Sub btnCancel_Click(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles btnCancel.Click
If insertSelected Then
btnDeleteRecord_Click(Nothing, Nothing)
insertSelected = False
End If
FillControls()
ToggleControls(True)
End SubThe form and controls can be brought into edit mode by
pressing either the Edit Record or the Insert Record button. When the
Insert Record button is selected, the program inserts an empty record
(row) to the table (the details of which we will see shortly) and brings
the form and controls to edit mode by using the ToggleControls(false)
statement. The Cancel button is used to cancel both editing of the current
record and the newly inserted record. When canceling the insertion of a
new record, the program needs to delete the current (newly inserted) row
from the table. We have used a Boolean variable 'insertSelected' in our
application, which is set to true when the user selects the Insert Record
button. This Boolean value informs the Cancel button whether the edit mode
was set by the Edit Record button or by the Insert Record button. Hence
the Cancel button's event first checks whether insertSelected is true and
if it is, it calls the Delete button's event to delete the current record
and sets insertSelected back to false.
If insertSelected Then
btnDeleteRecord_Click(Nothing, Nothing)
insertSelected = False
End IfNow fill the controls (text boxes) from the data in the
current record and bring the controls back to the normal mode.
FillControls()
ToggleControls(True) Inserting Records
To insert a record
into the table, the user can select the Insert Record button. A record is
inserted into the table by adding a new row to the DataTable's Rows
collection. Here is the event for the Insert Record button.
Private Sub btnInsertRecord_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnInsertRecord.Click
insertSelected = True
Dim row As DataRow = dataTable.NewRow()
dataTable.Rows.Add(row)
totalRec = dataTable.Rows.Count
currRec = totalRec - 1
row("artId") = totalRec
txtArticleId.Text = totalRec.ToString()
txtArticleTitle.Text = ""
txtArticleTopic.Text = ""
txtAuthorId.Text = ""
txtNumOfLines.Text = ""
txtDateOfPublishing.Text = DateTime.Now.Date.ToString()
ToggleControls(False)
End SubFirst of all we set the insertSelected variable to true,
so that later the Cancel button may get informed that the edit mode was
set by the Insert Record button. We then created a new DataRow using the
DataTable's NewRow() method. Then we added it to the Rows collection of
the data table and updated the currRec and totalRec variables.
Dim row As DataRow = dataTable.NewRow()
dataTable.Rows.Add(row)
totalRec = dataTable.Rows.Countcurr
Rec = totalRec - 1 The new row is ready to have the new values
inserted into it. Here we have set the artId field to the total number of
records as we don't want to allow the user to set the primary key field of
the table. Of course this is just a design issue. You may want to allow
your user to insert the primary key field value too.
row("artId") = totalRec
txtArticleId.Text = totalRec.ToString()We then cleared all the text
boxes, but filled the Date of the Publishing text box with the current
date in order to help the user, and finally set the edit mode by calling
the ToggleControls() method.
txtArticleTitle.Text = ""
txtArticleTopic.Text = ""
txtAuthorId.Text = ""
txtNumOfLines.Text = ""
txtDateOfPublishing.Text = DateTime.Now.Date.ToString()
ToggleControls(False) Deleting a Record
Deleting a record
is again very simple. All you need to do is get a reference to the target
row and call its Delete() method. Then you need to call the Update()
method of the data adapter and the AcceptChanges() method of the DataSet
to permanently save your changes in the data table to the physical
database. The event handler for the Delete Record button is:
Private Sub btnDeleteRecord_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnDeleteRecord.Click
Dim res As DialogResult = MessageBox.Show( _
"Are you sure you want to delete the current record?", _
"Confirm Record Deletion", MessageBoxButtons.YesNo)
If res = DialogResult.Yes Then
Dim row As DataRow = dataTable.Rows(currRec)
row.Delete()
dataAdapter.Update(ds, "article")
ds.AcceptChanges()
lblLabel.Text = "Record Deleted"
totalRec -= 1
currRec = totalRec - 1
FillControls()
End If
End SubSince selecting the delete record button will permanently
delete the current record, we need to seek confirmation from the user to
check they are sure they wish to go ahead with the deletion. For this
purpose we present the user with a message box with Yes and No buttons.
Dim res As DialogResult = MessageBox.Show( _
"Are you sure you want to delete the current record?", _
"Confirm Record Deletion", MessageBoxButtons.YesNo)If the
user selects the Yes button in the message box, the code to delete the
current record is executed.
If res = DialogResult.Yes Then
Dim row As DataRow = dataTable.Rows(currRec)
row.Delete()
dataAdapter.Update(ds, "article")
ds.AcceptChanges()
lblLabel.Text = "Record Deleted"
totalRec -= 1
currRec = totalRec - 1
FillControls()
End IfFirst we got a reference to the row representing the current
record in the data table and called its Delete() method. We then saved the
changes to the database and updated the totalRec and currRec variables.
Finally, we filled the controls (text boxes) with the last record in the
table. This concludes our demonstration application to perform common data
access tasks using ADO.NET. The complete source code of this program can
be downloaded by clicking here
Previous
Page Next
Page
|
