Using Data Sources with the DataGridView Control - A Product Maintenance application that uses a DataGridView control
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At this point, the DataGridView control and binding navigator toolbar provide all the functionality needed for an application that can be used to maintain the data in the Products table. Figure 14-9 shows how this application appears to the user at runtime. It also presents the code that Visual Studio generates when you create this application, which includes everything that’s necessary to make it work. As a result, you can create an application like this one without having to write a single line of code. If you’ve ever had to manually write an application that provides similar functionality, you can appreciate how much work this saves you.
When this application starts, the first event handler in this figure is executed. This event handler uses the Fill method of the TableAdapter object to load data into the DataSet object. In this example, the data in the Products table of the MMABooks database is loaded into the Products table of the dataset. Then, because the DataGridView control is bound to this table, the data is displayed in this control and the user can use it to modify the data in the table by adding, updating, or deleting rows.
When the user changes the data in the DataGridView control, those changes are saved to the dataset. However, the changes aren’t saved to the database until the user clicks the Save button in the toolbar. Then, the second event handler in this figure is executed. This event handler starts by calling the Validate method of the form, which causes the Validating and Validated events of the control that’s losing focus to be fired. Although you probably won’t use the Validated event, you may use the Validating event to validate a row that’s being added or modified. You’ll see an example of that later in this chapter.
Next, the EndEdit method of the BindingSource object applies any pending changes to the dataset. That’s necessary because when you add or update a row, the new or modified row isn’t saved until you move to another row.
Finally, the Update method of the TableAdapter object saves the Products table in the DataSet object to the MMABooks database. When this method is called, it checks each row in the table to determine if it’s a new row, a modified row, or a row that should be deleted. Then, it causes the appropriate SQL Insert, Update, and Delete statements to be executed for these rows. As a result, the Update method works efficiently since it only updates the rows that need to be updated.
Now that you understand this code, you should notice that it doesn’t provide for any exceptions that may occur during this processing. Because of that, you need to add the appropriate exception handling code for any production applications that you develop so that they won’t crash. You’ll learn how to do that next.
The user interface for the Product Maintenance application
The code that’s generated by Visual Studio
Private Sub Form1_Load(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles MyBase.Load
'TODO: This line of code loads data into the 'MMABooksDataSet.Products'
'table. You can move, or remove it, as needed.
Me.ProductsTableAdapter.Fill(Me.MMABooksDataSet.Products)
End Sub
Private Sub ProductsBindingNavigatorSaveItem_Click( _
ByVal sender As System.Object, ByVal e As System.EventArgs) _
Handles ProductsBindingNavigatorSaveItem.Click
Me.Validate()
Me.ProductsBindingSource.EndEdit()
Me.ProductsTableAdapter.Update(Me.MMABooksDataSet.Products)
End Sub
The syntax of the Fill method
TableAdapter.Fill(DataSet.TableName)
The syntax of the Update method
TableAdapter.Update(DataSet.TableName)
Description
- Visual Studio automatically generates the code shown above and places it in the source code file when you drag a data source onto a form. If necessary, you can edit this code.
- The generated code uses the Fill and Update methods of the TableAdapter object that’s generated for the table to read data from and write data to the database. It also uses the EndEdit method of the BindingSource object to save any changes that have been made to the current row to the dataset.
- The Validate method causes the Validating and Validated events of the control that is losing the focus to be fired. You can use the Validating event to perform any required data validation for the form.
- Users of a DataGridView control can sort the rows by clicking on a column heading and can size columns by dragging the column separators to the left or right. They can also reorder the columns by dragging them if that option is enabled (see figure 14-7).
Figure 14-9. A Product Maintenance application that uses a DataGridView control
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 This article is excerpted from chapter 14 of the book Murach's Visual Basic 2005, written by Anne Boehm (Murach, 2006; ISBN: 1890774383). Check it out today at your favorite bookstore. Buy this book now.
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