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Walkthrough: Handling Errors that Occur During Data Entry in the Windows Forms DataGridView Control

Handling errors from the underlying data store is a required feature for a data-entry application. The Windows Forms DataGridView control makes this easy by exposing the DataError event, which is raised when the data store detects a constraint violation or a broken business rule.

In this walkthrough, you will retrieve rows from the Customers table in the Northwind sample database and display them in a DataGridView control. When a duplicate CustomerID value is detected in a new row or an edited existing row, the DataError event will occur, which will be handled by displaying a MessageBox that describes the exception.

To copy the code in this topic as a single listing, see How to: Handle Errors That Occur During Data Entry in the Windows Forms DataGridView Control.

In order to complete this walkthrough, you will need:

  • Access to a server that has the Northwind SQL Server sample database.

To handle data-entry errors in the DataGridView control

  1. Create a class that derives from Form and contains a DataGridView control and a BindingSource component.

    The following code example provides basic initialization and includes a Main method.

    Imports System
    Imports System.Data
    Imports System.Data.SqlClient
    Imports System.Windows.Forms
    Public Class Form1
        Inherits System.Windows.Forms.Form
        Private WithEvents dataGridView1 As New DataGridView()
        Private bindingSource1 As New BindingSource()
        Public Sub New()
            ' Initialize the form. 
            Me.dataGridView1.Dock = DockStyle.Fill
        End Sub
        <STAThread()> _
        Shared Sub Main()
            Application.Run(New Form1())
        End Sub 
    End Class
  2. Implement a method in your form's class definition for handling the details of connecting to the database.

    This code example uses a GetData method that returns a populated DataTable object. Be sure that you set the connectionString variable to a value that is appropriate for your database.

    Security note Security Note

    Storing sensitive information, such as a password, within the connection string can affect the security of your application. Using Windows Authentication (also known as integrated security) is a more secure way to control access to a database. For more information, see Protecting Connection Information.

    Private Shared Function GetData(ByVal selectCommand As String) As DataTable
        Dim connectionString As String = _
            "Integrated Security=SSPI;Persist Security Info=False;" + _
            "Initial Catalog=Northwind;Data Source=localhost;Packet Size=4096" 
        ' Connect to the database and fill a data table, including the  
        ' schema information that contains the CustomerID column  
        ' constraint. 
        Dim adapter As New SqlDataAdapter(selectCommand, connectionString)
        Dim data As New DataTable()
        data.Locale = System.Globalization.CultureInfo.InvariantCulture
        adapter.FillSchema(data, SchemaType.Source)
        Return data
    End Function
  3. Implement a handler for your form's Load event that initializes the DataGridView and BindingSource and sets up the data binding.

    Private Sub Form1_Load(ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles Me.Load
        ' Initialize the BindingSource and bind the DataGridView to it.
        bindingSource1.DataSource = GetData("select * from Customers")
        Me.dataGridView1.DataSource = bindingSource1
        Me.dataGridView1.AutoResizeColumns( _
    End Sub
  4. Handle the DataError event on the DataGridView.

    If the context for the error is a commit operation, display the error in a MessageBox.

    Private Sub dataGridView1_DataError(ByVal sender As Object, _
        ByVal e As DataGridViewDataErrorEventArgs) _
        Handles dataGridView1.DataError
        ' If the data source raises an exception when a cell value is  
        ' commited, display an error message. 
        If e.Exception IsNot Nothing AndAlso _
            e.Context = DataGridViewDataErrorContexts.Commit Then
            MessageBox.Show("CustomerID value must be unique.")
        End If 
    End Sub

You can now test the form to make sure it behaves as expected.

To test the form

  • Press F5 to run the application.

    You will see a DataGridView control filled with data from the Customers table. If you enter a duplicate value for CustomerID and commit the edit, the cell value will revert automatically and you will see a MessageBox that displays the data entry error.

This application gives you a basic understanding of the DataGridView control's capabilities. You can customize the appearance and behavior of the DataGridView control in several ways:

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