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

  • Artykuł

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.

Prerequisites

In order to complete this walkthrough, you will need:

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

Creating the Form

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
        Me.Controls.Add(dataGridView1)

    End Sub


...


    <STAThread()> _
    Shared Sub Main()
        Application.EnableVisualStyles()
        Application.Run(New Form1())
    End Sub

End Class

    using System;
using System.Data;
using System.Data.SqlClient;
using System.Windows.Forms;

public class Form1 : System.Windows.Forms.Form
{
    private DataGridView dataGridView1 = new DataGridView();
    private BindingSource bindingSource1 = new BindingSource();

    public Form1()
    {
        // Initialize the form.
        this.dataGridView1.Dock = DockStyle.Fill;
        this.Controls.Add(dataGridView1);
        this.Load += new EventHandler(Form1_Load);
    }


...


    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        Application.Run(new Form1());
    }

}

  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 noteSecurity 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 (ADO.NET).

    		 
    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.Fill(data)
    adapter.FillSchema(data, SchemaType.Source)

    Return data

End Function

    private static DataTable GetData(string selectCommand)
{
    string connectionString =
        "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.
    SqlDataAdapter adapter =
        new SqlDataAdapter(selectCommand, connectionString);
    DataTable data = new DataTable();
    data.Locale = System.Globalization.CultureInfo.InvariantCulture;
    adapter.Fill(data);
    adapter.FillSchema(data, SchemaType.Source);

    return data;
}

  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( _
        DataGridViewAutoSizeColumnsMode.AllCellsExceptHeader)

End Sub

    private void Form1_Load(System.Object sender, System.EventArgs e)
{
    // Attach the DataError event to the corresponding event handler. 
    this.dataGridView1.DataError +=
        new DataGridViewDataErrorEventHandler(dataGridView1_DataError);

    // Initialize the BindingSource and bind the DataGridView to it.
    bindingSource1.DataSource = GetData("select * from Customers");
    this.dataGridView1.DataSource = bindingSource1;
    this.dataGridView1.AutoResizeColumns(
        DataGridViewAutoSizeColumnsMode.AllCellsExceptHeader);
}

  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

    private void dataGridView1_DataError(object sender,
    DataGridViewDataErrorEventArgs e)
{
    // If the data source raises an exception when a cell value is  
    // commited, display an error message. 
    if (e.Exception != null &&
        e.Context == DataGridViewDataErrorContexts.Commit)
    {
        MessageBox.Show("CustomerID value must be unique.");
    }
}

Testing the Application

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.

Next Steps

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:

See Also

Tasks

How to: Handle Errors That Occur During Data Entry in the Windows Forms DataGridView Control

Walkthrough: Validating Data in the Windows Forms DataGridView Control

Concepts

Protecting Connection Information (ADO.NET)

Reference

DataGridView

BindingSource

Other Resources

Data Entry in the Windows Forms DataGridView Control