Walkthrough: Implementing Virtual Mode in the Windows Forms DataGridView Control

Artykuł
11/16/2012

When you want to display very large quantities of tabular data in a DataGridView control, you can set the VirtualMode property to true and explicitly manage the control's interaction with its data store. This lets you fine-tune the performance of the control in this situation.

The DataGridView control provides several events that you can handle to interact with a custom data store. This walkthrough guides you through the process of implementing these event handlers. The code example in this topic uses a very simple data source for illustration purposes. In a production setting, you will typically load only the rows you need to display into a cache, and handle DataGridView events to interact with and update the cache. For more information, see Implementing Virtual Mode with Just-In-Time Data Loading in the Windows Forms DataGridView Control

To copy the code in this topic as a single listing, see How to: Implement Virtual Mode in the Windows Forms DataGridView Control.

Creating the Form

To implement virtual mode

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

The following code contains some basic initialization. It declares some variables that will be used in later steps, provides a Main method, and provides a simple form layout in the class constructor.

Imports System
Imports System.Windows.Forms

Public Class Form1
    Inherits Form

    Private WithEvents dataGridView1 As New DataGridView()

    ' Declare an ArrayList to serve as the data store. 
    Private customers As New System.Collections.ArrayList()

    ' Declare a Customer object to store data for a row being edited.
    Private customerInEdit As Customer

    ' Declare a variable to store the index of a row being edited. 
    ' A value of -1 indicates that there is no row currently in edit. 
    Private rowInEdit As Integer = -1

    ' Declare a variable to indicate the commit scope. 
    ' Set this value to false to use cell-level commit scope. 
    Private rowScopeCommit As Boolean = True

    <STAThreadAttribute()> _
    Public Shared Sub Main()
        Application.Run(New Form1())
    End Sub

    Public Sub New()
        ' Initialize the form.
        Me.dataGridView1.Dock = DockStyle.Fill
        Me.Controls.Add(Me.dataGridView1)
        Me.Text = "DataGridView virtual-mode demo (row-level commit scope)"
    End Sub


...



End Class

using System;
using System.Windows.Forms;

public class Form1 : Form
{
    private DataGridView dataGridView1 = new DataGridView();

    // Declare an ArrayList to serve as the data store. 
    private System.Collections.ArrayList customers =
        new System.Collections.ArrayList();

    // Declare a Customer object to store data for a row being edited.
    private Customer customerInEdit;

    // Declare a variable to store the index of a row being edited. 
    // A value of -1 indicates that there is no row currently in edit. 
    private int rowInEdit = -1;

    // Declare a variable to indicate the commit scope. 
    // Set this value to false to use cell-level commit scope. 
    private bool rowScopeCommit = true;

    [STAThreadAttribute()]
    public static void Main()
    {
        Application.Run(new Form1());
    }

    public Form1()
    {
        // Initialize the form.
        this.dataGridView1.Dock = DockStyle.Fill;
        this.Controls.Add(this.dataGridView1);
        this.Load += new EventHandler(Form1_Load);
        this.Text = "DataGridView virtual-mode demo (row-level commit scope)";
    }


...


}

#using <System.Drawing.dll>
#using <System.dll>
#using <System.Windows.Forms.dll>

using namespace System;
using namespace System::Windows::Forms;

public ref class Form1: public Form
{
private:
   DataGridView^ dataGridView1;

   // Declare an ArrayList to serve as the data store. 
   System::Collections::ArrayList^ customers;

   // Declare a Customer object to store data for a row being edited.
   Customer^ customerInEdit;

   // Declare a variable to store the index of a row being edited. 
   // A value of -1 indicates that there is no row currently in edit. 
   int rowInEdit;

   // Declare a variable to indicate the commit scope. 
   // Set this value to false to use cell-level commit scope. 
   bool rowScopeCommit;

public:
   static void Main()
   {
      Application::Run( gcnew Form1 );
   }

   Form1()
   {
      dataGridView1 = gcnew DataGridView;
      customers = gcnew System::Collections::ArrayList;
      rowInEdit = -1;
      rowScopeCommit = true;

      // Initialize the form.
      this->dataGridView1->Dock = DockStyle::Fill;
      this->Controls->Add( this->dataGridView1 );
      this->Load += gcnew EventHandler( this, &Form1::Form1_Load );
   }

private:


...


};

int main()
{
   Form1::Main();
}

Implement a handler for your form's Load event that initializes the DataGridView control and populates the data store with sample values.

Private Sub Form1_Load(ByVal sender As Object, ByVal e As EventArgs) _
    Handles Me.Load

    ' Enable virtual mode. 
    Me.dataGridView1.VirtualMode = True 

    ' Add columns to the DataGridView. 
    Dim companyNameColumn As New DataGridViewTextBoxColumn()
    With companyNameColumn
        .HeaderText = "Company Name"
        .Name = "Company Name" 
    End With 
    Dim contactNameColumn As New DataGridViewTextBoxColumn()
    With contactNameColumn
        .HeaderText = "Contact Name"
        .Name = "Contact Name" 
    End With 
    Me.dataGridView1.Columns.Add(companyNameColumn)
    Me.dataGridView1.Columns.Add(contactNameColumn)
    Me.dataGridView1.AutoSizeColumnsMode = _
        DataGridViewAutoSizeColumnsMode.AllCells

    ' Add some sample entries to the data store.  
    Me.customers.Add(New Customer("Bon app'", "Laurence Lebihan"))
    Me.customers.Add(New Customer("Bottom-Dollar Markets", _
        "Elizabeth Lincoln"))
    Me.customers.Add(New Customer("B's Beverages", "Victoria Ashworth"))

    ' Set the row count, including the row for new records. 
    Me.dataGridView1.RowCount = 4

End Sub

private void Form1_Load(object sender, EventArgs e)
{
    // Enable virtual mode. 
    this.dataGridView1.VirtualMode = true;

    // Connect the virtual-mode events to event handlers.  
    this.dataGridView1.CellValueNeeded += new
        DataGridViewCellValueEventHandler(dataGridView1_CellValueNeeded);
    this.dataGridView1.CellValuePushed += new
        DataGridViewCellValueEventHandler(dataGridView1_CellValuePushed);
    this.dataGridView1.NewRowNeeded += new
        DataGridViewRowEventHandler(dataGridView1_NewRowNeeded);
    this.dataGridView1.RowValidated += new
        DataGridViewCellEventHandler(dataGridView1_RowValidated);
    this.dataGridView1.RowDirtyStateNeeded += new
        QuestionEventHandler(dataGridView1_RowDirtyStateNeeded);
    this.dataGridView1.CancelRowEdit += new
        QuestionEventHandler(dataGridView1_CancelRowEdit);
    this.dataGridView1.UserDeletingRow += new
        DataGridViewRowCancelEventHandler(dataGridView1_UserDeletingRow);

    // Add columns to the DataGridView.
    DataGridViewTextBoxColumn companyNameColumn = new
        DataGridViewTextBoxColumn();
    companyNameColumn.HeaderText = "Company Name";
    companyNameColumn.Name = "Company Name";
    DataGridViewTextBoxColumn contactNameColumn = new
        DataGridViewTextBoxColumn();
    contactNameColumn.HeaderText = "Contact Name";
    contactNameColumn.Name = "Contact Name";
    this.dataGridView1.Columns.Add(companyNameColumn);
    this.dataGridView1.Columns.Add(contactNameColumn);
    this.dataGridView1.AutoSizeColumnsMode = 
        DataGridViewAutoSizeColumnsMode.AllCells;

    // Add some sample entries to the data store.  
    this.customers.Add(new Customer(
        "Bon app'", "Laurence Lebihan"));
    this.customers.Add(new Customer(
        "Bottom-Dollar Markets", "Elizabeth Lincoln"));
    this.customers.Add(new Customer(
        "B's Beverages", "Victoria Ashworth"));

    // Set the row count, including the row for new records. 
    this.dataGridView1.RowCount = 4;
}

void Form1_Load( Object^ /*sender*/, EventArgs^ /*e*/ )
{

   // Enable virtual mode. 
   this->dataGridView1->VirtualMode = true;

   // Connect the virtual-mode events to event handlers.  
   this->dataGridView1->CellValueNeeded += gcnew
       DataGridViewCellValueEventHandler( this, &Form1::dataGridView1_CellValueNeeded );
   this->dataGridView1->CellValuePushed += gcnew
       DataGridViewCellValueEventHandler( this, &Form1::dataGridView1_CellValuePushed );
   this->dataGridView1->NewRowNeeded += gcnew
       DataGridViewRowEventHandler( this, &Form1::dataGridView1_NewRowNeeded );
   this->dataGridView1->RowValidated += gcnew
       DataGridViewCellEventHandler( this, &Form1::dataGridView1_RowValidated );
   this->dataGridView1->RowDirtyStateNeeded += gcnew
       QuestionEventHandler( this, &Form1::dataGridView1_RowDirtyStateNeeded );
   this->dataGridView1->CancelRowEdit += gcnew
       QuestionEventHandler( this, &Form1::dataGridView1_CancelRowEdit );
   this->dataGridView1->UserDeletingRow += gcnew
       DataGridViewRowCancelEventHandler( this, &Form1::dataGridView1_UserDeletingRow );

   // Add columns to the DataGridView.
   DataGridViewTextBoxColumn^ companyNameColumn = gcnew DataGridViewTextBoxColumn;
   companyNameColumn->HeaderText = L"Company Name";
   companyNameColumn->Name = L"Company Name";
   companyNameColumn->AutoSizeCriteria = DataGridViewAutoSizeColumnCriteria::HeaderAndRows;
   DataGridViewTextBoxColumn^ contactNameColumn = gcnew DataGridViewTextBoxColumn;
   contactNameColumn->HeaderText = L"Contact Name";
   contactNameColumn->Name = L"Contact Name";
   contactNameColumn->AutoSizeCriteria = DataGridViewAutoSizeColumnCriteria::HeaderAndRows;
   this->dataGridView1->Columns->Add( companyNameColumn );
   this->dataGridView1->Columns->Add( contactNameColumn );

   // Add some sample entries to the data store.  
   this->customers->Add( gcnew Customer( L"Bon app'",L"Laurence Lebihan" ) );
   this->customers->Add( gcnew Customer( L"Bottom-Dollar Markets",L"Elizabeth Lincoln" ) );
   this->customers->Add( gcnew Customer( L"B's Beverages",L"Victoria Ashworth" ) );

   // Set the row count, including the row for new records. 
   this->dataGridView1->RowCount = 4;
}

Implement a handler for the CellValueNeeded event that retrieves the requested cell value from the data store or the Customer object currently in edit.

This event occurs whenever the DataGridView control needs to paint a cell.

Private Sub dataGridView1_CellValueNeeded(ByVal sender As Object, _
    ByVal e As System.Windows.Forms.DataGridViewCellValueEventArgs) _
    Handles dataGridView1.CellValueNeeded

    ' If this is the row for new records, no values are needed. 
    If e.RowIndex = Me.dataGridView1.RowCount - 1 Then 
        Return 
    End If 

    Dim customerTmp As Customer = Nothing 

    ' Store a reference to the Customer object for the row being painted. 
    If e.RowIndex = rowInEdit Then
        customerTmp = Me.customerInEdit
    Else
        customerTmp = CType(Me.customers(e.RowIndex), Customer)
    End If 

    ' Set the cell value to paint using the Customer object retrieved. 
    Select Case Me.dataGridView1.Columns(e.ColumnIndex).Name
        Case "Company Name"
            e.Value = customerTmp.CompanyName

        Case "Contact Name"
            e.Value = customerTmp.ContactName
    End Select 

End Sub

private void dataGridView1_CellValueNeeded(object sender,
    System.Windows.Forms.DataGridViewCellValueEventArgs e)
{
    // If this is the row for new records, no values are needed. 
    if (e.RowIndex == this.dataGridView1.RowCount - 1) return;

    Customer customerTmp = null;

    // Store a reference to the Customer object for the row being painted. 
    if (e.RowIndex == rowInEdit)
    {
        customerTmp = this.customerInEdit;
    }
    else 
    {
        customerTmp = (Customer)this.customers[e.RowIndex];
    }

    // Set the cell value to paint using the Customer object retrieved. 
    switch (this.dataGridView1.Columns[e.ColumnIndex].Name)
    {
        case "Company Name":
            e.Value = customerTmp.CompanyName;
            break;

        case "Contact Name":
            e.Value = customerTmp.ContactName;
            break;
    }
}

void dataGridView1_CellValueNeeded( Object^ /*sender*/,
    System::Windows::Forms::DataGridViewCellValueEventArgs^ e )
{
   Customer^ customerTmp = nullptr;

   // Store a reference to the Customer object for the row being painted. 
   if ( e->RowIndex == rowInEdit )
   {
      customerTmp = this->customerInEdit;
   }
   else
   {
      customerTmp = dynamic_cast<Customer^>(this->customers[ e->RowIndex ]);
   }

   // Set the cell value to paint using the Customer object retrieved. 
   int switchcase = 0;
   if ( (this->dataGridView1->Columns[ e->ColumnIndex ]->Name)->Equals( L"Company Name" ) )
         switchcase = 1;
   else 
   if ( (this->dataGridView1->Columns[ e->ColumnIndex ]->Name)->Equals( L"Contact Name" ) )
         switchcase = 2;


   switch ( switchcase )
   {
      case 1:
         e->Value = customerTmp->CompanyName;
         break;

      case 2:
         e->Value = customerTmp->ContactName;
         break;
   }
}

Implement a handler for the CellValuePushed event that stores an edited cell value in the Customer object representing the edited row. This event occurs whenever the user commits a cell value change.

Private Sub dataGridView1_CellValuePushed(ByVal sender As Object, _
    ByVal e As System.Windows.Forms.DataGridViewCellValueEventArgs) _
    Handles dataGridView1.CellValuePushed

    Dim customerTmp As Customer = Nothing 

    ' Store a reference to the Customer object for the row being edited. 
    If e.RowIndex < Me.customers.Count Then 

        ' If the user is editing a new row, create a new Customer object. 
        If Me.customerInEdit Is Nothing Then 
            Me.customerInEdit = New Customer( _
                CType(Me.customers(e.RowIndex), Customer).CompanyName, _
                CType(Me.customers(e.RowIndex), Customer).ContactName)
        End If
        customerTmp = Me.customerInEdit
        Me.rowInEdit = e.RowIndex

    Else
        customerTmp = Me.customerInEdit
    End If 

    ' Set the appropriate Customer property to the cell value entered. 
    Dim newValue As String = TryCast(e.Value, String)
    Select Case Me.dataGridView1.Columns(e.ColumnIndex).Name
        Case "Company Name"
            customerTmp.CompanyName = newValue
        Case "Contact Name"
            customerTmp.ContactName = newValue
    End Select 

End Sub

private void dataGridView1_CellValuePushed(object sender,
    System.Windows.Forms.DataGridViewCellValueEventArgs e)
{
    Customer customerTmp = null;

    // Store a reference to the Customer object for the row being edited. 
    if (e.RowIndex < this.customers.Count)
    {
        // If the user is editing a new row, create a new Customer object. 
        if (this.customerInEdit == null)
        {
            this.customerInEdit = new Customer(
                ((Customer)this.customers[e.RowIndex]).CompanyName,
                ((Customer)this.customers[e.RowIndex]).ContactName);
        }
        customerTmp = this.customerInEdit;
        this.rowInEdit = e.RowIndex;
    }
    else
    {
        customerTmp = this.customerInEdit;
    }

    // Set the appropriate Customer property to the cell value entered.
    String newValue = e.Value as String;
    switch (this.dataGridView1.Columns[e.ColumnIndex].Name)
    {
        case "Company Name":
            customerTmp.CompanyName = newValue;
            break;

        case "Contact Name":
            customerTmp.ContactName = newValue;
            break;
    }
}

void dataGridView1_CellValuePushed( Object^ /*sender*/,
    System::Windows::Forms::DataGridViewCellValueEventArgs^ e )
{
   Customer^ customerTmp = nullptr;

   // Store a reference to the Customer object for the row being edited. 
   if ( e->RowIndex < this->customers->Count )
   {

      // If the user is editing a new row, create a new Customer object. 
      if ( this->customerInEdit == nullptr )
      {
         this->customerInEdit = gcnew Customer(
             (dynamic_cast<Customer^>(this->customers[ e->RowIndex ]))->CompanyName,
             (dynamic_cast<Customer^>(this->customers[ e->RowIndex ])->ContactName) );
      }

      customerTmp = this->customerInEdit;
      this->rowInEdit = e->RowIndex;
   }
   else
   {
      customerTmp = this->customerInEdit;
   }


   // Set the appropriate Customer property to the cell value entered. 
   int switchcase = 0;
   if ( (this->dataGridView1->Columns[ e->ColumnIndex ]->Name)->Equals( L"Company Name" ) )
         switchcase = 1;
   else 
   if ( (this->dataGridView1->Columns[ e->ColumnIndex ]->Name)->Equals( L"Contact Name" ) )
         switchcase = 2;


   switch ( switchcase )
   {
      case 1:
         customerTmp->CompanyName = dynamic_cast<String^>(e->Value);
         break;

      case 2:
         customerTmp->ContactName = dynamic_cast<String^>(e->Value);
         break;
   }
}

Implement a handler for the NewRowNeeded event that creates a new Customer object representing a newly created row.

This event occurs whenever the user enters the row for new records.

Private Sub dataGridView1_NewRowNeeded(ByVal sender As Object, _
    ByVal e As System.Windows.Forms.DataGridViewRowEventArgs) _
    Handles dataGridView1.NewRowNeeded

    ' Create a new Customer object when the user edits 
    ' the row for new records. 
    Me.customerInEdit = New Customer()
    Me.rowInEdit = Me.dataGridView1.Rows.Count - 1

End Sub

private void dataGridView1_NewRowNeeded(object sender,
    System.Windows.Forms.DataGridViewRowEventArgs e)
{
    // Create a new Customer object when the user edits 
    // the row for new records. 
    this.customerInEdit = new Customer();
    this.rowInEdit = this.dataGridView1.Rows.Count - 1;
}

void dataGridView1_NewRowNeeded( Object^ /*sender*/,
    System::Windows::Forms::DataGridViewRowEventArgs^ /*e*/ )
{

   // Create a new Customer object when the user edits 
   // the row for new records. 
   this->customerInEdit = gcnew Customer;
   this->rowInEdit = this->dataGridView1->Rows->Count - 1;
}

Implement a handler for the RowValidated event that saves new or modified rows to the data store.

This event occurs whenever the user changes the current row.

Private Sub dataGridView1_RowValidated(ByVal sender As Object, _
    ByVal e As System.Windows.Forms.DataGridViewCellEventArgs) _
    Handles dataGridView1.RowValidated

    ' Save row changes if any were made and release the edited  
    ' Customer object if there is one. 
    If e.RowIndex >= Me.customers.Count AndAlso _
        e.RowIndex <> Me.dataGridView1.Rows.Count - 1 Then 

        ' Add the new Customer object to the data store. 
        Me.customers.Add(Me.customerInEdit)
        Me.customerInEdit = Nothing 
        Me.rowInEdit = -1

    ElseIf (Me.customerInEdit IsNot Nothing) AndAlso _
        e.RowIndex < Me.customers.Count Then 

        ' Save the modified Customer object in the data store. 
        Me.customers(e.RowIndex) = Me.customerInEdit
        Me.customerInEdit = Nothing 
        Me.rowInEdit = -1

    ElseIf Me.dataGridView1.ContainsFocus Then 

        Me.customerInEdit = Nothing 
        Me.rowInEdit = -1

    End If 

End Sub

private void dataGridView1_RowValidated(object sender,
    System.Windows.Forms.DataGridViewCellEventArgs e)
{
    // Save row changes if any were made and release the edited  
    // Customer object if there is one. 
    if (e.RowIndex >= this.customers.Count &&
        e.RowIndex != this.dataGridView1.Rows.Count - 1)
    {
        // Add the new Customer object to the data store. 
        this.customers.Add(this.customerInEdit);
        this.customerInEdit = null;
        this.rowInEdit = -1;
    }
    else if (this.customerInEdit != null &&
        e.RowIndex < this.customers.Count)
    {
        // Save the modified Customer object in the data store. 
        this.customers[e.RowIndex] = this.customerInEdit;
        this.customerInEdit = null;
        this.rowInEdit = -1;
    }
    else if (this.dataGridView1.ContainsFocus)
    {
        this.customerInEdit = null;
        this.rowInEdit = -1;
    }
}

void dataGridView1_RowValidated( Object^ /*sender*/,
    System::Windows::Forms::DataGridViewCellEventArgs^ e )
{

   // Save row changes if any were made and release the edited  
   // Customer object if there is one. 
   if ( e->RowIndex >= this->customers->Count && e->RowIndex != this->dataGridView1->Rows->Count - 1 )
   {

      // Add the new Customer object to the data store. 
      this->customers->Add( this->customerInEdit );
      this->customerInEdit = nullptr;
      this->rowInEdit = -1;
   }
   else 
   if ( this->customerInEdit != nullptr && e->RowIndex < this->customers->Count )
   {

      // Save the modified Customer object in the data store. 
      this->customers[ e->RowIndex ] = this->customerInEdit;
      this->customerInEdit = nullptr;
      this->rowInEdit = -1;
   }
   else 
   if ( this->dataGridView1->ContainsFocus )
   {
      this->customerInEdit = nullptr;
      this->rowInEdit = -1;
   }
}

Implement a handler for the RowDirtyStateNeeded event that indicates whether the CancelRowEdit event will occur when the user signals row reversion by pressing ESC twice in edit mode or once outside of edit mode.

By default, CancelRowEdit occurs upon row reversion when any cells in the current row have been modified unless the QuestionEventArgs.Response property is set to true in the RowDirtyStateNeeded event handler. This event is useful when the commit scope is determined at run time.

Private Sub dataGridView1_RowDirtyStateNeeded(ByVal sender As Object, _
    ByVal e As System.Windows.Forms.QuestionEventArgs) _
    Handles dataGridView1.RowDirtyStateNeeded

    If Not rowScopeCommit Then 

        ' In cell-level commit scope, indicate whether the value 
        ' of the current cell has been modified.
        e.Response = Me.dataGridView1.IsCurrentCellDirty

    End If 

End Sub

private void dataGridView1_RowDirtyStateNeeded(object sender,
    System.Windows.Forms.QuestionEventArgs e)
{
    if (!rowScopeCommit)
    {
        // In cell-level commit scope, indicate whether the value 
        // of the current cell has been modified.
        e.Response = this.dataGridView1.IsCurrentCellDirty;
    }
}

void dataGridView1_RowDirtyStateNeeded( Object^ /*sender*/,
    System::Windows::Forms::QuestionEventArgs^ e )
{
   if (  !rowScopeCommit )
   {

      // In cell-level commit scope, indicate whether the value 
      // of the current cell has been modified.
      e->Response = this->dataGridView1->IsCurrentCellDirty;
   }
}

Implement a handler for the CancelRowEdit event that discards the values of the Customer object representing the current row.

This event occurs when the user signals row reversion by pressing ESC twice in edit mode or once outside of edit mode. This event does not occur if no cells in the current row have been modified or if the value of the QuestionEventArgs.Response property has been set to false in a RowDirtyStateNeeded event handler.

Private Sub dataGridView1_CancelRowEdit(ByVal sender As Object, _
    ByVal e As System.Windows.Forms.QuestionEventArgs) _
    Handles dataGridView1.CancelRowEdit

    If Me.rowInEdit = Me.dataGridView1.Rows.Count - 2 AndAlso _
        Me.rowInEdit = Me.customers.Count Then 

        ' If the user has canceled the edit of a newly created row,  
        ' replace the corresponding Customer object with a new, empty one. 
        Me.customerInEdit = New Customer()

    Else 

        ' If the user has canceled the edit of an existing row,  
        ' release the corresponding Customer object. 
        Me.customerInEdit = Nothing 
        Me.rowInEdit = -1

    End If 

End Sub

private void dataGridView1_CancelRowEdit(object sender,
    System.Windows.Forms.QuestionEventArgs e)
{
    if (this.rowInEdit == this.dataGridView1.Rows.Count - 2 &&
        this.rowInEdit == this.customers.Count)
    {
        // If the user has canceled the edit of a newly created row,  
        // replace the corresponding Customer object with a new, empty one. 
        this.customerInEdit = new Customer();
    }
    else
    {
        // If the user has canceled the edit of an existing row,  
        // release the corresponding Customer object. 
        this.customerInEdit = null;
        this.rowInEdit = -1;
    }
}

void dataGridView1_CancelRowEdit( Object^ /*sender*/,
    System::Windows::Forms::QuestionEventArgs^ /*e*/ )
{
   if ( this->rowInEdit == this->dataGridView1->Rows->Count - 2 &&
        this->rowInEdit == this->customers->Count )
   {

      // If the user has canceled the edit of a newly created row,  
      // replace the corresponding Customer object with a new, empty one. 
      this->customerInEdit = gcnew Customer;
   }
   else
   {

      // If the user has canceled the edit of an existing row,  
      // release the corresponding Customer object. 
      this->customerInEdit = nullptr;
      this->rowInEdit = -1;
   }
}

Implement a handler for the UserDeletingRow event that deletes an existing Customer object from the data store or discards an unsaved Customer object representing a newly created row.

This event occurs whenever the user deletes a row by clicking a row header and pressing the DELETE key.

Private Sub dataGridView1_UserDeletingRow(ByVal sender As Object, _
    ByVal e As System.Windows.Forms.DataGridViewRowCancelEventArgs) _
    Handles dataGridView1.UserDeletingRow

    If e.Row.Index < Me.customers.Count Then 

        ' If the user has deleted an existing row, remove the  
        ' corresponding Customer object from the data store. 
        Me.customers.RemoveAt(e.Row.Index)

    End If 

    If e.Row.Index = Me.rowInEdit Then 

        ' If the user has deleted a newly created row, release 
        ' the corresponding Customer object.  
        Me.rowInEdit = -1
        Me.customerInEdit = Nothing 

    End If 

End Sub

private void dataGridView1_UserDeletingRow(object sender,
    System.Windows.Forms.DataGridViewRowCancelEventArgs e)
{
    if (e.Row.Index < this.customers.Count)
    {
        // If the user has deleted an existing row, remove the  
        // corresponding Customer object from the data store. 
        this.customers.RemoveAt(e.Row.Index);
    }

    if (e.Row.Index == this.rowInEdit)
    {
        // If the user has deleted a newly created row, release 
        // the corresponding Customer object.  
        this.rowInEdit = -1;
        this.customerInEdit = null;
    }
}

void dataGridView1_UserDeletingRow( Object^ /*sender*/,
    System::Windows::Forms::DataGridViewRowCancelEventArgs^ e )
{
   if ( e->Row->Index < this->customers->Count )
   {

      // If the user has deleted an existing row, remove the  
      // corresponding Customer object from the data store. 
      this->customers->RemoveAt( e->Row->Index );
   }

   if ( e->Row->Index == this->rowInEdit )
   {

      // If the user has deleted a newly created row, release 
      // the corresponding Customer object.  
      this->rowInEdit = -1;
      this->customerInEdit = nullptr;
   }
}

Implement a simple Customers class to represent the data items used by this code example.

Public Class Customer

    Private companyNameValue As String 
    Private contactNameValue As String 

    Public Sub New()
        ' Leave fields empty. 
    End Sub 

    Public Sub New(ByVal companyName As String, ByVal contactName As String)
        companyNameValue = companyName
        contactNameValue = contactName
    End Sub 

    Public Property CompanyName() As String 
        Get 
            Return companyNameValue
        End Get 
        Set(ByVal value As String)
            companyNameValue = value
        End Set 
    End Property 

    Public Property ContactName() As String 
        Get 
            Return contactNameValue
        End Get 
        Set(ByVal value As String)
            contactNameValue = value
        End Set 
    End Property 

End Class

public class Customer
{
    private String companyNameValue;
    private String contactNameValue;

    public Customer()
    {
        // Leave fields empty.
    }

    public Customer(String companyName, String contactName)
    {
        companyNameValue = companyName;
        contactNameValue = contactName;
    }

    public String CompanyName
    {
        get
        {
            return companyNameValue;
        }
        set
        {
            companyNameValue = value;
        }
    }

    public String ContactName
    {
        get
        {
            return contactNameValue;
        }
        set
        {
            contactNameValue = value;
        }
    }
}

public ref class Customer
{
private:
   String^ companyNameValue;
   String^ contactNameValue;

public:
   Customer()
   {

      // Leave fields empty.
   }

   Customer( String^ companyName, String^ contactName )
   {
      companyNameValue = companyName;
      contactNameValue = contactName;
   }


   property String^ CompanyName 
   {
      String^ get()
      {
         return companyNameValue;
      }

      void set( String^ value )
      {
         companyNameValue = value;
      }

   }

   property String^ ContactName 
   {
      String^ get()
      {
         return contactNameValue;
      }

      void set( String^ value )
      {
         contactNameValue = value;
      }

   }

};

Testing the Application

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

To test the form

Compile and run the application.

You will see a DataGridView control populated with three customer records. You can modify the values of multiple cells in a row and press ESC twice in edit mode and once outside of edit mode to revert the entire row to its original values. When you modify, add, or delete rows in the control, Customer objects in the data store are modified, added, or deleted as well.

Next Steps

This application gives you a basic understanding of the events you must handle to implement virtual mode in the DataGridView control. You can improve this basic application in a number of ways:

Implement a data store that caches values from an external database. The cache should retrieve and discard values as necessary so that it only contains what is necessary for display while consuming a small amount of memory on the client computer.
Fine-tune the performance of the data store depending on your requirements. For example, you might want to compensate for slow network connections rather than client-computer memory limitations by using a larger cache size and minimizing the number of database queries.

For more information about caching values from an external database, see How to: Implement Virtual Mode with Just-In-Time Data Loading in the Windows Forms DataGridView Control.

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Walkthrough: Implementing Virtual Mode in the Windows Forms DataGridView Control

Creating the Form

To implement virtual mode

Testing the Application

To test the form

Next Steps

See Also

Tasks

Concepts

Reference

Other Resources

Dodatkowe zasoby