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Tutorial: Implementar el modo virtual en el control DataGridView de formularios Windows Forms

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Si desea mostrar grandes volmenes de datos en formato de tabla en un control DataGridView, puede establecer la propiedad VirtualMode en true y administrar de forma explcita la interaccin del control con el almacn de datos. Esto le permite ajustar el rendimiento del control en esta situacin.

El control DataGridView proporciona varios eventos que puede controlar para interactuar con un almacn de datos personalizado. Este tutorial le gua a travs del proceso de implementar estos controladores de eventos. En el ejemplo de cdigo de este tema se utiliza un origen de datos muy sencillo para fines de ilustracin. En una configuracin de produccin, normalmente cargar slo las filas que necesite mostrar en cach y controlar eventos DataGridView para interactuar con la cach y actualizarla. Para obtener ms informacin, vea Implementar el modo virtual mediante la carga de datos Just-In-Time en el control DataGridView de formularios Windows FormsPara copiar el cdigo de este tema como un listado sencillo, vea Cmo: Implementar el modo virtual en el control DataGridView de formularios Windows Forms.

Crear el formulario

Para implementar el modo virtual

1. Cree una clase que deriva de Form y contiene un control DataGridView.

El cdigo siguiente contiene alguna inicializacin bsica. Se declaran algunas variables que se utilizarn en pasos posteriores, se proporciona un mtodo Main y un diseo de formulario sencillo del constructor de clase.

Visual BasicCopiar cdigo

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

_

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

C#Copiar cdigo

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)";

}

...

}

2. Implemente un controlador para el evento Load del formulario que inicializa el control DataGridView y rellena el almacn de datos con valores de ejemplo.


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

C#Copiar cdigo

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"));


"Bottom-Dollar Markets", "Elizabeth Lincoln"));


"B's Beverages", "Victoria Ashworth"));

// Set the row count, including the row for new records.

this.dataGridView1.RowCount = 4;

}

3. Implemente un controlador para el evento CellValueNeeded que recupera el valor de celda solicitado del almacn de datos o el objeto Customer actualmente en edicin.

Este evento aparece cada vez que el control DataGridView tiene que dibujar una celda.


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

C#Copiar cdigo

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;

}

}

4. Implemente un controlador para el evento CellValuePushed que almacena un valor de celda editado en el objeto Customer que representa la fila editada. Este evento se produce cada vez que el usuario confirma un cambio de valor de celda.


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


Me.rowInEdit = e.RowIndex

Else


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

C#Copiar cdigo

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);

}


this.rowInEdit = e.RowIndex;

}

else

{


}

// 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;

}

}

5. Implemente un controlador para el evento NewRowNeeded que crea un nuevo objeto Customer que representa una fila recin creada.

Este evento aparece cada vez que el usuario especifica la fila de nuevos registros.


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

C#Copiar cdigo

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;

}

6. Implemente un controlador para el evento RowValidated que guarda las filas nuevas o modificadas en el almacn de datos.

Este evento aparece cada vez que el usuario cambia la fila actual.


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 Not (Me.customerInEdit Is Nothing) AndAlso _

e.RowIndex < Me.customers.Count Then

' Save the modified Customer object in the data store.

Me.customers(e.RowIndex) = Me.customerInEdit


Me.rowInEdit = -1

ElseIf Me.dataGridView1.ContainsFocus Then


Me.rowInEdit = -1

End If

End Sub

C#Copiar cdigo

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;



}

else if (this.dataGridView1.ContainsFocus)

{



}

}

7. Implemente un controlador para el evento RowDirtyStateNeeded que indica si se producir el evento CancelRowEdit cuando el usuario seale la inversin de fila presionando dos veces ESC en el modo de edicin o una vez fuera del modo de edicin.

De forma predeterminada, se produce el evento CancelRowEdit con la inversin de fila cuando se ha modificado alguna celda de la fila actual, a no ser que la propiedad System.Windows.Forms.QuestionEventArgs.Response est establecida en true en el controlador de eventos RowDirtyStateNeeded. Este evento resulta de utilidad cuando se determina el mbito de la confirmacin en tiempo de ejecucin.


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

C#Copiar cdigo

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;

}

}

8. Implemente un controlador para el evento CancelRowEdit que descarta los valores del objeto Customer que representa la fila actual.

Se produce este evento cuando el usuario seala la reversin de la fila presionando dos veces ESC en modo de edicin o una vez fuera del modo de edicin. No se produce este evento si no se ha modificado ninguna celda de la fila actual o si se ha establecido el valor de la propiedad System.Windows.Forms.QuestionEventArgs.Response en false en un controlador de eventos RowDirtyStateNeeded.


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.rowInEdit = -1

End If

End Sub

C#Copiar cdigo

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.



}

}

9. Implemente un controlador para el evento UserDeletingRow que suprime un objeto Customer existente del almacn de datos o descarta un objeto Customer no guardado que representa una fila recin creada.

Se produce este evento siempre que el usuario elimina una fila haciendo clic en un encabezado de fila y presionando la tecla SUPR.


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


End If

End Sub

C#Copiar cdigo

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.



}

}

10. Implemente una clase Customers simple para representar los elementos de datos utilizados por este ejemplo de cdigo.


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

C#Copiar cdigo

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;

}

}

}

Probar la aplicacin

Puede comprobar el formulario para asegurarse de que se comporta de la forma prevista.

Para comprobar el formulario

Compile y ejecute la aplicacin.

Aparecer un control DataGridView rellenado con tres registros del cliente. Puede modificar los valores de varias celdas de una fila y presionar dos veces ESC en el modo de edicin y una vez fuera de ste modo para invertir la fila completa a sus valores originales. Cuando modifica, agrega o elimina filas del control, se modifican, agregan o eliminan objetos Customer del almacn de datos, tambin.

Pasos siguientes

Esta aplicacin proporciona conocimientos bsicos de los eventos que debe controlar para implementar el modo virtual en el control DataGridView. Puede mejorar esta aplicacin bsica de varios maneras:

Implemente un almacn de datos que almacena en memoria cach los valores de una base de datos externa. La cach recuperar y descartar valores segn sea necesario de modo que slo contenga lo que es necesario para la presentacin a la vez que utiliza una pequea cantidad de memoria en el equipo cliente.

Ajuste el rendimiento del almacn de datos en funcin de sus requisitos. Por ejemplo, quiz desee compensar las conexiones de red ralentizadas en lugar de las limitaciones de memoria del equipo cliente utilizando un tamao mayor de cach y minimizando el nmero de consultas de base de datos.

Para obtener ms informacin sobre cmo almacenar en memoria cach valores de una base de datos externa, vea Cmo: Implementar el modo virtual con la carga de datos Just-In-Time en el control DataGridView de formularios Windows Forms.

Vea tambin

Tareas

Cmo: Implementar el modo virtual en el control DataGridView de formularios Windows FormsReferencia

DataGridViewVirtualModeCellValueNeededCellValuePushedNewRowNeededRowValidatedRowDirtyStateNeededCancelRowEditUserDeletingRow

Conceptos

Procedimientos recomendados para ajustar la escala del control DataGridView en formularios Windows FormsImplementar el modo virtual mediante la carga de datos Just-In-Time en el control DataGridView de formularios Windows FormsOtros recursos

Ajuste del rendimiento del control DataGridView en formularios Windows Forms

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